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

[snowcaine]

Blew two XS825 belts in ~160 miles. On the second blow, primary bolt sheared off. Pics below.

On 2/15, first time out with 192 studs, clutch temps were both running super hot. Friend behind me smelled burned rubber occasionally when he got close to me at stops. After ~100 miles of riding, we drag raced. No problem. Then I foolishly immediately did another WOT pull. Belt literally disintegrated. I have no idea where it went. I have a few pieces and cords, but I have no idea where 90% of the belt went. XS825.

Swapped the belt out that night to another new XS825. Pulled the primary because a decent amount of belt cord got wrapped behind the primary on the stub shaft. Torqued the primary back down 108 ft-lbs, backed off, then 43 ft-lbs.

On 2/16, did another ~60 miles and went out on the lake before putting sleds away. At ~8,500 RPM, belt blew and this is what I saw when I opened it up:

Blown Belt and Sheared Primary Bolt

• snowcaine
• Feb 17, 2020

Blown Belt and Sheared Primary Bolt

• snowcaine
• Feb 17, 2020

How do I fix this problem? I mentioned this being the first time out with 192 studs because two weeks ago pre-studs I was WOT every other corner and over-revving at ~9,300 RPM with no blown belts. I added arm weights to the TAPP clutch and now I'm sitting right at 8,950 - 9,000 RPM WOT but destroying belts now that I added studs.

My secondary has a 43/34 Dalton helix with a black/purple 114/175 spring. Because of the initially high clutch temps (too hot to touch), my thought was the secondary is keeping too much pressure on the belt.

Now that I blew another below not even at WOT, I'm guessing my stub shaft got whacked in when I blew the first belt.

I really need some help from the knowledgeable members please! Thank you!

 

[KnappAttack]

Too much pinch in the secondary for the 825 belt would be correct. Everyone is doing that heavy secondary setup with the TAPP because they don't want to or won't take a bunch of weight out of the primary. Might do fine on the 8DN, but way overkill on the 825.

Check that stub shaft! Hope its not bent now too.

Next time lap the clutch to the shaft w/valve lapping compound.

 

[ISLANDRACING]

325 mi on this 8DN Tapp/pro4 combo. Extreme full throttle to full brake corner to corner trail riding, came out into a field, whacked it then BAM. Tapp runs cool to ever so slightly warm, Pro4 very warm, but can hold hand on it. Combo is smooth as hell when riding but belt life is definately concerning.

 

[Tcat100]

Too much pinch in the secondary for the 825 belt would be correct. Everyone is doing that heavy secondary setup with the TAPP because they don't want to or won't take a bunch of weight out of the primary. Might do fine on the 8DN, but way overkill on the 825.

Check that stub shaft! Hope its not bent now too.

Next time lap the clutch to the shaft w/valve lapping compound.

I run more helix than that with no issues in 4000 plus miles. How does this spring compare to the arctic/STM green? One thing I would say is that anytime I veered from that green spring in the secondary, didn't like the results. But its not that his helix is too much, more likely it's not enough. Only the 32 I finally ended with kept the heat in the secondary low enough.

 

[sledding rocks]

View attachment 153271 325 mi on this 8DN Tapp/pro4 combo. Extreme full throttle to full brake corner to corner trail riding, came out into a field, whacked it then BAM. Tapp runs cool to ever so slightly warm, Pro4 very warm, but can hold hand on it. Combo is smooth as hell when riding but belt life is definately concerning.

can u share more detail of your setup with the Tapp and pro 4 ?

 

[ISLANDRACING]

can u share more detail of your setup with the Tapp and pro 4 ?

43/34 with the black/purple also. tapp: +1 rollers, longer roller bolt empty to bring r's down for the 8DN

 

[sledding rocks]

I run more helix than that with no issues in 4000 plus miles. How does this spring compare to the arctic/STM green? One thing I would say is that anytime I veered from that green spring in the secondary, didn't like the results. But its not that his helix is too much, more likely it's not enough. Only the 32 I finally ended with kept the heat in the secondary low enough.

arctic /stm green 96lb/157lb
black /purple 114lb/175lb (snowcaine ) to much spring

 

[Crossfire12]

View attachment 153271 325 mi on this 8DN Tapp/pro4 combo. Extreme full throttle to full brake corner to corner trail riding, came out into a field, whacked it then BAM. Tapp runs cool to ever so slightly warm, Pro4 very warm, but can hold hand on it. Combo is smooth as hell when riding but belt life is definately concerning.

It was the extreme full throttle full brake and then hammer it again, with all this HP. That’s why the belt broke, try that with your car a bunch of times and see how the tranny holds up!!!! RIDE it like a four stroke not a two stroke and you will save on belts.

 

[WinterWolf]

It was the extreme full throttle full brake and then hammer it again, with all this HP. That’s why the belt broke, try that with your car a bunch of times and see how the tranny holds up!!!! RIDE it like a four stroke not a two stroke and you will save on belts.

Yup. With this much power you can pretty much snap belts at will if you do that.

 

[WinterWolf]

My TAPP has been cool/cold every time I checked it...even after big rail bed miles(25-30 miles of high speed running 80-100 mph plus)), Pro 4 warm to quite warm but could put hand on it. XS belt looks fine with 300 miles on it so far.

I don’t punch mine and then full brake it, and then full punch it again though...I know that’ll cause issues. I don’t need to ride like that it in N. Maine though with the big duper highway trails.

 

[sledding rocks]

Blew two XS825 belts in ~160 miles. On the second blow, primary bolt sheared off. Pics below.

On 2/15, first time out with 192 studs, clutch temps were both running super hot. Friend behind me smelled burned rubber occasionally when he got close to me at stops. After ~100 miles of riding, we drag raced. No problem. Then I foolishly immediately did another WOT pull. Belt literally disintegrated. I have no idea where it went. I have a few pieces and cords, but I have no idea where 90% of the belt went. XS825.

Swapped the belt out that night to another new XS825. Pulled the primary because a decent amount of belt cord got wrapped behind the primary on the stub shaft. Torqued the primary back down 108 ft-lbs, backed off, then 43 ft-lbs.

On 2/16, did another ~60 miles and went out on the lake before putting sleds away. At ~8,500 RPM, belt blew and this is what I saw when I opened it up:

Blown Belt and Sheared Primary Bolt

• snowcaine
• Feb 17, 2020

Blown Belt and Sheared Primary Bolt

• snowcaine
• Feb 17, 2020

How do I fix this problem? I mentioned this being the first time out with 192 studs because two weeks ago pre-studs I was WOT every other corner and over-revving at ~9,300 RPM with no blown belts. I added arm weights to the TAPP clutch and now I'm sitting right at 8,950 - 9,000 RPM WOT but destroying belts now that I added studs.

My secondary has a 43/34 Dalton helix with a black/purple 114/175 spring. Because of the initially high clutch temps (too hot to touch), my thought was the secondary is keeping too much pressure on the belt.

Now that I blew another below not even at WOT, I'm guessing my stub shaft got whacked in when I blew the first belt.

I really need some help from the knowledgeable members please! Thank you!

fyi last season my buddy tuned hurricane 290 hp sled , he decided to put on the stm primary and secondary clutches , he started out with a 44/38 helix with the green arctic spring . he's secondary was so hot u could not touch it , once he went with a weaker spring (epi purple spring ) helped with lower temp on his secondary , I agree with mike knapp the black /purple is over kill ,

 

[Big_Phil]

It was the extreme full throttle full brake and then hammer it again, with all this HP. That’s why the belt broke, try that with your car a bunch of times and see how the tranny holds up!!!! RIDE it like a four stroke not a two stroke and you will save on belts.

I have to disagree. If you cant ride like this without cooking a belt, your clutching calibration is incorrect. If you break an xs825 period, your clutching is off. Its not the power. We run 8JP belts on our turbo viper, pulls 1.1 60 foot times on the TD GPS , 420++hp. We can do 100 passes on a belt without breaking it. Hot lapped it countless times during testing and racing.

A well setup car can launch hard 1000s of times without breaking things.

 

[snowcaine]

Too much pinch in the secondary for the 825 belt would be correct. Everyone is doing that heavy secondary setup with the TAPP because they don't want to or won't take a bunch of weight out of the primary. Might do fine on the 8DN, but way overkill on the 825.

Check that stub shaft! Hope its not bent now too.

Next time lap the clutch to the shaft w/valve lapping compound.

Mr. Knapp, thank you for your knowledge. What do you mean by lap the clutch to the shaft with valve lapping compound? Sorry for my ignorance. Thanks.

 

[KnappAttack]

Mr. Knapp, thank you for your knowledge. What do you mean by lap the clutch to the shaft with valve lapping compound? Sorry for my ignorance. Thanks.

What you do is clean both the shaft and inside clutch surfaces and apply a bit of valve lapping compound to one surface or the other, then apply pressure to the clutch while spinning it on the shaft to provide a perfect fit so they can mate up over the entire surface they are supposed to seat on. Once this is done clean off both surfaces and bolt the clutch on. But on the 998, only spin the clutch in the direction the engine would run as to make sure not to turn the crankshaft backwards, possibly having the exhaust cam come out of time.

Valve lapping compound has abrasives in it, so it would be like sanding both sides to a perfect fit to one another rather than sitting on high spots. This prevents the clutch from spinning on the shaft or perhaps coming off the shaft if the bolt broke.

Just do this to the clutch and shaft rather a valve and head.

 

[74Nitro]

I have to disagree. If you cant ride like this without cooking a belt, your clutching calibration is incorrect. If you break an xs825 period, your clutching is off. Its not the power. We run 8JP belts on our turbo viper, pulls 1.1 60 foot times on the TD GPS , 420++hp. We can do 100 passes on a belt without breaking it. Hot lapped it countless times during testing and racing.

A well setup car can launch hard 1000s of times without breaking things.

I think the point crossfire is making is that the brakes were locked, and the secondary was not given time to shift back,(because it wasn't turning), and then the throttle is hammered while the belt has some slack.