Lawn mower belt tensioner. How to adjust belt tension on riding lawn mower

US4925437A. Belt tensioner device for lawn mower. Google Patents

Publication number US4925437A US4925437A US07/324,615 US32461589A US4925437A US 4925437 A US4925437 A US 4925437A US 32461589 A US32461589 A US 32461589A US 4925437 A US4925437 A US 4925437A Authority US United States Prior art keywords movement range belt biasing means set forth Prior art date 1988-03-17 Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.) Expired. Lifetime Application number US07/324,615 Inventor Takanori Suzuki Kazuyoshi Takada Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.) Yamaha Motor Co Ltd Original Assignee Yamaha Motor Co Ltd Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.) 1988-03-17 Filing date 1989-03-16 Publication date 1990-05-15 Priority claimed from JP63-64280 external-priority 1989-03-16 Application filed by Yamaha Motor Co Ltd filed Critical Yamaha Motor Co Ltd 1989-05-19 Assigned to YAMAHA HATSUDOKI KABUSHIKI KAISHA, DBA YAMAHA MOTOR CO., LTD., A CORP. OF JAPAN reassignment YAMAHA HATSUDOKI KABUSHIKI KAISHA, DBA YAMAHA MOTOR CO., LTD., A CORP. OF JAPAN ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: SUZUKI, TAKANORI, TAKADA, KAZUYOSHI 1990-05-15 Application granted granted Critical 1990-05-15 Publication of US4925437A publication Critical patent/US4925437A/en 2009-03-16 Anticipated expiration legal-status Critical Status Expired. Lifetime legal-status Critical Current



  • F16H — GEARING
  • F16H7/00 — Gearings for conveying rotary motion by endless flexible members
  • F16H7/08 — Means for varying tension of belts, ropes, or chains
  • F16H7/10 — Means for varying tension of belts, ropes, or chains by adjusting the axis of a pulley
  • F16H7/12 — Means for varying tension of belts, ropes, or chains by adjusting the axis of a pulley of an idle pulley
  • F16H7/1254 — Means for varying tension of belts, ropes, or chains by adjusting the axis of a pulley of an idle pulley without vibration damping means
  • F16H7/1281 — Means for varying tension of belts, ropes, or chains by adjusting the axis of a pulley of an idle pulley without vibration damping means where the axis of the pulley moves along a substantially circular path
  • F16H — GEARING
  • F16H7/00 — Gearings for conveying rotary motion by endless flexible members
  • F16H7/08 — Means for varying tension of belts, ropes, or chains
  • F16H2007/0802 — Actuators for final output members
  • F16H2007/0808 — Extension coil springs


A garden tractor or lawn mower including a belt driven mower blade and an improved tensioning arrangement for the driving belt. The tensioner mechanism provides a first range of tensioning during normal driving loads and a second, more rigid range of tensioning when abnormal loads are encountered so as to reduce belt wear but insure that the belt will not jump off of the driving or driven pulleys.


This invention relates to an improved belt tensioner device and more particularly to a belt tensioner device of the type utilized in driving a lawn mower.

Flexible drives such as belts or chains are utilized for a wide variety of purposes. These drives have particular advantage in that they permit the drive to accommodate variations in path of relative movement between the driving member and the driven member. For example, frequently flexible drives are used to drive the mower blades of a riding type lawn mower or a lawn mower attachment for a riding tractor. Flexible drives are employed for transmitting the drive from an engine driven shaft to the mower driving shaft and these shafts may be supported for rotation about non-parallel axes. In conjunction with such arrangements, the mower actually may move relative to the body of the driving vehicle as the vehicle covers the terrain to be mowed. By employing a flexible drive, such relative movement is accommodated.

However, it is desirable to insure that the tensioning on the drive belt is maintained the same regardless of the relative position of the mower and its driving engine. Therefore, various forms of belt tensioners have been employed so as to insure such tensioning. In conjunction with the belt tensioner, it is desirable that it does not maintain too high a tensioning force because of the resulting wear and shortening of the life of the belts. When such degrees of relative movement are accommodated, the tensioning force should not be too great. However, there are conditions such as abrupt acceleration, deceleration or conditions which put a load on the driving belt which can cause it to become disengaged from the pulley under these extreme conditions.

It is, therefore, a principal object of this invention to provide an improved belt tensioner which will permit a relatively low, uniform tensioning force but which will also resist the abrupt change in tensioning due to sudden changes in driving or driven loads.

It is a further object of this invention to provide a tensioner for a flexible drive that will accommodate all conditions, not place undue tension on the flexible drive, but will insure that it does not become disengaged.

It is, therefore, a still further object of this invention to provide an improved belt tensioner that can provide variable tensioning forces depending upon the conditions encountered.

This invention is adapted to be embodied in a tensioner arrangement for a flexible drive that is comprised of a guide member that is engaged with the flexible drive and biasing means that acts upon the guide member for exerting a biasing force of a first magnitude during a first movement of the guide and a biasing force of a substantially greater magnitude upon movement of the guide in an amount greater than the first range.

lawn, mower, belt, tensioner

FIG. 1 is a side elevational view of a lawn mower or garden tractor driving a lawn mower attachment constructed in accordance with an embodiment of the invention. Portions of the tractor are shown in phantom.

Referring first primarily to FIG. 1, a garden tractor driving a lawn mower attachment or a riding lawn mower is identified generally by the reference numeral 11. Although the invention has particular utility in such applications, it is to be understood by those skilled in the art that the invention will have utility in other applications.

The lawn mower 11 is comprised of a frame assembly 12 that is supported for movement along the ground upon a pair of dirigible front wheels 13 and a pair of driven rear wheels 14. An internal combustion engine 15 which may be of any known type is supported in a suitable manner on the frame 12 and drives an output shaft 16 that is rotatable about a generally longitudinally axis relative to the frame 12. A propeller shaft 17 is drivingly coupled to the engine output shaft 16 and, in turn, drives an input shaft 18 of a hydrostatic transmission 19. The hydrostatic transmission 19 has an output shaft which drives a final drive assembly 21 for driving a rear axle 22 to which the rear wheels 14 are drivably coupled in a known manner.

A rider’s seat 23 is supported on the frame 12 over the rear wheels 14 and in proximity to a transmission control shift lever 24 that can be employed for shifting the hydrostatic transmission 19 between a forward drive position, a neutral position and a rear drive position. In addition, a steering wheel 25 is supported forwardly of the rider’s seat 23 for steering the front wheels 13 in a known manner.

In addition to powering the tractor 11, the engine 15 may be employed for driving an accessory such as a lawn mower attachment, indicated generally by the reference numeral 26. The lawn mower attachment 26 is comprised of a frame attachment in which one or more cutter blades 27 are supported for rotation about a vertically extending axis upon a mower shaft 28. The mower housing is supported for rolling movement along the ground on wheels 29. The mower attachment 26 is supported relative to the frame 12 by means of a parallel linkage system comprised of links 31 and 32 so that it may be lowered to ride on the ground via the wheels 29 or raised to an inoperative position. A control lever 32 operates through a linkage system so as to raise and lower the mower 26 in a known manner.

The mower blades 27 are driven from the engine 15 by means including an electrically operable clutch assembly 32 positioned at the forward end of the output shaft 16 for drivingly coupling the output shaft 16 to a driving pulley 34 that is fixed to the driven element of the clutch assembly 33.

A flexible belt 35 is trained over the driving pulley 37, a tensioner mechanism, indicated generally by the reference numeral 36 and illustrated in more detail in FIGS. 2 through 4, and a driven pulley 37 that is journaled on the mower housing. The driven pulley 37 is coupled to a second pulley 38 and a driving belt 39 transmits drive from the pulley 38 to a pulley 41 that is affixed to the mower shaft 28.

Referring now primarily to FIGS. 2 through 4, the tensioner mechanism 36, which forms the subject of the invention, will be described in detail. The tensioner mechanism 36 is comprised of a drive side pulley 42 that is rotatable about an axis that extends transversely to the axis of the pulley 34 and to that of the pulley 37. The pulley 34 has trained around it the driving flight 43 of the belt which transmits the driving forces to the driving pulley 37. A return flight 44 of the belt 35 is trained around a return pulley 45 that is journaled for rotation about an axis parallel to the axis of the drive pulley 42 and which returns the belt to the engine driven pulley 34.

The supporting and tensioning mechanism for the pulleys 42 and 45 includes a bracket assembly 46 that is mounted to a cross member 47 of the frame 12 by means of bolt and nut assemblies 48. The bracket assembly 46 carries a supporting shaft 49 at its lower end upon which supporting bushings 51 and 52 are rotatably journaled. The bushings 51 and 52 are axially fixed relative to the supporting shaft 49 by bolts 53 and 54. A first arm 55 is affixed to the outer end of the bushing 51 and carries a shaft 56 at its rearward end. The pulley 42 is journaled upon the shaft 56 by means of an antifriction bearing 57 and is held axially in place by a retaining nut 58. In a like manner, there is provided a support arm 59 that is affixed to the outer end of the bushing 56 and which carries a supporting shaft 61 upon which the pulley 45 is journaled by means of a bearing 62. The pulley 45 is held axially to the shaft 61 by means of a nut 63.

For providing normal tensioning of the belt 35, there are provided a pair of control arms 64 and 65 which are affixed to the bushings 51 and 52 inwardly of the lever arms 55 and 59. Tension springs 66 and 67 are affixed at one end to the upper ends of the control arms 64 and 65, respectively. The opposite ends of the springs 66 and 67 are connected to brackets 68 and 69 which may be affixed to or form a part of the frame cross member 47. As a result, the action of the springs 66 and 67 will urge the control arms in a clockwise direction so as to cause like rotation of the supporting arms 55 and 59 and maintain a uniform tension on the driving belt 35. The degree of tension will depend upon the angular position of the control arms 64 as shown in FIG. 5 wherein the displacement of the control arms is indicated on the ordinate by the dimension D1 whereas the tension is indicated on the abscissa by the dimension T1. It will be seen that the effect is linear, as is well known with coil spring assemblies.

As the housing of the mower 25 moves up and down, the operation of the springs 66 and 67 will maintain a uniform tension on the belt 35. This tension is generally of a relatively low magnitude in order to insure that there will not be undue wear placed upon the belt 35. However, under sudden changes in load such as starting or stopping of the engine 15 or some impact condition on the mower blades 25, the force on the belt 35 can abruptly increase and the spring 66 and 67 may not be adequate to maintain the belt 35 in engagement with the pulleys under this condition. Therefore, there is provided a more rigid tensioning member which is comprised of an elastomeric block 71 that is affixed to the bracket 46 by means of bolts 72. The elastomeric block 71 is adapted to be engaged by a stop 73 formed on the supporting lever 55 when the position D1 is reached at the extreme upward condition. When this occurs, the block 71 will act in parallel with the springs 66 and 67 and provide a progressively increasing resistance to movement during the range of movement D2 which tension is shown by the line T2. As a result, the tensioner in effect provides two different rates; one relatively low rate during the normal range of angular movement and a substantially higher, more progressive rate at higher ranges of angular movement. This will insure that the belt is not unduly tensioned under normal running but will provide a resistance to the belt from jumping off of the pulleys under large loading.

As a result, it should be readily apparent that the device is particularly adapted for maintaining good tensioning under all conditions without adversely affecting the belt. In the illustrated embodiment, the tensioner is comprised of a pair of coil compression springs and an elastomeric spring. It should be readily apparent that other forms of spring arrangements can be employed so long as they provide the non linear characteristics as aforedescribed or, alternatively, a first range of tensioning under a first range of movement and substantially more rigid tensioning under a more extreme range of movement. Various other changes and modifications may be made without departing from the spirit and scope of the invention, as defined by the appended claims.

Claims ( 8 )

A tensioner arrangement for a flexible drive comprising a guide member engaging said flexible drive and biasing means acting upon said guide member for exerting a biasing force of a first magnitude during a first range of movement of said guide and a biasing force of a substantially greater magnitude upon movement of said guide in an amount greater than said first range.

A tensioner arrangement as set forth in claim 1 wherein the biasing means exerts a linear resistive force during the first range of movement.

A tensioner arrangement as set forth in claim 2 wherein the biasing means exerts a progressively increasing resistive force upon movement outside of the first range of movement.

A tensioner arrangement as set forth in claim 1 wherein the biasing means includes a first linear spring acting within the first range of movement.

A tensioner arrangement as set forth in claim 4 wherein the biasing means further includes a non linear spring acting outside of the first range of movement.

A tensioner arrangement as set forth in claim 4 wherein the biasing means includes a coil spring acting in the first range of movement.

A tensioner arrangement as set forth in claim 6 wherein the biasing means further includes an elastomeric spring acting outside of the first range of movement.

A tensioner arrangement as set forth in claim 1 wherein the biasing means comprises a guide supported for pivotal movement about an axis.

US07/324,615 1988-03-17 1989-03-16 Belt tensioner device for lawn mower Expired. Lifetime US4925437A ( en )

Applications Claiming Priority (2)

Family Applications (1)

Cited By (10)

Families Citing this family (1)

Patent Citations (3)

Cited By (15)

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How to adjust belt tension on riding lawn mower

Are you interested to find out how to adjust belt tension on riding lawn mower?

Lawn mowing is one of the most significant responsibilities that a homeowner must fulfill to make the lawn look great. You have to mow it just the right way, and combined with other external components in the yard, you can create a masterpiece of visual design.

To achieve this aesthetic, you have to make sure that your lawnmower is cutting grass the right way. If it is not mowing grass properly and leaving uncut patches on the lawn, there might be a problem with a loose drive belt.

Lucky for you, fixing a loose drive belt is not difficult, and you only need a socket wrench for the entire procedure.

What are the steps in how to adjust belt tension on riding lawn mower?

The drive belt of a typical riding lawn mower is below the mower deck. It connects the transaxle pulley to the drive shaft of the engine and channels power and torque to the rotor blades.

After constant and extended usage, the quality of the belt will degrade and loosen due to the extension of the tensile cords.

If an extension is not significant, you can only adjust the belt tension to become tighter. If it is too degraded, then you have to replace it.

Here are the steps in adjusting the belt tension of a riding lawnmower:

    Examining the current mower belt

Before doing the belt adjustment procedure, you have to check the current status of the belt if it needs to be tightened.

A typical riding mower has a blade engagement lever beside the steering wheel. Its function is to push the rotor blades to the grass as the cutting deck is lowered to the yard.

To check if the drive belt needs adjustment, turn on the ignition and increase to maximum the throttle lever. Then you have to engage the rotor blades by pressing the lever upwards.

If the blades instantly mow once the lever is pushed, then the drive belt is still tight.

If there is a whirring noise after pushing the lever, there is belt slippage, thus necessitating adjustment immediately.

Before undergoing the adjustment process, bring the riding lawnmower to an area with a flat surface so you can work properly. To enable parking mode, press the parking brake.

You also need to practice safety, so you have to disconnect the power cable to avoid being electrocuted./

At this stage, you already know that your riding lawnmower is not cutting grass properly because the drive belt is slipping.

Before troubleshooting this issue, you need to check on the status of the mower deck and its parts. Lower the mower deck by pulling the blade engagement lever.

And check on these components:

  • Drive belt – Check if everything is complete and there are no missing components. Look if there are cracks and chunks of it missing. If there are, you do not have to adjust it anymore but replace it.
  • Swingarm – Springs and pulleys are mounted on the swingarm. A pin is connected in one end of the arm and on the other is for rotating. You have to make sure the whole arm can freely rotate, and if not, remove any residue or debris present and put some oil in its pivot.

If these parts in the mower deck are properly functioning, unlock the blades by pressing the lever again. Also, check on the spring, which connects to a cable and is also attached to the lever.

Check if it is springy, stretched, and loose. Check on the belt at the same time if it is also loose, and if it is, then continue to the next step.

Lock the rotor blade lever since you saw that the belt is loose. Also, take note of the wire from the blade lever is connected to the springs. It is fastened to a bracket located on the mower deck.

Unscrew the bolts on the bracket and pull the wire towards you. Do not remove the bolts and loosen them.

Screw in the bolts back and check if the belt will also stretch and tighten. If it does, settle in the position and tighten the bolts by turning them clockwise.

Once done, check on the belt again to make sure the tightness is just right.

Once done, reattach the power cable to the battery.

Turn on the ignition of the mower engine to full throttle after pulling back the bracket. Push the lever upwards of the blade control lever and check if it will immediately cut the grass.

If you notice that the blades are cutting immediately, the belt has optimum tension.

What are the steps in replacing the drive belt on riding lawn mower?

If the belt drive is too degraded and tightening does not work, you need to replace it.

  • Activating the mower’s parking mode – Before undergoing the replacement process, bring the riding lawnmower to an area with a flat surface so you can work properly. To enable parking mode, press the parking brake.
  • Disconnecting the battery cable in the lawnmower – You also need to practice safety, so you have to disconnect the power cable to avoid being electrocuted.
  • Disengaging the mower’s sparkplug wire – At this stage, the ignition is off, and no electricity is flowing in the engine. It is because the battery cable has been disconnected. Another safety precaution is to disconnect the sparkplug wire, so lift the hood and look for it to detach it.
  • Disassembling the mower deckTo start in disassembling the mower deck, lock the blades and lower the deck by pushing the engagement lever. Remove the drive belt from the engine pulley, which is attached to the drive shaft, and also release the belt holders.
  • Detaching the mower deck from the main body – You will need to disconnect the mower deck from the body. It is done by removing the supports linking the mower deck to its body from both sides. Remove all washer support and retaining pins from the lift links, suspension arms, and rear end brackets. You have to be aware that once all the abovementioned components are removed, make sure that the detachments are done from both sides.
  • Taking a picture of the belt in the mower deck – You will need to document the positioning of the belt on the deck and its passage through the pulleys by taking a snapshot on your smartphone.
  • Removing the old mower belt – Take out the belt wrapped around the three pulleys, which are two mandrel pulleys and one idler pulley.
  • Attaching the new belt to the mower – Fasten the new drive belt by wrapping it around the idler and mandrel pulleys, and be sure it also goes through the belt keeper.
  • Reattaching the mower deck – In assembling the mower deck back, reattach the lift links, suspension arms, rear-end brackets, and other supports. Use the retaining pins and washers to secure the linkages and connect the battery to the engine pulley.
  • Testing your lawnmower – With everything assembled and attached back to the original position, lift the hood to reconnect the sparkplug. Key in the ignition switch and drive through a grassy area to check if the belt replacement procedure worked. If not, then the drive belt is not the problem, which means you need to take it to a repairman to get fixed.

Does learning about how to adjust belt tension on riding lawn mower important?

It is, and when your riding lawnmower is not cutting grass as it is supposed to, the drive belt is the likely culprit. Once it will happen, you already know what to do to fix it.

How To Tighten Drive Belt On Cub Cadet?

A Cub Cadet drive belt needs to be tightened periodically so that it does not slip off the pulley. We have researched the proper DIY method for adjusting the drive belt tension, and here’s what we found.

Tighten the Cub Cadet drive belt by replacing the spring tensioner or trimming some segments of itt. The spring tensioner provides a certain amount of tension, allowing the belt to run smoothly. Over time, it can wear out and need replacing.

If a worn belt cuses loose tension you can adjust the brake link for a temporary fix. Replace the worn drive belt for a permanent fix.

Most people think that they need to replace the drive belt when they notice that the belt is slipping. This could be the case, but it’s just one side of the coin, and we’ll look into this. In addition, we’ll walk you through not only how to tighten the drive belt but when you should replace it. So keep reading below to learn more!

Why Is It Important To Check Drive Belt Tension In Cub Cadet?

When you mow your lawn, you’ll see the blades spin quickly to cut the grass. The drive belt, which connects the motor to the blades, spins around the pulleys and provides the necessary tension to rotate the blades.

However, in some cases, the belt tension is too loose. A loose drive belt can cause a lawnmower blade not to spin. If your Cub Cadet engine is running fine, but it is not moving forward, you could have a loose belt.

However, if it does run, yet skips and jumps when you try to cut grass, this is because the drive belt is not able to grip the pulley. To keep the belt in place, it’s crucial to know the proper tension. If you loosen the belt, you’ll reduce its effectiveness.

What Provides Tension To The Drive Belt?

There are two components of your Cub Cadet that provide tension to its drive belts: the spring tensioner and the drive belt itself.

The spring tensioner is a wearable part found in many Cub Cadet lawnmowers and is usually attached to one of the V-pulleys. The other component is the drive belt itself. A worn drive belt should be replaced if it shows signs of fraying.

How To Replace The Spring Tensioner To Tighten Cub Cadet?

If the spring tensioner of your lawnmower has lost its ability to hold the drive belt in place, it’s time to replace it. Below are the steps to follow when replacing your Cub Cadet spring tensioner:

Remove The Cutting Deck

You should see a small bracket that holds the deck belt in place in your front engine pulley. Determine the bolt size (usually 8 mm) and loosen it up using the right socket size power tool.

Once you have the bracket removed, slowly pull the deck pulley down. Check for bowtie clips within the deck frame and take them out. The deck frame should loosen up, and you should be able to move it away from the cutting deck.

You’ll see a bowtie clip and spring attached to the cutting deck. These two connect the deck to the blade engagement cable. Pry the spring and bowtie clip out so you can separate the deck from the cable.

The video below illustrates the process:

Turn Your Cub Cadet On The Side

Once you have the deck out, turn your cub cadet on the side, so you expose the underside and start working on replacing the spring tensioner.

Alternatively, you can also jack it up so you can get to the bottom of it. It’s much easier if you do it sideways though when replacing the drive belt.

Locate The Spring

You should be able to identify and locate the spring easily. Just look for the V-pulley with a spring.

Remove The Spring

The spring is attached to a bolt and a V-pulley. You can pry both ends of the spring loose using a cutter-type plier.

Attach The New Spring

Once you remove the old spring, you can put a new one in place. Be sure to use a replacement part that fits your model of Cub Cadet mower. A temporary fix would be to trim segments of the old spring and reuse the spring.

However, we don’t recommend this, as the spring has already been stretched out and has little remaining life in it. It’s just a matter of time before the spring loses tension again or worse, breaks because of corrosion.

Also, you might consider spraying anti-rust on the surface while working on replacing your spring tensioner or drive belt for an added layer of protection.

Follow The Steps In Reverse Order To Put The Parts Back

The last thing you want is to end up with a DIY project that turns out to be bigger and more complex than anticipated. It’s important to document everything you do when working on projects, especially when it is your first attempt.

You want to be able to refer back to your notes and photos to help you identify any missed steps.

Taking pictures and videos of the installation or replacement process helps you recall and visualize the exact steps you took to complete your project.

How To Replace The Drive Belt Of Your Cub Cadet?

One of the best ways to tell if a lawnmower’s drive belt needs replacing is by inspecting the condition of the drive belt itself. If you see any damage, rips, cracks, or cuts, then you know that it’s time to change it.

Pro tip: when replacing either the spring tensioner or drive belt, you might as well replace the two altogether to save you time in the future.

Here are the steps to replace your Cub Cadet drive belt:

Remove Cutting Deck

Follow steps 1 and 2 above.

Remove The Clutch

You will see a bolt that attaches the clutch of your Cub Cadet to the motor. Loosen the bolt and disconnect the connecter that connects the clutch to the motor. You should be able to remove the drive belt after doing this.

Put The New Drive Belt

Slip the belt into the transmission pulley and into the motor pulley first. Once you have it in there, start working your way until the belt is slipped into each of the pulleys.

The groovy side of the belt should go to the V-pulleys, and the flat side of the belt should go to the idle pulley. You should have a diagram somewhere on your Cub Cadet, so just refer to it for guidance.

Put Everything Back Together

It’s very easy to get lost when putting the different parts of a machine like your Cub Cadet back again.

It’s important to keep track of the steps when replacing parts. You might find yourself confused about which parts go where, which is why it’s important to document the replacement process. This is a great way to be able to see if you did something wrong or not.

The video below should illustrate how the entire process is done:

Telltale Signs Of A Failing Drive Belt

A frayed Cub Cadet drive belt can make your mowing job much more difficult. A torn or frayed belt will be the cause of many problems that could cost you hundreds of dollars to repair. Here are the telltale signs to look out for of a failing Cub Cadet drive belt.

Losing Tension/Slippage

It’s important that the belt should be tight to avoid slipping. However, the belts can wear out ,and when they do, they lose some of their elasticity and become loose. As a result, the pulleys on the motor and the transmission become separated when the belt gets slack.

Engine Overheating

A worn lawnmower belt is a silent killer. Over time, an undetected worn belt may slip without warning. This means the belt may not be able to move the pulleys effectively and could cause your lawnmower to stutter and run intermittently while you’re mowing.

This will cause the engine to work harder than it should. It may even break down altogether, causing your lawnmower to grind to a halt. If you’re noticing excessive heat coming from the engine, this could indicate the belt is failing.

What Is The Purpose Of An Idler Pulley?

There’s an idler pulley in almost every machine. So what does an idler pulley exactly do, and why is it important?

An idler pulley is a part of the machinery where the belt passes through, providing a means of supporting the belt without slipping or getting damaged. It’s a crucial machine component that allows the motor to spin at a constant speed.

A pulley is a tool that allows one machine to work with another machine. In the case of an idler pulley, it’s a part of a belt system that allows a machine to move along with the rotation of the pulley.

In addition, it’s a device that is used to reduce friction and vibration between belts and pulleys. It is a mechanism that is used for providing tension and speed of the belt.

Should You Worry If The Idler Pulley Fails?

A common failure that occurs in a pulley mechanism is the idler pulley. These pulleys serve the purpose of taking the load of the machine and distributing it through various parts of the machine.

When the idler pulley fails, the load that it was meant to distribute will become concentrated on the remaining pulleys.

This can cause extensive damage to the drive belt and could lead to its destruction. As a result, you need to replace the idler pulley as soon as possible.

If your idler pulley fails, the drive belt may slip and no longer transmit the required power to the cutting blades. This can cause the blades to stop working, leaving you stuck in a very precarious situation.

In Closing

There are actually no settings that you can use to adjust the tension settings of your Cub Cadet drive belt. However, you must pay attention to the warning signs that your Cub Cadet needs a spring tensioner replacement. A loose drive belt is not something you should ignore.

Mower Deck Belt Replacement – Step by step

Replacing belts on your mower is like replacing tires on your car; there are only so many miles in them. Replacing a deck belt can be a challenge, especially if the mower throws the belt and you don’t know the routing, but we’ll get it figured out!

Getting the correct belt is the first important step. Some manufacturers place a label detailing the belt part number and belt routing. Try under the hood or under the footrest; if not, check out “Belt routing.”

Deck types vary. Some are easy to work on, some not so much. It’s important to check over the deck looking for any damaged or loose components, especially if your old belt was damaged and not just worn out. You don’t want to damage the new belt needlessly.

Most mowers won’t require deck removal to fit the belt; others will. So take some time and consider the routing, don’t put extra work on yourself. Take lots of photos; it saves time and head-scratching later.

What’s Involved?

Fitting the new belt means removing some plastic protective covers. And in most cases, it involves wrapping the belt around the pulleys and making sure the belt guide (guide not on all pulleys) is on the outside of the belt. The last pulley to fit is the crank pulley (engine pulley).

Tensioned or Not

A tension-ed belt is a deck drive belt that is always tight on the pulleys. Push-button blade engages type mowers usually run an always tension-ed belt. Replacing it will require manhandling the belt onto the side of the crank pulley, then turning the crank pulley clockwise by hand until the belt slips on.

If your mower has a lever, then you likely have a slack belt which is then tensioned by moving the blade to engage the lever. This type of belt is easier to replace and will take no time at all.

Tensioned – This type of belt is always tight on the pulleys.

Un-Tensioned – This type of belt setup is slack on the pulleys until you engage the blades.

What Deck Type?

Cutting deck setup types vary from side discharge; rear discharge; mulching decks; front decks; cutting, and sweeping.

They may have features such as single-blade; twin-blade; tri-blade; tensioned belt; manual tensioned belt; electromagnetic blade engagement; fan assisted deck; timed overlapping blades, and so on.

The one thing they all have in common – is the deck drive belt. It’s how engine power is transferred into cutting power.

Timed Deck

A timed deck means both your mower blades are set at a fixed angle in relation to each other. The toothed belt maintains the blade position; this allows the blades to overlap.

Some say the overlapping blades give a superior cut; I like the lawn finished with the overlapping twin cut, especially the smaller decks.

This deck type is also referred to as an interference deck. They call it Interference because if the blades go out of time, they’ll smack each other.

Resetting the timing of the blades or replacing the belt is a job that can be done without much difficulty, but it does require removing the deck, tension assembly, and various plastic guards. No special tools are needed.

Rear – Rear discharge is great at collecting grass but doesn’t like long grass so much.

Timed – Timed deck has a toothed belt that can break or slip out of time. Timing the blades allows them to overlap.

Mulching – Some decks will have a flap that closes off the chute when the operator wants to mulch.

Side Discharge – Side discharge is great for tall grass and rough terrain.

Measuring The Belt

A belt will be marked with a type code, length, and part number. Belts are usually measured by their inside length (Li) or outside length (La); if you can find this info on the side of your old belt, great! But usually, it’s worn away.

Some mowers like Husqvarna place a sticker inside the hood with a list of helpful part numbers like belts, filters, plugs, etc.

What Belt Width? – The width and depth of a belt are also very important. A new V belt should fit snugly into a v pulley; the belt should sit just proud of the pulley’s shoulder. A belt that sits further down into the pulley is worn out.

What Belt Length? – If your belt was shredded, then you’ll need your make and model number to order the correct belt. An easy way to measure an old belt – use a string to follow the outside of the belt; now measure the string.

This measurement will be marked on belts by the letters La (outside measurement); alternatively, run the string around the inside of the belt; this measurement is the Li measurement.

A faster way to measure an intact belt is to make a circle of the belt and measure inside to inside, then multiply by 3.14. The result is the Li belt size.

Sizing – Sometimes easier said than done!

Markings – Check under the hood of your mower; you may get lucky with a part number sticker, but be cautious with the Husqvarna labeling; they are often wrong belt part numbers.

Check your old belt for markings; if none, get the tape and some string. These belts are measured in mm.

lawn, mower, belt, tensioner

Pulley – The new belt will be the full width of the pulley. Worn belts usually stretch in length and become narrow in width.

Check Belt Routing

Belt routing, needless to say, is important. On some mowers, it’s possible to put a belt on the backways, which makes the blades turn backward. Not much use for yard work.

If you can, make a diagram or take some pictures of the old belt in place. First, you’ll need to remove both plastic protection pulley covers, one on each side. Some mowers have a handy sticker showing the deck belt routing under the footrest.

That’s great advice, but what if your belt has snapped or derailed? Then you’ll need to check out the links below. Bear in mind, even if you don’t see your maker in the list, check the link out anyway because lots of make share the same decks.

Look at the pulley configuration to see if yours looks similar.

Belt Routing Links

The following link to Google belt routing pictures:

Sticker – Check under the footrest of your mower; some models have a belt routing sticker. This sticker is on a Husqvarna tractor.

Check out the Amazon link below for deck belts.

What Belt Type?

Belts are belts, right? Well, No. The correct belt is crucial. An ill-fitting or wrong-type belt will cause endless trouble. Throwing the belt, vibration, poor cutting, and collecting, and because the belt doesn’t fit correctly, it won’t last very long. I had one customer who fitted a belt that was so tight it broke the end of the crankshaft. Ouch!!

There are many different types of belts; however, when it comes to lawnmowers, they are usually fitted with a standard V-type belt. Other belts used are AA belts, timed belts, and poly V belts.

Sure, you can fit a basic quality belt with a polyester cord, but it’s going to wear out quickly; for durability, you’ll want Kevlar; they cost more but last a lot longer. Some models will only work well with OEM belts, like John Deere and MTD.

I recommend fitting only OEM (Original Equipment Manufacturer). Fitting a belt can be a challenge. Reassembling and discovering what doesn’t work right can be demoralizing.

V Belts

V belts are so-called because of their cross-section shape (wider at the top than the bottom). They are used almost exclusively to drive power from lawn tractor engines to their transmissions. They are also used to drive deck blades. The V belt drives power from one side of the belt only.

They come in different heights/widths and are marked type A, B, C, D. The most common V belts used on mowers are the A and B types, and obviously, they come in a long list of lengths.

Each belt is marked by type and belt length; it may also have a part number. Unfortunately, the markings usually wear off, making the ID process difficult.

AA Hex Belts

The AA belt is a double-sided hexagonal belt; it is mostly used on tractor mower decks to drive the blades. The belts are unique as they have the ability to drive from either side of the belt.

AA Hex Type – This is a double-faced belt; it gives greater flexibility to deck design, as it allows both sides of the belt to drive. It’s used on higher-end tractor decks.

Toothed (Timed) Belts

A mower-toothed or timed belt does two jobs, it transfers power and, at the same time, keeps the mower blades from hitting each other. The toothed belt is a very exact belt in that the teeth of the belt must match that of the mower cogs.

Timed Belt – This type of belt has become more popular in recent years. It’s fitted to mower decks with overlapping blades.

A Type

A Type.This is the most common type of lawn tractor belt; it’s used by many lawn tractor drive systems and most decks too.

B Type

The B-type belt is a heavy-duty A belt; it’s an older well-fed brother.

Check Belt Wear

Belts have a difficult job and can be the cause of various issues. Regular inspection will tell you if your belt is at the end of its life. Things to look for are flat-spotting, glazing, cracking, fraying, and contamination.

As you know, a V belt should sit just proud of the pulley shoulder; if it’s a lot lower than the shoulder of the pulley, it’s worn out.

How Long Do They Last?

The life of a belt is hard to gauge, it really depends on how much grass you’re cutting and how heavy the workload is, but usually, we’re talking years. Typically a belt should be changed after 3-4 years, but we know this doesn’t happen.

A worn or damaged pulley can shorten the life of your belt. An engine or transmission oil leak can destroy the belt, you can try cleaning it, but it causes slip. A derailing belt can get twisted and damaged, and a mower that throws belts regularly probably has a worn or damaged pulley.

But the real killer of belts – tall, heavy grass jams the blades, which causes flat spots on the belt. The flat spot will then cause a lot of vibration, which in turn can throw the belt.

Belt damage is usually caused on the first cut of the season when the grass is heavy. So if your grass is tall and heavy, just take a little off on the first pass and make a second pass with the deck a notch lower. Yes, it’s twice the mowing, but it’s better for your mower and your lawn.

lawn, mower, belt, tensioner

Flat Spot – Flat spotting is usually caused when the blade jams, but the engine pulley keeps running. This has a grinding effect on the belt.

The flat spot will cause excessive vibration in the mowing deck. The fix is – Replace the belt.

Blistering – This can happen when a belt gets old, and the material starts to break down. Your mower won’t cut or collect very well. Better to take care of it now, before it breaks.

Glazing – This belt has a shiny hard surface that is not much good for traction. A belt like this will cause horrible vibration in the mowing deck.

Frayed – Wear and tear, this belt is at the end of its useful life.

Cracked – Natural wear and tear

Check Pulley Wear

A pulley’s job is to route the belt around the chassis of the mower or mowing deck and transfer power from the engine pulley to the driven pulleys. As a rough guide, pulleys usually wear out at the same time as a belt, so best to check them while you have the belt removed.

Tension and idler pulleys should move freely, be quiet when spun, and should feel smooth when turned. If they’re worn, now’s the time to take care of it; when a pulley bearing breaks, it will likely damage the belt.

Spin To Test

You don’t need to remove them to check. Spin them while the belt is off; they should be smooth and quiet. Changing them now is easy.


Most pulleys come with the new bearings pressed in place; the exceptions are driven pulleys (Mandrel, engine, or transmission pulleys).

Pulley Types

Pulleys come in all sizes, some metal and some plastic. Tensioners and idlers will have a bearing fitted, and when it wears out, the whole pulley is replaced. Pulleys are usually broken into two main types, flat or V.

A flat pulley is not a driven pulley; it runs on the back of the belt, which isn’t powered (unless it’s on a AA belt).

A V pulley can be driving, driven, tensioner, or idler. A V pulley is described as a driven pulley if it’s connected directly to the output, such as a transmission or a blade Mandrel.

The driving pulley is the engine pulley; it’s the pulley supplying the power. Both the driven and driving pulleys are fixed to shafts using a key and key-way.

A tensioner pulley is part of a moving arm, which, when operated, applies tension to a belt. A tensioner pulley can be a flat or V pulley.

A stationary pulley is usually known as an idler, and its job is to route the belt around the chassis of the mower or mower deck; they can be flat or V-type.

Pulleys – Metal or plastic, V type or flat, driven or idle. So many choices.

V Pulley – This is a V pulley; the driving side of the belt is making contact with the pulley.

Flat Pulley – A flat pulley on a V belt setup is never a driven pulley. Its job is to change the direction of the belt and guide it to the next pulley.

Fitting A Belt

Fitting a cutting blade deck belt that is just worn is the easiest, as you can see the routing of the old belt, and make a diagram or take pictures. Removing the old one also gives you an idea of how challenging fitting the new one will be.

As you know, there are a few variations of deck belt setups; most mowers will have one belt to drive the blades that are either a tension-ed or a un tension-ed belt. The belt can be fitted to both of these types of setups without removing the deck from the mower.

The timed belt setup is a little more involved but not complicated. It has two belts as do so some of the larger John Deere mowers. They can be a challenge as they have many pulleys, and you’ll need to remove the deck.

Pulley Covers

Likely you’ll have already removed the two plastic pulley protection covers, one on each side of the deck. Usually, 2 or 3 screws on each side. They’re not there to protect the pulley. They’re there to protect us from catching body parts in the pulleys.

The latest generation mowers are far more challenging to access as the nice people in the health and safety dept. have been working nights and weekends to find new ways to challenge us.

Removing Belt

Here’s a quick run-through of what we’ll be doing, but it’s all covered in the steps below with pictures. With the covers removed, start by removing the belt from the engine pulley. Often the engine pulley will have a belt guide; its job is to prevent the belt from derailing. Depending on the type of belt guide (if fitted), you may need to remove them first.

As you know, some belts will be tensioned all the time. By tension-ed, I mean the belt is tight around the engine pulley all the time.

The belt tensioner will allow for movement (it’s spring-loaded) so the easiest way to do this is by pulling the belt over the side of the engine pulley and then, with both hands, turning the engine pulley until the belt falls off (Removing the spark plug makes turning the pulley easy).

With the belt off the engine pulley, it’s easy to guide it off the other pulleys. Check your old belt against your new belt, just to be sure.

The un-tensioned belt is simple to fit, and by un-tensioned, I mean the belt is loose around the engine pulley until you engage the blades. The belt can usually be maneuvered around the guides without much trouble.

As with the tension-ed belt, remove the belt from the engine pulley first.

Fitting Belt

Reference your diagram or pictures of routing. Refitting the belt is identical except in reverse order, fitting the engine pulley last by pulling the belt onto the side of the pulley and turning the engine over.

Timed Belt

Most mowers have a simple deck belt setup, like the one covered in this guide is more complex. The demo mower used here has two deck belts driving the mowing deck.

The first one is the main input belt which is powered directly by the engine. This belt is easy to replace, and you don’t need to remove the deck, just some plastic covers.

The second belt is the output belt, and it turns both blades in time. This allows the cutting blades to overlap and catch that annoying tuft of grass you sometimes see in the middle of your cutting strip.

To replace the output belt also known as a toothed belt or timed belt, we need to remove the deck from the mower. It’s not difficult to do, and the whole job shouldn’t take more than an hour.

This guide covers a timed deck belt replacement procedure. Most timed decks will look something similar. It’s more complex than other deck belt setups but not difficult to work on. In this guide, I will: remove the deck; inspect belts; replace the belt; tension the belt; set the timing of the blades.


No special tools are needed on this mission, but an impact gun would make life a lot easier. When you try to open bolts attached to pulleys, they tend to spin, which is a real pain. Sure, you can wedge it or grab it with grips, but you risk damaging the face of the pulley, and that in turn can damage your new belt. Nooo!

The impact makes small work of pulley bolts, and the better brands have a torque setting built-in which makes reassembly a gift. It’s a super tool to have in the trunk of your car; it makes changing a wheel look NASCAR slick. So treat yourself or drop a few hints before fathers day.

Chute – On this model mower, the chute is fitted through the center of the mower. Not all mowers will have a chute like this. If your mower is side discharge, then you don’t have one.

Remove – As said earlier, you may not need to remove your deck to fit a belt. On this model mower, removing to fit the belt just makes life a little easier.

Pins – Locate the deck arms. Most mowers will have one at each of the four corners. The deck will be fixed to the deck arms with Cotter pins. (Some may have nuts and bolts) Remove the two front pins and the two rear pins.

Slide – The deck will be free to move forward, which allows you to remove the deck drive belt from the engine drive pulley. In some cases, you may have a cable to remove; this depends on the blade engage type.

Push – With all pins removed and belt off, just push the deck sideways and it will pop off the arm bushing mounts. Apply some grease when refitting. Hey, I make that sound easy!

Inspect – Go ahead and turn the deck over to inspect the blades and blade boss (blade attachment). It’s likely that the blades are damaged; if they are, replace them.

Bent – If your blades are bent or worn, now is the time to take care of them. Replacement blades are easy to fit when the deck is off.

Boss – When your blade hits something hard, the blade boss pins are designed to break; this saves damaging more expensive components.

Replace – Check washers and bolts for damage. Blade bolts and washers are specially designed, so only use the original kit.

Remove – Remove plastic protection covers.

Pulley – Remove the drive belt tension assembly.

Key – Remove and store the key and the spacer ring safely.

Remove – Remove the timed belt protective cover.

Belt – Remove the broken belt, and check for damage.

Loosen – Loosen both pulley bolts; the bolts are positioned on the underside of the pulley.

Remove – Remove the two guide bolts. Remember to fit these after fitting the belt, but tighten them last.

Loosen – Loosen the two guide bolts.

Loosen – Loosen the lock-nut on the adjusting bolt, and thread it all the way out.

Push – Now push the tensioning assembly in all the way so it hits the adjusting bolt.

Set to 90° – Set the deck blades at 90° to each other.

Mark – Now mark the two main blade pulleys and the deck body as per the picture. Marking them with paint gives us a clear reference point when fitting the new belt.

Align – Keep your paint marks aligned and fit the belt to the tension assembly last.

Check – Check your paint marks again; it’s OK if you’re out by one or two teeth.

Routing – This is a typical timed belt routing.

Adjust – Adjust belt tension first, and tighten down the lock-nut. Do not tighten pulley bolts or guide bolts at this stage.

Check – Check belt tension as you adjust. Leave some play in the belt; it should deflect by about 1/2″ at its longest run.

Check 90° – Check that the blades are at 90 degrees. If all is OK, go ahead and fit the guide bolts, but don’t tighten them yet. Tighten the two pulley bolts, and now tighten the four guides.

Rebuild covers and fit the deck in reverse order; that wasn’t so bad!

Related Questions

Why does my deck belt keep breaking? Common reasons new belts keep breaking:

Why does my mower deck shake? Mower decks commonly shake because:

  • Engine not at the correct rpm
  • Engine not running correctly
  • Blades damaged
  • Deck belt damaged or worn
  • Spindle bearing damaged or broken

As you’re a MacGyver type, you’ll likely find the Riding mower troubleshooting and the Video repair library useful.

Hey, I’m John, and I’m a Red Seal Qualified Service Technician with over twenty-five years experience.

I’ve worked on all types of mechanical equipment, from cars to grass machinery, and this site is where I share fluff-free hacks, tips, and insider know-how.

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