Rocker cover torque

[mfairbairn]

Basic question. How tight should I tighten the rocker cover with a new cork gasket? I fitted a new one a couple of years ago, but I think I probably overtightened it, because I now get a dribble of oil leaking all the way round. Also, would there be any harm in using a silicone sealant as well (such as Locite SI5926 'Blue Silicone' http://bit.ly/2W4BzYe ), just to make extra sure? My car is a Singer 9 HP Le-Mans Longtail.

[Phillip]

Is it tin or alloy?

[mfairbairn]

To be honest, I'm not sure. If it helps, though, I'm pretty sure it's original. I've also attached some photographs.

[ColinB]

Looks very much like tin to me.

[Phillip]

Yep...certainly a 'tin' rocker cover.

Leaking all the way around is unusual, especially if it didn't do it before.

How much 'pressure' can be exerted on the cover is really based on the height of the threaded pedestals that the cover is bolted to. This determines the gap between the rocker cover and face of the block. The tin cover actually has a pressed ridge in the mating face to further improve sealing, which is why I asked which kind it is. The alloy cover has a smooth face.

The only way you could distort the cover by over-tightening is if the threaded pedestals are too short and the top face of the cover would distort down, reducing the strength of the cover and the force it can exert on the gasket to maintain a seal.

The problem of leaks can be further complicated if the head or block have been shaved, or are not an original pair, or if the front timing cover isn't original to the engine. This can create a difference of height between the top face of the timing cover and the top face of the head meaning a consistent even seal is not possible around the entire rocker cover without some messing about with sealers or extra pieces of gasket material. I notice some black goop around that area in your photos.

It is also possible your new gasket is not thick enough.

The first thing I would try is to remove the gasket and bolt down the cover, then try to measure the gap left between the head and cover. The gasket should be thicker than the gap to allow for compression and a good seal. A good quality cork or composite gasket material is important to get a nice compression. I buy it in rolled sheets and cut to size with a hobby knife. The head face and rocker cover face should be clean, dry and oil-free before assembly.

since the weakest part of the seal is the smooth surface between the face of the head and the gasket, I usually use a black sealant between those two surfaces and rely on the ridge on the tin cover and the compression / thickness of the gasket for the seal between those surfaces. Then it is easy to remove the cover for maintenance and the gasket stays in place. Oil laying around in the head also tends to stay there with the height of the gasket acting as a 'dam', so to speak.

As to torque, there are no figures, but you can go by the engineers guide, which would give you a torque for a given nut / bolt size and grade, but, to be honest, I use a ring spanner and 'nip' down the nuts by feel, watching the gasket compress as I do. The threaded pedestals have shoulders on them at the end of the threads, so the cover can't be bent by further tightening.

Hope that helps!

[mfairbairn]

Blimey, Philip, that's a very comprehensive reply! Many thanks indeed. I'll give that a go at the weekend and let you know how I get on.

[Phillip]

My pleasure Martin, hope the information proves useful.

BTW, was your father's name Alex Fairbairn by chance?

[mfairbairn]

Yes, spot on. Alex (or Sandy). Unfortunately, I took nothing to do with the car (or cars in general) when he was alive, so now having to learn from scratch.