Buying a head what shim ranges are tolerable.

I've found a head off of a 05 looks as if it had low hours on it, wondering what size shims would be tolerable considering im going to drop 400

Just did our 06 450 last night, ranged from 190 to 165. On a YZ450F I personally would not use a shim thinner then a 130... at that point you are only about .05mm above the retainer. OEM uses down to 120.. but on our 2006 head wth OEM valves, that would be BELOW the retainer

Edited by E.Marquez

Was the 165 on the center intake? All my shims were 178 from the factory and have pretty much held since new.

Was the 165 on the center intake? All my shims were 178 from the factory and have pretty much held since new.

Well your going to make me lie,, as I really do not remember......

.. I'm thinking intakes were a 185 and 2 ea 190 when first checked as they came out. (this is a new bike to us, and valves had been adjusted prior I believe.

But clearances on all three intakes were below .10mm... center intake ended at a 1.75 shim for .12mm clearances... the other two intakes were ...ummm, something else..:p.. I only remember the center one, cuz we had to do it twice...:smirk:

There are probably too many variables in that question for there to be a good answer. OEM heads for installation are built at the factory with shims in the 175-190 range, usually closer to 180-185.

A head that's been repaired or rebuilt might have almost anything in it, depending on what was done and how well. The only way to know would be to pull the valves and inspect them. Even then, the valves are used. Kind of have to take the seller at his word.

intake from left to right are 188 189 182...
those are typical factory build shims. If both are in the same condition, the '05 head is a little better unit.

Any differences in a 05 head compared to an 03?

Minor, subtle, but yes. Like I said, it's the better of the two in they're both good.

the 05 has a better intake port and chamber shape smoother running and more top power

on the bottom out side of the intake the 05 is marked 5XD-00 the 03-04 5TA

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