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Hi all, I have an MTD 604 (model number 13AV604G671). I purchased this machine second hand and the motor runs well but have had a continuous problem with belts snapping.

I have been using high-quality parts not cheap belts. The local mower shop has "had a look" but cannot see any problem (although happy to sell me more belts..!) Despite this, I only get a few hours (4?) of mowing before the belt gives up and snaps. This is ridiculous.

Now, I have done a bit of detective work. Having just replaced the belt (again!) I did 10min of mowing and inspected the belt. Clearly the top of the belt has rubbed to black while the bottom and outside remain as new. At least this eliminates half the belt path. There is one pulley that looks plain wrong to me so was hoping one of you may be able to clarify. I attach a photo of the deck showing the pulley in question - also a shot underneath to show what I think is a strange angle and with two possible rub points indicated.

What do you think?

I can not find the the parts break down for your deck.
What is the serial number on the tag, DOM or the serial of the engine.

That is not a deck I am familiar with to my eye it looks like a spacer is missing from under the upper belt.
The upper pulley looks too small the belt keepers should be almost touching the pulley
Or perhaps this deck uses a heavier B section belt .

Do you have one of the old belts.
The wear pattern and breakage will tell us what is happening.

That deck was only used on a few mowers over a 1 or 2 year period, Heck that deck was a mid year change and the parts diagram for the deck was a sheet of paper stapled into the back of the owners manual. the diagram wasn't on the dealer parts lookup program. Bert that deck uses a 1/2 belt and both idler pulley arms pivot to absorb shock loads. the pulley to guide clearance seems fine since this appears to be an electric clutch engagement deck. It didn't stay in the system very long for a very good reason. And one of the problems with this deck was it likes to eat belts since the 1/2 belt doesn't hold up to heavy grass and the fact that both idler arms pivot would allow for excessive belt slippage.

To the OP Make sure you have the correct model number because it doesn't show up in the parts lookup system, including the dealer system. Also make sure that pulley that you have circled isn't leaning forward causing the front edge to run low. The pictures seem to indicate that the deck may be shifted forward since the main idler arm seems to be sitting too far back and allowing the upright part of that arm to almost rub the belt.

Got these 2 deck-belt diagrams from the MTD model 604 manual (operators guide)

..

Did a lil more digging... I THINK he has a 42in. deck .......

ILENGINE said:

That deck was only used on a few mowers over a 1 or 2 year period, Heck that deck was a mid year change and the parts diagram for the deck was a sheet of paper stapled into the back of the owners manual. the diagram wasn't on the dealer parts lookup program. Bert that deck uses a 1/2 belt and both idler pulley arms pivot to absorb shock loads. the pulley to guide clearance seems fine since this appears to be an electric clutch engagement deck. It didn't stay in the system very long for a very good reason. And one of the problems with this deck was it likes to eat belts since the 1/2 belt doesn't hold up to heavy grass and the fact that both idler arms pivot would allow for excessive belt slippage.

To the OP Make sure you have the correct model number because it doesn't show up in the parts lookup system, including the dealer system. Also make sure that pulley that you have circled isn't leaning forward causing the front edge to run low. The pictures seem to indicate that the deck may be shifted forward since the main idler arm seems to be sitting too far back and allowing the upright part of that arm to almost rub the belt.

Click to expand...

Thanks.
Hopefully very few found their way down here which would be odd because most of what fails in the USA gets dumped down here.

Thanks team for your knowledgeable replies.

I've attached a couple of pics to clarify (hopefully) the model and how the top of the belt has been wearing.







I also now realise the bearing for the pulley is on the way out. Not terrible but certainly some movement. It looks for all the world like it need to move down at the back, and up at he front by about 5mm.

To answer another couple of questions above.

1. Yes, 42" Deck
2. Electric clutch

For the record I prefer the old manual blade engage ... less to go wrong IMHO.

OK
Assuming you are stuck with this deck I would be inclined to get a much longer bolt for the pivot bolt on the tensioning arm and move the rear pulley forward so it becomes a fixed idler pulley and the belt routing becomes the usual T shape.
If there is enough depth on the engine pulley for a 5/8" belt then fit one.
Tensioning should always be on the slack side of a belt or chain for that matter so the only tensioning arm should be on the out side of the engine pulley.
By the look of the shape of the curved tab which resembles a belt keeper it looks like the original design had a fixed idler in this position.
At this point in time you have very little to loose and as it is coming to the end of the season you will have some mucking around time.
You might need to go to a grade 8 or 9 bolt and put a stiffening plate under the deck to stop it leaning.
When you have finished moving the pulley get some 5/8 rope and run it around all of the pulleys.
Stretch it till the tension arm is at 1/2 to 1/3 of its movement and that amount of rope is the belt you need , rounded off to the nearest whole inch.

Idler pulleys are specified by these dimensions which was pinched of the Stens on line catalogue.


The image is not true and double row bearings have not been used for decades.
Also the centre is a stepped bush pushed into a standard deep groove bearing, not an inner race extending out of the bearing.
Armed with this information you can measure the distance from the bolt hole to what looks like a belt keeper then look for a idler that will fit.

The left side deck idler pulley can be rotated until the flat part of the curved idler arm contacts the left rear deck lift bracket becoming a fixed idler pulley.