Possible Rod bearing problem

6 replies to this topic
  • s3706

Posted January 03, 2005 - 10:04 AM


I was out riding new years eve and the bike seemed to be running fine. When all of the sudden on my last lap of the day the motor started making this clanking noise like something let loose inside the motor so I killed the motor and rolled of the track. When I got home I tore the top end down and I could see where the skirt on the front side of the piston had come in contact with the cylinder wall there was some slighty scoring on the cylinder wall. I checked the rod and there is a very small amount of up and down movement. My guess is that the rod bearing on the crank needs to be replaced or maybe I just need a new piston and to have the cylinder repaired.
What do you guys think?

what a sucky way to start off the New Year?

  • grayracer513

Posted January 03, 2005 - 11:11 AM


Try to recall exactly what the noise was like. In general, rod bearings will rattle when the load is removed from them at speed. So, if you raise the engine rpm and then chop the throttle, the rattle should immediately grow louder.

Pistons will usually rattle more under a load than when free, so if the rattle is louder as the engine speed increases than when holding one speed, it is more likely a piston than a rod.

The scuffing on the skirt is not good, and the piston pretty much certainly needs to be replaced. If you can actually feel or measure vertical clearance in the rod bearing, it's probably bad, too, since it should have only about .001" of play or less. Pull up on the rod with one hand and tap the toop with a rubber mallet or your other hand and see what that looks like.

Good luck :cry:

  • s3706

Posted January 03, 2005 - 11:55 AM


When I started it backup after hearing the noise there was no real noise at idle, but when I would rev it up you could hear the clanking noise like the piston was hitting the cylinder. I think I will hone the cylinder and put a new a piston in it and see how it runs. The bike is a 2000 426 maybe it is time to rebuild the crank with a new rod kit. :cry:

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  • curtains23

Posted January 03, 2005 - 02:08 PM


Do not run this engine, strip it, any play in the bearings is BAD NEWS, if there is any play it will allow the piston to hit the cylinder head or valves,strip it, sort it and then run it on motul v300 sport, the oil is beyond belief, and will not destroy the clutch ... GOOD LUCK

  • grayracer513

Posted January 03, 2005 - 04:43 PM


If it's a '00 426, that raises the possibilty of the noise being a loose balancer shaft key. The '00 used a key to locate the balancer shaft drive gear instead of splines like the later models have. These quite commonly work loose, beat up the keys and cause the sort of noise you're talking about. Check it out.

But check that rod carefully, too. :cry:

  • felony

Posted January 04, 2005 - 06:32 AM


replace the rod immediately,i went through the same thing this summer,i saw the scuffing on the cylinder and the rod "seemed" tight so i just replaced the piston,BAD move.the bike locked up and after tearing it down again,i took it to a performance shop and when they looked at my cylinder,they told me my rod was bad,ANY play in the rod will cause a "twisting" motion and the side to side motion will cause piston scuffing on the cylinder.so i had to get a new cylinder after that :cry: .i know its not good news but if you have to,get the new crank assembly and be done with it.my 01 was on the original bottom end so i figure4 yrs aint too bad..lol good luck

  • s3706

Posted January 04, 2005 - 07:47 AM


Last night I used a feeler gauge to check the side to side movement of the rod on the crank and it was .011. I am going to split the cases and send the crank off to be rebuilt with a new rod kit and have the cylinder repaired.

Thanks for the Info. :cry:

While the thumper is being repaired I have to ride the 2 smoke. :cry:

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