Are These All The Parts I'll Need For a yz400f Engine Overhaul?

Well, I raced the first race of the year last weekend, only to have my 400 start making a weird noise going up a hill 3rd gear pinned. I got scared, so I babied the engine through the end of the moto. I got back to the pits and told my dad, we both agreed it was coming from the head, and that it deffinately wasn't normal.

So I pulled the valve cover off yesterday only to find that both my exhaust valves are currently measuring something like .19mm when they are supposed to be between .25-.30mm. And to make things worse they have been adjusted once before, and I had just checked them 2 rides ago (and the first ride was only about 15min long). So in about 1.5hrs they went from .27mm-.19mm. If these valves aren't shot I don't know what would be.

So I have decided to bite the bullet, and completely rebuild the engine, since the last thing I want it to do is lock up on the face of a jump.

So I am going to order the following parts

-All 5 valves

-All 5 valve springs

-All 5 valve seals

-All 5 valve cotters

-Head gasket

-Base gasket

-Cam tensioner gasket

-Cam chain

-OEM Piston

-Piston rings

-Circlips

-Piston pin

Am I missing anything? And with the help of the TT Store, all the parts listed up come to a total of $250. :bonk:

Thanks, any help is greatly appreciated.

Oh, and one other thing, My dad has a valve compressor that fits his Gravely L8 lawn tractors(You probably don't know what those are), and I am wondering if by some kind of miracle it would fit my 400s head? I can get a picture if you guys want.

You will need a mag cover gasket too.

Any excessive flakes in your oil filter - anything like the pictures in the post from a couple of days ago? A high mileage YZ/WR400 usually has a failing con-rod big-end bearing partly symptomized by excessive flakes and a knocking noise under power (not to be confused with pinging). If so, you'll want to go further and have the crank rebuilt with new bearings and rod. This was my experience with my "been around the block a couple of times" WR400.

Well, I don't have any excess oil flakes, nor knocking, and my oil is changed after every ride, so I think my crank is fine, but I check it be sure when I tear it down.

This would be a great time to throw an auto decomp exhaust cam in there if you have not already done so.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now