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'08 Head & Cylinder

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Give me your input on what you see in the head/cylinder pictures. (She ran great, but I'm a novice rider.)

The cross hatching looks fresh. Or is this a by-product of Nikasil regarless of hours on cylinder? The piston had a tiny amount or carbon starting to collect in the center, I believe it was fairly new, maybe in line with the Accumulated Ride Time. I'm the third owner, and when I bought it, it already had a Vapor installed with 68:xx:xx ART. I'm @ 87:xx:xx ART now.

I'm sending the head into AS Racing for a port and polish, and the TRX valve conversion. A TRX piston and an '02 R cam will replace OEM.













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Cylinder is perfect.

Piston and head show evidence of a great deal of oil blow-by.

It should look like caked on Chocolate Milk powder, not an over-cooked steak.....

My stock head at 300 hours:


...and second rebuild at 175 hours..


The rings were probably never seated properly.

You should be checking the service limit of the piston, and replace the rings (and piston/wristpin if out of service limits).

Paul does great work. You will need to go up to a 170-175 main jet.

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some of the carbon comes from the stock crankcase venting to the airbox, if you haven't re routed the hoses. So wouldn't be too quick to blame the rings or valve seals entirely

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The cylinder looks very good- the cross hatch will last a ling time. Things to watch for are scoring at the very front and back of the cylinder bore where the piston skirt rubs once it starts wearing. I check the sealing surface of the top of the cylinder and the bottom of the head by wet sanding both with a piece of emery paper taped to a thick piece of glass or marble. Lightly hone the cylinder for a few strokes using a fine grit ball type hone. You just want to give the rings something to seat against. Use a non-synthetic oil for the first hour or so to help with break in.

Definitely replace the timing chain anytime you replace the top end.

I prefer to break in a top end riding it under high load but staying away from high rpms for more than a second or two. Aggressive woods riding is usually very good for break in type riding.

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MX Tuner - I'll give the "emery paper taped to a thick piece of glass" a shot. :lol:

Krannie - "Three hard-riding 15-min runs, after 3-4 min of warm up." :)

i4bikes - "...replace cam chain..." En route.

highmarker - I have not rerouted the hoses, is the how-to/purpose in the sticky?

Thanks for the input riders.

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