Differences in 2004 and 2008 crf250r engines?

[CollinHouse]

Hi guys,

I bought an 08 that had a new head, valves, and piston put on it. Seemed like it had a valve installed wrong and had dropped the valve. Turns out it has a 04 motor in it so the new parts didn’t work on it and the valves were hitting the piston. The head looks like it’s the same just smaller valve guides, but just want to be sure. I’m ordering two new valves to replace the bent ones sticking with the 08 parts, but will replace the 08 piston with one for the 04. Anyone know for sure if I can use the 08 head and valves with the 04 motor and piston?

[dakh]

I'm running an 08 head on what I think are 05 cases (only 99% sure about that).  Yes intake valve stem is 0.5mm thinner on 08 head or some such, different cam profile and I'm guessing valve springs, different shape of the intake/exhaust runners in the head.  Other than that everything fits fine.  If you look at aftermarket parts, pistons and cranks are usually listed as fitting 04-09 model years.

Either timing was off/jumped, or there was some incompatibility between the cam and piston shape and timing or something else.  Personally I would look for a different answer to what happened than just the fact that parts were off of different years.  

BTW how do you know it's an 04 bottom end?

Also my understanding is that there's some incompatibility in the OEM cylinders between 04 (and maybe 05) and later years, something about the oil galley that goes to the squirt nozzle to bottom of the piston.  Aftermarket cylinders are Ok and maybe later cylinders fit on earlier cases but not vice versa.

[dakh]

Also in my experience one would have to be VERY hamfisted to not notice valve to piston contact.  Unless it is very very subtle.  The motor just won't turn over from the kickstart.  I usually leave the spark plug out and kick the motor through carefully first time around after assembly just to make sure I am not messing things up.

[CollinHouse]

It’s at a good powersports mechanic that I’ve been using for years, and he said the timing was fine. He thinks the piston was the problem. He must have looked up the number on the case or something to figure out it was an 04, but that’s just my guess. He realized it when he noticed the different valve stem size. It still has the same cylinder so he was going to order an 04 piston and keep the 08 head, just replacing the two bent valves.

[Igomoto]

Was the piston installed backwards? That would be my only guess since the 04-09 uses the same piston/valves (same part numbers). The cylinder was updated in 05- 

 

As Dakh stated you would notice valve/piston contact from the beginning. There are circumstances where an after-market cam is way too aggressive for the stock or worn out springs and you can get contact that way. So it might be worthwhile to check the part number on the cam- 

Edited August 31, 2019 by Igomoto

[CollinHouse]

It wasn’t running when I bought it and it turned over but didn’t have any compression so I thought it dropped a valve or the timing was off but the mechanic said that the valves got bent from hitting the piston, I’ll have him check the cam part number.

[CollinHouse]

This sucks. Just got the bike back 700 bucks later and within 10 minutes of riding the exhaust valves got bent again. 04 engine and cam and piston only difference is 08 valves, springs, and head. But everywhere I look online says that the 08 parts should be fine on it. It’s still in time and everything so I am confused why this keeps happening...

[mlatour]

damaged valve guide from previous failure(s)

weak/broken exhaust valve spring

weak/broken cam chain tensioner (they are a wear item usually replaced during top end refurbs)

cam chain skipped a tooth on a worn/damaged crankshaft timing gear

Edited September 12, 2019 by mlatour

[Garage_Dog]

Did you use new valve keepers?

Did you install a new cam chain?