Blew Belt, Sheared Primary Bolt Off, 2 XS825 Belts Gone in ~160 miles

[74Nitro]

Good to here another member is experiencing what I have also. 3k on last xs belt. It’s now my spare. 9400 miles with stock clutches and barely any kind of roller wear or issues. I blew up two carbon belts in the first 5 hundred miles. None since. Switched to more helix angle and also did the hurricane offset tool thing. 170 is very respectable for a long 30 mile pound. I run big wide open stuff in the UP and I usually run in the 140’s. But I have been into the mid 150 ‘s on long hard pulls. Also when temps are running a bit higher outside I have noticed I run slightly warmer also. But I have not seen more then 155 with setup. I have run this set up with 3 different belts and minor adjustments on spring tension in secondary. I also played around with different secondary springs. I have run setup almost 9 k. IMO most are running slightly to much weight and or to much secondary tension. I run fairly heavy secondary but I also use a higher helix angle. I’m not a huge big end guy but I can run up into the mid to upper 120’s on speedo. Conditions dependent obviously. 270 tune.

What angle r u using?

 

[ClutchMaster]

What angle r u using?

Jon’s running an stm 38 which is around the same as a Dalton 40~41, stm’s for whatever reason are off.

 

[ClutchMaster]

Probably cause not many running that combo.


60.8 measured from back of primary to front of secondary on his setup may be way out of whack.

Well what’s the Magic number?

 

[ISLANDRACING]

Well what’s the Magic number?

That's what were trying to figure out on this combo because the is no tool, nor does anyone have a set # yet. My TAPP/PRO4 is 59.1 mm offset( spacer and circlip removed )

 

[NYTurbo]

Well what’s the Magic number?

Depends on how your coming up with the 60.8. If your saying it's within Yamaha specs that really means nothing depending on how your measuring the offset and taking into account the sheath thickness.

 

[ClutchMaster]

Depends on how your coming up with the 60.8. If your saying it's within Yamaha specs that really means nothing depending on how your measuring the offset and taking into account the sheath thickness.

Of course I know that. I thought Dave would have given a specification. STM gave me their spec when I bought my clutch but it was slightly off imo, just ballpark. Obviously it’s close to what others have so it’s not the taper being machined incorrectly, just saying.
Anytime you buy an aftermarket clutch/clutches you should verify belt straightness.

 

[snowcaine]

Ok little update. Received the TAPP clutch back from Dave extremely fast. Finally received and installed the new stub shaft assembly. Many thanks to J&J Racing for sending me a loaner stub shaft in the interim, and many thanks to Tcat100 for clutching and general sled setup advice. I would be trailering my sled to his house this weekend for clutch measurements, but corona.

Based on the measurements I took and the visual comparisons I made, it appears the old stub shaft was "pushed into" the bearing housing assembly approximately 1.5 mm compared to the new stub shaft assembly. In other words, the stub shaft was pushed in toward the crank ~1.5 mm compared to the new assembly. It also appears the clutch-side of the outer bearing on the old unit has an inward concave look compared to the new stub shaft assembly.

If blowing a belt can cause a stub shaft to move inward, I believe what I measured and saw confirms that hypothesis. I was running at the outer limit of Yamaha's offset spec (although I was running a TAPP/Pro 4 combo, so who knows what value that even has) to begin with, so I believe an additional 1.5 mm of offset caused by the stub shaft moving inward would likely contribute to prematurely blowing a second belt, which I did in ~60 miles.

Old And New Stub Shaft Side-by-Side Comparison

• snowcaine
• Mar 18, 2020

Old Stub Shaft Bearing Seat View

• snowcaine
• Mar 18, 2020

New Stub Shaft Bearing Seat View

• snowcaine
• Mar 18, 2020

Crank And Housing With Stub Shaft Assembly 2

• snowcaine
• Mar 18, 2020

Crank And Housing Without Stub Shaft Assembly 1

• snowcaine
• Mar 18, 2020

 

[sledding rocks]

That's what were trying to figure out on this combo because the is no tool, nor does anyone have a set # yet. My TAPP/PRO4 is 59.1 mm offset( spacer and circlip removed )

ok , heres how I set my offset , stock primary and stock secondary , I ended up 59.7mm , using a straight edge on the back side of the primary and measuring from the outside of the secondary which is 59.3mm , this offset gave me 2500miles of trouble free belt issues , I also had to remove 2mm off my secondary post to get me this offset , zero spacers , circlip still in place ,
now im using Tapp/stock secondary , looking at the Tapp vs stock primary , side by side on the bench looks pretty equal , but once I bolted the Tapp and measured the clearance to the back of the engine , it gave me just under 1mm more clearance then the stock clutch , so therefore I added a spacer to the stock secondary and ended up with 59.3 offset ,this offset worked well also ,
now I set up my Tapp / stm secondary , this was alittle bit more tricky , hard to compare the stock secondary vs stm on the bench , the stm using much thicker material on the face , so this is how I did it , I opened up my stock secondary put a straight edge in the centre of it and closed up the secondary then applied it on the sled , then rotated the secondary and the straight edge setting on the inside of the primary and took a measurement and put a mark on the clutch were the straight edge touch the primary .this gave me a base mark , now I repeated the same procedure with the stm secondary using the straight edge , I had to remove the spacer to get 59.3mm offset , circlip still there , hope this helps