Yz400f head on 426

My 2002 yz426f head is trashed.. Theres carbon in the intake ports, i have a good tight 1998 yz400f head that i can put on it but i just have one question, will the head work and be fine on my bike? Cause i believe the rev limiter is 500rpm higher on the '02 426

Theres carbon in the intake ports,


So what?

Is that normal to have carbon in the intake ports? Theres buildup

Arround all 3 intake seats. And i filled the port with solvent and you can see seepage from all 3 valves

Yes, it's normal.  So is the seepage.  If you have someone remove, clean, and inspect the valves for wear, you'll have a much better idea of their actual condition. 

Well i removed all 5 valves, and there was just shit built up on the seats and valve faces, ive cleaned both up, so ill be reinstalling them later today. Just curious, can i just use regular engine oil on the valve stems, or do i use like a molybdenum disulfide oil? And do the intakes get oiled or just the exhaust? Id hate to go start it up and ride it and have a valve stick.

Edited by Yammer-Hammer

Of course you remembered to keep all the valves and the lifters and shims oriented so that you can return them to their original positions, right?  And you still have all 5 of the thin steel spring seat shims? 


Dip your finger in your regular engine oil, shake off the excess, then rub your thumb and forefinger together.  Now wipe the center of all 5 valve stems with your fingers.  No more than that.

Grey, of

Course i remembered to keep everything together, i have all the valves, keepers, springs, buckets and shims all separated in 5 separate bags. So i can put everything back exactly were it came out from.

Remember new valve seals.

I dont have the money for that... The old ones seal perfectly fine. What will happen if i dont get new ones?

A 70% probability of excessive oil consumption. At best.

Looks like im replacing them...... Why is the probability so high? Does it damage them to remove the valves? (FYI im reusing my old valves)

Also how does this bore look? I just got it cleaned up after honing it. In your opinion does it looks like the rings will seal good? This is my first cylinder ive ever honed ImageUploadedByThumper Talk1395112298.719844.jpgImageUploadedByThumper Talk1395112327.495527.jpg

Edited by Yammer-Hammer

Nice job.  Bore looks fairly good.  On little drag mark near the top of the second picture, but it should be fine as long as it isn't worn too much.


Did you measure it?

Thank you. And yes i measured it, its still round. Measured it in 10 different areas. So even tho im reusing my old valves i should replace my seals? And for the new seals do you use seal grease or engine oil

Even though.


Engine oil as I described earlier.  Once the springs are on, you can pour a little over them before installing the lifters.

I just called my local yamaha dealer and have all 5 seals on the order. $43 out the door. I guess it worth it since i have it apart.

Even though.

Engine oil as I described earlier. Once the springs are on, you can pour a little over them before installing the lifters.

One more question, do you install the seals first then install the valves, or do you put each valve in and then slip the seals over the end of the valve stems?

Either way works, without a valve is easier.

Are the 2002 426 cylinders plated or are they sleeved from the factory

Nikasil plated

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