450 Top End change

I bought my 450 in late April and have rode it off and on thru the summer. It is time to replace the stock rear tire, but I am wondering if I need to replace the top end? I have replaced two stroke top ends which I could do in my sleep, but a 4stroke :cry:? If I do need a top end change is it very difficult to do and do I need any special advice or tools? I want to keep this bike in mint condition, so when I ride hard there won't be any failures. Anybody got any suggestions?

I would say unless you have ridden the crap out of it 4 days a week you probably dont need to. If want to be proactive you can tear it apart and look at the piston and rings but it will probably cost you a gasket. Check out this link for instructions. It's for a YFZ quad but its the same motor and very helpful.


FYI: I am still on my stock 03 top end and I ride like 3 days a week. Granite its not my only bike I rode it the most till I got my 05 250.

The YZF's in general, and the 426 and 450 in particular have what I think is a spectacularly long service life. There does not seem to be a particular rule the can determine when you should rebuild them.

Obviously, you could tear the thing down every now and then and actually inspect it, but as much as you might enjoy that, riding it is more fun. So, here are some things that you can watch for that can help you decide.

1) A drop in performance that's not related to jetting or other modifications. Compression tests are difficult to do with the auto-decompression device enabled, so it can be hard to gauge that, but other symptoms may also be present.

2) Valve clearances can tell you a lot. So little wear takes place in the few parts involved in opening the valves that the virtually never gain clearance. Normally, the clearance will be reduced as the valves wear into their seats, moving the top of the stem closer to the cam. A drop in shim size of 10-12% percent indicates and amount of wear at the valve face that probably should be attended to.

It isn't unusual, from what other members have posted, for a 450 to go for suprisingly long periods needing no adjustment. I have checked my '03 several times, and it looks like the next time, I'll actually have to reshim a couple of the intakes. Checking your clearances also gives you an opportunity to check the condition of your cam chain.

3)"Blue" smoke (oil smoke). A puff only on startup, especially after the bike sits a while, is usually leaking valve seals. Smoke under a load is usually rings.

4) Excessive blowby from the vent tube. Excessive is the important word here. Quite a bit is normal. Compare with another bike.

The main thing is to keep it good enough conditon to avoid a catastrophic failure, like tossing a rod, or dropping a valve. Costs WAY too much to fix that stuff.

Dude,don't touch it, just ride it, I put a hour meter on mine when I first got it in april, been riding the piss out of it every week since then, 122 hrs later haven't touched the top end once, I've had to do alot of other stuff, but no major enginework. just keep your oil, and air filter fresh and ride away. I've also kept a record of everything that has broke and at what hour, next year I'll do the same and see if the stuff wears consistantly,

by the way anyone interested in a 04 450, slightly used. :cry:

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