Duramax Head Gasket Thickness.

[More Power]

I received an email last week from a major manufacturer of cylinder head gaskets for the Duramax. Here's what was asked:

We currently offer three thickness' of head gaskets (as does GM) for this engine: .035, .037 & .039.
Do you think there is really a need for all three, or can we consolidate to the .037 thickness?

Here was my answer:

The different thicknesses among the offered head gaskets help compensate for a manufacturing tolerance in piston protrusion. If I were to suggest a single head gasket thickness, it would be the thickest gasket. This would accommodate a worst-case piston protrusion scenario, while producing only a slightly lower compression ratio for those engines with minimum protrusion.

The early Duramax 6600 was produced with an 18:1 CR and the latest Duramax 6600 is currently running a 16.8:1 CR. The slightly lower CR that a .004 thicker gasket might produce would not noticeably affect the Duramax.

What do you guys think?

Jim

[jdd75]

A question=If GM is using three different gaskets what do they
issue you for a replacement? I don't think they
will record which engine has which gasket.So if
they give you 35 and you should have 39 and
Something goes wrong,who pays!Or do the individaul
gaskets have different part numbers.

Sounds dumb to me!

I received an email last week from a major manufacturer of cylinder head gaskets for the Duramax. Here's what was asked:



Here was my answer:



What do you guys think?

Jim

[More Power]

You are (or the mechanic is) supposed to measure the piston protrusion for each piston at TDC. The gasket choice is based on the recorded values. I don't recall if the gaskets are marked with the thickness. If they are, then you'd replace them with the same...

Jim

[Duramaster]

When replacing the head gaskets, I install the same thickness gasket that was removed. There is a grade marking on the gasket. Actually it is a series of holes punched in the end of the gasket. They refer to right and left as well as grade A B or C and the holes also determine if the cylinder is oversized.

[DmaxMaverick]

I agree. A .004" increase in the chamber won't likely create a noticeable difference. However, this is a pushrod engine, and the valve travel index increase would be twice the gasket thickness increase. May still mean nothing in the real world, but could have a more significant difference in the engineering. Even hydraulic lifters have to operate within their design range. I don't know what it is for the Duramax, but it may be relevant.

Other than that, it makes little sense why they didn't just select the thickest gasket, and have only one. If they did, we wouldn't be having this discussion. Perhaps they did it knowing it could spawn just such a discussion. Engineers have a sick sense of humor.

[More Power]

The Duramax uses solid roller lifters and the rocker arms are adjustable, so varying head gasket thickness shouldn't be a problem.




Jim

[Rabbler]

When replacing the head gaskets, I install the same thickness gasket that was removed. There is a grade marking on the gasket. Actually it is a series of holes punched in the end of the gasket. They refer to right and left as well as grade A B or C and the holes also determine if the cylinder is oversized.

A good practice to follow but that assumes they used the correct gasket initially at the factory. I personally always measure piston height

[ARZ]

I hate to dredge up this old thread, but I don't see anyone addressing the biggest issue "The Valves Possibly Touching the Pistons".

If you take too much material off the head, you move the starting position of the valves closer to the pistons. Does anyone know how much you can take off of the heads?

Even the GM service bulletin does not address the piston to valve clearance.

Since the head is flat with no void in the head for the combustion chamber, only the recess for where each valve is located, and the small void left where the Glow Plugs install are the only voids changing volume, and this is VERY small change since the combined volume will be the diameter of each valve recess, and the glow plug hole minus the glow plug diameter.

Does anyone know if the valves could ever touch the head, if you took too much off of the head?

[Kennedy]

I'll make it simpler yet. The steps between the gasket thicknesses are so small it really makes no difference. We have only ever used and stocked the thicker units. We also only ever use the older style (mid series riveted) gaskets and not the new LML style cheapos.

It is my belief that the old style crimped gaskets are just as good as the riveted, BUT any Dmax head gasket job should use studs.