MHG Question, how much to take off of head and block?

[1988SupraDreams]

Okay guys, it turns out it's cheaper to put a MHG on the Supra than to replace the upper control arm on my buick, so I'm going to part out the buick.

My question is: Assuming that my engine has never been touched, how much will I need to machine off of the head and block to use a 1.2MM HKS MHG, and still keep the stock compression? Thanks all.

Added: HKS Bead type, not the stopper

 

[Doward]

The very minimum possible, to clean the deck.

What's the RA req'd for HKS MHGs?

 

[1988SupraDreams]

Define RA please, I've honestly never heard it, and I probably should've added that it's a Bead type, not the stopper.

 

[Doward]

Roughness average - basically how 'smooth' the finish is. Most machine shops that I know of, don't have a profilometer to actually check the RA (I know Partsco in Gainesville doesn't, talking our their ass bastards :3d_frown: )

 

[1988SupraDreams]

Roughness average - basically how 'smooth' the finish is. Most machine shops that I know of, don't have a profilometer to actually check the RA (I know Partsco in Gainesville doesn't, talking our their ass bastards :3d_frown: )

No idea... I'll find it though.

 

[JustAnotherVictim]

Okay guys, it turns out it's cheaper to put a MHG on the Supra than to replace the upper control arm on my buick, so I'm going to part out the buick.

My question is: Assuming that my engine has never been touched, how much will I need to machine off of the head and block to use a 1.2MM HKS MHG, and still keep the stock compression? Thanks all.

Added: HKS Bead type, not the stopper

I think they all have ~25-30 RA requirement.
If I'm not mistaken.

 

[starscream5000]

If you haven't heard of RA before, then you need to research on MHG's before you jump the gun and install one . If you don't have AT LEAST the RA spec required for your MHG, then it will most likely not seal and you will BHG. 1.2mm is thin, you may need to look at a 1.4mm at the least. We can't honestly answer your question as you haven't given us the info we need (how much material will be removed from the head and block, also, if there has been material removed from them before). Do not buy the MHG until you have the machine work done on the engine. Has this car had a BHG before?

 

[1988SupraDreams]

If you haven't heard of RA before, then you need to research on MHG's before you jump the gun and install one . If you don't have AT LEAST the RA spec required for your MHG, then it will most likely not seal and you will BHG. 1.2mm is thin, you may need to look at a 1.4mm at the least. We can't honestly answer your question as you haven't given us the info we need (how much material will be removed from the head and block, also, if there has been material removed from them before). Do not buy the MHG until you have the machine work done on the engine. Has this car had a BHG before?

I'm basing what I do on what you guys tell me, I'll tell the machine shop to take off however much needs to be taken off for the correct HG. And I've done plenty of research on HG's I've been doing it for a year now, Lurking is a great thing. I know that 1.2 is stock size, so yeah 1.4 does sound better. So if I use a 1.4MM Hg then the machine shop will need to take off .2MM Correct? It has the slightest and I mean SLIGHTEST BHG right now, 125 PSI of air into the 6th cyl yielded SLOW gurgling in the radiator. No bubbles or anything. .2MM seems to be very little though does it not?

 

[1988SupraDreams]

I think they all have ~25-30 RA requirement.
If I'm not mistaken.

You are correct sir.

 

[JustAnotherVictim]

Get the gasket after you find out how much is taken off.
Stress the after.

 

[1988SupraDreams]

Why do they even sell 1.2MM thick MHG's if you have to mill the head and block?

 

[CzA]

Quick question here, how do you know if the engine has been machined before? Is there anything in particular one can look for to see if it has had a HG replacement/machine work?

Thnx.

 

[JustAnotherVictim]

Why do they even sell 1.2MM thick MHG's if you have to mill the head and block?

Some people want to raise the compression or don't get the head or block surfaced so they don't want it.

Quick question here, how do you know if the engine has been machined before? Is there anything in particular one can look for to see if it has had a HG replacement/machine work?

Thnx.

You'd have to check the height of the head and block. No real other way to be positive.

 

[starscream5000]

Get the gasket after you find out how much is taken off.
Stress the after.

Right on, couldn't agree more . Tell the mechanic to take off the least amount possible to get both straight and smooth. To be on the safe side of things I would make sure the person you take it to can get the head and block down to an RA of at LEAST 20.

Since you've got a BHG, I would definitely play it safe and instal new bearings. Don't risk tearing it back down again because you've got rod knock and didn't want to change out the bearings. The coolant mixed in with the oil (which happens in a BHG) becomes acidic quickly and will eat away the soft metal of the bearings.

 

[CzA]

any chance of knowing what the stock height is form the block to the head is? And if their was work done to it , I take it the measurement would be less than stock due to machine work, but then again I guess the width of the gasket could play a role ?

 

[1988SupraDreams]

Right on, couldn't agree more . Tell the mechanic to take off the least amount possible to get both straight and smooth. To be on the safe side of things I would make sure the person you take it to can get the head and block down to an RA of at LEAST 20.

Since you've got a BHG, I would definitely play it safe and instal new bearings. Don't risk tearing it back down again because you've got rod knock and didn't want to change out the bearings. The coolant mixed in with the oil (which happens in a BHG) becomes acidic quickly and will eat away the soft metal of the bearings.

Yeah, I know about the bearing thing, I drained the oil, no coolant whatsoever.

I just got off the phone with my local machine shop (I've used them before and they've got their ducks in a row) and he said to just get the 1.2MM HG and to just shave the head? I asked him about doing the block and he said for a MLS HG that the standard procedure is to just shave the head. He said the block is smooth from the factory... I also mentioned that I had a minor BHG, and he said that it shouldnt make a difference on the block. Does this guy know what hes talking about?

 

[JustAnotherVictim]

If you want to be absolutely sure take it in.
Use a straight edge to check the deck, that should give you an idea oh how flat the block is.

 

[1988SupraDreams]

If you want to be absolutely sure take it in.
Use a straight edge to check the deck, that should give you an idea oh how flat the block is.

What about the size of the MHG? Should I use the 1.2MM like he suggests?

 

[Doward]

I seem to recall that the stock gasket was 1.0mm when compressed.

The MHG does not have this compression, so a 1.2mm is slightly bigger than stock.

 

[JustAnotherVictim]

I would still wait to see how much he takes off.
Reason is, with a 1.2mm you're already raising the compression ratio.
You should probably try to go with the 1.4mm if you're not doing the block. Although as I said, personally I would wait and find out unless you know exactly what you want to do with the compression.

You sure Doward? I could swear it was a bit more than that.
I might have been thinking 1.37mm uncompressed...