crf 450 after rebuild

dmast01 · Jan 6, 2005

I have an 03 crf 450 that i have owned and maintained since it was new. I just finished my second top end overhaul on the bike. This time I replaced all the valves and springs,as well as the piston and rings.My question is now when i start it i see a slight puff of smoke when it is revved when the engine is cold. when the engine warms to operating temp i see no puffs of smoke. The bike only has been ran in the garage for about 5 minutes but never ridden or put under a load. Is it that the rings are just not seated yet or did i do something wrong. I did not notice this with the last rebuild or before the rebuild.

mylesc · Jan 6, 2005

Did you replace the valve stem seals?

dmast01 · Jan 7, 2005

Yes i replaced the valve guide seals also. The bike seems to run very well other than the above problem.

WhiteBros426 · Jan 21, 2005

I've heard that a bit of smoke on start up is normal, even for the stock CRF's, not sure why it happens though.... Some say oil blow by? I wouldn't worry about it, but I tell you what happens with mine....Getting tomorrow! :)

Rich Rohrich · Jan 21, 2005

dmast01 said:
I have an 03 crf 450 that i have owned and maintained since it was new. I just finished my second top end overhaul on the bike. This time I replaced all the valves and springs,as well as the piston and rings.My question is now when i start it i see a slight puff of smoke when it is revved when the engine is cold.

What did you do to prepare the bore for the new piston and rings?

dmast01 · Jan 24, 2005

Thanks for answering my message Rich. All i did to the clynder was clean it brake parts cleaner and a lot of hot soapy water. I did not hone it or use a scotchbrite pad on it. I hear so many different opinions on how to prep a plated clynder. Do you think using the honda gn4 non synthic for a couple of changes might help the rings seat in. Any opinions would help. I dont want to tear it apart again but i will if i have to.

Rich Rohrich · Jan 24, 2005

If you are on your second top end and you haven't at least deglazed the cylinder it might be tough for the new rings to seal which will make it smoke especially at start up.

Single compression ring piston designs like the CRFs and RMZs are especially sensitive to the bore surface finish and should have the barrel honed during a top end rebuild using a proper Sunnen type horizontal hone. If that isn't an option than a 320 grit ball hone or at the very least a 7447 scotchbrite pad should be used.

I don't think the oil type is going to make any difference at this point.
Keep an eye on the oil consumption, if it doesn't seem excessive then the worst case is you might just be making a bit less power from the slightly lower cylinder pressures.

crf 450 after rebuild

dmast01

mylesc

dmast01

WhiteBros426

Rich Rohrich

Moderator / BioHazard

dmast01

Rich Rohrich

Moderator / BioHazard

Similar Topics

crf 450 after rebuild

dmast01

mylesc

dmast01

WhiteBros426

Rich Rohrich

Moderator / BioHazard

dmast01

Rich Rohrich

Moderator / BioHazard

Similar Topics

Privacy & Transparency

Privacy & Transparency