Wiseco vs. Stock

I have a 2000 YZ426 and was curious if anyone knows if a Wiseco piston has more piston slap than a stocker. I shimmed my valves to spec and checked the timing chain. They seem to be good but I still have a noise that is more than the typical noise these engines seem to produce. Almost like a tapping noise that is getting progressively louder. I even checked the key on the counter balance shaft and it seems to be ok. I pulled the head and jug off. It has a Wiseco 4693M09500 piston. I checked it out on google and it comes up as a standard bore 95mm piston. I will check more tomorrow to see if there are any signs of wear.

guessing but your cam chain tensioner may not have clicked up to where it was before you reset it when you put the piston in? it may need a little help

the cam chain was tight. No slack at all.

does noise go away after motor is warm?

Wiseco's do have a reputation for being a little noisier. Typically, piston slap will be heard as a double rattle while idling ("ka-dink"), and/or more often as a clank or clinking sound with each power stroke as you run the engine up under light throttle. The idle noise is usually almost impossible to pick out of all the normal racket caused by primary gear backlash and transmission rattle, but if it's bad, you can hear it. It isn't good, but it usually isn't a problem. It would be much more serious if a stock piston were to do this, since that would indicate something was wrong with it.

Also, remember that the 2000 has a balancer drive gear located on the crank by a square key, and the primary drive gear can loosen and allow this to rattle, which will eventually damage the crank beyond use. Might want to look at it.

I checked the key in the counter balance but it was fine. I did notice the wrist pin has some play in it. You can twist the piston about an 1/8 inch in either direction. It also has some side to side play too.

This twisting and lateral play, is it being done with the cylinder in place, or is the cylinder off the engine?

There should only be about .001" play in the wrist pin, so you should not really be able to rotate it very far. If you're looking at it from the top of the bore, you could be seeing rod clearance as being in the wrist pin. Side to side motion is not controlled to any great extent by the piston or pin either one.

This twisting and lateral play, is it being done with the cylinder in place, or is the cylinder off the engine?

There should only be about .001" play in the wrist pin, so you should not really be able to rotate it very far. If you're looking at it from the top of the bore, you could be seeing rod clearance as being in the wrist pin. Side to side motion is not controlled to any great extent by the piston or pin either one.

I checked it with the cylinder in place.

I put in a Wiseco piston in my '00 426 and it had an additional .001 clearance compared to the old piston I took out, and it made noticeable noise compared to the old 225 hr piston I took out, one good thing is it is still in the bike at 535 hrs and makes the same noise, no more and no less. Don't worry about it.

I checked it with the cylinder in place.

Having done it that way, you can't tell whether the rotation you're seeing is from clearance in the rod bearing, the wrist pin, or both. If you can really move it an eighth of an inch in rotation, I'd be concerned enough to pull the jug off and check both points.

i have the jug off now. I will check the play once I get home.

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