A lesson about used bikes

My buddy just bought a used 2003 YZ250. The bike ran pretty stoutly, and started first or second kick, although compared to my 09 it was a little easier to kick, which had me slightly worried.

Compression test revealed only 170psi of compression and a teardown revealed the following:

A little bit of blowbye.

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Probably about a thousandth of carbon build up on top of the piston. So thick that not only could you feel it with your fingernail, you could feel it with the pad of your fingertip. Wash pattern is almost unrecognizable at this point, but looks like the bike was running just a touch on the lean side.

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Here you can see where the skirt was rubbing on the exhaust side.

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It looks like the piston rubbed right through the nikasil.

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So, the lesson is as follows. If you are going to own a motocross bike, you should maintain it, and if you are shopping for a used bike you should ALWAYS check out the top end as soon as you get home. I even recommend taking a compression tester with you when you look at the bike. This bike was still running the factory chain and sprockets, stock front tire, and stock clutch and brake levers, so we know it was only lightly ridden, but from the looks of the top end, it was lightly ridden for 200 hours with absolutely no engine maintenance. It was literally a ticking timebomb in this condition.

Luckily for my buddy the bottom end is tight, and the cylinder head looks brand new. The powervalve was very clean, and we should have this thing buttoned up within a couple days, we live just a few miles away from Millenium Technologies :thumbsup:

Edited by djmamayek

hopefully the cost of the bike was low enough to offset the piston and cylinder work.....always a good idea to check the top end on a used bike!

hopefully the cost of the bike was low enough to offset the piston and cylinder work.....always a good idea to check the top end on a used bike!

It was.:thumbsup:

It's just really unfortunate that the jug is roached... At least the bottom end is happy as a clam though.

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