Gaskets - to seal or not to seal?

Technical MGB discussion
DickBrowne
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Gaskets - to seal or not to seal?

Post by DickBrowne »

That is the question…

I’m back into the garage today to (hopefully) cure one of my leaks - the most significant one seems to be from the side covers underneath the carbs. I have a new set of gaskets and can see this being a ten minute job. Spread over many hours.

I’m never 100% sure which gaskets really need a thin coat of halo at or the like, so am seeking guidance from the forum collective on this if I may - should I seal these gaskets, or leave them as nature intended?

Thank you in anticipation

Richard
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Paul Scott
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Re: Gaskets - to seal or not to seal?

Post by Paul Scott »

I waa advised to pop a smear of grease or vasoline on the tappet cover gaskets only Richard.

It worked for me..

Regards
Paul
1975 MGB Roadster
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DickBrowne
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Re: Gaskets - to seal or not to seal?

Post by DickBrowne »

Perfect - thanks Paul, that saves me a trip to Halfords 😊
Ian Fozzard
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Re: Gaskets - to seal or not to seal?

Post by Ian Fozzard »

The side cover/tappet cover plates have two kinds of gaskets available as far as I know. The original type is cork, and there is a synthetic rubber type which is supposedly an improvement.
I prefer the cork originals and would recommend very clean surfaces and a smear of hylomar on both surfaces, and don't overtighten the bolts. There is a torque value for the bolts but I don't have it to hand at the moment. It is a low value.
These covers are a known oil leak item!!

Ian F
1972 BGT, Blaze, Navy trim, recessed grill
1961 Midget, 948cc, Clipper Blue, Blue trim and weather gear
DickBrowne
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Re: Gaskets - to seal or not to seal?

Post by DickBrowne »

Thanks Ian - I’ve fixed it with grease for now, but will get some hylomar in, just in case mine is one of the tricky ones.

Quick supplementary - I had to polish the jet cover at the bottom of one of the carbs as it was sticking, but to get it all out I disassembled the carb. Above the cover there was a nut which tensioned a spring, which seems to be adjustable, but I cannot find any reference to what the nut actually does adjust - does anybody know?
Ian Fozzard
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Re: Gaskets - to seal or not to seal?

Post by Ian Fozzard »

That sounds like the adjustment mechanism for raising and lowering the jet height? With the top of the jet absolutely level with the bridge in the carb throat, wind down the jet 12 flats. That should give you a reasonable starting point for the mixture. The spring maintains the tension an prevents unintended movement of the jet.

Ian F
1972 BGT, Blaze, Navy trim, recessed grill
1961 Midget, 948cc, Clipper Blue, Blue trim and weather gear
DickBrowne
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Re: Gaskets - to seal or not to seal?

Post by DickBrowne »

Thanks Ian, that sounds like the kiddy ;)
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Charles Farran
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Re: Gaskets - to seal or not to seal?

Post by Charles Farran »

Important to not over tighten the covers as there is a danger of the covers distorting and the edges lifting. Recommended to change the seals that sit in the cup washers as well as leaks come from there as well. I seem to recall that John Twist recomends cork gasket for front cover & synthetic / rubber for rear.
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David Witham
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Re: Gaskets - to seal or not to seal?

Post by David Witham »

I have the brick red rubberish gasket on the rear cover and the cork type on the front.

Last time I had the engine out I replaced the cork gasket with a new one and sealed it with a loctite gasket sealant.

It is the first time I have had an oil tight seal there in 42 years of driving MGBs!
DickBrowne
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Re: Gaskets - to seal or not to seal?

Post by DickBrowne »

Over tightening is an interesting one. I’m aware of the ability of even reasonably thick metal across a small area to distort. The torque figure for the front cover is a mere 2ft/lbs, which is ridiculously low, and 3 ft/lbs less than my smallest torque wrench can manage, so I’ve used the best guess method, and made sure that the torque wrench didn’t click, but after running the engine for about 20 minutes, and three or four cycles of the cooling fan (so I know it was properly warm), there’s no leak. Well, there’s no leak from the side covers. Other leaks are available.

One thing I did notice when driving the car is that thee fine is slow to return to idle. If I rev it to, say 3000 rpm, and take my foot off the accelerator, the revs drop to 1500 rpm very quickly and then slowly from there down to sub 1000 rpm.

Looking at the carbs with the air filters off, the rear carb suction chamber slide seems to be unwilling to drop to the bottom of its travel, far less so than the front carb. If do lift the slide with my finger and let it go, it drops down really quickly and the idle speed drops quickly too.

I did need to polish the jet cover on the rear carb to stop it binding, would the slide benefit from a polish, or could it be that the spring has weakened over time and could do with replacing?

Also, what’s the record for supplementary questions?
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