Head Gasket thickness selection

IJ.

Grumpy Old Man
Authorized Seller
Contributor
Joined
Mar 30, 2005
Messages
38,726
Likes
5
Location
I come from a land down under
#1
Seen this question asked on many occasions, here's the HG's for dummies version ;)

1) Stock HG = 1.37mm compressed

2) Stock head = 116mm deck to valve cover surface

3) Stock block = 198.5mm from deck to main bearing saddle

If 2 and 3 are less that amount needs to be added to 1 to retain the stock compression ratio and squish/quench.

When resurfacing the Block be sure to take the Timing Case along to have it done at the same time or your new HG will fail in miles.


Block measurement = 198.5mm/7.81"
 

rayall01

Member
Authorized Seller
Joined
Oct 10, 2008
Messages
901
Likes
1
Location
Westfield, ma
#3
i already have my 1.2mm MHG from HKS
would it be ok to use since the head is resurfaced?
if not what would happen?
If the stock gasket is 1.37mm, then the HKS is already to thin for stock surfaces. Since you have already machined the head, (and hopefully the block as well), You will need to get a much thicker gasket to maintain the correct compression ratio, or you will get detonation issues. And if you haven't done the block, then don't even think about using a metal gasket, because it will not seal.
 
Likes: Supraross

kamikazemkiii

Active Member
Authorized Seller
Joined
Mar 21, 2009
Messages
1,221
Likes
0
Location
North Carolina
#4
If the stock gasket is 1.37mm, then the HKS is already to thin for stock surfaces. Since you have already machined the head, (and hopefully the block as well), You will need to get a much thicker gasket to maintain the correct compression ratio, or you will get detonation issues. And if you haven't done the block, then don't even think about using a metal gasket, because it will not seal.
i havent decked the block just resurfaced the head
my wiseco's are 9.1 compression
what size would you reccomend?
 

CyFi6

Aliens.
Authorized Seller
Joined
Oct 11, 2007
Messages
2,972
Likes
2
Location
Phoenix
#6
How much is considered safe to remove off the head/block before either is considered junk? I see this question often and it always seems to be unanswered. Also, why did HKS make a 1.2mm head gasket/ in what case should it be used?
 

IJ.

Grumpy Old Man
Authorized Seller
Contributor
Joined
Mar 30, 2005
Messages
38,726
Likes
5
Location
I come from a land down under
#9
How much is considered safe to remove off the head/block before either is considered junk? I see this question often and it always seems to be unanswered. Also, why did HKS make a 1.2mm head gasket/ in what case should it be used?
Going by the factory specs very little but in the real world 20 thou off either seems to work fine and possibly more off a late Heavy/Thick Block.
 

nsngarage

New Member
Authorized Seller
Joined
Jan 24, 2009
Messages
210
Likes
0
Location
Pittsburgh, PA
#10
Yeah i'd love to know when a head is considered unusable.. I have 3 of them that have come off of BHG cars, and they've all been resurfaced before. I'd much rather not use one that's gonna cause me MORE headaches lol..
 

max-89supra(t)

Member
Authorized Seller
Joined
Dec 12, 2008
Messages
160
Likes
9
Location
vancouver, wa
#11
hey if you measure the stock head gasket after it has been pressed its actually a lot thinner the the 1.2mm hks, keep that in mind, and ya its better to resurface both head and block when going with a mhg, found that out the hard way:cry:now i got my head resurfaced and will get my block resurfaced this weekend, will post pics soon
 

Ice

New Member
Authorized Seller
Joined
Oct 27, 2008
Messages
8
Likes
0
Location
Bellingham
#13
If the stock gasket is 1.37mm, then the HKS is already to thin for stock surfaces. Since you have already machined the head, (and hopefully the block as well), You will need to get a much thicker gasket to maintain the correct compression ratio, or you will get detonation issues. And if you haven't done the block, then don't even think about using a metal gasket, because it will not seal.
So i'm planning on using Fel Pro's MLS (multi-layer steel) gasket, and by what your saying i need to resurface the block as well or the gasket won't seal? Could i just clean it up with ..say..sand paper and a scraper? I have pulled the head off on my car bc of a BHG but im not looking forward to have to remove the block.
A sooner than later reply would be helpfull. Thankyou
 

chefma70

New Member
Authorized Seller
Joined
Mar 19, 2008
Messages
404
Likes
0
Location
Florida
#14
sorry to ask this but how the fuck do you measure a block and head???!

im using my dads ancient carpenter tools.so excuse my lack of knowlege for the newer tools
 

chefma70

New Member
Authorized Seller
Joined
Mar 19, 2008
Messages
404
Likes
0
Location
Florida
#16
I use a pair of Digi Verniers.
oh yea i have one of those...

takes a sip of gatoraid

puts bottle down.....well my machinist recommended a 2mm mhg cause my head has been decked before so i just going to listen to him.
 

jb dock

New Member
Authorized Seller
Joined
Jul 28, 2008
Messages
6
Likes
0
Location
canastota ny
#17
just put a mhg hks 1.2 mm in my 87 supra running at 15 lbs of boost for 1 month now no problems .not using any kind of drugs [just budlight].
 

rayall01

Member
Authorized Seller
Joined
Oct 10, 2008
Messages
901
Likes
1
Location
Westfield, ma
#18
So i'm planning on using Fel Pro's MLS (multi-layer steel) gasket, and by what your saying i need to resurface the block as well or the gasket won't seal? Could i just clean it up with ..say..sand paper and a scraper? I have pulled the head off on my car bc of a BHG but im not looking forward to have to remove the block.
A sooner than later reply would be helpfull. Thankyou
No, unless you mean you're going to do what I did. Read my build thread.

http://www.supramania.com/forums/showthread.php?t=92669
 

jdub

<B>Official SM Expert: Motor Oil, Lubricants & Fil
SM Expert
Authorized Seller
Contributor
Joined
Feb 10, 2006
Messages
10,730
Likes
3
Location
Valley of the Sun
#19
just put a mhg hks 1.2 mm in my 87 supra running at 15 lbs of boost for 1 month now no problems .not using any kind of drugs [just budlight].

That's a great idea...just pull a number out of your arse and use it. Base your recommendation on a whole month of use too. Highly credible post sport.

Since you appear to be new guy, these kind of posts are not tolerated in the Tech section. Especially one that has potential to cause damage.

To keep stock compression, the MHG needs to be at a thickness that will make up for the material removed from the block and head decks. Unless you know what you are doing, increasing cylinder compression and increasing boost is a sure fire way to blow your engine.
 

Drake69

Enjoyin' mah ride...
Authorized Seller
Contributor
Joined
Aug 24, 2009
Messages
648
Likes
1
Location
Richmond, Virginia, United States
#20
Okay, PLEASE forgive my ignorance, but from the way I read this, there are two choices....

1: Pull the head apart, inspect the head and block for warping or damage, take the head to a machine shop to get it milled if it needs it, measure how much of the head was shaved, jump online, order the appropriate MHG or HG with studs (if they are even in stock!!!), and wait for it to ship? (And I'm not even talking about how to mill the BLOCK yet, like taking IT out or trying to mill it in the shop...)

2: Buy an MHG ahead of time with more width than stock (like 1.5~2.0mm) with studs, pull the head apart, inspect the head and block for warping/damage, take the head to machine shop to get it milled irregardless of damage to match the amount of the MHG you just bought (equal to what the head and block had to be milled to to match the width actually), and them reassemble everything.

Since this is a HG for Dummies thread, what exactly is the recommended way of doing this, factoring time constraints and cost of this endeavour? For some of us, we're using our MKIII's as daily drivers, and as such can't be down for weeks at a time doing all this. For others, they won't/might not have the garage/shop space to take up for weeks at a time doing this. As a preventative measure, it makes perfect sense getting the HG done NOW and done RIGHT to avoid any headaches later on down the road, so more people will want to do this themselves or with friends who know motorwork. Or should the newbie just chuck all this and get it pro done and get raped by a stealership/machine shop in the process?

Again, forgive my ignorance and/or asinine tone. It's frustrating worrying about a BHG and not being able to do much about it but let it happen when you can supposedly prevent/postpone it.
 

kamikazemkiii

Active Member
Authorized Seller
Joined
Mar 21, 2009
Messages
1,221
Likes
0
Location
North Carolina
#22
Ok im alittle confused the first time around i resurfaced the head but not the block used a 1.2mm MHG and it blew. Now i have it apart again and the block and head seems to be good, unwarped, and uncracked. Would it be necessary to have it resurfaced again?

I have sanded and cleaned the head and block really good, I used a metal ruler to see if its straight and it appears to be. is their another/better way to go about making sure its unwarped myself?
 

rayall01

Member
Authorized Seller
Joined
Oct 10, 2008
Messages
901
Likes
1
Location
Westfield, ma
#23
Ok im alittle confused the first time around i resurfaced the head but not the block used a 1.2mm MHG and it blew. Now i have it apart again and the block and head seems to be good, unwarped, and uncracked. Would it be necessary to have it resurfaced again?

I have sanded and cleaned the head and block really good, I used a metal ruler to see if its straight and it appears to be. is their another/better way to go about making sure its unwarped myself?
You're kidding, right? You need a quality straight edge, long enough to extend beyond the ends of the block, or head, a set of feeler gauges, and then follow the procedure in the TSRM. Just cleaning the surface is not enough!
 

rayall01

Member
Authorized Seller
Joined
Oct 10, 2008
Messages
901
Likes
1
Location
Westfield, ma
#25
Is the HKS HG reusable ?
Yes, if there's no damage. You have to remove the rivets, and totally clean off all the viton that's on it, and then use Permatex copper spray sealant on every surface. If by some chance the viton is in perfect condition, then you won't have to do anything to it, but I doubt it.
 
Joined
Dec 1, 2009
Messages
10
Likes
0
Location
Green Bay, WI
#26
Considering that Cometic and other manufacturers make multiple thickness MHG's I doubt it would be an issue to find one to make up for material milled/decked however I was wondering if it is imperative to return the thinkness back to stock? I understand it will affect the quench and squish however I was under the impression that so long as I hook up my wideband and modify the fuel/timing parameters accordingly it shouldn't be a problem provided I have the necessary pistons to valve clearance and the pistons aren't protruding out of the cylinder bore? Perhaps returning the thickness back to stock is only necessary if I intend to use the stock parameters of the ECU? I just want to make sure prior to doing a rebuild.
 

IJ.

Grumpy Old Man
Authorized Seller
Contributor
Joined
Mar 30, 2005
Messages
38,726
Likes
5
Location
I come from a land down under
#27
Considering that Cometic and other manufacturers make multiple thickness MHG's I doubt it would be an issue to find one to make up for material milled/decked however I was wondering if it is imperative to return the thinkness back to stock? I understand it will affect the quench and squish however I was under the impression that so long as I hook up my wideband and modify the fuel/timing parameters accordingly it shouldn't be a problem provided I have the necessary pistons to valve clearance and the pistons aren't protruding out of the cylinder bore? Perhaps returning the thickness back to stock is only necessary if I intend to use the stock parameters of the ECU? I just want to make sure prior to doing a rebuild.
How did you manage that stock is 20 thou out of the holes....
 

89supra7mgte

New Member
Authorized Seller
Joined
Sep 20, 2009
Messages
797
Likes
0
Location
colorado
#28
Ok i am not familiar with rebuilding foreign engines (knowledable of american) Anyways i have a spare block and head that i am planning on rebuilding, not as a daily driver. I plan to build it from the bottom up inside and out. I have two mhg's one is the hks 1.2 and the other i believe is a 1.5, I know it would be a big jump to pull the rivets and make a 2.7 mhg, which would lower compression alot, but is it possible? Given i machine the block and head for use of an mhg? I plan to use bigger cams, and higher compression pistons.

I would go stand alone and upgrade fuel and air as necessary. Mind you this is only thoughts right now. just wanna know if it is is something that can actually be accomplished? any and all thoughts would be helpful.

I know by, if possible using this gasket set up i am gonna run into cam issues along with timing belt lengths and all that good stuff, but it will be done right if it can be.
 

rayall01

Member
Authorized Seller
Joined
Oct 10, 2008
Messages
901
Likes
1
Location
Westfield, ma
#29
I wouldn't try combining them, as the HKS stopper, at least, has three distinct parts, and I'm not sure about the other ones, but I wouldn't do it to my engine.
 

89supra7mgte

New Member
Authorized Seller
Joined
Sep 20, 2009
Messages
797
Likes
0
Location
colorado
#30
how do i tell the difference on them? the both look identical minus the steel thickness.

I take that back the one gasket might be a 2.0 it looks alot bigger than i originally thought. so maybe i can just work with that one and build around that?
 
Joined
Dec 1, 2009
Messages
10
Likes
0
Location
Green Bay, WI
#31
How did you manage that stock is 20 thou out of the holes....
Sorry, I'm still learning specifics about the 7M and was basing my post on experience w/ other engines where it usually isn't good to have the pistons sticking out. I'll have to remember this during my own rebuild so I don't thinks somethings wrong when I notice them sticking out. On a side note, it appears this post also shows an easy way to tell how much the block might have been decked is to measure how far the piston sticks out of the cylinder.

Besides my ignorant statement regarding the piston sticking out, would the rest of my logic regarding the tune hold true?
 

jdub

<B>Official SM Expert: Motor Oil, Lubricants & Fil
SM Expert
Authorized Seller
Contributor
Joined
Feb 10, 2006
Messages
10,730
Likes
3
Location
Valley of the Sun
#32
Do us a favor and don't post unless you're 100% sure...the 7M is a very unforgiving engine when it comes to build specs. This forum is littered with the results of from guys using "I heard" or "that's they way they do it on <insert motor>". Suggest you do a lot of reading before you attempt a rebuild on this engine.

The quench is important on this engine due to the heat produced from the higher dynamic compression under boost. On a MHG less than stock thickness, the combination of reduced quench and increased compression under boost can cause it to detonate in a nanosecond. The 7M does not tolerate this well at all, especially with stock pistons.

Most guys will go with stock thickness or slightly more and bump boost.
 

7mLove

Addict
Authorized Seller
Joined
Nov 11, 2009
Messages
121
Likes
0
Location
Barksdale AFB, Louisiana United States
#35
just to clarify with the superiors. in order for me to use an hks stopper 2.00mm (which im assuming its 2mm compressed) my specs should look like this?

115.67 - Head: deck to valve cover surface
198.2 - Block: deck to main bearing saddle
 

Northbaysupra

BAY AREA MKIII
Authorized Seller
Joined
Mar 19, 2010
Messages
135
Likes
0
Location
Petaluma
#36
Isnt it ok to a 2.0 hks stopper for lower compression. on a new head and block?? Im tryin to boost high. please say yes ! cus i already ordered it..LOL
 

Cokedoctor

Slow Boost
Authorized Seller
Joined
Oct 29, 2007
Messages
38
Likes
0
Location
Buffalo, NY
#37
What is the measurement of a compressed HKS 1.2mm HG? I have piston protrusion, and both the block and head were decked. My machinist is trying to find out what the compressed value of the HG is, to find out whether or not I have enough clearance, ultimately.

However...after reading on in this thread, I have picked up that I should maintain STOCK values, by running a thicker HG to give back material that was taken away when the block and head were machined. I have Wiseco pistons. The compression ratio has slipped my mind..but I know I kept it stock or as close to stock as possible when I bought them. Can someone explain to me, where exactly the main bearing "saddle" is? Is this the very "top" of where the crankshaft rides in the block?
 

Cokedoctor

Slow Boost
Authorized Seller
Joined
Oct 29, 2007
Messages
38
Likes
0
Location
Buffalo, NY
#39
Okay thank you. Was not sure if thats what it meant, or if it was pre-compressed value. I'm going to grab some values from the garage tomorrow if I have time, and throw them up here. I'll have piston protrusion values...maybe you guys can help me decide what HG I should use. I have learned this motor is a very critical engine to rebuild and values/measurements are key. Hopefully some good advice can be had. Thanks again.