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MG MGB Technical - Rocker box & side plate gaskets.

One of the few problem with my 73B that destroys my enjoyment of the car is oil leaking from the engine so I thought that I would share my successes with sealing the two most leak prone gaskets on the engine, the rocker gasket and the tappet cover plates. My objectives with these two gaskets were simple. Make the side plates leak free and for the rocker cover to seal and to be easily removed without destroying the gasket. This would allow the rocker cover to be removed, replaced and sealed without having to go through the process of scraping off the old gasket and refitting a one every time I need to adjust the valve clearances.

Rocker box

To achieve the results with the rocker box I used EvoStik to glue a cork gasket to the box. To do I scraped all traces of old gasket, sealant and then de-greased it with brake cleaner. This is essential otherwise the glue will not adhere to the rocker box. Then I put EvoStik on the gasket and the rocker box, allowed 10 mins for the glue to go tacky, pressed them together and left it overnight to set fully.
To seal the box/gasket to the cylinder head I took the advice of Andrew Child, who runs Rees Brothers in Aldershot, who recommended using water pump grease between the gasket and the head. To do this I put a thin layer of the grease on the gasket and then bolted up the cover. There will be some grease squeezed out when tightened up so wipe off with a cloth. When the engine is started some grease will ooze out as the engine warms, wipe this of. This has sealed very effectively and I have successfully removed and refitted it several times to adjust the valve clearances. When refitting, I always clean off the old grease and de-grease the mating surfaces with brake cleaner. Many thanks to Andy Child for this advice and I thought I’d share this tip here.

Side plates.

I have not had much success in making the front side plate seal effectively using rubber gaskets and read much in the archives on this topic. Part no. GUG5505GM, which is stated as being the correct gasket for my 18V engine, needs to be stretched to fit the front plate with the oil separator and has never seated well on it or against the engine. After several aborted attempts with rubber gaskets I decided to buy cork (part no. 12A1139). When I put the cork and rubber gasket side by side it was obvious that the rubber gasket is smaller than the cork. (See attached photo) When I matched up each gasket against the cut out on the engine block, the rubber gasket was clearly too small for the cut out. I suspect that when the rubber gasket is used and bolted up, the gasket is pushed into the cut-out of the block and therefore does not make an effective surface to surface seal. The cork gasket being bigger means that the plate presses evenly on the gasket and block, so as not push the gasket into the hole, and so will seal effectively.
Using the cork gasket, glued to the front cover with EvoStik as above, and Vital grey RTV gasket maker between that cork gasket and the engine block, I have achieved an effective seal with no leaks so far.
Products used.
Water pump grease: http://www.moss-europe.co.uk/Shop/ViewProducts.aspx?PlateIndexID=12280
EvoStik: http://www.bostik.co.uk/diy/product/evo-stik/Impact/6
RTV Make a gasket: http://product-ecatalog.com/vitaltechnical/product.php?p=49

I hope this helps others.

Richard.




Richard Thompson

Richard,

Thanks that's helpful. The leaks can be embarrassing.

Roger
Roger W

Richard

The rubber side cover gasket was produced for the rear cover, not the front. That's why it doesn't fit. Any listing of 2 x 12A1175 rubber gasket is not correct.
Good to see you have worked out the correct information yourself despite the misleading listings.

I have to say that I always put cork and rubber gaskets on dry and never have a problem with them. In fact the only time I did have a problem with cork was (40+ years ago) when I used goo. I tried many different goos and methods of application until I subsequently discovered acted like a lubricant and squeezed the gasket out varying amounts resulting in uneven clamping. I discovered the error of my ways accidentally - when finishing off an engine for a race day at the last minute. Didn't have time to try the latest permutation of goo, put it on dry and it never leaked ever after.

In fact the rocker gaskets used dry seem to recycle happily if the need arises.

Paul Walbran

My BL microfiche shows MGB '76 on were fitted with 2 x 12A1175. When I recently did some work on the engine of my '80 B I found both gaskets were rubber. Apart from routine servicing the engine is all original (40k miles from new) so I guess this is how it left the factory. They have never leaked, but I decided to replace them anyway. I fitted one cork and one rubber after having difficulty trying to fit the rubber one to the front cover. I suspect the rubber gaskets we are being sold now may be off-spec (a bit small, or not flexible enough).
Brian Shaw

Hi Brian,

I also suspect that what we are being sold today is not "exactly" the same as originally used. They are probably what is sometimes referred to as metric equivalents; long on metric but short on equivalence.

Richard
Richard Thompson

"I also suspect that what we are being sold today is not "exactly" the same as originally used"

Very little is, especially anything involving rubber.
PaulH Solihull

This thread was discussed between 04/03/2013 and 07/03/2013

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