piston and cylinder replacement?

Just tore down the engine to remove damaged piston and cylinder. cylinder just has a dime sized section where I guess the piston fused to it (no oil) Can the cylinder be refinished or just replaced? Before I replace these with factory parts, what is needed if I wanted to put a bigger-bore piston and cylinder into it? Can you give me the name(s) of aftermarket big-bore specialists and your opinion of putting one in.

Check around on plating. I had a ported CR250 which I re-plated. If it wasn't ported, it would have been cheaper just to replace the cylinder.

I too have a damaged cylinder. I have heard no great news, or any news really on boring out this bike. MXA did a eval on the White Bros. overbore kit. ACCORDING to MXA, this drastically reduced bottom end life. One person on this site had his cylinder bored. It worked for him w/ no problems. I am still up in the air what to do. All my work will be done over next winter.


99 WR, all YZ mods, de-octopused, OEM YZ tank and seat, jetting by Clark.


For clarification: WE'LL be having a KICK ASS time in Moab!! Right Mitchy & Bill?!!

Thanks Kevin, could you define plating and porting for me? Also how are you riding if you're going to do the work later?

I have some minor scrapes in my cylinder wall. They do not warrant repair immediately.

Plating is the Nickosil (spelling?) coating applied to your cylinder wall. Think of it as essentially a chromed bore. There are several companies out there that do this. It has been argued that some of these companies don't do a real good job at this. If this is in fact the case, you would be better off replacingthe cylinder w/ a OEM cylinder from Yamaha.

Porting on a two stroke involves cutting/enlarging the intake and exhaust ports. These ports are in the cylinder wall. On a 4 stroke, porting refers to head or valve work. No work is performed on the cylinder. On a ported 2 stroke, it behooves you to have the cylinder re-coated. Some of these port jobs go up to $300.00.

if you've got that kind of 'skidmark in your pants' on the bore look-you can save it! you have to buy a bottle of Acid & all the safety gear. you then have to use swabs & rub it in, agitating it. you can get these things back to new. remember that Nikasil is really tough! i mean really really tough. the piston should give up if it just nipped up.

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