Which piston?

Time to do a top end job on my 99 YZ400. No problems with the bike, just figure I'll do it since I won't be able to ride for the next 6 weeks. Anybody have any recommendations as far as which piston to use? Wiseco, stock, others? I'm just gonna stay stock diameter. Has anybody run into problems with scoring or anything on their cylinder walls?

Thanks in advance,


I remember reading a post or two of owners who had cylinder bore scratches. The problem was that they didn't know what caused the scoring. If I were you, I would first pull the cylinder and visually examine the bore...and then feel with the fingertips....rubbing circumferentially, and then vertically. From this info, you should have an idea if there is anything drastically amiss. Next, take your cylinder, piston, new rings, manual(specifications) to a reputable shop for boring and matching.

Not long ago, I rebuilt the topend on a Yamaha 80cc(4-stroke) 4-wheeler for a friend and had excellent results from an outboard motor repair shop. The bike had been run in to deep DEEP water and had seized and sat out in the weather for 6 years. This outboard guy had the latest machines and knew how to use them. My friend still rants about how good this engine runs. He had to install a throttle stop to slow it down for his kids. I'm simply pointing out how important it is to find a good shop. I wouldn't recommend just arbitrarily changing rings without taking critical measurements.

It just came to me.....about the 426 cylinder. Boring directly might NOT be an option. If the bore is plated, then it would need to be bored and then replated.

[This message has been edited by Boit (edited 03-16-2001).]


As long as the scoring is not to deep you can get away with lighty honing the cylinder. I have done this on several of my plated cylinders with great success.

If you have questions about depth of the scores have an expert check at it and measure it for you.


Check carefully to be sure that the scratches are scratches and not left over pieces of piston that are stuck to the cylinder. I have never done it, but i have heard of people using acid of some type to remove piston bits from plated cylinders and having great results. Aparently it doesn't erode the plating but will disolve the aluminum from the piston. I didn't catch the entire thread so this may not apply to your situation but if it does then I hope this helps.

ive been riding for 12 years a have used nothing but wiseco i love them ive never seized or blown up a bike with them not to say that thier is any thing wrong with yamahas pistons they might be just as good or better but i have had very very good luck with wiseco there is one in my 426 right now so far so good

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