Sealing a Valve Chest Cover
also known as the tappet cover.

I recently changed the engine in my car, taking out one that I deemed to be getting a bit past it, as it needed work doing on it on the work bench, and installed another engine in the car.  The old engine was oil tight or at least in Austin Seven terms, so when the new engine leaked oil from the valve chest cover area, I was not amused.  I had plenty of advice on “That's how it's meant to be”, “You'll never stop it” etc., well I had stopped it before, why not again.

I cut a new piece of rectangular/square section cork for the cover and proceeded to apply a chamfer to one edge.  For those who have not done a valve chest cover before, this is essential to ensure the cork beds or fits into the cover OK. However getting a nice even chamfer to that edge is not easy (or for me anyway).  I fitted the cover and fingers crossed did a 30+ mile run only to find it was still no better than before, oil dripping on to the driveway.

Taking heed of some overheard experiences, I decided to make a flat aluminium plate cover, there just happened to be some 1/4” plate lying around in the shed.....   I made a nice fitting cover, the holes for the retaining bolts a close fit on the shaft of the bolts, drill through a couple of exhaust manifold brass nuts to slip onto the bolts and help distance the bolt head far enough away from the cover so the threaded end of the bolts won't try and screw into the cylinders!  The close fit of the holes meant when I came to screw the plate on, the ends of the bolts found the screw holes within seconds, not my normal experience with the tin plate cover.  I replicated the four breather holes near the top two, although the thickness of the plate did allow me to angle them downwards back into the valve chest area.

I put plenty of sealant around the edges of the plate and when all set, I did another 30+mile run.  Still b****y leaking. When I removed plate there were two gouges in the back of the plate where the edge of a couple of the long nuts holding the block to crankcase had cut into it.   I admit it hadn't occurred to me to make up a gasket as well, although it would have to be a thick one to prevent the gouges. I have now made a gasket out of 50 thou. material (I have a few sheets and I find making my own helps me...), however I have not fitted the plate, yet.

Following on from the above, I remembered a thread on the Forum where a contributor had mentioned 'O' rings, so a quick trawl and I found the reference suggesting the use of 5mm 'O' Ring cord to replace the cork.   I bought a metre length (£6 a metre) and cut it to length and then bedded it in silicone sealant on the original Valve Chest Cover, leaving it clamped tight between to boards for 24 hours so the sealant sets and (should) hold the 'O' ring cord firmly in place forever.  Unfortunately that wasn't my experience, it wasn't loose, but then again, not 100% fixed.  I put the proper Valve Chest Cover with 'O' Ring cord into position and fiddled for ages trying to find the holes for the clamping screws - some people do it in seconds, others like me, need to have a coffee break.

Another 30+ mile run and.... wallah, so far no leak(s).  All that's left to do now is to reduce the oil dripping down from the front of the gearbox area. But that can wait for another day.

Beware:  Some owners have a phobia regarding silicone worms in the oily bits, so can also try seating the seal using good old grease. It doesn’t stick for long, but  long enough to line up and get the thumbscrews settled.

This article, written by Sandy Croall, originally appeared in CA7C Seven Focus, June 2012 p18.