Cyl. Thrust Zone Wear

Hey guys. Just wanted to get a few thoughts on this cylinder I pulled off last night. It seems to have some excessive wear in the thrust zone(s). I know that the the majority of the wear will occur @ the top of the range of the ring travel, but I haven't seen it this bad before as a hobby mechanic. On the EX side it looks like the rings have worn through the Nikisil, it's a pretty deep gouge. The INT side just looks like there's some material deposited on the coating, not actually worn. Background on the engine is '06 yfz450 (actually out of a quad) that I'm working on for a friend. He's only owned it for about six months now, and we know nothing of the previous maintenance. I pulled the jug off late last night, so I haven't taken any measurements yet, but the crank FEELS tight.

My guess is that the piston/cyl have some serious time on them.

What do you think?

Going to be getting some prices today on a replate vs. replacement.

EX Side


INT Side



The gray you see at the top of the bore on the exhaust side is aluminum showing through the plating. It needs to be replaced or redone. What you see is a normal wear pattern for a high hour 450.

The "thrust zone" is about an inch and a half down from there on the intake side. The area where the wear shows is where the rings twist as they reverse direction and are driven against the cylinder wall by combustion pressure.

Ok. Thanks.

I've seen this wear pattern before, just not completely through the plating.

I see that TT has a great price on an OEM replacement. Might just go that route.

Just wanted to update this thread. I ended up sending the jug and a new OEM piston to Millennium Technologies. The wear on the exhaust side wasn't enough for any further repair than just a replate. Ended up costing just a little over $200.

It looks like Mill. Tech. did a great job. The bore looks great as well as the exterior of the cyl. looks brand new.

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