The V8 Owners Forum -

I recently fitted a offy manifold to a rover v8, [500 carb] ..trouble is the bad running at low speeds was found to be air leak on manifold to the heads..[new comp gasket fitted].. so i removed it all and cleaned and refitted using another new comp gasket, this time with blue hylomar on each surface..... its now got air leaks on two different ports?????
The engine is low mileage vittese unit ,,, i never had problems with su cabs and injection on this engine,, what could be wrong with the manifold to get problems with flanges sucking air??

It could be that the sealing areas are a little smaller, one way to help is to dimple slightly with a centre punch so that it grabs the gasket. Castings can move around after machining so I would check all surfaces are flat and that the angles are correct. If you have skimmed heads or block the manifold may need machining.

Alan

Do you have comp gaskets as well on the heads or only on the intake side.
Only on the intake could mean a mismatch of parts.

It does not matter if you have tin or comp head gaskets. The difference in height between the two regarding the mating faces of the valley gasket will not create a problem such as this, unless the heads or decks have been excessively skimmed. And I mean EXCESSIVE !!
The normal problems with a part mismatch like this is oil leaks from the valley gasket front and rear rubber seals.


You have already seen proper sealing with two other inlet manifolds on this engine yes???
And the engine has not been altered or modified between the times you used the S/U manifold or the EFI manifold?

Then you fit the offy manifold and it leaks... Twice??

I'm guessing that a process of elimination will lead to only ONE conclusion at this time ? Maybe you need to run a straight edge along the manifold faces?

Which port leaked on round one. And which ports leaked on round two of this installation Steve?

Also!!
I would not use Hylomar on an inlet manifold. It stays pretty soft and prone to being mis shaped under positive or negative pressures which can lead to blow by if the mating faces are not true. I use Red Hermetite or Fernox LSX silicone sealer on my inlet manifolds. And they all get at least 24hours drying time before use.

Perry