Yeah, that threw me for a loop. I'll report on the warpage tomorrow.

 

I've always followed FM's recommendation that stock gaskets are good to ~84.5mm, as long as your pistons don't sit proud of the block at TDC.

​​​​​​​https://flyinmiata.com/products/94-0...11ad014c&_ss=r

 

Well the bad news is that the head is .0025" out of flat in the longitudinal centerline between 2 & 3 (no surprise). But i it also seems to have a .005" twist in the diagonal that is at it's worse starting at 2 and stretching almost to 4 on the exhaust side of the head. It's like someone clamped the head at 2 and twisted it clockwise along the centerline. All that being said, a trip to the machine shop is in order. I'm thinking that a .005 skim will give me a flat cylinder head (but I'll discuss it with the shop).

The worse news is that - what I thought was the "good one", turned out to be the head that suffered the "Road Atlanta Incident". There is evidence of melted aluminum (from the torched piston) in the combustion chamber of #4. And the whole head is bent out of shape. At it's worse, it's maybe .010 from flat. But if you exaggerated the deformations, the head would look like a motocross track with whoop-de-doos everywhere! I don't think that one is worth trying to salvage.

So...any thoughts before cotnacting my machine shop?

 

Well, that sucks. The only thing I would add is measuring hardness. Try to save the one that has not softened and seems closer to flat.

 

Doesn't sound good. I think I would be looking for another head, otherwise seems like throwing good money after bad.

Buying another raises the question of what problems a new/used one might bring, but you now know the big questions to ask - flatness and hardness.

 

The cam journals are built into the head...
No good (easy) way to line bore them.
The .0025 can be milled out but the .005 twist is more than the cam alignment can take long term.
A good machine shop can "Heat-Treat" the cylinder head and remove some/most of this twist.
They figure out which way they want to change it, heat it up around 400 degrees, then put it on their press with corrective shims and let it cool down.
They try to get it within .004 and then do a final milling.
When they are doing this, I believe ALL of the valve seats move a tiny bit, stuff shifts around.
For a daily driver/appliance car this usually works fine.

No way I'd use a "heat treated" head for a serious build.

 

So, the consensus is - "Get another head"...DAMN!

Now here comes the "clutching at straws / denial" part of the conversation; What if I throw caution to the wind, have that shop shave the head .010 as-is (knowing that I've changed the CR and possibly ventured into interference territory) and try not to do any track days until I can find a straight, hard used head (that sounds kinky)? It's been two days without FrankenMiata and I'm starting to suffer withdrawal symptoms.

 

I mean... That is probably what I would do if I didn't have any fresh spare heads ready to go. Race season is basically upon us and major machine work will likely be delayed very soon. It will obviously cost you some gaskets and labor and whatever they charge to mill it flat, probably not much. Meanwhile I would be sourcing a decent head and have it gone through.
But that's me, and I often sacrifice in order to make the next event.
I would get it milled and send it.

 

Quick update; I got the head shaved 5-thou (I chickend out on the 10-thou boast). Then, when I went to lap the valves, I saw that there were some tool marks on the valve seat on the #2 cylinder no. 2 exhaust valve. Now, I don't know if that was a "pre-existing condition" (I don't think so), or a machinist slip while re-surfacing the head. BUT I took it back to the shop to have all of the valve seats done. You know "While you're in there".

So, another week without FrankenMiata

 

Careful friend, you’re getting pretty deep into this bandaid/quick’n’dirty fix on a very suspect head….

 

This'll be my final excuse to do a K24 swap - I've said too many times, "The next time I blow it up, I'm swapping to a K24!!" (What would you estimate that a K24 with a BW 6750 would peak at? )

(..or maybe an LS?)

 

Power or money wise? Both higher numbers than you'd expect

 

I've spent so much money on this BP-powered car, what's 10 or 15 more bands?

 

Good idea. Just when people are deciding the K-swap has hairs on it.

 

I got the head back yesterday - the shop owner said "mea culpa" so that one seat was done gratis. I had the others done as well "While you were in there". I lapped the valves last night, and I'll finish assembling the head tonight.

New additions are;

• FM Coolant reroute to replace the DIY Kia Sephia Tstat housing, ???-sourced stand-off, Escalade-based return hose abomination that I've been running for the past 10 years
• NIB ID1050's since i can't replace just one ID1000
• Of course the new Cometic gasket

The expectation is that everything will go together perfectly and I will be track-ready in no time, with no ill effects. The brutal reality is that the mere fact of opening the engine will cause some tuning adjustments, at the very least. Or it will introduce new oil and water leak sites, cause combustion chamber "weirdness" because of the 84mm gasket, re-warp the head because it is soft (looking at you @Gee Emm ), or nay one of a myriad of problems...

But, who said this would be easy?

 

Okay, the car is 90% back together. I'll be changing the oil tonight, making sure I didn't leave anything loose and firing it back up tonight after work.

Any future disasters will be documented in my Build Thread.