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Head gasket advice from Missy's desk

Missy Good Wench

Missy Good Wench

Wild Blonde from Cloud Mt
Messages
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Location
Newberg Oregon
As most of you know my dually truck (DaHoooley) had a complete engine BUILD last summer with almost all of the major engine parts being replaced.

Block, heads, pistons, rings, bearings, lifters.
Saved the crank and the cam and the peripherals is about all.

Now to the point
I ended up using a COMETIC MLS head gasket on one side due to the block having been decked once before I got it and then we decked it again. :eek:

The head gaskets by Cometic are a multi layer stainless steel and are riveted together in a few spots around the edge.
The gaskets are coated with a special material to assure a good coolant seal as well.

The Cometic gaskets are also RH and LH specific
The water ports that do nothing up front ( except promote corosion and block erosion) are not in the Cometic gaskets.

The deck and the heads need to be very smooth when using these gaskets so if you have the shop machine the decks, have them done smooth as a baby's BUTT.

The cometic gaskets are solid stainless in all layers and are "coined up" or if you will, have ridges to mechanically seal the compression.

If you are at all anal about having coolant leaks as I was, the company rep advised me to simply spray the gaskets on both sides lightly with copper coat and then install. (Warm and fuzzy feeling ya know)

Another plus is that these gaskets can be ordered to custom thicknesses too.

I needed one that was .070 thick and these numbers are a Compressed thickness.

With the piston at TDC on a 6.5 TD you should end up with about .035" clearance between the head and the piston.

If your pistons are above the deck a little you can always order a slightly thicker gasket.

These gaskets are a real plus when you have a block that needs a second time around on being decked. (far better than tossing out an otherwise perfect peice of Iron.

DaHoooley has been on the road now for a while and is running perfect.

Smoothest 6.5 I have ever owned.

.020 oversized pistons, "T" precups, a set of 6.2 rods, Stock GM heads from Gawd knows what. 93 I Was told

Used the one cometic gasket on the Turbo side and the felpro +.010 on the other side.

The next time around on any 6.5 Build I will definately use the cometic gaskets.

These are far and away a better choice than the composition gaskets.

For one they are all metal and not metal/fabric
There is no coolant contact in the front water passage area to cause the erosion commonly seen around cyls 1 and 2 fire ring.

Missy says don't build without them. :D

(This was not a paid solicitation) :smile5:

Any questions, call the friendly folks at Cometic (find them on the web)

OH BTW
Cometic offers a stock thickness gasket in their catalogue

Missy
 
buddy said:
Thanks a bunch, so what if youre not having the block or head resurfaced?
Click to expand...

Order stock thickness. :D

Oversize gaskets let you equalize for machine work... or lower compression - as a few have tried. Not sure how effective that is, but they seem to think it's a good idea.
 
But what if I want a superior quality cometic gasket at stock thickness or just lower compression, will it seal just fine? Is there a standard polishing for deck surfaces before putting gasket on?
 
The factory finish should be fine.

Many shops finish these with a cut that looks like it was done with a JOHN DEERE PLOW :eek:

Smooth is the buzz word.

Most 6.5's that have many miles on the clock will need to have the decks cut anyway because of errosion around the fire rings on cyls 1 and 2

IIRC the stock cometic gasket is .045" thick when compressed

Remember, any numbers you give Cometic are to be figured as Compressed thickness not free unused thickness.

Seems to me that a stock gasket (new one) that had been bolted up and then removed mic'd out at .041"-.043" thick

If you cut the decks .010 you would add that to the thickness of the stock spec gasket. .055" thick compressed and when all bolted up your internals will clear at around .045".

It is very important on these engines to install pistons one and two, a degree wheel and then find true and absolute TDC for these cyls and then use a depth mic and find out exactly where the pistons are in relationship to the deck surface.

Remember these suckers have very little room inside when the pistons come to the top of the stroke.

NO ROOM FOR RAGS, GLOW PLUGS AND OR OTHER LEFT OVERS. :eek:

If you want to drop the compression its best to use pistons that have the pin center moved up a tad to drop the piston in the hole a little.

Using a much thicker gasket can screw with valve train geometry.

The whole idea is to keep things where they belong.

For most applications that are not being boosted clear to the moon the stock compression ratio is great. They start well in all weather and run fine.

If you are hell bent on 15-20 PSI boost and such plus nitrous, alky/water mix and other such stuff then you probably are needing to pony up for some 18:1 slugs.

If you plan on some such thing, I would also recommend a P400 or at least a fresh block plus a forged crank and a fluid damper and a rabbits foot in the glove boxs just for luck.

My focus here is for reliability and durability of the head gaskets and the block decks.

A set of good head studs is definately not a bad choice but the stock type TTY bolts from Felpro will suffice for most engines.

Here is Missy''s recommendations for torquing.

Through the first time to 20 ft pounds
Second time to 55 pounds
Third time to 55 pounds to even them up
Fourth time 1/4 turn more. 5th time through, start with the last bolt tightened and bring the torque wrench up slowly until the bolt just starts to move then note the reading.

Now go through and even all the bolts to that final torque reading.

I found that after the 1/4 turn, the first bolts done tended to be a lot looser than the last ones.

Just make them all the same and your done at that point. If you get one that gets real froggy, replace the set.

I have seen some of these TTY bolts that turn into taffy and just wont take a set.

I did this procedure on the DaHoooley and the bolts all came up real nice.

The cometic gaskets will see the bolts hold a lot closer torque as the gasket does not squash out as easy as the fabric gaskets do..

Took a lot more of my arse a pulling on the wrench to get that last 1/4 turn on the side with the cometic gasket.

MGW
 
Awesome, I was really just wondering if one was to blow a head gasket and not taking block out want to put a Cometic in would work good with just polishing it nice with drill or air die grinder.

Unfortunately a forged crank is not available, but Scat has confidence in their new casts, and will make a billet one for a few thousand dollars.
 
I talked to peninsular on the phone a couple months ago and a forged 6.5 crank was avail for about $900 + shipping.

Edit: $949 on their website



.
 
Last edited:
I wanted to add this info:

Its a GM technical bulletin advising do NOT use Surface Conditioning Discs- scotchbrite discs- flapper discs etc on head gasket surfaces. Use a scraper and elbow grease instead.

Many reasons but the biggest is that it can quickly and easily remove enough metal to cause an uneven gasket mating surface and cause a leak


http://www.chicagoengines.com/tech/bulletins/General-Motors-Position-Surface-Conditioning-Discs.htm

Another article ref on the same subject:

http://www.enginebuildermag.com/Article/67078/gaskets_seals_sealants_and_fasteners.aspx



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I don't like Cometics, just hoping they have a better fire ring on the GM than my turbo Dodge stuff. We can't get ours to seal under boost, the fire ring isn't built properly and cause's compression to leak quite easily. :sad:
 
The cometic type gaskets are also what is used on the DURAMAX. Keep in mind though when using them to keep the gaskets clean and dry, and DO NOT get any cleaners on them as that can damage them. COMETIC gaskets are made using multi layers of sstainless steel coated in neoprene for sealing. I know that DODGE went to them back around 98 or 99 for there small 4 cylinder engines that were plagued with oil leaks in the pressuruzed oil galley area where the o-ringed FEL-PRO gaskets would leak. I read before that copper coat is not reccomended for most applications, but MOPAR has a special sealer that is designed just for COMETIC MLS gaskets that is made up of mostly organic elements that will not harm the gaskets or cause dissimiliar metal corrosion.
 
You are right on installation, it has to be clean. Mopar went to an MLS gasket for the Neon, its not a Cometic. We've since found out it wasn't the gasket really, just crappy clamping and other small things, :(

Cometic says to use either high temp copper spray or Hylomar, which is what I think the organic stuff is.

Cometic does build a good gasket, sometimes, ):h
 
turbovanman said:
No offense but honestly what does that have to do with anything? A gasket is a gasket, if they can't make it hold on a lowly 2.2/2.5, how the hell will it hold on a diesel? :eek:
Click to expand...

No Cometics for me either. Engines that come with a factory mls don't use Cometic they have there own design of mls. I had very bad luck with my Cometics, in a lower boost situation,they might work,but I'm not going to use them again.
 
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