head gasket?

[dieseldummy]

Once upon a time a someone told me that thicker head gaskets were avalible in place of low compression pistons. Is there anytruth to this or not? Just trying to weight my options. thanks.

[DmaxMaverick]

The thicker gaskets are intended for use when the block's deck height has been reduced by milling. There are 3 standard sizes. The thicker gaskets may be useful to reduce the compression ratio. You would have to calculate the chamber volume to find out how thick the gasket would have to be to achieve a specific ratio. Off the top of my head, I think the gasket would have to be too thick to gain anything. That doesn't mean that someone hasn't done it successfully.

If it works, it sure would be a lot more practical than replacing 8 pistons.

[patrick m.]

if they are available, i would stay away from them (unless they are of copper construction)

[jeffreydmet]

I'm not sure what the stroke on these engines is but if the bore & stroke is equal the stroke would be 4in. A lot of engines are about equal on bore & stroke. Anyway I did the math and with this stroke assuming going from a 19.5:1 to 17:1 compresion ratio would require adding .034" to the head gasket thickness.

[turbovair]

Bore on this engine:4.060
Stroke on this engine: 3.820

[jeffreydmet]

With a 3.820in stroke you would need to add .026" added to the head gasket thickness to change from 20.2: to 18:1 compression ratio.

[dieseldummy]

is it safe to assume that the 3 thicknesses are: stock, stock plus .010, and stock plus .020?

[roclongrider]

Anyone on here actually done this?

[Scooby]

I'd like to know if this has been done too. I was wondering if there was any way to reduce compression with head modifications- ie. more clearance volume. The head gasket idea sounds easy, I just wonder if the thicker gaskets would last with the high compression.

[dieseldummy]

Well, assuming that .026 is need to reduce compresion to near 18:1, and assuming that the thickest gasket available is .020, then if a person used the thick gasket on a head and block that didn't need resurfaced, then it would almost work. Are my math skills flawed, or does this seem right to anyone else.

[cruzer]

Has anybody actually found or purchase these head gaskets? If so who makes them and what are there part #s? When I did my motor the machine shop tried to find shims or gaskets that were thicker because of decking and could not find. A Victor gasket kit came w/the rebuild kit. IIRC the Victor head gaskets were 0.030 & I used Felpros they were 0.040. I know for sure felpro's were 0.010 thicker. I maybe wrong but I think felpro only shows 1 #. I guess felpro figures you're going to machine something.

There are cheaper ways to achive 0.020-0.030 reduce comp w/o puchasing high dollar 18:1 pistons.

[turbovair]

The only thing about using thicker head gaskets that I can see is that a thicker head gasket gives cylinder compression more surface area to "push" against.If the head and block were not acceptably flat, a thicker head gasket might have a shorter life span and blow more easily.Add aditional boost and the issue would seem to get worse.

[dieseldummy]

I have looked all over and no one seems to know anything about different head gaskets, so i would say that my friend was lying, or knows something that we don't and wont share it. If the head gasket idea is out of the question does anyone know anything about increasing the volume of the pre combustion cups?

[tom.mcinerney]

I'm pretty sure two members in the past year made posts about copper head gaskets, these were lost in the 'great erase',don't recall if associated with compression issue; i'll look for a hard copy.....I'd suggest a phone call to John at Kennedy Diesel, or Bennie at Avant Salvage[both advertisers].

[cruzer]

Mahle makes a 0.010" reduced comp height piston for the same money as stk mahle pistons. You can also get a wrist pin bushing that are offset 0.010". There's 0.020". My master rebiuld kit was the same $ w/stk or 0.010" reduced comp. pistons. 18:1s where considerably more.

FYI if you were going to buy 18:1s, Kennedy's pistons were cast to be 18:1. I believe he reduced comp. by altering the top where the indentation is and allows the piston to come up to the top of the cyldr. They also control the burn like stk pistons. Mahle 18:1 pistons are
stk w/the wrist pin hole drilled higher in the piston, so the piston does not come to the top of the cyldr bore. That's the way it was explained to me.

[Jim P]

I just have a little to add here.

Stock pistons come up past the top of the block .010"(on a 95 anyhow) I used the .010 shorter pistons and also bored my wrist pin bushings off center .010 and my pistons now stick down .010 below the top of the block. I also removed some material around the valves to further lower the compression. Actually I think I went a little low on the compression. My truck smokes like a super stock pulling tractor when it is cold. Only theirs is black, mine is blue.

I don't think you can actually buy the offset wristpin bushings. You just have to use stock ones and bore them. The new bushings have about .025" of stock for final machining after pressing them in the rod.

[dieseldummy]

It sounds like you all know quite a bit about this sort of thing. I was just trying to come up with some ideas of what i could do to lower my compression without going into the whole motor, because there doesn't see to be anything wrong with it. I do need to change my head gaskets and thought that maybee there was something that i could do while i had the heads off. thanks for the info.

[Jim P]

I do know that when I bought my rebuilt kit from rebuiltdiesel.com , They said that they had some kind of thicker head gaskets to lower the compression. I have necer used them so I can't really say if they hold up or not.

[turbovair]

I think that if GM thought they could lower compression simply with a set of thicker head gaskets, that what they would have done. Would have been MUCH cheaper.We all know how much the General loves his money.