Profile_Name

Hello,

Im trying to get my 20R head rebuilt, and i cant find a minimum height for the head height.

The shop says its currently at 3.940" and the head needs to be resurfaced, how much more material do i have before i need to start running spacers and thicker head gaskets?

13Swords

Don't have a direct answer for your question but do have some other info that might help.

The 20R head surface warpage limit according to an FSM is 0.15mm or 0.0059 inches. By the way that's 1/64th of an inch in fraction value.
Source: http://www.retrojdm.com/ScanViewPage...ifications.jpg

The 20R is a non-interference engine, which means that even if your timing chain breaks, the valves & pistons will not hit each other, like in the 22R, which is an interference engine.
That should mean you can cut down the head a bunch without any valve interference.

The main consideration I think would be maintaining height for the timing chain to have the correct tension. I don't think resurfacing a stock head (one that has NOT been resurfaced or "cut" before) would have much if any effect on this, & I wouldn't think you'd need a thicker head gasket.
Even if your head had the maximum warp (insert joke here) of 0.0059", taking off 0.006" or 6 thousandths of an inch should make much difference. I don't see why you'd even need a thicker gasket or a spacer.

The above are my opinions only, your mileage may vary.

Profile_Name

But the problem isn't warpage, its that the head is 0.020" under the spec of 3.960" and the head would need to be surfaced anyway as there is pitting in the coolant passages near my exhaust ports which need to be welded back up.

What i'm asking is, is that 2 hundredths of an inch going to make a difference within the timing chain, valve clearance and other systems i haven't thought of yet? and how much of that undersizing can i take away with either a thick gasket, or figuring out how to install a shim with my OEM replacement gasket?

13Swords

I still don't see this as much of a problem. 0.020" is between 1/32" & 1/64". Have a look at a tape measure with 32nd's of an inch markings; it's a very small thickness. If your timing chain & tensioner are new there shouldn't be any problems, mostly because the tensioner has right at 1 inch of travel available to it, to take up the slack in a worn chain.
Even is it is a 1/32" difference, that means a 1/64" difference in each side of the chain. I find this negligible. I've seen worn & stretched timing chains on 20R's that had nearly an inch of slack in one side, & the engine was still running, and the chain hadn't jumped a tooth yet.
And that was with the tensioner at full extension.

Valve clearance where? Shouldn't make any difference in clearances at the cam & rocker arms. Should also be no problem with valve to piston clearance. Again, the 20R is a non-interference engine; there are no valve reliefs cut into the pistons like on the 22R's.

I've had a look around and head shims out there all seem to be 0.020" thick, so using one of those with a head gasket would actually make the head "taller" than stock. Again I don't think this is a big issue & do not think you really need the shim, just a good quality head gasket.
Of course if you want to install a shim, it's your engine. Up to you.

swampedout

you could calculate how much you lost from the head being shaved and find a thicker head gasket to get that height back but like 13swords said, youre only affecting chain tension.
it shouldnt have too much slack in it from what youre describing but im not an engine builder

swampedout

But now that Im looking, if you want a slightly thicker gasket, youre going to pay for it.