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Head Gasket Thickness for Machined E12 Head


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I recently had an E12 engine head machined down to 5.047" (~128.1938mm) - (it's been decked a few times in it's life) - what head gasket should I get? And what else should I know?


I understand the stock head is 5.0787" (129.0mm +/- 0.1mm) and the minimum is 5.070" (128.775mm) - this is below that. I also understand some A/X folks go as low as 127.5mm but need to start doing crazy things with chain tensioning and cam adjustment.


VR makes a 1.5mm (p/n 11121734279) and a 1.8mm gasket (p/n 11121734280).

Goetze does as well.

IE/Cometic makes MLS gaskets 1.2mm / 1.4mm or pretty much anything else custom.


In theory I understand I should get the 1.8mm thicker Victor Reinz gasket but I don't understand why.

What are the advantages of Multi-Layered Steel? What would go wrong if I just put on the 1.5mm VR gasket I had as a spare? At this level do I need to worry about claying my cylinder heads to make sure there's not contact with the valves?


Edited by pmg
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What camshaft and pistons are you running?  If you are using flat top pistons and a stock camshaft you won't have a piston/valve clearance issue.  If you are running a cam with more lift and duration you should check the clearances.  Do a test assemble with the VR gasket and see if you have enough chain tensioner travel to get the job done.  If so you are good, you will just need an adjustable timing gear to get the cam timing set correctly.


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1970 1602 (purchased 12/1974)

1974 2002 Turbo

1988 M5

1986 Euro 325iC

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 I don't understand why.

Compression ratio, cam timing, and, as Byron says, clearance.


I agree, with flattop pistons, you'll be fine in both cases.  With domes, it's worth checking, because that's easy and cheap, and contact is not.

Unless you have a very high dome, compression will probably be ok, at 128.25 cam timing will not be TOO early

(but an adjustable top sprocket is easy to do) and you just have to check clearance- there are too many variables.


That welding would scare me, just based on a picture I saw on the internet.  It crosses the combustion chamber into the water jacket, it was obviously done

after the head was cut, and it's not smooth, which will give a place for hotspots to form and preignition to happen.





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"I learn best through painful, expensive experience, so I feel like I've gotten my money's worth." MattL

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Thank you very much Toby, Preyupy - you guys are wizards.


So advantage of using the standard VR 1.5mm gasket is I get more compression / more power.

The disadvantage is that my valves may not clear, I have to run higher octane fuel (I can only buy 91 in California - will that work?), and I have to be extra careful for detonation and pinging.


In theory, I'm fine with that. Or rather, I would prefer that. It sounds great actually. Why do some people say not to plane the head to increase compression? ("It's a bad way to achieve that.")


Here is the lower half before finishing.


Two big concerns:


1) I made triple certain I was lined up at TDC with the timing chain ring notch directly under the oil pressure bar. When I pulled the head off, I saw this. Those pistons do not look TDC. It looks like the previous owner(s) mounted this one or two or three teeth off. (Sidenote, these are domed pistons, yeah?) (also, you can see where the gasket blew between 3 & 4 - that's what started me down this road - not a concern here.)




2) There's tiny dings from the intake valves on each cylinder. Close up below:


Those - really look like they shouldn't be there. 


Does this mean the last person to put this back together got timing off?



On the positive side. The head came back today. Toby, to your observation, it was lightly finished, two cracks appeared, those were fixed, and it was refinished. This is the final result:




You can see the discoloration where the weld was put in between the top two cylinders (4 and 3) and the second discoloration between the combustion head and water jacket at the second combustion chamber from the top (3). The cam alignment was all redone at the same time and the valves all looked good. (I was worried based on those dings that the valves would be off.)


So tldr:

1) Should I be concerned about those dings on the tops of the pistons?

2) Do I need the thicker gasket now that it's been established I have domed pistons?

3) How do I identify what camshaft I have? To my knowledge it's stock. Pic here: http://imgur.com/AiaQJrD

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if your concerned about compression how about using the correct 121 head casting for those pistons. The difference in the TDC of the cam gear and the seeming deck height of the pistons might be the overall diminished under minimum spec of the head thickness you are seeing. that is not three teeth on the cam gear.

Edited by dar_on
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Ahh, ok that looks better.


1- no, not if the head's been redone and the valves ground (and they seal).  Your cam timing may explain it, but it probably 

happened when you pulled the head.  It looks really fresh.  Be very careful not to let the open valves on your fresh head

get bumped, even gently.  They're easy to bend when you're reinstalling.


2- probably not.  Use your standard gasket, put a blob of plasticene 'clay' on the tops of the pistons, put the timing chain on and roll it over twice.

Remove the clay carefully, cut it in section, and measure the minimum thickness- if it's over .080", you'll be fine  <edit>  Yeah, you might

want to because of the head/piston mismatch.


3- can't tell from that...  and even if it looks stock, it may be reground.  #2 will give you a go/ no- go test on it.


<edit>  daron's right- those pistons work better on a 121 head.  On an E12, they'll be more prone to detonate.




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"I learn best through painful, expensive experience, so I feel like I've gotten my money's worth." MattL

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Thank you Toby for being incredibly clear and helpful (as usual). I'll clay the engine, if it looks good, put on the stock 1.5mm gasket. If it fails down the line, I'll swap it out for a 121.


Man, Daron, your comment really twerked my day. I really wish I had known this head did not match this block before spending $720 to get it up and running.  $720 is crazy maybe, but in the process I learned it was previously ported so it seemed worth saving. (For reference it was $70 to resurface, $285 for the cam work, and $365 for the two tricky welds and repairs for the cracks). And this is after saving for a year to get it back to life. I now feel dumb, bummed, and penny-wise, pound foolish. A couple of expensive lessons here and I'm not out of the woods yet.


So reading between the lines here, I should swap out the pistons or the head to match for ideal performance, but I can put this head on this block now that I've gotten this far.


Basically, the engine will run but be even more prone to detonate, but I'm not insane for carrying forward with this path? (Or is putting the wrong head on the wrong body something one should absolutely not do?)

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If it doesn't hit, try it.

And it shouldn't.  But do clay it.  

If you want to really know, cc the head, and measure the piston dome carefully,

and calculate the C/R.  I have found that valve condition affects compression ratio

A LOT, and have started 'cc'ing' everything by first swapping valves around.


What will be less than ideal is the 'squish', the band around the edge of the piston.

And THAT is what may or may not lead to detonation.  2002 head design is 'multi- hemispherical'

in that the head has multiple hemispherescast into it- you can see them in your head pic.

The valve forms the 'roof', and then the casting tapers the valves into roughly a section of a sphere.

There are several sections of spheres combined to make the chamber, thus, 'multi.'


The 121 piston will move gasses around differently than the E12.  But since the dome isn't huge,

it'll work (some high- dome pistons simply block the flame front- thus Alfa twin spark heads, etc).

How WELL it works is a different matter.  If you use a thicker gasket, lowering compression a bit,

you'll reduce the chance of trapped pockets of fuel/air missing the spark and igniting later,

and improve the chance that the flame front will travel evenly through the combustion chamber.  Slightly.


Yeah, bummer, but don't panic, and if it clays OK, try it.  In F1, this stuff is science.  In a street car,

if it goes a bit organic, it's not a total loss.


Good luck,




"I learn best through painful, expensive experience, so I feel like I've gotten my money's worth." MattL

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You failed to explain is the reason for the piston "valve indents."  Were they preexisting?  Did someone miss a shift and over-rev the engine?  Weak valve springs?   Is there an aftermarket "high-lift" cam installed?  Perhaps I missed your explanation, but is it possible that the reason for your mismatched head and piston combination is that those indents occurred with the original head and resulting valve damage made it easier to simply swap in a later E12 head?    My concern is to avoid repeating the problem.  


Without determining what caused the damage, the fact that you have made valve-to-piston clearances even tighter than before gives greater cause for concern.  Unless you intend frequent engine R&R, a thicker head gasket would provide a greater margin of safety.  In any event, I would be sure to snug things up and rotate the engine to check for play-doh displacement or, if you are good with calipers, measure twice for interference, with extra room - for good measure.


Your mismatch is not ideal, nor is it the end of the world.  Bathtub style cylinder head matched with (your) bathtub style piston crowns generally rendered higher compression numbers.  The generally recognized advantage of the later piano top piston crowns and matched open combustion chambers is that combination tends to breathe better, but generally at the expense of a reduced compression numbers.  (Use of the term “general” connotes the existence of exceptions.)  For a street engine the power numbers are a virtual wash.  Using the piano style pistons with the closed bathtub style combustion chambers typically requires removal of material from each combustion chamber.  Since your combustion chambers are of the relatively “open style,” there is probably nothing to remove.  However, the piston-valve ding may indicate the need to notch or recess the area of each piston that is susceptible to valve contact.  Play-doh should establish the existence of any interference or probable interference.  And if interference is likely, notching can be accomplished with the pistons in situ with a die grinder.  However, the much preferred course is to remove each piston so that it can be matched an balanced with all reciprocating mass.



In theory I understand I should get the 1.8mm thicker Victor Reinz gasket but I don't understand why.


If you don't understand why, then it is hard to appreciate the theory.  Most of this theory has been discussed many times over on this forum.  To the extent it has not been made clear by the earlier replies, once you plane the head beyond recommended specifications, your valve timing will likely be affected (slightly retarded).  (This sets aside the obvious potential for decreased piston-valve clearance.)  There are two obvious means of correcting the timing.  First, by using a thicker gasket to restore the geometry of the parts synchronistically driving the cam, i.e., restoring the distance between the cam and crankshaft using the fixed-length timing chain.  The second means of correcting the valve timing issue is to use an adjustable cam gear (mentioned by Preyupy).  Adjustable cam gears are commercially available - or you can make your own by appropriately modifying the gear with "slots" versus "holes"  and changing the gear's dowel.  (Search cam gear.)








Edited by percy
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You guys are wonderful. Percy,  Toby, thank you so much for taking the time to school me on this. Your posts reflect a deep mastery of the subject.


Great update here - thicker gasket came in, installed it, car is running again! :D:D:D


This is without a doubt the most challenging thing I've undertaken on a car (dismantle and put back together half an engine). Old hat maybe for you guys but I'm super thrilled. SUPER thrilled.


Interesting discoveries:

  1. When the previous owner swapped the heads, the chain slipped one tooth. This explains why the pistons where not at TDC when the mark was at the TDC notch. Because the timing chain was '1 tooth off' I was running into all these problems last year with the engine running rough and not stopping on shut off. I tried adjusting the dizzy, the float, the spark plug gaps, setting the ball on the timing light. Nothing, nada. Adjust one thing, problem comes up somewhere else. Now I understand.
  2. I clayed 4 valves. Good thing as one came loose during the operation. Gap was at 0.095" with the 1.80mm gasket - enough for me to feel comfortable with as it's above that 0.080" margin  you mentioned Toby - no need to bust out the angle grinder(!).
  3. Given there was 'plenty' of clearance - Percy - I suspect the those indents were made by the original head that died many moons ago.

Current troubleshooting areas:



Two problems now that everything is back together.

1. The car wants to die really quickly on startup until it's warm. Even with a high idle. I kind of need to keep it at 3,000rpm(!) for a few minutes which seems excessively high. I understand the weber 34/36 has a fast idle if you punch the gas peddle before starting but I can't seem to get that to work - what's the trick?

2. The car is surging on acceleration. I look like a doofus pulling out of the driveway at 5mph and 5,000 rpm. I think this is either something wrong with my carb throttle linkage (highlighted in yellow) or that the intake manifold isn't secure well enough and is rolling on engine acceleration causing a slight tug on the throttle cable making the surge.


Between the machine shops and disassembly I some how lost my coolant divider (highlighted in purple). I found another one from an E21 at the junkyard but it doesn't have the inlet on the "rear" side. Kind of leaks. Sort of sealed with permatex. I've already ordered a fancy one from Blunt that gets me three sensors plus the E12 head compatibility but it has to ship from Germany. In the mean time I plugged that intake line return with a bit of white plastic. From reading elsewhere in the forums this helps with warm up at low temperature. No idea on the surging though.

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Congratulations on a running car. That's a real accomplishment, especially with mix and match parts.

The startup issue is likely choke and possibly mixture.

There are 3 common choke types on a 32/36 weber, electric, water, and manual. Search for weber choke on the FAQ to figure out which you have and how to set it up.

To check linkage, with car off, disconnect the linkage and move the throttle cam on the carb so you can see the range of motion. Then connect the linkage and have an assistant press the pedal while watching the cam on the carb to see if you're getting full range of motion. Adjust accordingly.

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BMW Lotus Healey Miata x 2

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