Replacing Engine Parts...

I have about 75 hours on my bike (2008 RMZ250) right now, about 30 or so is of hard riding. The motor is all stock, and I do oil changes every 6 hours and filter changes every 12 hours. I've been checking the valve clearances about every 20 hours and they haven't moved yet. I clean the air filter whenever there is a couple of dirt spots on there (around the sides and bottom of it is where it builds up.) My bike still starts on the 3rd kick every time, or sooner; I'm doing it like the manual says: two slow kicks and then a third to start it.

I'm starting to really race now and I'm getting relatively much faster than I was. I'm revving it out before I shift, and am on the limiter right before I land from jumps especially when I race.

I'm just wondering what all stuff I should be replacing in the engine, and when; and I'm on a really tight budget.

My question is should I replace stuff when:

1. My bike is hard to start

2. The valves go out of spec

3. After I've adjusted my valves several times

4. After a set number of hours

5. After the compression gets too low

6. Or other?

By "stuff" I mean piston, valves, crank, clutch, etcetera.

I know these things wear out, and I'm just wondering when you guys think I will be needing to start replacing things...


I have a 2007 RMZ250.

1) I have found that if my valves are even a little out of spec(I run 0.008" Exhaust and 0.004" Intake) that my bike doesn't start very well.

2)3)4) I am going to send my head to Eric Gorr at and have him rebuild my head for about $500 with steel valves. That site answers most of your questions better than I could. Believe it or not that is a good price for the work. I looked into buying the parts and doing it myself and I can't hardly buy them for what he charges.

5) After compression lowers replace you pistons and possibly valve guides

6) I will buy the Tusk tools to split cases and pull/install crankshaft when necessary:;jsessionid=F43EA8D45F82EEAF676609C35C97194D?navType=type&navTitle=Tools%2FShop&webTypeId=140&webCatId=22&stockId=143201&prodFamilyId=17167

7) The stock clutch basket is a piece of dung. Mine wore out fairly quickly because it is unanodized aluminum. I replaced it with a Barnett basket that is anodized aluminum with stainless steel fingers riveted in. I have an Athena 290cc kit, ported head, Hotcams. With that healthy a motor the Barnett clutch basket has taken the abuse and stood up to it. Highly recommended.

Good luck.

Reading that just made me more scared Lol.

Thanks for the response though. More are welcome..

That link was a bit confusing. So I'll ask it here...

You know on a 2-stoke for a top-end rebuild all you do is replace the piston. For a top end on a 4-stroke what all is included?

Do you just buy a new piston and valves, or do you have to buy springs and a bunch of other stuff and get your head machine cut etcetera?


So it's the $500 dollar service, PLUS a piston kit?

500 was just just for the head work... a piston and gasket kit run about 190 and will be similar to a two stroke kit..a crank will run about 270 for a kit....

I race hard motoross only these days and change my 250f pistons every 25-30 hours (this may not sound alot but actually is along time when I count one race day as one hour) and have my valves checked in between piston changes. Along with regular oil changes every 2nd or 3rd ride and religous air filter changes every ride, you engine should do u good for a long time!

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