Straight eight manifold gaskets

[Guest imported_JPIndusi]

I am planning to install a replacement valve body and intake and exhaust manifolds on a 1953 straight eight engine. The shop manual says exhaust manifold gaskets are not used, only intake manifold gaskets are to be used. I assume they are referring to aluminum crush disks which fit over the intake manifold pilot rings. For the exhaust manifold they say coat the mating surfaces to the cylinder head with a mixture of graphite and engine oil.

However, I have purchased a set of manifold gaskets that cover both the intake and exhaust ports.

The first method would seem to allow the exhaust manifold some movement for slipping as it warmed up from dead cold. The second method using the gaskets for both manifolds would seem to allow little or no slippage.

Can someone advise me on the better of the two methods to try?

Thanks - Joe, BCA 33493

[Mrbuick714]

Hi Joe ! you might read your 1940 service bulletins,where Buick states that they have gone to the four rings instead of the non metallic gaskets. There is much movement of the manifold with respect to the head. When I drove straight eights,I often snapped the end manifold bolts off. Also,when installing the manifold on the head,dont OVER torque the nuts that hold the manifold to the head,if the manifold cant "slide" a bit, you will wind up with a two-piece exhaust manifold !

[Patrick W. Brooks]

Hello Joe: I am going to check my 53 Shop Manual at my garage tomorrow and may do a further response. However, you MUST have the entire manifold assembly checked to see if it must be milled before being installed. Many exhaust manifolds are broken because they are not milled flat before installation and this pulls them out of shape causing breakage as a result of stress after installation. A machine shop puts the bolted together manifold assembly on a flat metal table and uses flat feeler gauges to see if milling is required. My recollection is that it should not be more than four thousands out of perfect. In any event, have it checked before bolting up and getting the exhaust hot. Patrick W. Brooks

[Guest 53and61]

As I recall, the manifold surfaces for the exhaust and intake where they fit against the head are not in the same plane -- maybe a mm different. Gaskets were intended under the intake manifold but not the exhaust. So if you bolt the manifolds and valve housing together and have the manifolds milled to the same plane, you'll have destroyed the intended geometry. When mine leaked, I bought a gasket set that included gaskets for both the exhaust and intake joints with the head, but the intake gaskets were thicker. They worked fine. The shop manual calls for starting with snug but moveable mating of the manifolds to the valve body so these joints can slide as the manifold-to-head bolts are tightened. Then the manifold-to-valve body bolts are tightened. You could make an argument for milling the manifolds separately and minimally, but I'm uncomfortable milling them as an assembly unless gaskets are available for the resulting geometry.

[Guest imported_JPIndusi]

The manifold gasket set I bought from CARS or Bob's about 1-2 years ago is in three pieces, one section for the middle and one for each end. The material is of uniform thickness for where it seals the intake and exhaust ports. The car currently appears to have these gaskets in place.

I have also read where the shop manual says to snug up on the bolts from the manifolds to the valve body and then tighten, and they give a torque specification of about 25 ft/lbs for the head bolts.

Joe

[Guest 53and61]

Joe's experience suggests that milling the assembled manifolds would be OK. It could be that there's enough room for motion in the sliding joints that the slight offset isn't important.

[Patrick W. Brooks]

Hello Joe: I have now had time to review both my 52 and 53 Shop Manuals. As I remembered the 53 covers only the V-8 and refers the reader back to the 52 Manual for the straight eight. Therefore, I am unable to determine what you have read about the gaskets only used on the intakes. What I believe you are referring to is that the intakes only use what is called a "pilot" which is the circular ring which compresses into the intake ports. These pilots are found under Group 3.267 and fit from the 40 Series in 39 through the 53 Special, series 40 and 50. You must carefully clean both the intake ports and the intake manifold itself as these pilots seat themselves tightly in these ports. The pilot or ring compresses in the head port on a beveled surface so that it compresses tightly to seal out air which might enter and dilute the mixture of air and gas delivered from the carb. The pilot compresses so both ends meet tightly as you pull up the manifolds tight. I always bevel or chamfer the outside edge of the pilot as with age the bevel in the intake ports in the head collect carbon and rust and the pilot with catch on the rough areas and not pull up completely. When this happens you can often hear the leak and the engine runs rough. In addition, the manifold gasket will wiggle and you know it is not tight. I have some of the circular disks you mention and looked in the parts book under Group 3.270 to find that both the disks and the complete eight hole gaskets are listed. I always use the eight hole gasket and would recommend it rather than the disk although I have some NOS disks as well.

On the matter of milling the assembled manifolds, I would suggest you hold a straight edge against the head and you will find it is straight with absolutely no offsets. When different used and new manifolds and valve body are assembled they will almost never fit perfectly. They must be carefully assembled on a flat metal table to be certain the assembly is as flat as possible. I have done this on my cast iron table saw top as I know it is flat. Usually, I go to my machine shop and do it on their flat metal table and then use flat feeler gauges to see if it must be milled. I have been going to an engine rebuilding/machine shop locally for over twenty years and the owner lets me use their equipment for rebuilding purposes. We check and if the manifolds are not within tolerance the manifold assembly is milled to be flat so when it bolts up agains the head it will not stress the exhaust manifold and cause it to crack. I have personally used the mill to do an assembled manifold system on a several occasions. The head can also be warped but this has only happened to me once and is uncommon. I recently went through this process when I had to buy a valve body for the system on my recently acquired 1940 Super Coupe. The exhaust manifold gets much hotter than the intake as the passage of cool air through the intake makes it run much cooler. Therefore, stress on the exhaust manifold will cause a crack much more quickly. Hope this helps. Hope to see you in Batavia. Patrick W. Brooks

[Guest 53and61]

The '52 shop manual, in paragraph 3-12, states that intake manifold-to-head gaskets AND pilot rings are used, and that graphite plus oil with no gasket is used between the head and exhaust manifold. So there must be an offset. The possible slippage in the joints with the valve body may be enough to allow assembly with or without this offset, i.e. without or with intake and exhaust gaskets of equal thickness.

[The Old Guy]

There are two different methods of installing the manifolds on a straight eight. The first and most commonly used is with the full gasket.this system was used up until the 263 engine came out I think, but don't quote me. The second system used four embossed steel washers that fit over the intakes rings. The intake rings are the spring steel pieces that fit in the intake manifold mating surfaces and the head.These embossed washers fit around the rings and effectively sealed the intake while allowing the exhaust manifold to move. The intake should be on a plane with the exhaust manifold with the rings in place. This means that the intake is recessed by about .010-.015 ( or the thickness of the washer.

[Guest 53and61]

Joe's description is consistent with the shop manual (for the 263) and precisely what I found when I dismantled my own manifold assembly. Given all the info collected on this thread, I'd bet that Patrick's recommendation of milling the mating surfaces of the assembled unit to one plane is safe.

[Patrick W. Brooks]

Good Morning All: Joe T. and Chris are right on target and we are all on the page, so to speak. I did a 1953 Special engine in 1998 and this discussion has helped me remember what I figured out at that time. My conclusion at that time was that it was best, for me at least with that manifold assembly, to mill it flat and not mess with the disks and special mixture of graphite and oil. I was completely mystified by this mixture discussion in my 52 Shop Manual and still am. I cannot believe I could prevent exhast manifold leaks by trying some mystical formula instead of a acutal gasket. In any event, assembly of the entire manifold assembly will tell Joe I. how much need be milled and allow a reasoned decision. I would like to know what conclusion Joe reaches and what he eventually does. Do a post for us Joe. Thanks for another great discussion all. Patrick W. Brooks

[Guest imported_JPIndusi]

I am going to try to use the 4 pilot rings and crush disks on the intakes and the oil and graphite mixture on the exhaust manifold. The idea of graphite and oil seems strange but I suspect that the anti-seize compounds used on bolt threads might be similar. Evidently some people have tried this approach and it works. I plan to do this in the early winter and I will post the results.

Thanks to all who responded.

Joe, BCA 33493

[Guest imported_JPIndusi]

Well it's nearly a year later and I finally got the replacement intake/exhaust/valve body installed on my 53 Special. I tried to use the shop manual approach with the crush rings over the pilot rings for the intake ports and the graphite and oil mixture for the exhaust but I just couldn't get it just right. I put a straight edge on the intake and exhaust manifolds and it looked perfectly flat. However, the exhaust manifold was used and even though I cleaned it up the best I could it didn't seem to quite work. I then went to plan B which was to use the intake/manifold gasket set. This is lot of work in this heat were having. I got the front broken stud out and used all new studs, anti-seize, and new brass nuts. Got the flapper valve free and working in the valve body as well. Also new gaskets and exhaust ring. Runs real quite now. I suppose if I went for a new exhaust manifold the shop manual approach might work.

Anyway it's done in time for some eastern Long Island shows and parades. These new gaskets are not great quality but that is what's available. A local old timer says that some older gaskets had metal both sides with a good material (probably asbestos) inside but I haven' seen any. Hope it lasts a bunch of years.

Joe, BCA 33493

[Mrbuick714]

Check page 12, 1940 BPS bulletins.

[Guest imported_JPIndusi]

MrBuick714:

I would like to but do not have 1940 service bulletins. If you find the time, send me a copy of the page if you have it. No rush.

Joe, BCA 33493