Head Gaskets, why 3?

[BlkMax]

I know that there are three different thicknesses for the Dmax head gaskets.

I was told by a stealer parts guy that some trucks have different thickness gaskets from one side to another.

My first question is why would GM need to have different thickness gaskets on the same engine? Are the machine tolerances that bad that they are balancing cylinder volume with gaskets?

My second question is which thickness would you want to use on a rebuild, or would you want to keep the same thickness gasket as what came out?

Off the top of my head, for a rebuild I would think you would want to use the thinnest gasket, so you would have less chance of a blow out at elevated boost pressures.

 

[duramaximizer]

I have heard that the closer you keep the tolerances, the better the heads flow. I think some people use the different gaskets for different compression ratios or to allow more clearances between the valves and the pistons which is critical.

 

[dmaxalliTech]

There are three different gaskets to allow for production tolerance in the rotating assembly.

There are different rod and main bearings from GM as well for production tolerances.

 

[BlkMax]

There are three different gaskets to allow for production tolerance in the rotating assembly.

There are different rod and main bearings from GM as well for production tolerances.

I can understand different tolerances for the rod and main bearings. We are talking about oil film thickness between rotating assemblies. Are the head clearances that tight from a stock standpoint?

I have heard that the closer you keep the tolerances, the better the heads flow.

This would make more sense to me, but not at a stock power level. Would the factory really dink around with this so much? I would think they would just slap the thick one in and call it good.

I think some people use the different gaskets for different compression ratios or to allow more clearances between the valves and the pistons which is critical.

When I was building SBC stroker motors we were checking rod bolt and cam clearances, as well as valve to piston clearance with the higher compression pistons and higher lift cams. That would make sense on a built motor.

I understand the clearance issues between the various components, but how does one select the correct thickness head gasket for the Duramax when doing a rebuild?

Is this something that can be determined by measuring the top of piston to deck height? What are the specs?

If it is assumed that the compression and valve clearance issues are being controlled by de-lipping or cutting the pistons, which head gasket should be used?

I am not trying to be argumentative at all, I would just like to understand my engine a little better. At some point, I am going to have to rebuild the bugger.

 

[LBZ]

I can understand different tolerances for the rod and main bearings. We are talking about oil film thickness between rotating assemblies. Are the head clearances that tight from a stock standpoint?

This would make more sense to me, but not at a stock power level. Would the factory really dink around with this so much? I would think they would just slap the thick one in and call it good.

When I was building SBC stroker motors we were checking rod bolt and cam clearances, as well as valve to piston clearance with the higher compression pistons and higher lift cams. That would make sense on a built motor.

I understand the clearance issues between the various components, but how does one select the correct thickness head gasket for the Duramax when doing a rebuild?

Is this something that can be determined by measuring the top of piston to deck height? What are the specs? This is exactly how you determine what gasket to use. You measure your piston protrusion and then pick your grade of gasket reccomended by GM to give you the correct clearance. I don't remember the number off the top of my head for some reason .050" to .088" of clearance between the piston at TDC and the head seems to ring familiar, but I'm sure someone here can give you the right numbers.

If it is assumed that the compression and valve clearance issues are being controlled by de-lipping or cutting the pistons, which head gasket should be used?

I am not trying to be argumentative at all, I would just like to understand my engine a little better. At some point, I am going to have to rebuild the bugger.

Your best bet if you are thinking about building your own engine is get a GM manual for that year of engine. It will have all the specs and P/N's you will need and there are some very specific build points that need to be followed EXACTLY as GM reccomends to save yourself headaches down the road. Some specs and P/N's have been changed as well from year to year so you need to be sure you use the right specs and parts!!

 

[BlkMax]

Thanx,
I have the GM Shop Manual for my truck (all 5 volumes ). The head section is not one I have had to dig through.

Hopefully that is not a section that I will need for a while. Next summer will tell the tale...

 

[LBZ]

I believe there are more than three choices as well-I think there may actually be 5 or 6 different gaskets available!!

 

[mplteddy]

From GM there are 3, and then i think they offer one for oversized piston applications, I'd have to check though.

 

[MadMaxx61]

Here is the info I have found on this forum

So at total of 6:
(1) Grade A
(2) Grade B
(3) Grade C
(4) Block Over-Bored
(5) Block Over-Bored and Deck Milled
(6) Block Over-Bored +.060 Call Guy Tripp at SoCal

Gasket Grade..................Compressed Gasket Thickness
A............................0.0354-0.0394
B............................0.0374-0.0413
C............................0.0394-0.0433
2 other gaskets listed in service manual
Block Over-Bored 0.010-0.030 in ...............0.0394-0.0433
Block Over-Bored 0.010-0.030 in and Deck Milled 0.008 in....0.0492-0.0532

 

[mplteddy]

Thanks...guess i forgot one:thumb:

 

[MadMaxx61]

lol Np

That is why I have a huge doc file full of info like that I keep so that when I go to do it all I dont have to search for days. lol

 

[BlkMax]

Here is the info I have found on this forum

So at total of 5:
(1) Grade A
(2) Grade B
(3) Grade C
(4) Block Over-Bored
(5) Block Over-Bored and Deck Milled

Gasket Grade..................Compressed Gasket Thickness
A............................0.0354-0.0394
B............................0.0374-0.0413
C............................0.0394-0.0433
2 other gaskets listed in service manual
Block Over-Bored 0.010-0.030 in ...............0.0394-0.0433
Block Over-Bored 0.010-0.030 in and Deck Milled 0.008 in....0.0492-0.0532

Thanx again...I had seen that on an earlier search. I understood the overbore and deck milled gaskets, but I guess I did not expect the tolerances to be quite so tight, especially with a stock motor.

This thread has also answered my other question as to which one should be used.

 

[maine04max]

where can I find these manuals for the motor?????

 

[LBZ]

Ebay or GM.

 

[FMOS]

From GM, the service manuals aren't cheap. I recall them being about 500-600 bucks??? I've got a set and they come in handy for quite a few things.

Not that its worth much, but what I did when I replaced my head gaskets and had the heads trued/ground a bit was use the thickest gaskets. I had an "A" and a "B" come off, had the heads spot ground slightly in a few locations and to avoid measuring accurately or having issues I went with the "C" gaskets. No issues so far.