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Leaking Push Rod Tubes

Matty

Well Known and Active Forum Website User
VOC Member
My exhaust push rod tube has leaked a little oil for some years and because I have had to have a repair done to the head, I have naturally changed the bottom seals for the push rods in the expectation of curing the slight leak when I replaced the cylinder head.

I checked the push rod tube for circularity, correct diameter and damage before I replaced it and it was a tight fit in the seal.

It still leaks a little and now I have no idea why.

Presumably to do a proper fix, I will have to remove the head again - though I seem to remember an owner saying that he had managed to cut a new seal and then fit it round the tube with some sealant. I do not think however that I could get the seal into the crankcase on my bike - it is too tight a fit onto the pushrod tube.

For the moment I have put some special silicone type seal round the tube seal and then a thin layer of Araldite and this seems to have worked.

This must be an old problem - and I know for a fact that some old aluminium push rod tubes as originally fitted to my bike (I have had it since 1956) were 25thou undersized in diameter which leaked for years until I fitted stainless ones.

Has anyone got a good fix without taking the head off again or any ideas please on what the problem might be or special instructions on how the seal should be fitted ?

Matty
 

davidd

Well Known and Active Forum Website User
VOC Member
I think you have done the best that can be done. I do remember the post you are referring to. The best solution I have seen is Robert Watson's, which is to install a thin aluminum sleeve in the push rod tube hole in the case. The installed sleeve has an "O" ring grove cut in it. Very tidy and servicable. You will have to take the head off, though and have access to the equipment or someone who could do the job.

I do have a set of Colin Taylor's push rod tubes which disassemble more easily from the outside and use O rings in the upper seal while leavin a threaded spigot in the head, but you would have to take the head off to get the old tube out, and other than being new and round, do nothing for the lower seal. I have not run Colin's tubes, but they look like the racing push rod tubes installed on the Flashes with the big port heads.

David
 
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Jim Richardson

Well Known and Active Forum Website User
VOC Member
I have just redone my Prince, which leaked like a sieve, I was a bit concerned with all the talk about badly machined D crankcases, but I installed the tube seals with a smear of a non setting gasket cement (whose name I can never remember, Brown, Sticky and very smelly) and it has been ok, there is now only a small leak from somewhere around the primary, but I have better things to do than chase that at present.
I have also run the standard D breather + plus one from the front inlet rocker cap back through 2 Enfield, Duck billed breather tubes and so far have found no oil in my catch bottle.
 

stumpy lord

Well Known and Active Forum Website User
VOC Member
I asume you are talking about the lower seals leaking on your push rod tubes . If so a quick and easy cure is to winkle out the old seal, de grease the recess and then, fill it up with Black silastic, Run a wet finger around the joint. now let the Dragon snoot go of, and you will have an oil tight joint that looks just like the real thing.
cheers stumpy lord.
 

jellywrestler

Well Known and Active Forum Website User
Non-VOC Member
is it leaking top or bottom? i recently had issues with getting seals to even fit in there, went to a knowledgable seal place and they gave me pipe seals that were stepped. ie normal seals have the same depth whereas these had a lesser depth on i think the inside seal
 

Matty

Well Known and Active Forum Website User
VOC Member
Thanks everybody

Have re-checked my breather, which is timed OK and puffing out of the pipe - so don't think this is the problem.

The leak was from the bottom of the push rod tube and at the moment seems OK with the smear of sealant and small layer of Araldite after it had set.

The sealant I am using is KENT Sili Gasket which is used "in the trade", is black, sets quite hard but rubbery and I am sure would work well for Stumpy Lord's fix if my present bodge fails.

Thanks again

Matty
 
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