time to rebuild topend- how to tell??

[rexdog]

Just got a used 05, how do i know if it needs a new top end. I have rode it once, it doesn't smoke has plenty of power doesn't seem to rattle or nothing. Should i do a compression test on it, or play it safe and throw in a new top end. I have no idea if or when it has last had a new topend. Also how does a hot start work, since it goes into the carb, should you use it when the bike is hot only. Thanks for any help...

[sexybbq]

yes do a compression test and get back to us with results. hot start is really only needed if you dump the bike or stall it really

[rexdog]

cool, thanks man i'll get back on here after i do a comp test..

[MX1967]

Four strokes are like a maintenance free battery...they work great right up to the day they quit. A compression test is a good idea. I've seen a properly maintained 450 start the day out fine then loose the big end bearing without warning. I had my 06 YZ450F rebuilt at 100 hrs without having a single problem so now I'm good for another 100 hrs but that was with me maintaining & riding the bike...everybody's different.

Edited October 27, 2010 by MX1967
Grammer

[MxDonk]

A compression test will tell you nothing. Do a leak down test, anything above 7% leakage I would start worrying. The good thing is, you can tell where its leaking. If you take your air filter off, listen in the airbox, listen at the exhaust, and also remove the engine timing plugs. If you hear air at the airbox, your intake valves are going, exhuast, your exhuast valves are going, engine plugs, your rings arent sealing.

[Noppy]

But make sure that you adjusted your valves properly first, or is that BS?

[MxDonk]

Yes and no, I mean if the valve face is cupped no matter the adjustment it will not seal. However, if you find youre slightly leaking from the intake, then yes, go ahead pull the valve cover and check the clearances. Then after you have the correct clearance, leak it down again and confirm.