1G Min head thickness for OEM headgasket?

[dwb]

What is the minimum thickness of a 1g head to still run an OEM headgasket without piston to valve clearance issues on a stock/OEM build?

I *believe* my head was never milled previously and the machinist had to take 0.008" from the deck. From my research, this is the max amount according to Mitsu. Another 0.001" was taken off the block deck. So 0.009" was milled between the two, which puts me 0.001" over Mitsu spec.

So I measured my head thickness to be sure. Unfortunately my calipers are not the highest quality nor calibrated. It came out to be 5.190" which puts me at 0.010" shorter than a new head. So either the head had been milled previously unbeknownst to me, my calipers are not accurate, or the machinist took off more than 0.008". I'll try to find a calibrated tool to verify. Anyway, if I take this at face value, I'm at 0.011" total material removed between the two deck surfaces or 0.003" over Mitsu spec.

I've read some things about "AREA" spec, which says 0.015 total can be removed without adjustment. I'm within that spec, but what does "AREA" spec mean and is it a reliable source?

I already have a new Mitsu OEM HG and would prefer not to waste it, but I could still go with a thicker HG if needed.

6bolt block/rods/crank, 1g head/cams, 2g pistons.

 

[CrackedDSM]

Sorry to be unhelpful but you could always just clay the piston to valve clearance. That would tell you immediately and doesn’t take long at all. I’d just use a super cheap eBay gasket or something when you do it so if it’s a wash, you’re not wasting $50+ on an OEM composite.

 

[dwb]

Sorry to be unhelpful but you could always just clay the piston to valve clearance. That would tell you immediately and doesn’t take long at all. I’d just use a super cheap eBay gasket or something when you do it so if it’s a wash, you’re not wasting $50+ on an OEM composite.

It's all good. I've seen it mentioned time after time but I've yet to find the procedure on how to clay the pistons. Is there a tech article or something I can reference? As far as a HG to use for this procedure, can I use my used/old OEM HG?

 

[CrackedDSM]

It's all good. I've seen it mentioned time after time but I've yet to find the procedure on how to clay the pistons. Is there a tech article or something I can reference? As far as a HG to use for this procedure, can I use my used/old OEM HG?

Let me see if I can find a walkthrough but from what I remember when we did it, it was just ordering the clay and using a predetermined amount on a piston and then measuring the depth that’s left.

And I wouldn’t use an old HG as if it’s composite it’ll have been crushed, heated, and lost some material upon removal. Even the MLS I wouldn’t do it for the same reasons minus leaving material behind.

Edit - this is from JE Pistons themselves. Looked pretty good from what I saw when I skimmed. Click me big boi

 

[bastarddsm]

It depends on a million different things. but the limits are piston to valve clearance, what you will accept for head gasket life, and what you will accept for cam timing error. I think it's likely that the mitsu spec comes from cam timing error and emissions. Cutting the head/deck retards cam timing.

For me the biggest limit is head gasket life. the more you deck a head the less rigid the deck is and the easier it is to push a head gasket. So for my talon I like to keep them minimal cuts. 0.010" or less.

I have a head on one of my cars that's probably got 0.030" cut off of it. It's a stock boost 14b car, so it's not an issue.

It sounds like you will be just fine with your current situation.

 

[dwb]

Thanks @CrackedDSM, that gives me a pretty good idea. Now, what did my kids do with all that playdoh they never used

Another couple questions about this procedure - do I only need to clay a single exhaust and intake valve requiring only two solid lifters? With stock 1g cams and STD size valves, is it 0.08" clearance limit for the exhaust and 0.10" for intake valves? I can't say I've seen these numbers in the 1g FSM, just digging them up from old posts here.

Speaking of the 1g FSM, I see a new head is not 5.200" as I have found numerous times on this site. It is 5.197". So, again, using my measurements at face value that puts me in a better position right at the limit of 0.008" removed from both surfaces.

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[CrackedDSM]

Just do two.

 

[dwb]

I ended up with around 0.2" on both the intake and exhaust valves. Well within the 0.1" limit. This was with two shimmed lifters as close as I could get to zero lash and my old OEM headgasket. I figure that old gasket was a bit on the thin side so that's even more clearance when I install the new OEM HG.

The zero lash lifters (lash adjusters) were the hardest part. Ended up using a ~1.5mm thick washer with some folded pieces of aluminum foil underneath the empty lifters. It was helpful to only install the rockers for the two valves I was working with. Was so much easier to see and feel the lash when it's not moving a bunch of extra valves.