Crank nearing failure?

5 replies to this topic
  • Jake92

Posted June 17, 2008 - 06:40 AM


I have a hint of the little man with a hammer it seems in my motor. Only 15 hours on Piston and cam chain. 135 on Bottom end. How do I tell if my crank is indeed going out? Any secrets?

  • William1

Posted June 17, 2008 - 07:15 AM


Pull the barrel and see if the rod can be wiggled and if the crank can be wiggled in the bearings.

  • grayracer513

Posted June 17, 2008 - 07:39 AM


The manual shows how to measure the rod for wear. If it's really noisy, the clearance will show.

The piston could be the cause if it's a forged unit, particularly a Wiseco.

Rod noise is usually a "double" rattle that is most pronounced at higher revs when letting off the gas. It may disappear under a load.

Piston slap may be similar, but is more often a single knock, synchronized with the power stroke, and worse under a load at low speed. Usually not present at higher rpm.

Primary gear backlash is common and normal. It occurs most at idle, and almost never in gear.

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  • Jake92

Posted June 17, 2008 - 09:47 AM


Thanks gray as it sounds like mine is slap. Stock yamer piston though about 15 hours ago. Cheap insurance though. I notice it mostly under load at lower RPM's.

  • mkporn

Posted June 17, 2008 - 11:58 AM


You might check your clutch hub also. Just had a 06 450 that had a bit of knock. Told the guy that his problem was not a rod or slap but he wouldn't listen. I tore his motor down and upon re assembly noticed exessive slop in the clutch hub..........He didn't want to replace so I finished his motor with out a new hub, guess what......that knocky knocky was back and he was pissed. Told him to get a clutch hub and pressure plate......he did and the knocky knock was gone.

With the bike running at idle do you hear the knock? if you pull the clutch does it lessen?

Just a thought.

  • grayracer513

Posted June 17, 2008 - 12:17 PM


With the bike running at idle do you hear the knock? if you pull the clutch does it lessen?

Just a thought.

A knock is one thing, but don't confuse that with the growling rattle the transmission typically makes in neutral with the clutch out.


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