Part number for 8-bolt Cometic head gaskets...

Hello guys. I have looked and found quite a lot of information on the Cometic gaskets here. They seem to all have the 14-bolt pattern for the Stage blocks / heads.

I have a stock-type engine and would like to get 8-bolt Cometic headgaskets for it. Both the block and the heads are 8-bolt.

Could someone point me in the direction of a list of part numbers, indicating which are 8-bolt? I had expected to find this by searching, but after 20 minutes, I can't seem to locate the needed info. Time to ask the experts. :)

Thanks for the help!
Sincerely,
David
 

pacecarta

LOGGED OUT
Staff member
all cometics have 14 bolt holes ..just bolt em up , the extra holes on a non stage motor are not an issue , just make sure to get the thickness and bore that you need .
 
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Great, thank you for the information!

I have put 110,000 miles on my turbo 3.8 FWD build, and finally starting to have a slight compression leak at the front head, in the center. This happened when something went wrong with the system and it overboosted on me.

It had stock gaskets with ARP studs, ECM set for 18 PSI. Would show 16 or so on mechanical boost gauge.

Not too upset - I think that was a good service life for a build like this. :)

Hopefully the Cometic gaskets will help it survive any more events like this long enough for the fuel cut to kick in.

Sincerely,
David
 

ek02

Well-Known Member
Do some research here about using Cometics without having the deck and heads machined flat and smooth. Coolant leaks are common, but they work great with proper machine work.
 

earlbrown

runs with scissors
They will omit those holes if you ask them to.

There's only one caveat... The person you talk to is NOT smart enough to understand which one's you want omitted.

Luckily for me, The 3 they omitted (of the 6 I wanted) were right so I still had the 8 holes I needed to mount the heads.
 
They will omit those holes if you ask them to.

There's only one caveat... The person you talk to is NOT smart enough to understand which one's you want omitted.

Luckily for me, The 3 they omitted (of the 6 I wanted) were right so I still had the 8 holes I needed to mount the heads.

That's funny. :) I had read that before (that omitted holes were possible), however I was hoping that someone would stock them that way. In the end; I ordered the normal 14-bolt gaskets from a supplier who had them in stock. They should arrive tomorrow.

Do some research here about using Cometics without having the deck and heads machined flat and smooth. Coolant leaks are common, but they work great with proper machine work.

Yes. Agreed and that is a concern I have. When I built the engine several years ago, the heads and block were machined. I am 100% sure it has not been run hot since I am the only one who has driven it. The surfaces still look very good, and I can not find any areas with measureable warpage using a straight edge and a light.

This is the area of the block where the original gasket was blown. No evidence of burning or channeling the deck surface:


Same area of the head:


And for laughs - the old gasket. Mind you that I did get 115,000 miles out of it, so not too upset.


The ARP studs definitely held the torque. I had tightened them to 90 Lb-Ft when the engine went together. Last night, I broke two chrome sockets without being able to remove even one nut. Today I got a 1/2 inch drive 12 point impact socket and was able to get the heads off!

Also, this engine has 115,000 miles on it, with Shell Rotella T 15W40 oil. It has seen oil changes every 4000 miles, with a few overdue changes in the 5 to 6000 mile range. The engine is still absolutely clean. Very highly pleased with the performance of this oil.


Sincerely,
David
 

earlbrown

runs with scissors
Before I run cometics I always go over the surfaces with a diamond sharpining stone and something light like WD-40.

Its also a good idea to get a 45* countersink and put a nice bevel on the block and head's headbolt holes. A nice healthy bevel can help spread out the clamp load closer to where you need it.
 
Before I run cometics I always go over the surfaces with a diamond sharpining stone and something light like WD-40.

Its also a good idea to get a 45* countersink and put a nice bevel on the block and head's headbolt holes. A nice healthy bevel can help spread out the clamp load closer to where you need it.
Thanks for the pointers. I didn't have my computer with me today and didn't see your reply until after I finished the torqueing. I see how a countersink could help concentrate the clamping force around the compression seal bead. That's a good idea.

I did go over the block and head surfaces with a stone-like tool and checked with straight-edge and couldn't find any warpage. There were some stains on the block where the old gasket had been. The machine work was done, then the engine was run with stock gaskets. As added insurance, I put a very thin skim coat of Permatex Right Stuff around the water ports.

Caterpillar uses a similar rubber-coated steel shim gasket on the 3500 series diesel engines. It is famous for oil leaks where people have buffed the block or head and caused low spots. I have been successful with using the Permatex Right Stuff in this application so I used it here.

Sealant around water ports on the block:


And on the head:


Gasket in place on the studs:


And it's all torqued.


Someone may notice the "shortened" studs at the outboard edge of the block. This is due to the fact this is an LG3 engine. It's slightly different from the LC2, and the exhaust header would not clear a full-length stud in those locations.

After torqueing the heads, I worked on the intake manifold. It needed a dilled and tapped hole for a manifold temperature sensor. I believe that measuring the temperature here, as opposed to the charge pipe, will help me to tune out a heat-soak problem that causes it to run lean and run rough when started after sitting about 20 minutes in summer.

Also made an EGR blank plate. I tried tuning with the EGR and could get equal fuel milage with or without it. Going to remove and simplify things.

Hope to get the engine back together tomorrow.
Sincerely,
David
 
It's almost ready to go back in the car. Will keep posted here if there are any coolant leaks. I doubt it will leak!

Made some repairs to damaged exhaust system insulation today. Added some insulation and shielding here and there, as well as reinforced some brackets that were not very well built.

Removed the "open" crankcase breather and fabricated a steel pipe to connect to the valvecover. This is supported securely and will allow a hose to be clamped on and routed to a demister filter so that the crankcase blowby can be dealt with without oil residue going on the engine or into the intake system.


Insulated the rear manifold and reinforced the bracket holding the downpipe to the manifold.


Repaired some damaged insulation on the downpipe, as well as added insulation to the crossover pipe (turbo / wastegate mount pipe).


Welded on a shield below the turbo mounting point. Made it by slitting a piece of 2.5" exhaust pipe and opening it up to make a "U" cross-section piece. This should help stop some radiant heat from reaching the electrical wiring and other underhood parts.


Almost ready to go back in! I will re-wrap the harness with new convoluted tube and do some other minor repairs first. The steering pump leaks horribly between the reservoir and the pump. That will have to be addressed because it leaks all over the harness and even drips on the exhaust.
 

earlbrown

runs with scissors
Since those surfaces were ran with thick gaskets (and you didn't countersink the holes, I'd recommend a couple of GM seal tabs with the initial water. Then one tab when it proves itself and you switch to antifreeze.
 
Since those surfaces were ran with thick gaskets (and you didn't countersink the holes, I'd recommend a couple of GM seal tabs with the initial water. Then one tab when it proves itself and you switch to antifreeze.

Yes! Those seal tabs are good stuff. I always like to use them as added insurance.

Honestly - I'll start out with antifreeze, with seal tabs. I pressure test my builds with air pressure and soap solution before installing them.... both the crankcase and cooling system. It really helps to cut down on time spent fixing leaks with engine in car.
 

earlbrown

runs with scissors
Since you've already set up a test rig for pressure testing, go ahead and pressurize the intake tract too. That will often show some interesting surprises.
 
Since you've already set up a test rig for pressure testing, go ahead and pressurize the intake tract too. That will often show some interesting surprises.

That would be interesting - I have done this with custom built turbo exhaust systems, but not the intake. Doing it with the exhaust revealed some air escaping the crankcase breather, and some coming back through the intake. But I didn't have the intake capped off so that was just exhausting out the TB.

It will be a while before I get back to this project because I'm on duty at work now; offshore.
 

earlbrown

runs with scissors
When you get home, here's how to do it. Step one) But a can of delicious Chef Boyardee ravioli.. Step two, eat said delicious Chef Boyardee ravioli...

Knock a hole in the bottom and install a tire valve stem. Set your air compressor regulator to around 30PSI or so, and use a clamp on chuck with the 'custom Italian TR pressure test adapter'
Clamp the can in your MAF pipe or straight to the turbo. You might have to index the crank or back off on the rocker shafts if you have a huge bumpstick.

Simple Green works good for bubbles as you can rince it pretty easy without a lot of residue plus it has that pleasant smell.
 
When you get home, here's how to do it. Step one) Buy a can of delicious Chef Boyardee ravioli.. Step two, eat said delicious Chef Boyardee ravioli...

Knock a hole in the bottom and install a tire valve stem. Set your air compressor regulator to around 30PSI or so, and use a clamp on chuck with the 'custom Italian TR pressure test adapter'
Clamp the can in your MAF pipe or straight to the turbo. You might have to index the crank or back off on the rocker shafts if you have a huge bumpstick.

Simple Green works good for bubbles as you can rince it pretty easy without a lot of residue plus it has that pleasant smell.

LOL I like your Italian TR Pressure Test Adapter idea! :)

I did pressure test the cooling system, but did not take time on the intake. I had a longer than expected offshore job and just got home recently!

So, I have breathed a sigh of relief because all the coolant didn't immediately pee out on the floor as fast as I poured it in LOL. Will have to see how it holds up after a few heat / cool cycles. The engine started up readily without drama and sounds exactly like it did before.

While the engine was out, I did some needed maintenance on the car. The engine / EFI install and turbo build I did at a farm without much to work with. So, I took advantage of this opportunity to make some fixes. I already showed the exhaust system rework. As for the car its self with engine out; there were a few things.

Previously, the A/C dryer was touching the exhaust insulation wrap on the downpipe. The A/C was very adequate but I know this was bad all around to have anything rubbing. So, I brazed an extension into the pipe between the evap. core and drier. This moved it out of the way. Then, fabricated a new bracket. This works with a later-model car's drier insulation sheath which I got from a junkyard. I figure any improved insulation will be a Good Thing.

Also, pulled off the evaporator cover and found a horrible mess of leaves and pine straw. Cleaned that out and the blower moves a lot more air now. :) I couldn't believe I found this much crap in there.... the air conditioner has been very good in this car!



As the engine went back in, it got all new radiator and coolant hoses.

Here it is all back together!


Can't wait for a test drive. I will be careful with it at first, datalogging and making sure I find the root cause of the overboost it had.

I did replace the wastegate control valve and the MAP sensor just to be on the safe side if there's an intermittent problem. Verified the Turbonetics Evolution wastegate is working freely and not leaking internally in the air side. Couldn't find a smoking gun root cause.

Sincerely,
David
 
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