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Just had both intake valves done on my 2006 CRF250r. Noticed some pitting on the piston and head. They are small pits into the metal. Some one told me that it's (pre-ignition). Is this true and if so, could some one explain what it is?

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where are the pits mainly? along the outer edge or all over.. its can be either pre-ignition or detonation, whats your compression ratio? what fuel octane are you using? carbon build up on the piston? it can be also that your ignition timing may be off..

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The pits are are in spots near the middle of the piston. The pits on the head are around the intake valves, but not close to the edge of the valves. I do not know abot the compression.There was some carbon build on the piston and head. I thought that it might be because I am a little on the slow side.

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My bet is it's detonation. Cheap low octane fuel and ignition timing is the leading cause of detonation. Being that you don't know the compression ratio, your safest bet is to use at minimum 91 octane. 93 would be more appropriate. Also, did you buy the bike new and has the timing chain been replaced? Most people don't play with the timing on these bikes. They're usually set up real close from the factory.

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I got the bike new from the dealer. I use premium or super unlead gas. Still don't know about the compression. If it is a timing issue, How do I check it?

(FYI) When I removed the head I alinged the punch marks on the gears on the right side of the engine. (top dead center) The marks on the cam gear were level with the head and the cam loabs were facing the rear and slightly up. I also used a permanate marker to mark the cam gear and the chain. All went back to the marks when I put back together.

Is it possible that the cam gear and the chain could be off alittle and not really show when riding it?

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Do you know how many hours are on it? It may be that the timing chain needs replaced. Maybe we're on the wrong path also. The 06 we had, the valve seats started chipping around the outside of where the valve seats. The valves sealed and it ran, but before long, one of the pieces scored the cylinder which caused it to lose compression. Maybe your's pooped the piece out of the exhaust and didn't do anything but bang up the aluminum on the piston and head. Just a thought.

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