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Discussion Starter #1 (Edited)
t100rc brought up a method for fixing case leaks on the M/H thread, and I posted this response. Since it was off topic in the other thread, I'm re-posting and starting a new one, devoted to curing oil leaks in general.

t100rc described a method of sealing case leaks I was taught long ago, using a piece of plate glass and sandpaper to get a flat surface. I learned that one from a mentor long ago, and it was also taught at the mechanic's school I attended.

Years ago I worked at a Triumph dealership, and I picked up this method from the owner.

Blacken the mating surfaces of the cases (felt tip marker works great). Put a mild abrasive paste on the mating surfaces. Align the cases as they will fit together on assembly, mating surfaces touching. Using very light pressure and circular motion, and very small circles, lap the cases to each other. Any non-matching areas will show black after a brief effort.

Wipe off abrasive from areas that are lapped in. Continue until all black is removed. To check, re-blacken and start over. When the black is uniformly removed after just a little lapping, the cases are matched. Clean cases carefully to remove all traces of abrasive.


Anybody else got a favorite leak fix tip?
 

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I used good gasket's, clean area and Hylomar!!

bike dosen't even leak a drop after 5 years!!!

you can use and buy the best stuff on earth but if the surface isnt clean or flat your pissing away your time and money
 

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the old man's shop guys did basically the same thing except they didn't lap them to each other. This is probably even better because one side can 'absorb' the other side's imperfections. You can probably get them tight and remove less material in your method. The way I saw it was each half was worked in circular motion on light sandpaper adhered to a sheet of glass. I like the concept of 'lapping' the cases together.
 

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OOPs

I posted in the other thread before seeing this one.
It is always better to use a straight/flat surface to get one surface in a true plain. then bring the other surface to meet it. This is especially true where one of teh surfaces is a flattish cover, because it may be bent.
I had a primary chaincase welded after throwing a primary chain through ir. and it was not entirely straight afterthat. but after being lapped it was oiltight without gaskets.
 

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After lightly sanding joining surfaces to clean up joining areas on sheet glass. Check surfaces for level and true place a A3 sheet of paper on a 4 -6mm thick plate glass sheet and smear both cases joining surfaces with a line light oil (or spray matching edges with DW-40 or the likes and wipe inner and outer surfaces with a dry clothe so that only the matching edges are wet to mark) and place on paper evenly. Remember the surface must just be wet to show imperfection or use a second piece of paper. Repeat process to make level.

After doing all that work I use a carpet knife to clean up and ever so slightly chamfer the inner edges of both surfaces. So that when looking at the jointing surfaces in section the two edges (or matching surfaces) with the gasket passing through will have a larger area sealing between the gasket and the case on each side. Making a small V-joint all along the inner joining area.

Lastly use a good flexible gasket sealer and once joined and tightened properly. Stand the motor up in its normal position as it would be in the frame to dry.

That’s my 2 cents worth.
 

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After lightly sanding joining surfaces to clean up joining areas on sheet glass. Check surfaces for level and true place a A3 sheet of paper on a 4 -6mm thick plate glass sheet and smear both cases joining surfaces with a line light oil (or spray matching edges with DW-40 or the likes and wipe inner and outer surfaces with a dry clothe so that only the matching edges are wet to mark) and place on paper evenly. Remember the surface must just be wet to show imperfection or use a second piece of paper. Repeat process to make level.

After doing all that work I use a carpet knife to clean up and ever so slightly chamfer the inner edges of both surfaces. So that when looking at the jointing surfaces in section the two edges (or matching surfaces) with the gasket passing through will have a larger area sealing between the gasket and the case on each side. Making a small V-joint all along the inner joining area.

Lastly use a good flexible gasket sealer and once joined and tightened properly. Stand the motor up in its normal position as it would be in the frame to dry.

That’s my 2 cents worth.
That .02 is worth a quarter IMO.

TD
 

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I'm more of a learner than adviser on this topic and so this post is pretty much an enquiry. I've no experience with engine cases, but assume the factory machining would be a reasonable fit. Surely in the 21st century we have advanced with gasket forming materials that would take up minor variations between the surfaces for a leak free joint.

My question is then: why go to so much effort to hand machine the mating surfaces when as stewdog68 points out, a quality modern gasket sealant will do a reliable job? On car engines I've seen amazing results with sealants used instead of paper gaskets for an oil leak free seal.

I am mindful that this hand maching technique may well be reliable for some initiated mechanics, but I'd bet there would be very mixed results among the uninitiated.

RR
 

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I'm more of a learner than adviser on this topic and so this post is pretty much an enquiry. I've no experience with engine cases, but assume the factory machining would be a reasonable fit. Surely in the 21st century we have advanced with gasket forming materials that would take up minor variations between the surfaces for a leak free joint.

My question is then: why go to so much effort to hand machine the mating surfaces when as stewdog68 points out, a quality modern gasket sealant will do a reliable job? On car engines I've seen amazing results with sealants used instead of paper gaskets for an oil leak free seal.

I am mindful that this hand maching technique may well be reliable for some initiated mechanics, but I'd bet there would be very mixed results among the uninitiated.

RR
The tooling used to make all the Triumph stuff right up until the end in the early '80s was, for the most part, from the late 30s - early '40s and was recovered from the bombed out Coventry facility after the war ended ... when they closed down the factory in 83 (I think) they were still running overhead belts to drive the machines ...

Triumphs tolerances were not the greatest ... and all British machinery is engineered to leak oil. That's why the Brits don't make TVs ...
 

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What makes a rebuild a great rebuild or a fantastic job or even a concourse build? Attention to detail in correctness in all aspects being it routing of cables or matching of original specifications details and finishes for that year and no oil leaks. The material used and the machining tolerances then were mostly happy go lucky and not as good as it is today. I agree with t100rc on his comments.

You can still rebuild a motor and use poor quality gasket sealer and have leaks on push rod tubes or engine cases. Remember attention to detail. Rebuild everything twice, first a dry run (practice run) and when you are very sure a final set.
Good luck
 

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Discussion Starter #12
Matching up the cases isn't the only factor. Proper assembly and materials are just as important. You can't change the design of vertically split cases or control for unequal expansion and contraction as case temperature changes, but starting with well-matched cases certainly helps keep things oil tight. Proper assembly includes clean matching surfaces, good quality gaskets and sealer, and tightening fasteners to the correct torque in the correct sequence.

If an initial marking and lapping showed the cases weren't pretty close to matching, I would start with the plate glass. Only the least amount of metal possible should be removed in the process. You can't take out major gouges (you know, like the kind of toolmarks left by a very large screwdriver) without ruining the cases.
 
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