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Discussion Starter · #1 ·
Working on a buddy's '98 Cat ZR600. All the seals are original, so we thought we'd replace at least the crank seals. Upon splitting the case, I discovered some scratching on the end of the crank and in the case:
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Also there are heat cracks in the crank.
The PTO side is coming apart:
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We have to order a new pto side of the crank and have it replaced.
The sled ran top notch and would've never suspected this happening. Now, we are doing a full rebuild as I also found a piston skirt that's starting to crack. Lucky it was caught now and not on the trail.[confused2] Have also seen the other thread about it on here.

So, what causes this? Is it just something that happens once in a while or what?
 

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the crank is pressed together so in time they can come lose and move around.
 

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Press fits can move as the engine heats and cools, this is how they get out of sync as well.

The more power the engine outputs, the more likely it is to happen, and why racers weld the cranks... [thumb]
 

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ZR600's eat cranks. they are high vibration motors and just shake the crank apart over time. how many miles were on the sled?

my dads '98 ZR600 has been through 2 cranks in its 14,000 mile lifespan. he also has a 5500 rpm clutch engagement, the constant high rpm is probably one reason it doesnt like cranks. both cranks also broke in the same spot, right in the middle. ironically, both times it broke, he was just coasting at 25mph.
 

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Discussion Starter · #5 ·
I believe there's approx. 4500 miles on the motor. Right now the clutch engages about 4500 rpm's. It was a ton higher before we rebuilt the clutches and put a different kit in them. Hopefully the motor holds up a couple years after getting it fixed. If not, he said he's coming over to Polaris.[:D]
 

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hard launches, landing a jump under power can really shorten a cranks life span.
 
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