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MG Midget and Sprite Technical - Rocker box leak

Hi
A couple of weeks ago I check tappets etc. Oil low today so topped up and it leaked straight past gasket on rocker cover - yes the two bolts were tight and it looked ago. Swapped over for a new one but it still seems to be weeping. Does it go on dry or with hylamer or???????????????????
dave
Dave Price

Dry should be fine
Dave O'Neill 2

I can NEVER get a seal without using Hylomar
Glynn (1275RWA) Williams

Pressure is negligible. Have you got a cork in the breather?
Nick and Cherry Scoop

The way I do mine is completely leak proof and very reuseable

I permanently attached the cork to the valve cover with rtv/holimeyer, then on the matting surface of the cork to the cylinder head I use finger smear of white lithium grease ... it heats up, and sets in for a leak proof seal and is easily released with just a wack of a rubber mallet..and just keep repeating over and over...

If you get to much white lithium grease on the seal, you may need to retighten the 2 screws that hold the valve cover on, as the grease will shink a bit on the 1st engine heat up

Its not my discovery, but it sure works well

Btw... as to your current leak, look for horizontial seperation in the cork...not common but ive heard of it happening, and also look for any missing chunks on the corks mating surfaces

Prop
Prop and the Blackhole Midget

Since I first read of Prop's procedure I have used it myself. I can confirm that it is effective.

I used to use Hylomar, which is good but I always made an unholy mess with it, being a bit ham-fisted.

I now use Sikaflex to stick the gasket to the rocker box and the white grease the other side as Prop says.

Before I put the box back on the head I clean/degrease the mating surface on the head with a rag and some meths.
No leaks :-)

(Thanks Prop)
RS Hughes

Opps...

yepp definatly clean the old grease off the head

Thanks RS

Prop
Prop and the Blackhole Midget

Check what material your gasket is made from and if the oil is getting past it or whether it's actually coming from the top bolts.

I have always had oil coming from the rocker cover, especially from around the bolts on top. I recently treated the cover to a coat of paint and new rubber grommets for the bolts along with a black gasket from my local factor.

The grommets cured the top leak but the black gasket was rubbish. No matter how I tweaked it, adjusted it and tightened it it leaked -copiously, especially towards the back.

I was about to resort to a smear of oil or Hylomar but decided to try re-fitted the old cork gasket first without any grease or sealer - and that has sorted it. I think the softer cork moulds itself to the cover and any imperfections on the head much better than this new black material.

I gave the engine a thorough de-greasing and washdown afterwards. I've just got back from two days of hard hill-climbing and there's no trace of oil leakage and the engine is the cleanest it has ever been!

C
Colin Mee

Gasket thickness is also important.

When fitted properly, with the correct spacers under the bolts (actually nuts) the bolts (nuts) bottom out on the rocker pedestal nuts, which also have to be the correct thickness, in order to achieve the correct clamping force on the gasket.

The rubber seals also need to be in good condition and of the correct thickness and their caps also need to be in place. There's quite a lot to it, really.

If any of the parts are missing or incorrect, you may not have enough clamping force on the gasket, or it could even be over-compressed.

I have sometimes had to put a washer on top of the pedestal nut in order to get the right fit.
Dave O'Neill 2

As Dave just said. Unless you have the correct spacers, you tend to overtighten the cover, which distorts it, and then it leaks.

As long as you have good rubber seals at each end, and a decent cork gasket(dry, assuming it's held in place correctly), you should only need to do the bolts up reasonably tight.

But if your cover has been disrorted by over clamping in the past, you'll have to flatten it out first, else it'll keep leeking.
Lawrence Slater

Mating faces must be clean.

Cork rocker box gasket must locate correctly. IIRC the box has a slight raised edge to it - well mine does. Gasket fits inside this edge. Mine is the ribbed version though...

Have you stuck too much oil in?

..and echoing Nicks comment, look to the root cause. It really should not leak as pressure is minimal...breather clogged perhaps, or crankcase blowby too great, PCV not working or blocked etc....

Is your rear crankcase seal leaking?



Mark O

This thread was discussed between 17/05/2015 and 18/05/2015

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