Joined: Aug 2017 Posts: 3,329 Threads: 372
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was thinking about the leakiness issue.
Silicone gaskets have followers but there is the issue of tightening down and tolerances.
What about adding a bead of sticky silicone (which also comes off reasonably easily when cured) EXTERNAL to the joint, almost like the waterproofing of the bottom of tiles round the bath. Would the strength of the adhesion hold against gas pressure enough for it to be worth trying? Indeed, has anyone every experimented so on a leaky but well running engine? Was thinking about the ledge on front and back and the pesky oil pump drive cover. Could even be added round the square bolt etc. If a suitable product worked and was easily removeable under greater 'load'.
Joined: Aug 2017 Posts: 926 Threads: 22
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Location: Near Cambridge, UK
Car type: 1928 tourer (mag type), short chassis Gould Ulster
I have found Sikaflex quite good for sealing the bottom of the block; it has 2 functions: it seals and it is an adhesive. If used on a properly cleaned pair of surfaces you will have to use levers to remove the block. It does not eliminate the need to tighten down properly. As for silicone sealants they only work properly when applied to very clean surfaces. As for the core plug above the oil pump I suggest Wellseal.
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What is the tightening down and tolerance issue with silicone base gaskets Jon?
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I was really thinking of the many engines that are in and running fine but leaky... I realise all the options for rebuilding.
I know you like them Ruairidh but some builders don't and won't use them presumably because they think it introduces a compressible layer unnecessarily. I have no experience whatsoever but I am interested in the diverse thoughts of all the regular builders.
Some have still had oil leaks starting after a while where they have used silicone gaskets.
And it does mean that you are tightening something down which has potential to affect the fine tolerances of tappet gaps over time?
Joined: May 2018 Posts: 2,110 Threads: 110
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Location: Llandrindod Wells
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Hi Jon
I’m a believer in silicon gaskets and yes I have had to tighten nuts and check tappets, but only once so far.
I doubt you could get the external joint clean enough for silicon to stick under the oil pressure no matter how small this is.
IMHO live with the leaks or dismantle and do the job properly.
Cheers
Howard
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First make sure the top of the crankcase is flat, I think every one I've rebuilt has fretting damage particularly on the camshaft side. I use a 0.010" varnished paper joint and that's it.
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I have also been thinking about this for a while as my engine leaks a bit at this joint. I came to the conclusion that an external bead of sealant wouldn't do it - but would also be interested to hear if anyone has tried this? As Howard says, it seems unlikely that it would stick given the inevitable lack of cleanliness of the surfaces.
So next, I have wondered about fitting a silicon gasket with the engine in the car - by lift in the block slightly and pulling the gasket over the block from the top, having snipped the connections between the cylinders as they don't need to seal. Is this sensible? Has anyone tried it?
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Not liking them and actual issues are two very different things and should not be mixed Jon.
I have fitted over 60 of these to engines now, none have failed or caused issues with tappet clearances after a 48 hour settling period. I.e. don’t continuing to keep tightening and tightening.
They must be fitted to spotlessly clean surfaces that have at least some semblance of flatness at outset.
My own cars are testimony to the tremendous suitability of these items in doing exactly what they should.
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Running a bead around the outside of the block joint will work for a short while but is ultimately going to fail.
Do the job properly or just put up with a bit of an oil leak.
Joined: May 2018 Posts: 2,955 Threads: 558
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Car type: 1929 Chummy, 1930 Chummy, 1930 Ulster Replica, 1934 Ruby
15-07-2021, 11:48 AM
(This post was last modified: 15-07-2021, 12:14 PM by Tony Griffiths.)
What Dave Mann in his modesty failed to mention is that he spends an afternoon or two carefully lapping the top of the crankcase to a ground-finished, 3/4" thick steel plate. On the camshaft side of the crankcase he often finds the distortion (fretting) can be severe and, to remove this, sometimes means taking off so much metal that the engine number (stamped on the off-side) almost disappears. The base of the block is surface ground and the result, with a paper gasket, is an engine that never leaks oil from the block-to-crankcase joint. The devil, as always, is in getting the details right.
