cometic head gaskets
 

What is the proper head torque for a 350 super stock motor with .036 cometic head gaskets with studs, they are seeping at the corners at 75 lbs. Thanks

Re: cometic head gaskets
 

That isn't a torque problem, most likely. More apt to be warpage or finish. Adding torque is not the solution.

Re: cometic head gaskets
 

I have used & reused those for a few years now, with no issues. I'm with Alan.

Re: cometic head gaskets
 

Have you ever checked the block and head for flatness? Recently? Also Cometic will tell you to use the "torque specs " that the head bolt or head stud manufacturer recommends SBC usually is 65 but if you are using ARP because of the lube they use to install the studs I'm sure you have to go higher --Even tho Cometic does not recommend it have you tried re torquing the heads to see if they are in spec just in case you mighta missed one-- However if its the ends leaking most likely the heads are not truly flat and might need to be resurfaced--FED 387

Re: cometic head gaskets
 

^^^^^^^ Never heard of anybody using 75 lbs either.

Re: cometic head gaskets
 

Removed intake, leaking in the middle inside also, deck surface too rough for those gaskets I suspect

Re: cometic head gaskets
 

They need a smooth finish. I have seen corner automotive machine shops with cutters on their head & block miles set up for a rough finish. Ridges. Not what we need.

Re: cometic head gaskets
 

This is a question on what to do about this problem . If its found that the surface finish is too rough , what can be done to correct this or make due with it . I am thinking that the engine has already been setup with the correct deck height and combustion chamber volume so if the block was re-decked, to correct the surface finish, then it might not pass tech , same with the heads . Can some sort of sealer be used like Permatex Copper Gasket Sealer ? I recently disassembled an engine with Cometic head gaskets and there was no gasket sealer on the head gaskets . Is this normal for Cometic gaskets ?

Re: cometic head gaskets
 

Fed,
Actually using the ARP lube typically requires LESS torque on the same fastener. A torque wrench basically measures friction and the ARP lube makes less friction so it requires less torque to get the same stretch on the fastener.

That being said, the torque shown for ARP head studs with their lube is 80 ft lbs so if the Rick only torqued them to 75 that is really not enough. Also depends on the brand of studs and what lube was used on them.

Re: cometic head gaskets
 

Rick,

Are they ARP studs ? Did you use ARP lube or just oil ? If they are ARP studs the torque spec is 80 lb ft with ARP lube. If you used oil it would be higher.

I personally think that the finish would really have to be bad to make them leak. If you could see some of the factory cylinder head finishes that I see you would understand why I say that. They are pretty terrible yet they don't leak. I always put the proper finish on them when I machine them but I don't know if it is your problem.

Now if the deck or the heads have low spots in them I could see it.

Years ago one of the Fel Pro performance engineers told me to do the following when torqueing race engine heads.
1. Torque the heads as usual to the correct torque.
2. Let them sit overnight
3. Start with the first bolt in the pattern, loosen it 1/2 turn and then torque it back to specs in one step. Continue through the pattern one bolt at a time doing the same thing.

This method works much better than just putting your toque wrench on and re-torqueing the fastener because typically the breakaway torque to get the bolt or nut moving again is a lot more than the final torque spec.

If you try this, mark one of the bolts or nuts before you loosen it. Then re-torque it and see how much more it turns. I typically see close to 1/8 turn.

I do this on almost every engine I do and have basically not had any head gasket issues.

Re: cometic head gaskets
 

I only go 70# on a small block with ARP lube, and when I use them over, I always use copper coat. I've never blown a cometic. Will copper coat help you? Don't know, but may be worth a shot.

Re: cometic head gaskets
 

Gulius always has us use 72 with lube Ed ,,,, All his motors are studded

Re: cometic head gaskets
 

It is studded and I torqued up to 85 with oil on threads, still seeping. I have never had a block machined this rough always smooth. I had composition gaskets in it before. Seems strange that I believe the owner before me used cometic gaskets. Will have to go back to regular gaskets.

Re: cometic head gaskets
 

I use 70 with lube. But, Gulius would know. If I could afford it, I would have one of his instead of my home made engine.
And, the surface finish, Cometic told me I need a smooth finish. Those rough ones like composite gaskets better.

Re: cometic head gaskets
 

If the block was plate honed its best to go with what was used for hardware and torque during the plate honing procedure if it was plate honed to achieve good ring seal.

Studs do to the fine thread seem to distort cylinders more then bolts from what I have seen.

Re: cometic head gaskets
 

I have a big Chevy from Schmidt that failed between 5-7 due to cutter marks using cometic gaskets. Only posting to say that composite is my only fix but why is the cutter pattern not the same between bores. It's as if the block machine was cutting at angle (side to side) making most of the between bore deck verticle pattern and others a bit more /// direct between bores. Is there a standard for deck tooling path? I just assumed parallel to crank. Sorry if I'm hi-jacking.
Thanks
Bryce

Re: cometic head gaskets
 

Thin coat of copper coat on all three pieces will fix the problem I have done it that way for a while now. greg

Re: cometic head gaskets
 

Bryce,
The finish should be the same across the entire deck surface including between the bores. Here is an Olds block I just finished.

Re: cometic head gaskets
 

Bill,
That is a fantastic finish. Here's the Steve Schmidt finish and the difference in pattern and where the combustion escaped.
Pretty terrible. Thanks for sharing.
Bryce

Re: cometic head gaskets
 

Good grief that is pretty terrible for a modern shop. Wonder if someone wasn't paying attention :(

Re: cometic head gaskets
 

Looks like a broach was used, certainly not CBN or grinder.

Re: cometic head gaskets
 

Bryce,
I was thinking about this a little. Do you have a picture of the entire deck surface in one shot ? Did it look like it was done in two different cuts ?? I have seen some Dart blocks come with a pretty terrible finish from the factory that almost looks like they made two passes with different cutters. I does not matter because I am going to surface it anyway but I wonder if yours is just the factory finish ?

Just thinking out loud :)

Re: cometic head gaskets
 

Milling machines like a Storm Vulcan 85 B can leave a poor finish if the carbide cutters are not kept sharp and or the speed is too fast.

You hit some weld spots on factory blocks and just general wear causes them to leave a "file finish"after a while.

I ran one for years.....

I never got to use the CBN cutters and we never had a grinder....

Wheel had to be crated up and sent out or replace your own cutters but that was usually not a good scenario.......all it took was one cutter to be slightly high or low....

I have an old Van Norman rotary broach at home and it's a real dinosoar.....it needs to go to the scrap pile....

Re: cometic head gaskets
 

I remember those days well. I used to spend hours getting the new bits set up perfect. So glad for modern technology :)

Re: cometic head gaskets
 

When I deck my blocks I actually get a back cut which is the flattest surface and most tub grinders have lead built into them which when the head is tipped its not as flat as most think.

http://i7.photobucket.com/albums/y27...ps6bc47e60.jpg

Re: cometic head gaskets
 

Bill,
I do not have an overall pic of the decks but it was definitely just one pattern. No return travel pattern or variance other than how it looked like an angular path as mentioned before. If I recall correctly, the deck height was 9.804. seems like not alot left for a factory cut. I will be running some Fel-pro 1057 (wire ring composite) gaskets for this go-round.
Thanks
Bryce

Re: cometic head gaskets
 

Re: cometic head gaskets
 

I brought this procedure up at a racers breakfast I go to on Saturday mornings and the guys thought I had 2 heads. My engine builder from years ago told me of this procedure. But it was on studs not bolts. I think using cometic gaskets you do not need to do this step anymore.

Re: cometic head gaskets
 

I have a simple practice that I use with MLS gaskets. The problem is with the stretch of the fastener. I use plenty of copper coat ( like a whole can on two gaskets). After the head is torked on, I let it set 24 hours. Then, "one at a time", I untork the fastener and re tork it to spec with one pull on the tork wrench. I've actually had motors stop weeping, doing this on the dyno. Right or wrong....works for me.

Re: cometic head gaskets
 

On my sbc I didn't spray coating as I was informed by many not to. If you had good luck spraying then I will on next rebuild for piece of mind as I run alot of nitrous and feel leary of not coating them. Thanks for the info.

Re: cometic head gaskets
 

You have to be careful with this as most MLS gaskets have a coating on them from the manufacturer that is there to help them seal. Putting another coating on them might actually make it worse. I prefer to go with whatever the gasket manufacturer recommends.

Re: cometic head gaskets
 

Jeff
I have always sprayed my Cometic head gaskets with Copper head gasket spray with no problems to date.

I have seen quite a few old Cup engines that have used cometic gaskets that were sprayed with Copper head gasket spray. If they are using it that's good enough for me.

Re: cometic head gaskets
 

Rick, are you going to be ready for the Miramichi NHRA races???
Terry K

Re: cometic head gaskets
 

OEM head gaskets require a "smoother" surface finish to seal coolant and oil passages. The "rubbery paint" is there to provide a micro-seal against leaks. OEM head gaskets are beaded to provide an effective sealing load around these passages and the chamber.

A torque wrench measures torque, not friction as someone stated earlier.

Torque = friction coefficient x tension x thread diameter (for elastic region bolts).
Friction coefficient is generally 0.1 ~ 0.3.

Adding oil or other lubricant will increase the bolt tension over a dry or unlubricated condition. Something a friend and I did at work years ago with a strain gauged bolt to see for ourselves.

Re: cometic head gaskets
 

In lieu of the Copper head gasket spray I would recommend Hylomar spray.
Do not use the Permatex/Loctite Hylomar sold at most auto stores; it's a watered down version of Hylomar.
The best Hylomar is the Yellow can industrial version.

Re: cometic head gaskets
 

Ron,
That is correct and what I was trying to get at was the fact that the friction will significantly affect the preload on the fastener for a given torque. My choice of words were not the best :)

Re: cometic head gaskets
 

I have used Cometics with zero issues for at least 5 years. I have reused the same gaskets 3 times with no additional coatings and also another set 2 times with copper coat spray. This is a 15-1 compression engine and with or without the copper coat there was no leaks. Pretty smooth finished block and heads. I generally block sand the heads if they are off with wet 400 paper in a wash tank. Cometics work very well for me.

Re: cometic head gaskets
 

Thanks for all your comments guys, the block is just machined too rough for those gaskets

Re: cometic head gaskets
 

Listen to Rich.

Re: cometic head gaskets
 

Something else to consider on a SBC is the size of the dowel pins. The OE dowel pins are .309" diameter. If .3125" (5/16") pins are used the head can bind on the pins. This will prevent the head from clamping properly to the block in the lower corners. Several companies sell SB dowel pins that are actually 5/16" roll pins.