'98/99 Vmax 700 clutch heat

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ceekay

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Dec 5, 2021
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Both my 700s are heating up clutches. Every forum post says they should be slightly warm or cool to the touch, but mine are always warm or sometimes too hot to hold your hand on, especially the stationary sheave. The inner sheave is always hotter than the outer. The primary is always too warm, but the secondary is only sometimes too warm. After long, constant throttle stretches, they're always much cooler than low-speed stuff.

I've adjusted center-to-center as close as I can to 267-270mm per manual, bought a SnoStuff offset tool for offset of 15mm, cleaned my clutches, scuffed the sheaves with Scotchbrite, cleaned my belts, adjusted belt tension/height in secondary, and they still get warm or hot. I've had both engines out, and motor mounts seem fine. I'm using 8DN belts in both sleds. I haven't noticed burnt rubber on the sheaves.

The sleds run and ride great, rev up to about 9k, and no belt squeal. One sled is running a fresh Comet 108EXP with appropriate tuning based on their charts, and the other has a stock Yammie. The stock clutch has spider cracks near the shaft on both sheaves - I don't know if these are new, but I think I need to replace it now.

If I could find one of those expensive tools that hold the center-to-center and offset specs in place while you tighten the mounts, I would buy it, but I can't find one anywhere. Pretty much willing to do anything just to solve the problem and not have to worry about my clutches exploding.

Also, the secondary clutch has free play on the shaft, and I understand this to be by design. When adjusting the 15mm offset, should I press the sheave flush with the jackshaft bearing, or pull it out the other way? Neither the Yamaha nor Clymer manuals mention this.

Does anyone have any ideas?
 
Well, 9000 rpm is your issue. These early 700 red headed motors originally had a 8CH belt. They no longer make it, and the 8DN is a harder compound. You will need to add heavier rivets to the weights, or use a heavier weight than the stock 8CH. I like RPM to be around 8500 with that motor.
 
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what degree is your secondary clutch set at? Its all about pressure > if your sec. is too loose , you spin belt more , creating heat! try running 70 or even 80* on your clutch, see if that dont help and unless you have triple pipes on those you should be topped out at about 8500 to 8700 rpm!
 
Thanks for the tips. Checking GoPro footage confirms, WOT runs puts the needle right on 9k RPM and it sticks there. That's the sled with the Comet clutch - not sure about the one with the stock.

yammy said:
what degree is your secondary clutch set at? Its all about pressure > if your sec. is too loose , you spin belt more , creating heat! try running 70 or even 80* on your clutch, see if that dont help and unless you have triple pipes on those you should be topped out at about 8500 to 8700 rpm!
Click to expand...
Cleaned the secondary real well before 4 days of riding last weekend and set it per the manual to 60* (slots 3-3). Will definitely try 70 or 80* and see what happens.

Other question - would y'all bother rebuilding a Yamaha primary? I know most guys here stick to stock, and the library of tuning data is extensive, but my only Yamaha options seem to be buying OEM for close to $400 JUST for the 2 sheaves I need to replace (tiny cracks near the shaft) or gambling on an eBay primary for $300+ with likely the same issues.

I bought a Comet 108EXP primary for around $350 which has held up fine (with the exception of some over-rev apparently), and that seems like my only affordable option as of now.
 
You only need more weight in the primary weights, or, you could also try a lighter spring in the primary. Either one will drop rpm.
 
Pulled the Comet primary today to take a look. Turns out I have AC-1 weights which are 5 grams lighter than the AC weights I should have. Conveniently, I had a spare set of new AC weights that I just put in. If we get snow again this season, I'll try it out.

As for the sled with the stock clutch, I have 8CH weights which I believe are stock. I can't tell what spring I have; I think the colors are long gone/worn off. Free length is 81.8mm which should be in spec. Not sure why this one is also heating up.
 
That one is heating up because it’s slipping more with the harder belt.
Just like every other 1997. It needs more weight also.
 
Well, we got a crazy snow storm that dumped ~10" of the heaviest, wettest snow I've seen. I installed the 5-gram heavier weights in the Comet clutch I had on the 700 XTC, stock secondary at 60* twist, and I couldn't even ride. My RPMs did drop to a nice 8500 at WOT, but it was 42+ degrees out, the snow was terrible like glue, so much resistance on the skis, and felt like the track would rather spin than push the sled forward.

Worst part, the clutches were COOKING no matter what I did. I tried an 89L belt, a newer Ultimax, and the 8DN I have, and a combination of secondary twist angles from 50*-80*. Nothing seemed particularly better or worse. Primary and secondary were getting very hot and so was the belt. This is after literally 1-minute rides in the staging area.

Checked all the standard stuff: track moves free, chain tension is not too tight, brakes are free, etc...

I'm at a loss. Sucks to have such a great running powerful sled that I can't ride because of this. Any other suggestions are welcome.

Thinking about buying a lighter spring for the Comet primary to get some more bite on the belt, and keep going lighter until it starts to bog.
 
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