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Omniscient Aardvark
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Discussion Starter · #1 ·
The clutch on my bike grabs if I rev it above around 6,000 RPM. It'll jerk very hard, the engine speed will drop, and then it'll start slipping again until it gets revved up again. It's been doing that ever since I got it a couple of years ago. Actually, it didn't do it the whole time. I was forced to do an engine swap at one point. Shortly afterward, I could launch the hell out of the bike at 10,000 RPM. But now, it's started doing it again, so I don't think it's the clutch itself since it's another engine.

The only thing I can think of is the oil. I used to always run Mobil 1 MXT4 in the old engine. When I first got the new engine, I initially ran some cheaper oil, Pennzoil or Valvoline or something (but without the energy conserving label) while I was making sure everything was working right. This was when I was able to rev up high and take off. Just a couple of weekends ago, I switched to VR4. (They were out of MXT4.) I noticed just a few days ago it was doing it again. So the oil is my only guess. Does it make sense that the expensive racing oils would make my clutch grab? Anyone had this problem? It's very annoying and very embarrasing. I rarely rev it up high enough to notice, but when I do, it feels like something's going to break.
 

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second chimp in space
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3,344 Posts
is there any slack in your cable? there's an adjuster where the cable comes out of the lever. Make sure there's noticeable slack, and that it never gets tight if you move the handlebars side to side.
 

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Omniscient Aardvark
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812 Posts
Discussion Starter · #3 ·
It's definitely not the cable.
 

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second chimp in space
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3,344 Posts
So the clutch was perfectly fine for a while with the new engine, then started slipping?
How much do you like those high-rpm launches? It could just be wearing out.

Next time you change the oil pop the clutch cover off, take out a couple disks and measure them. Also measure the springs. The tolerances are in the service manual, I'm sure you can find a pdf of it.
 

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1,510 Posts
10 000 rpm launches will not help the life of your clutch check cable or make sure the hydralics has good fluid and is bleed up properly. But I'd say you've ethier fired the steels in the clutch or simply worn it out. It could also be an affect of fried engine oil might be worth shunting an oil change through it with a good quality bike specfic oil (car oils can do wierd stuff to clutches as well).
 

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Omniscient Aardvark
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812 Posts
Discussion Starter · #6 ·
The clutch is not slipping, it's grabbing. I've never had it slip. It's definitely getting friction. I'm pretty sure it's not worn in any way. I've only done high rev launches two or three times with this new engine. Note that the "new" engine is actually a used one from eBay, but I've only put maybe a thousand miles on it since I got it and I've been taking it very easy, not one wheelie.

The grabbing really worries me. It feels like it's going to break the chain or something. So I don't do it, but it sucks having a high performance sportbike that you can't wring out.

Again, I'm thinking it's the oil, but I find it highly unusual that Pennzoil doesn't do it while $10/qt Mobil 1 4T racing oil does. It's motorcycle racing oil. I have a racing motorcycle. What the crap? I may switch back to the cheap oil soon to check it, but it pains me to watch that expensive oil drain out.
 

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So let me get this straight…

You hold the clutch IN, bike in 1st gear I assume…. Then when you rev the engine everything is fine until the engine gets over 6K right? Then you say the clutch grabs hard even thou you are still holding it in?

Sounds strange to me, almost like some centrifugal force is acting on the clutch causing it to close.
 

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Omniscient Aardvark
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812 Posts
Discussion Starter · #8 ·
So let me get this straight…

You hold the clutch IN, bike in 1st gear I assume…. Then when you rev the engine everything is fine until the engine gets over 6K right? Then you say the clutch grabs hard even thou you are still holding it in?

Sounds strange to me, almost like some centrifugal force is acting on the clutch causing it to close.
No. It doesn't grab until I start to release the clutch. Once I hit the friction zone, it'll jerk hard, the RPM will drop, and the clutch starts to slip again until it revs back up. I've even tried just letting out the clutch at low RPM until there's just a little friction, holding that exact position, and then giving it throttle. It does the same thing. I wish I had a bike cam that I could use to record this.
 

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second chimp in space
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3,344 Posts
If you're doing highway speeds and you suddenly floor it, will the clutch slip? Without touching the clutch lever at all.

another test:
run the bike up to a wall or tree or other immovable object, and put it in 1st gear. Slowly release the clutch lever. Does the engine die, or does the clutch slip?
 
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