x-flow breathing/leaking

[zefarelly]

I run several cars with crossflow ford engines, why is it when you fit an aluminium rocker cover the things leak, but with a steel cover they dont.

As I understand it with a standard twin choke weber the block breather vents to the inlet manifold and this creates a slight vacuum though the vent in the rocker cover ???

with twin 40's fitted the block vents to atmosphere through a filter and the rocker cover wants to vent oil . . . . . .on one car I use a catch tank (wich can collect 150ml in a hardish 120 mile run) Im using a little K+N filter vent as an experiment on another car at the moment to see if that works without leaking . . . .

any ideas ? thanks

[Red Dog]

The rocker cover is part of the crankcase and is subjected to pressure from the bottom side of the pistons. The more worn your piston rings, the greater the pressure. The harder you rev, the greater the pressure. If you have blow by from a cylinder to the pushrod holes caused by a leaky head gasket, this will also increase crankcase pressure.
The connection to the carb is used to reduce the normal pressure and recycle the oily vapour and burn it in the combustion chamber. It will not cope with a faulty engine
If you remove the connection you must have a catch tank to catch the gunk that comes out. It is a good idea to have a filter (as you have done) or mesh screen in the pipe to encourage the vapour to condense and return some of the liquid to the crankcase.
The alloy rocker covers are usually very good but surfaces must be flat. You could try using a bit of Hylomar on both sides of the gasket. Silicone is not good, as it seems to make the gasket slide out of position and it is a swine to clean off. Use a soft/weak thread sealer - Loctite 572 is good - to stop those tiny unc threads on the cover retaining screws from working loose.

[zefarelly]

thanks red dog, I dont think I have engine problems, just leaks! Ive put a filter on the block breather and the steel pressed rocker cover with a gauze vented cap . . .seems ok

the other car/engine uses a catch tank so is not a problem (apart from a split in the dipstick hose!

[Tony Harman]

If you're using an alloy rocker cover don't use the standard cork type gasket, they always leak, you should use the proper paper type gaskets for these.

[zefarelly]

that was the first thing I changed, thanks Tony, they just squeeze themselves out!

I think catch tank is the only way to go . . . .Im suprised sump gaskets/seals dont leak more given the pressure down there . . . . .

[Dave Brand]

Originally posted by zefarelly
that was the first thing I changed, thanks Tony, they just squeeze themselves out!

Just a thought - are you overtightening the retaining screws? That will certainly cause problems with the standard cork gaskets, although I would expect it to be less of a problem with a thinner gasket.

[zefarelly]

its not the gaskets that leak, with an ally cover the oil seeps out of the pin hole in the filler cap, and I put a mini filter at the other end and it leaks through that . . . .steel cover on now, (later 711 type with longer neck) now no leaks . . . . .ally ones look nice, and perhaps cut tappet noise a bit, but are a pain in the 'arris without a catch tank.

something I saw last night suggests using a catch tank which self drains into the sump. seemed like a reasonable idea.

[GTV27]

You could set up an oil-air separator which puts the oil back into the sump and the air into the inlet manifold.

[zefarelly]

the one good side effect is a thin oil film around the engine bay which will stop my inner wings rusting ;-)

[GTV27]

Yeah, I've got an Alfa, so I can appreciate that - Don't breathe the fumes thou, lots of nasty (toxic) stuff in burnt oil fumes.

[zefarelly]

I always drive with the window open . . . . .keeps the windows from steaming up in this weather.

[norman-normal]

If you notice on all racing engines, designed as such, the alu cam covers have many small bolts or studs all around the lip of the cover. Its because alu has no springieness, it has great resistance to bending, but once bent it stays that way.

Over tighting will surely make it worse; but it will allways leak.