Head Gasket thickness selection

[mcammarn]

CORRECTION: machince shop called me and they told me they did shave some off the block. they just didnt charge me for it.
they said 3thousands (.003) was taken off.
so now ive got to send my block in with the timing cover to also get that shaved to now.

so with a total of .009 taken off, will this effect the size of hg needed now?

 

[mcammarn]

anyone know if stock oem hg will work? or will i need or could i use a mhg? and if so what size?

 

[TheMaxx]

Use the gasket you have now if you plan on doing a full rebuild, since you will be opening the engine back up anyway. If you don't plan to rebuild it just get a MLS and be done with it.

 

[IJ.]

If the Surface RA is within Spec go Metal, a 1.5mm would get you close to stock CR/Quench.

If the surfaces are too rough a stock Composite isn't going to have a negative effect.

 

[mcammarn]

im sorry but whats RA? and lets say i do get 1.5mm mhg and its to thick, will that cause a problem?

If the Surface RA is within Spec go Metal, a 1.5mm would get you close to stock CR/Quench.

If the surfaces are too rough a stock Composite isn't going to have a negative effect.

this was just rebuilt, unless your talking about top end.

Use the gasket you have now if you plan on doing a full rebuild, since you will be opening the engine back up anyway. If you don't plan to rebuild it just get a MLS and be done with it.

sorry for all the questions, just want to do it right the first time.

 

[Numba1Stuna]

What's up guys? Finally at the stage in my complete rebuild to measure for my head gasket! Got my digital calipers in the mail yesterday and put them to use today. So I've read this thread a couple times when I first joined and just ran though it again. Just wanted to post up my numbers and get the seal of approval from the great IJ.

So stock numbers are:
1) 1.37mm for the head gasket.
2) 116.00mm for the head.
3) 198.50mm for the block.

My readings were:
115.60mm for the head, difference from stock being .40mm
197.88mm for the block, difference from stock being .62mm
Add the stock head gasket size 1.37mm to .40mm and .62mm and I come up with 2.39mm head gasket size needed.

Does that sound correct to you guys, 2.39?

Would you recommend a 2.4mm head gasket?

Thanks in advance!

 

[IJ.]

Not sure if a 2.4 is available, 2 and 3 are for sure but there will be a slight compromise using either, 2 is going to give you more off boost throttle response but depending on fuel you maybe be limited in boost and timing, opposite with a 3 but it'll be a bit doughy off boost.

 

[Numba1Stuna]

Awesome, thanks for the response. Did a little looking on ebay and found this head gasket: http://www.ebay.com/itm/330800056593?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649

I have a question about it before I buy it though... I still have the stock bore on this block, 3.26" or 83mm. I noticed that this head gasket has an 84mm bore. Is that something to be concerned about or will it work without issues? Not sure if it needs to exactly match bore size or not, so that's the big question.

As far as thickness goes, my measurements, if they are correct, tell me that I need a head gasket at least 2.39mm in thickness, this head gasket is .095" or 2.413mm. So I think that part is good, right? Also, with it being closer to what I need exactly rather then choosing a 2mm or 3mm, how will that affect what you had mentioned in the previous post? Just kind of balance it out? Is there anything else that I need to be concerned about? Thanks again.

 

[IJ.]

The larger bore in the gasket won't affect anything (I ran the 86mm Stoppers on a stock bore) I wouldn't get too caught up in the fractions you're talking about, in reality unless you're in a race class and trying to Win you'll never notice a difference as a layer of carbon is going to have more CR change.

 

[Numba1Stuna]

Thank you again IJ. I plan on keeping the 90 stock(my 91 is the powerhouse). So it is finally decided I guess lol. 2.4mm thickness with 84mm bore.

I'm going to start a for sale thread either today or tomorrow to help fund the rest of the needed parts/gaskets!

Sent from my G2x using Tapatalk 2

 

[Numba1Stuna]

Ok, once again have a question. I have slight electrolysis on the bottom of the head still after the mill. I'll attach pics to show you. Is this anything to be concerned with when using a MHG?

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[Numba1Stuna]

I did a search for electrolysis, but could not find anything relevant to this issue...

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[Grandavi]

electrolysis? Are you talking about the corrosion on your head? Im not a machinist, but your head doesn't look machined well enough. That looks like corrosion from a leaking head gasket that sat far too long...

my comment and thought.. but I am not an expert.

 

[supraguy@aol]

I would lay a head gasket over that head surface, to see if any of that corrosion will impinge upon the sealing surfaces.
If it does, you either gotta shave it more, or toss it.

 

[Numba1Stuna]

Well, I guess I can do up to .6mm more off the head and just get a 3.0mm MHG. They don't make them bigger then 3mm right? I'll stick a composite on there and see if it is in the sealing area.

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[AbsoluteSpeed]

They do make a thicker HG but are very difficult to come by.
When I built the motor in my first supra the machine shop ended up using a copper gasket that was 6mm (I think)

Honestly you would be much better off finding a new head it you need anything a over a 3mm gasket.

 

[fienloco]

Rebuilt my 7m .40 over on bore 4thou off the head, 8thou off tge block 2.0 MHG. Performance now is null. Any suggestions on the math or size of gasket I should have gone with or should go with?

 

[B shaw]

If compression is your only issue and you have the funds, why not buy pistons that help to lower compression? I did that with my 89t because I was going with forged internals anyways so it seemed like a good idea to me. Compression ratio comes out to a bit under stock, which isn't a bad thing. Am I correct in that line on thinking?

 

[Grandavi]

Rebuilt my 7m .40 over on bore 4thou off the head, 8thou off tge block 2.0 MHG. Performance now is null. Any suggestions on the math or size of gasket I should have gone with or should go with?

Are you talking 7mge? What compression do you have?

 

[VegaSupra]

Just read every post in this thread. Excellent info here.

One question I didn't see an answer for though...

Is it ever a good idea to open up a perfectly working 7M, resurface the head, and replace a stock HG with a 1.37mm or 2.0mm MHG?

My Supra is basically all stock and original from 1991. I do see in the original owner's maintenance notes that he retorqued the head bolts at 46K miles. (now has 72K miles)

But here's why I ask... over the next few weeks, I will be installing the following all at once.

57trim CT-26 upgraded/rebuilt by Albert
Intake (basic open air cone type filter)
Full 3-inch widemouth downpipe from Driftmotion
Full 3-inch exhaust
3-inch test pipe from Titan
Type RS BOV

I will not be raising boost on purpose (not buying a boost controller), but with the 57trim, and all the extra breathing room, I am guessing this will push me well over 300hp and will most certainly raise the "stock" boost level to at least 10 or 12 psi. I actually wish this weren't true, but I guess there's nothing much I can do about that.

If you were me, would you be concerned about blowing your stock original retorqued HG? What would you do?