How Long Between Top Ends - WR450F???

I've got an '04 WR450F with all the free mods and she runs great. Currently the odometer is showing 940 miles with probably 700+ of that being mx miles. I've changed the oil about every two-three rides (most rides are only 25-40 miles) and it's almost always very clean. I hear a little noise in the top but have heard much Much MUch MUCh MUCH worse in running CRF450R's that had never been torn into.

How many hours between rebuilds on these guys?



I'm pretty new to the whole dirtbike thing, but everything I've heard from reliable tuners/builders indicates that about 95% of people doing "top end" jobs on their 4 strokes (CRF's aside) are simply wasting money for the sake of a cool paperweight.

I have 2000 yz426 and i just completed my first top end job on it, i have approx. 500 hours on it. the cylinder and piston were still very tight, but the valve guides started leaking i was getting blue smoke on start up.

When you start to notice a power loss, thats when you do a rebuild.

do the head when your valve clearances start closing up. By this I mean after you reshim it (smaller shims) to get correct specs, and in a short period of time the clearance closes up again, it's time to replace the valves , do a seat job and maybe replace the guides as well. For a 450 I'd like to think this would be at least a few years away. As for the piston/rings , when it needs it. A leakdown test is the only sure way to test this.

Thanks guys!


Yes, thanks I needed that advice as well. Granted I'm only at 100 miles but...

Yes, thanks I needed that advice as well. Granted I'm only at 100 miles but...

100 miles?????? :cry: You better get to riding!!!! :cry:

100 miles?????? :cry: You better get to riding!!!! :cry:

Tell me about it! Lack of time and riding partners has hindered this riding season greatly. Next year will be much better, it better be cause it can't get much worse.

I have over 1300+ miles on mine and I just checked the valves and they were spot on. There is no need to do a top end until there is a problem. ie. Blue smoke or really tight valves. Just enjoy the ride until then. Just for info, I am working on a two-stroker for the third time in two years with a top end replacement. Four-strokes don't have this problem.

I would say you can get 3 valve adjustments and about 10,000 miles before it is time to rebuild her with new valves,guides, springs, piston & rings. :cry:

Tell me about those two-smokers! We have an '03 KX125 we bought used in February of this year. This is the third top end (one is my fault) and also is requiring a crankshaft during this rebuild.

I've had enough of the two-strokes.....


I have over 4000 hard trail miles on my Wr426 01 the valves are still in spec and it still runs strong. No worries!


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