Head gaskets

[mike cobine]

Re: Head gaskets

and you didn't call? Heck, I could have had you safe in my garage in 30 minutes.

And I'm sure that beats the heck out of what you ended up doing.

[Joe L.]

Re: Head gaskets

Michael-----

Usually, when an engine is rebuilt the heads will require surfacing. The MINIMUM cut is usually .010" and, more often. it's .020", or greater. So, with a composition gasket you usually end up RESTORING the original dimensions (and intake manifold "fit geometry"). In fact, that's one of the reasons that most engine builders use a composition gasket. It's if you use a steel shim gasket after a cut has been taken on the heads that you might end up with a problem.

I've found that the steel shim gaskets work pretty well "the first time around" (i.e. from the factory). The "next time around" (i.e. at rebuild time) they might not work as well. Why, I don't know.

There may be some cooling differences between shim type gaskets and composition. However, in the last 20 years there have been a HUGE number of engines built from the "get-go" with composition type gaskets, including aluminum head/cast iron block, aluminum block/cast iron head, and cast iron block/cast iron head types. That includes small block Chevrolets of both aluminum and cast iron head types. Composition type have pretty much "taken over the field". There must be some good reasons for that since composition are a lot more expensive than steel shim type.

As I've mentioned before, for me, personally, functionality always comes before originality. My experience has shown me that composition are functionally better than steel shim, at least at rebuild time. Once-upon-a-time, as I mentioned previously, I thought that steel shim were the "only way to go". After my experiences with them (at engine rebuild, of course), I changed my opinion.

[Joe L.]

Re: Head gaskets

Verle----

Here's one of my experiences: when I removed the cylinder heads from my original 1969 300/350 in 1975, there was significant evidence of corrosion of the steel shim gaskets. They were not "corroded through", of course, but there was evidence of corrosion damage. I had been a "regular coolant changer" from the get-go, too. I was "deathly afraid" about damage to my aluminum radiator since, in those days, "conventional wisdom" was that aluminum radiators were a HIGH RISK for corrosion damage. So, I changed my coolant annually. In any event, there was also evidence on the gaskets of a "leak path" between the cooling passages and the combustion chamber.

My "first time around" with the engine in the car was to replace the short blck with a factory-new short block and use my reconditioned original heads. I used GM steel shim gaskets when I assembled the engine.

Not too long thereafter, for reasons that I won't go into here, I removed the original heads (thinking that they were the source of another problem I was having) and replaced them with a set of NEW GM heads with all new parts. When I removed the original heads, I noted that there appeared to be a "leak path" between cooling system passages and one or two cylinders. As I say, these heads had been reconditioned and were definitely surfaced as part of that. They had been mated to a brand new GM short block. But, the gaskets appeared to have leaked.

The "next time around", I used GM stainless steel shim type gaskets. Once-upon-a-time these were available under GM #3916336. This was with the replacement short block and the NEW GM heads. Both the heads and the short block surfaces were checked for flatness.

Several months later, chasing another problem, I removed the heads again. Examining the gaskets, there still appeared to be a leak path between some of the cooling passages and some of the cylinders. That was it for me and steel shim gaskets. My machinest, who had about 40 years experience building engines which included MANY racing engines around here (many of the local engines that were raced at the old Fremont Drag Strip were built by him), told me that I was a fool to have used the steel shim gaskets in the first place. I never did again.

[Lonnie Johnson]

Re: Head gaskets

Hmmmmmm, about the "blue" coloring, never made the connection before, but the kid I bought the car from in 1973 did tell me the engine was "blueprinted"! Just joking of course, but couldn't resist! Yah, the gaskets I took off were the fel-pro type. Block deck and heads are true and in good shape, so guess I'll go with the steel shim type and see what happens.
Thanks all for your responses.
Lonnie

[Michael H.]

Re: Head gaskets

Much of what you say is exactly the same thing that I said in my original post. IF the block and head surfaces are in good condition and have not been resurfaced, I prefer original steel gaskets.

I don't understand why you've had such an unusual number of problem with your 69 head gaskets but that certainly has to be the exception, not the rule. There are too many small blocks in the world with well over 200,000 miles and decades old with poor maintenance, that have none of the problems that you describe. If that happened to me, I would probably feel the same way that you do about steel head gaskets.

If you think about the incredible number of Chevrolet V8 engines that have been built in the last 50 years, and the incredibly small number of head gasket failures, you have to agree, the steel gasket was definitely not a bad design decision.

I've probably seen as many, or more, comp head gasket failures as steel gasket failures over the years, so I can't agree that the comp gasket is a better design.

[Joseph T.]

Re: Head gaskets

Verle

One of these days..I will remove and open up the original engineering workorder engine in my 57 Nassau/Daytona car.

This is a special order engine assembly and pre-production fuel unit.

Any advise on what special markings I might look for on internal parts or any recommended process for engine disassembly...or someone who has the hands and the understanding to do it for me.

Joe

[Art A.]

Re: Head gaskets

Joe,

An Engineering Work Order Engine is not just a "special order engine assembly" as you call it. It was hand built in the Chevrolet Engineering engine room. The term special order implies that someone off the street could have ordered such an engine from GM and that is just not the case. It is truly one of a kind and probably the only one in existence from that era.
There may be some very interesting unique parts inside that engine and if I were you I would find someone, it's too bad Clem is retired, who REALLY knows the inside of a vintage race engine to handle that engine VERY carefully.

Art

[Duke W.]

Re: Head gaskets

The clock runs on BOTH antifreeze and brake fluid while a car is in storage, but not on fresh engine oil.

Duke

[Duke W.]

Re: Head gaskets PS

Even with good antifreeze, localized corrosion can occur in cooling system nooks and crannies unless the antifreeze is occasionally circulated.

For this reason I recommend draining and drying the cooling system if storage is expected to last more than two to three years.

Duke

[John H.]

Re: Head gaskets

The steel shim gaskets not only depend on surface flatness for sealing, but also are very sensitive to surface finish roughness in micro-inches, within a fairly narrow tolerance range (that produced by the factory broach process); even with a "flat" surface, a surface finish outside of that range can result in sealing failure.

[Joe L.]

Re: Head gaskets

John-----

Yes, that could well be the source of the problem "the second time around". Rarely, will the heads and block deck surface be finished to the original "factory finish". While the block may still retain the factory finish, the "roughness coefficient" may well change due to cleaning of the surface. The heads will not usually be restored to the original factory finish due to the fact that they're usually rotary milled at the machine shop. So, this may all account for why the steel shim gaskets work well "the first time around" but, as in my experience, not so well the "second time around".

Another possible factor is that while cylinder heads are usually machined at engine rebuild, block decks are not (ESPECIALLY for vintage, "matching number" Corvettes). So, at least with respect to cylinder head FLATNESS, if not roughness coefficent, the cylinder heads should be pretty close to perfect. The block deck is generally NOT machined. Usually, the block is "ok", but that doesn't mean that it's perfect. It might be "ok", but still not perfect enough for a good seal with shim type gaskets.

In many cases, there may even be some leakage with the original installations but it never reaches the "acute stage" which causes engine problems. With all pre-73 Corvettes, there was no coolant recovery system. So, some loss of coolant was normal. One never knew if the loss was being "burped out" of the overflow hose OR if it was being "processed" in the engine. You just knew that you had to "top off" the coolant from time-to-time.

The real danger of the "sub-acute" stage coolant leak paths is that block or cylinder head corrosion damage can be occuring with no knowledge on the part of the owner. Suddenly, when the engine is torn down for rebuild, one finds a corrosion-induced groove in the block or cylinder heads. If it's in the heads, no problem. They're likely going to need to be surfaced, anyway, and the groove will be thus removed and the head surface restored. However, if the groove is in the block, then that's going to require the block to be decked. I don't know of any other practical way to restore the block deck surface to serviceability. Of course, the "impact" of decking the block is something that "strikes fear into the hearts" of Corvette owners.

Based upon my experience, I found that the use of the steel shim gaskets resulted in what appeared to be leak paths between cooling passages and cylinders. No significant damage was done to my original block and the several sets of SERVICE steel shim gaskets that I used were not in the engine long enough to cause any leak-path problems, even though they did leak. Not that it would really matter, anyway, since this was a replacement short block with no "numbers" which might be compromised if decking were ever required.

I have found that the Fel-Pro PermaTorque gaskets are pretty much bullet-proof as far as combustion seal and coolant seal is concerned. I'll have a chance to further evaluate the long-term performance of these gaskets when I "autopsy" this engine (after I get it out of the car).

After my experience with the steel shim gaskets (which, as I say, I was once absolutely sold on as being the only way to go), I'd be very reluctant to use them again at rebuild time. I mean, is having the little exposed "tabs" of the head gaskets as-original worth the chance that the gaskets won't seal properly, result in block deck damage, and the later need for "decking"? I'm not even a "numbers guy" and I don't think so.

[Joe L.]

Addendum

Something I forgot to mention is that with the new MLS gaskets, the block and cylinder head roughness coefficient is ULTRA CRITICAL. I had mine checked with the "ZL-1" and they were within the required range. So, I went the MLS route for this engine, even though I already owned the PermaTorque gaskets. This is one of the advantages of my absurd procrastination on this project----technology moves ahead and you get a chance to take advantage of it!

Actually, after the wonderful performance that I've had with the Fel-Pro PermaTorque gaskets, I thought long and hard about the change to MLS. However, Cometic makes an MLS gasket uniquely applicable to ZL-1 engine assemblies, so I decided to give it a try. I'm not too concerned that I'll be disappointed.

A word of caution, though, with MLS gaskets: the gaskets are made up of multiple layers of stainless steel material. The intermediary layers are extremely thin (as one might expect since the TOTAL compressed thickness of the gasket I'm using is .040"). Not only are they thin, they are SHARP. Just like a razor blade only SHARPER. If your finger happens to get into this area (while you're installing the heads on the engine, for instance), one can get a nasty cut. Don't ask me how I know this, though. Just take my word for it.

[Mark #28455]

I'll just stick with the fel-pro's

As you said earlier, I too have used plenty of the fel-pro gaskets on my engines and despite many abuses, overheatings, etc, I have never had any trouble with them even years ago before they had the sealing rings.

Good luck,
Mark

[mike cobine]

Any good hot rodder can tell you

that blocks are not solid items, but plastic. That is why you bore and hone cylinders with torque plates. This is why the truly high horse engines are built with seasoned blocks, not new ones. That is why an old trick is to drop a block into a salt water canal to age it, rust it up, and then machine the rusted block because it is harder.

Blocks distort under a torque load, and not always evenly.

The steel shim gasket will work on a new block and a new head because they are flat, completely, and with the perfect machining finish on them.

But after they have heat cycled a few thousand times, overheated a dozen or more, been held in torque for several years, they are not perfectly flat anymore.

After machining for a rebuild, they are not consistent in deck thicknesses as some areas have pulled up during aging and been cut more than other areas. So now the deck is weaker in the thinner areas and so pulls more such that some areas are tighter and others not. Those that are tighter seal, and those that are not, gradually leak with a steel shim gasket.

A composite gasket fills those slight gaps while a steel shim gasket does not.

It is hard to imagine that something like a cast iron block with only a few thousands of an inch machined off of it can move and change that much, but in practice, it does. Joe's experience is the norm.

[Verle R.]

Re: Addendum

Joe,

A number of years (many?) ago I wrote an article for the Restorer about building a ZL-1 engine. We used an NOS block with used heads. We used FelPro gaskets and it is still doing well.

Verle