When to replace the piston?

2007 crf250 ---I have one season on the bike about 35 hours. The manual says to replace the piston every 6 races or 15 hours. Did I screw up? I raced it 4 times. Is the thing toast ? I hate to spend the time opening up the engine if I can wait longer. I haven't noticed a decrease in power, but how can you ----doesn't this happen graudually?

Thanks in advance

its going to be hard to tell decrease in power overtime... the manual says replace every 6 hours but the manual also says ONLY USE HONDA OIL AND GRIPS AND HONDA CHAIN LUBE!!!!! every 6 races is only if you take racing really seriously at about 15 hours/6 races is apparently when Honda determines that you will start loosing power. but if your a novice most of the time your only on the track for 10 mins...so how do you figure. I would recommend replacing your piston and rings especially with about 35 hours on it. In my 250 i replaced my stock piston with a JE high comp piston, they run about $150 for piston and rings. You will definitely feel a difference in power replacing your stock piston with that. Im sure you can wait longer untill you need to swap out your old piston/rings but why risk having it blow up later.

I ran my 07 a full season (don't know/care how many hours), but I know I had more than 35; I rode damn near 100 days total. If you motor ain't open and you're not doing anything inside @ the moment, I wouldn't screw w/ it, but that's just me. OEM stuf is cheap enough that when you do go in there, just do it while it's easy.


When you have to start push starting your bike,usually the valves need reshim. 2nd time bike needs a push replace it all. IMHO if you are not racing the oem is the best route. I have seen alot of 250fs with HC pistons and kits and it is to much for the 250. It is already running at such high rpms. Get a 450 if you really wanna step up faster.:thumbsup:

oww, no dude your fine, most people go about 50 hours before they change their piston (including me) you (should) start to loose power at about 30-40 houres, you can go 70-80 houres before things start getting dangerous.

the manual has such strict service limits so they cant get sued and stuff.

I did mine around 80. It was fine. Some guys go near 200 with theirs.

I did mine around 80. It was fine. Some guys go near 200 with theirs.

:thumbsup: that seems risky

I like tearing down the motor every 30 hours for performance, because that is when I start to notice a loss of HP... Measure the outside diameter of the piston skirt and if it is above the service limit, re ring to restore performance and ride again. If it is below the service limit, replace the piston, rings, wrist pin, and clips.

You can safely leave the pistons in 70-80 hrs, performance will suffer... But no more... Don't leave the pistons in too long, because when they wear the piston to cylinder clearance is excessive which causes piston slap, and the piston can also rock in the bore, ultimately leading to piston failure.

I did mine around 80. It was fine. Some guys go near 200 with theirs.

im one of those guys :thumbsup:

the funny thing is, all the bikes that are really well maintained seem to blow up or have issues... and i rock up with my 04 crf with a 2 year old piston and she never fails... haha

If it aint broken dont fix it. You'll know you need a new piston after your engine blows up and your walking back to the pits...

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