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Last year I bought a BM heart throb clutch kit. After the first 150 miles the primary spring broke. After the second 150 miles the second primary spring broke. When I asked for my third spring from BM, I requested the color of an Arctic Cat spring that would work. When BM emailed me back with the info they made a comment that maybe I had a bent crank. I although I took this with a gain of salt it did make me think. Up till this year I was taking the clutch off with a long handled breaker bar because I didn't have an impact like I do now. Is it possible I bent the crank? I have heard that bent cranks are more common in bigger displacment engines that have blown belts at high RPM's. How do you bend a crank other wise? Can I check it or do I need to take it to a dealer? If so how much cash to check it out? I ride a 99 ZL 600 Carbed with approx 3200 miles. Any info will help, after Im done working on the kids sleds I'm going to go through mine. Thanks in advance.
 

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Just a thought, But is all you want to do is check if the crank output bent and not running true?
 I would pull the clutch and place a dial on it near the end - then I would slowly turn the engine with the plugs removed and watch if the needle indicates if your not running true. Even the smallest deflection here will be too much.
But the real test is to pull your crank out and run 2 dials on it - while turning your crank between 2 roller V blocks.
   Alot of work though, I only do this when I change crank seals.

Good luck

P.S. If your output is not running true you would probably have a large increase in vibration and be breaking engine mounts.
 

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Johnny torque: Don't use a impact gun to remove clutch the impacts will damage your crank. I always use a bar and rope in the cylinder. One more thing did you have trouble before you installed the kit? Dino.
 

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Johnny,

I have had a simmiler problem on 00 ZR600EFI.  Though I was gitting about 200 - 250 miles per primary spring.  This was using the stock A/C 9-post primary.  I was using an EPI clutch kit though I belive that the problem is universal.  After breaking the two springs My dealer and I started to look a little deeper.  The first thing that we found is the spring seats in the clutch were  out of spec(to tight) .  So the Clutch goes to a local Machine shop to get that corrected.  ran 300 miles and snap goes the spring again. Pull the clutch and off to the dealer again. The dealer checked the clutch for ballance, and it was fine.  Then He told me to check the Crank Runout, said that it should not be more than .002"; so I setup a dial indicator on and find that it was .0001" out under the spec.  Next we tried another clutch to insure that is was not a binding problem Same thing 325 miles later.  being a little frustrated I tried a different brand spring that had the same rating (165-300). Snap again.  This time Dealer suggested to Try a Sno-Pro clutch.  After some recalabration and re-shiming to get it to perform more like the 9 Post unit thiings were better. I went 900 miles without the spring breaking. But it still broke on the last ride of the season.

I have a friend with the exact same sled as I have, he is still running the stock clutching and has had no problems.

After talking with a customer service rep at EPI, He said that the A/C primary clutches do not run long with the heavier springs.  Duh... at this point.  

The problem is that I like the way this thing runs with my modified EPI setup (added heavier weights). I have an engaugement of 4900 and a max of 8600.  Right where it should run.   I tried a different setup using a lighter spring and weights and a straight 51 degree helex.  This setup went 1200 miles with out a problem, but did not pull as hard.

So the next step is to try a Ti spring from Speedwerx. They say that Titainium is stronger and more durable.

Also, I do like the Sno-Pro clutch better.  It is lighter and runs much cooler. It is very simmilar to the Polaris 6 post unit.

Let me know what you come up with.

6Mile
 

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I would absolutley agree that it must be the clutch.  As for runout, there is a tolerance for that and you will need to look it up in the Cat book.

As far as heat in the primary clutch, that wouldn't have anything to do with weight, or how many posts it has, it would have to do with the clutch alignment.  As you probably know, you should check alignment when you change them.

I have aligned my clutches, and I can put my hands on the clutch after running hard, and they are only warm to the touch.  I am also putting a lot more power through them.
 

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this does happen alot that the springs in these kits do snap. if u want to check your crank out an easy way its quick. u just take your belt off. start the sled. put a staight edge across to the primary and u will see the runn out real fast it will be just a little but a little is to much. on the thunders,and machz i know for a fact that it does happen.when u snap a belt on top end check the crank. we just checked my buddy's out on his thunder cause he snapped a couple of belts up top and guess what? its out. he went thru two primaries they just craked. he was running a goodwin clutch kit/
 

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I would be careful with Ti. If is the same size as steel it is not as strong. Also, the problem with Ti is that is likes to twist, easier than steel.
 

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6mile
try a titaninm hot seat performance 140/330 pol 10 al weights 51.5  grams 56/50 helix yellow spring 4 th hole
turn motor at 8500-8600 long runs 8200 rpm short
I think you will like
gofast  
 

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No a breaker bar will not hurt your crank. The clutch screw threads will strip first.

Detonation, water in the cylinders (head gasket too), broken rings, and running them with extremely worn clutches all can bend cranks.

With the crank out of the engine, support at each end on the outermost 2 main bearing surfaces, put a Dial Indicator on the middle main, the runout will show up on the dial. Check the books for runout tolerances.
 

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I have had this trouble since 1998. The spring fits too tight in the cover,it should spin(easily)both directions in the cover!! Instead of machining the cover I have been grinding the side of the spring(not too much!!)and haven't had ANY problems since,give it a try!!
 
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