The V8 Owners Forum -

Hi, I have just replaced my composite manifold gasket, again, as I had a leak at the rear seal....or so I thought. I cleaned all surfaces twice before using The Right Stuff to seal the rubbers to both sides and bolted it all back together.

To begin with it was perfect and then I noticed that the gasket was turning from its pale grey to oil stained and following a 500 mile round trip to Goodward I have oil around the rear seal.

It appears that the gasket lets the oil soak through which then pools at the rear (yes the engine slopes a bit to fit in the MGB) and then slops over the metal bracket onto the top of the bell housing.

Is this normal ? Am I using a cheap gasket ? Is there too much pressure in the manifolds (it is vented into the Air Filter) ? Should I use a metal gasket ?

Any suggestions would be appreciated before I change to a tin gasket.

Regards Ian

Is it actually a composite gasket? The later black ones I've seen are simply plastic coated steel. As opposed to the lacquer coated bright steel ones.

Could it be 'The Right Stuff' is attacking the plastic? Normally, all that is needed is a smear of Hylomar on the very end of the rubber.

Rocker covers leaking and allowing oil onto the gasket? I have never known a valley gasket to be porous!

Chris.

I believe it is a composite gasket and I was sold it as so, it is a softish light grey material and not black. It is certainly not a metal one.

I don't think that it came from the rockers as it started at the bottom/middle of the gasket and then spread out and its not comming from anywhere near the Right Stuff....or at least it doesn't look like it does.

I had read a thread about over pressure in the rockers, but I do vent one side into the air filter and the other has a small mushroom breather. I wondered if it was therefore a pressure/venting problem.

Maybe I have one of those "after market" products which is up to its job.

Is composite better than tin or should I put a tin one back like it had. Its from a 1995 EFI Disco, but now has Edelbrock 500.

If composite is better can anyone suggest a good suplier ?

You really need a proper breather set up on there, if the bores are passing to much it can cause the gasket to blow/bow upwards. you might not see this when the engine is at tick over but underload it will happen. Is there any crease marks in the inlet gasket ?

hirot wrote:I believe it is a composite gasket and I was sold it as so, it is a softish light grey material and not black. It is certainly not a metal one.

I don't think that it came from the rockers as it started at the bottom/middle of the gasket and then spread out and its not comming from anywhere near the Right Stuff....or at least it doesn't look like it does.

I had read a thread about over pressure in the rockers, but I do vent one side into the air filter and the other has a small mushroom breather. I wondered if it was therefore a pressure/venting problem.

Maybe I have one of those "after market" products which is up to its job.

Is composite better than tin or should I put a tin one back like it had. Its from a 1995 EFI Disco, but now has Edelbrock 500.

If composite is better can anyone suggest a good suplier ?

A composite coated valley gasket should be Black and not Grey !
Its just a tin gasket with a coating.
If yours is seeping oil into the valley so it builds up and then runs over the valley gasket clamp at the rear then something is wrong??

It sounds like the gasket is porous. Or the oil is leaking from somewhere else onto the surface of the gasket in order for it to build up like that.

Or its seeping from the bolt hole in the gasket clamp because its not been sealed properly.

JSF55 wrote:You really need a proper breather set up on there, if the bores are passing to much it can cause the gasket to blow/bow upwards. you might not see this when the engine is at tick over but underload it will happen. Is there any crease marks in the inlet gasket ?

I cant see how this could ever happen even with the most crappy and worn engine running nitrous and boost with the rings blowing by in shed loads.


If the valley gasket deforms due to excess crankcase pressure then you are in serious trouble because the pressure required to do this is very high indeed. I'm not talking a few psi here. I'm talking a shock load of 100's of psi as a fast pressure wave like a huge backfire.
And once it has deformed, it stays deformed in a big way

It does not bow out of shape and then go back to normal at low rpm.

hirot wrote:Hi, I have just replaced my composite manifold gasket, again, as I had a leak at the rear seal....or so I thought. I cleaned all surfaces twice before using The Right Stuff to seal the rubbers to both sides and bolted it all back together.

To begin with it was perfect and then I noticed that the gasket was turning from its pale grey to oil stained and following a 500 mile round trip to Goodward I have oil around the rear seal.

It appears that the gasket lets the oil soak through which then pools at the rear (yes the engine slopes a bit to fit in the MGB) and then slops over the metal bracket onto the top of the bell housing.

Is this normal ? Am I using a cheap gasket ? Is there too much pressure in the manifolds (it is vented into the Air Filter) ? Should I use a metal gasket ?

Any suggestions would be appreciated before I change to a tin gasket.

Regards Ian

Can you show us a picture of the problem area?

DaveEFI wrote:Is it actually a composite gasket? The later black ones I've seen are simply plastic coated steel. As opposed to the lacquer coated bright steel ones.

Could it be 'The Right Stuff' is attacking the plastic? Normally, all that is needed is a smear of Hylomar on the very end of the rubber.

Right Stuff will not attack the comp coating on these gaskets.

mgbv8 wrote:

JSF55 wrote:You really need a proper breather set up on there, if the bores are passing to much it can cause the gasket to blow/bow upwards. you might not see this when the engine is at tick over but underload it will happen. Is there any crease marks in the inlet gasket ?

I cant see how this could ever happen even with the most crappy and worn engine running nitrous and boost with the rings blowing by in shed loads.


If the valley gasket deforms due to excess crankcase pressure then you are in serious trouble because the pressure required to do this is very high indeed. I'm not talking a few psi here. I'm talking a shock load of 100's of psi as a fast pressure wave like a huge backfire.
And once it has deformed, it stays deformed in a big way

It does not bow out of shape and then go back to normal at low rpm.

Hi Perry, "klunk" on the old nsra forum had this problem, poor breathers and poor engine caused the tin gasket to bow up and down giving that wobble board sound ! he even had pictures of the gasket when it finally stuck in the up position, not able to retrive them as the old server is now u/s, john

The gasket was faulty then. Or it wasnt secured properly. My guess would be a cheap / very thin gasket coupled with reasonable blow by.

It must have been blowing by so badly that the breathers where almost whistling?

Yeah the engine was changed not long after, i remembered some of the later posts and found them, it was a good write up .... yet again gone forever !

I'm also remembering different valley gaskets I've seen now?
I have seen bare metal ones which had the ridges rolled in for stiffness. And I can also remember seeing tin ones on old engines I've stripped that were smooth and flimsy. The comp coated ones I use now dont need the extra stiffness because they are quite stiff.

I've still not seen a Grey one??

What is a composite one made of? And if it is thicker than steel wouldn't there be problems with manifold to head alignment? If the same thickness, what material has the same strength?

Only 'problem' with the steel type was some went rusty and looked unsightly. Coated ones should be OK.

Came with an engine i bought last week, marketed by a 4x4 company