Chris Lockhart

No one answered on the other thread, so I'll start a new thread to ask my question.

I had removed the heads, looked at the corrosion and measured the depth of the worst spots at about .060". Then I set them aside and haven't really done anything, assuming they needed to be welded. Well I finally pulled out the WSM and checked the OA thickness of both heads, and then looked at the minimum thickness specs before requiring the thicker 1.4mm head gasket.

Any experts please let me know if I'm looking at this correctly. The "new part" spec is 147 +/- 0.1mm minimum thickness. I measured the LT head at an average of 149.99mm and the RT head at an average of 149.87mm. So, if I'm understanding this correctly, technically I can have 2.99mm taken off the LT head, and 2.87mm off the RT head and still be within the "new part" specs, correct??
If so, I should be able to have most, if not all of the corrosion spots machined off, without even removing the max allowed. I want to take the minimum amount while still leaving an even, mostly corrosion free surface. I'm thinking about 1.78mm would do it. Am I on the right track with these dimensions? TIA.

Cosmo Kramer

Your measurement must be incorrect. You can't pull that much material off the head, the spec is only +- 0.1 mm. Whatever the difference between the thick and stock head gasket will be the limit you can machine off.

Strosek Ultra

Note it is incorrect to measure the total height of the cylinder head. The correct height measurement is between the surface facing the crankcase and the machined protrusion sitting at the outer end of each head where the lift points are located. According to the WSM only 0.3 to 0.4mm should be machined off but I do not think it will be a problem to go as far as 1.0mm. The CR will be slightly increased.
Åke

Chris Lockhart

Only 0.1mm? Well then I damn sure am not reading it right. Hell that's only .004".

Cosmo Kramer

Yep, so as per WSM you can take off 0.3 mm +- 0.1 mm and use the thicker gasket.

Chris Lockhart

Thanks guys. Boy was I reading it wrong. Well, that's why I asked. LOL.

Chris Lockhart

Strosek Ultra, Cometic does have .075" thick head gaskets. So you think that if I were to take off a full 1.0mm (from both heads) and run the .075" gaskets, that would be safe in a boosted application? (12 psi Jag/Eaton with Simard Tool head studs/nuts) That's a 1.9mm gasket versus the 1.4mm from the WSM.

GlenL

What is "safe" to you? The thicker gaskets add back head volume so the CR doesn't get too high. I'm doubtful that it needs the 0.5mm between piston and valves.

Cosmo Kramer

Stock is 1.1 mm and the gasket you mentioned is 1.9 mm. So that allows 0.8 mm +- 0.1. 1.0 mm removed with the extra thick gasket would put you 0.1 mm past spec which isn't that much. Problem is when you go boosted you don't want a tighter combustion chamber.

If you milled 0.8 mm from the heads will the outside edge of the pits be further from the fire ring?

Chris Lockhart

Yes that "should" put the corrosion pits far enough away from the fire rings at least enough for me to feel comfortable.

Chris Lockhart

Glen basically I was thinking of taking 0.6mm more off than the WSM says, so if at -0.4mm it requires the 1.4mm gasket, I figured at -1.0mm the 1.9mm that Cometic has listed would put things within about 0.1mm of the specified clearances, if I'm on the correct path.

FredR

Chris,

If you have 0.060 inches of corrosion that would need 1.5mm of material to be removed or the head to be welded at the pitted areas and then re-machined. With welding repairs the problem is eliminating undercut at the start of the weld. Whether or not this is possible I do not know short of welding the entire head flange face and then machining back to stock or whatever finish elevation you require.

928motorsports has a range of high build gaskets available to order up to 0.120 inches thick.

If you want or need to remove those pits that sounds like a lot of material but maybe do able if those gaskets can do the trick.

Regards

Fred

Strosek Ultra

If you are going to machine the heads why don´t you weld the pits first? It will reduce the amount of material needed to be machined off to a minimum. If you are not a handy welder yourself I am sure you can find someone around where you live. Welding should not be too expensive.
Åke

Kevin in Atlanta

Chris, found a machine shop near me to clean up and check out a set of heads that cam off an 87 engine that suffered a cracked cylinder.

I'll let you know how they do.

Chris Lockhart

Thanks Kevin.

Strosek, unfortunately it's harder than it sounds in my area to find someone qualified to do the welding, and do so at an affordable level. I have a couple of options on the welding, but I wasd mistaken on the measurement point on the head thickness, as you pointed out. I was measuring surface to surface, not surface to side lug. (Thanks for pointing that out BTW.) With my dimension mistake I thought that I could take up to .120" off the heads which would negate the need to weld. That's why I asked for help double checking my measurements. Something seemed to good to be true. I went and re-measured and they are right at 5.779 IIRC.

So I'm back to square one. I'll finish stripping them and take them to both shops to evaluate their welding capabilities/equipment. One said he would "try' and the other shop said they needed to see them first.