2007 YZ450F Top End Rebuild

My bike is approaching 90 hours of practice and Race time and I feel like it is time for a new top end. The bike is getting slightly harder to start when it is cold for the first time of the day. I may need 6-8 kicks on the first start of the day. Once warmed up, it always starts 1st-2nd kick. I just checked all my valve clearances and they are all within spec.

Intake 1 - .10

Intake 2 - .10

Intake 3 - .15

Exhaust 1 - .20

Exhaust 2 - .20

I cannot find my paperwork where I wrote down the baseline specs when it was new.

I always change the oil at least every 6 hours, oil filter change every other oil change, and a clean newly oiled air filter every ride day.

I know I need to change the cam chain and figured while I have it apart, I might as well do anything else I need to while in there. Replace piston and rings?

I am leaning towards a CP piston and upping the compression to 13.5:1 Good choice?

At 90 hours a new piston and rings would be a good idea. The CP 13.5 is a good piston. I would also replace the valve springs (they're cheap) and stick some new valve stem seals in there while it's apart. From there it should be good for another 90 hours.

At 90 hours a new piston and rings would be a good idea. The CP 13.5 is a good piston. I would also replace the valve springs (they're cheap) and stick some new valve stem seals in there while it's apart. From there it should be good for another 90 hours.

What's a good way to remove valve stem seals without damaging the head?

What's a good way to remove valve stem seals without damaging the head?
Exactly how do you normally remove valve seals??

I never have, I'm curious how this is done cause when I think about how I might attempt to do so I would probably damage the head.

Remove the valve springs, remove old seals, put the new ones on. No hammers or crow bars involved.

I have almost 90 hours on my 09'. Everything said above would apply to me as well, maint. ride condtions and so on.

Already recieved my OEM piston, rings, timing chain, wrist pin and circlips. Did not even think about doing my springs or seals. What is yalls opinion on this? SHould I do it now or not worry about it? Thanks.

DJ

I did my 08 at 100hrs. All OEM, did the valve seals but not the springs. Cant see the springs being a problem yet, but the doing the seals make sense while its apart.

YZF valve springs are ordinarily quite reliable, but they are also too inexpensive not to replace at $25 a set. At that price, the potential trouble they could cause just isn't worth taking the risk.

Thanks again Team Thumpertalk! WIll order seals and springs now. Thanks.

Exactly how do you normally remove valve seals??

Once the valves and springs have been removed reach in with a pair of needle nose pliers and pull the seals off of the valve guides.

Did not even think about doing my springs or seals. What is yalls opinion on this? SHould I do it now or not worry about it? Thanks.

The springs will sack out over time and begin to lose pressure. The stock springs are relatively cheap compared to what you have spent already so there is no good reason not to replace them while you are already this far in.

As far as the valve stem seals go, anytime I remove the valves the seals get replaced. Like the springs they too are dirt cheap and much easier to do now than have to pull everything back apart to replace one later.

While the valves are out is also a perfect time to remove carbon from the combustion chamber, valves, and exhaust ports plus there is no way to completely inspect the valves, seats, and guides without removing the valves.

Exactly how do you normally remove valve seals??
Once the valves and springs have been removed reach in with a pair of needle nose pliers and pull the seals off of the valve guides.
I knew that, of course, but I was curious as to what kind of damage he might be concerned about doing to the head through whatever process he normally used, or imagined being used. Struck me as a very odd question, somehow. :smirk:

I thought they were pressed in! :smirk:

Had no idea they just slid out... Going to have to do some more reading. Thx.

I think you're thinking of the valve guides. The seals are easy.

I didn't know they were two parts, thought the valve guide was the seal... Thx for the clarification

Where can you buy a new set of valve springs for $25 for a complete set?

That price quote is a year old. TT OEM currently sells all five for $37.72

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