Mower Deck Belt Replacement
Tension-ed or Not
This type belt is always tight on the pulleys.
This type belt setup is slack on the pulleys until you engage the blades.
What Deck Type?
Rear discharge great at collecting grass, but doesn't like long grass so much.
Timed deck has a tooted belt which can break or slip out of time. Timing the blades allows them to overlap.
Some decks will have a flap that closes off the chute when the operator wants to mulch.
Side discharge is great for tall grass and rough terrain.
Measuring The Belt
What Belt Width?
What Belt Length?
Sometimes easier said than done!
Check under the hood of your mower, you may get lucky with a part number sticker, but be cautious with the Husqvarna labelling, they are often wrong belt part numbers.
Check your old belt for markings, if none, get a tape and some string.
These belts are measured in mm.
The new belt will be the full width of the pulleys.
Worn belts usually stretch in length and become narrow in the width.
Check Belt Routing
Belt Routing Links
Check under the foot rest of your mower, some models have a belt routing sticker.
This sticker is on a Husqvarna tractor.
This is a common deck fitted to lots of makes.
This type deck has a Mandrel brake, apply the blade engage lever after you have removed the belt from the engine pulley.
This allows you remove the belt.
What Belt Type?
AA Hex Belts
This is the most common type lawn tractor belt, it's used by many lawn tractor drive systems and most decks too.
The B type belt is a heavy duty A belt, its older well fed brother.
AA Hex Type
This is a double faced belt, it gives greater flexibility to deck design, as it allows both sides of the belt drive.
It's used on higher end tractor decks.
This type belt has become more popular in recent years. It's fitted to mower decks with overlapping blades.
Check Belt Wear
How Long do they last?
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, a mower that trows belts regularly, probably has a worn or damaged pulley.
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 - Replace the belt.
This can happen when a belt gets old, the material is starting to break down.
Your mower won't cut or collect very well. Better to take care of it now, before it breaks.
Cracking mostly happens to cheap belts. My advice is to only fit Kevlar long life belts.
This belt has a shiny hard surface, not much good for traction.
A belt like this will cause horrible vibration in the mowing deck.
Wear and tear, this belt is at the end of its useful life.
Check Pulley Wear
Metal or plastic, V type or flat, driven or idle. So many choices.
This is a V pulley, the driving side of the belt is making contact with the pulley.
A flat pulley on a V belt set up is never a driven pulley. Its job is to change the direction of the belt and guide it to the next pulley.
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).
Fitting A Belt
On this model mower the chute is fitted through the centre of the mower.
Not all mowers will have a chute like this. If your mower is side discharge, then you don't have one.
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.
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.
When all pins are removed, just push the deck sideways and it will pop off the arm bushing mounts.
Apply some grease when refitting.
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.
Remove the deck drive belt from the engine drive pulley, as you slide the deck forward.
Or if your leaving the deck on the mower, just pull the belt over the side of the pulley and turn over the engine (by hand) by turning the pulley, (spark plug removed) until the belt falls off.
Hey, I make that sound easy!
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.
If your blades are bent or worn, now is the time to take care of it.
Replacement blades are easy to fit, when the deck is off.
When your blade hits something hard, the blade boss pins are designed to break, this saves damaging more expensive components.
Check washers and bolts for damage. Blade bolts and washers are specially designed, so only use original kit.
Remove plastic protection covers.
Remove the drive belt tension assembly.
Remove and store safely the key and the spacer ring.
Remove timed belt protective cover.
Remove broken belt, and check for damage.
Loosen both pulley bolts, the bolts are positioned on the underside of the pulley.
Remove the two guide bolts.
Remember to fit these after fitting the belt, but tighten last.
Loosen the two guide bolts.
Loosen the lock-nut on the adjusting bolt, and thread it all the way out.
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.
Now mark the two main blade pulleys and the deck body as per picture.
Marking them with paint gives us a clear reference point when fitting the new belt.
This is a typical timed belt routing.
Keep your paint marks aligned and fit the belt to the tension assembly last.
Check your paint marks again, it's OK if your out by one or two teeth.
Adjust belt tension first, and tighten down lock-nut.
Do not tighten pulley bolts or guide bolts at this stage.
Check belt tension as you adjust. Leave some play in the belt, it should deflect by about 1/2" at its longest run.
Check that the blades are at 90 degrees.
If all is OK, go ahead and fit the guide bolts, but don't tighten yet.
Tighten the two pulley bolts, and now tighten the four guides.
Rebuild in reverse order and don't forget to fit the spacer ring and key.
That wasn't so bad!
- Wrong belt routing
- Misaligned pulley
- Damaged pulley
- Belt guide missing
- Belt guide damaged
- Belt too loose
- Belt too tight
- Belt too narrow
- Wrong belt type
- Blade obstruction
- Engine not at the correct rpm
- Engine not running correctly
- Blades damaged
- Deck belt damaged or worn
- Spindle bearing damaged or broken