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Exhaust port thread repair

Ray Bear

Forum Website User
Non-VOC Member
Hi all, I have searched the forum with no sucess to what is the normal proceedure to repair a stripped thread on the exhaust port, are they best welded & re-threaded or a brass sleeve inserted , or tap out the thread a larger size & have an oversize retainer nut made up ?? thanks Bill
 

john998

Well Known and Active Forum Website User
VOC Member
Hello Bill,
Best repair is a bronze insert. Bob Dunn did 2 for me many years ago and both are still good.
Not sure if any one can offer this service in Oz though. Don't like the idear of welding as it may afect the heat treatment of the alloy.
Regards John.
 

john998

Well Known and Active Forum Website User
VOC Member
Hello,
I think with Bobs repair he machines out the old thread and drives in an insert, friction fit, then re-threads that.
It requires a mounting device to hold the head to do the boring.
Regards John.
 

Ducdude

Well Known and Active Forum Website User
VOC Member
I have no idea if this will work for you..BUT on my 52 shadow the front port threads were dicey and no matter how patiently or carefully I held the pipes I could not get the threads to catch....So, I cleaned up the area well with brake clean and bronze wire brush and bought and fresh new exhaust keeper and with liberal amounts of grease I worked it in and out like a die to reform the damaged threads. I took my time and used a sharp dental pick to remove the swarf. Little by little I got the keeper further and further in till I got to the good clean threads at the bottom. Then I was good to go...

If you have completely damaged threads this will probably not work, but it was worth mentioning just in case.

Eric
 

Albervin

Well Known and Active Forum Website User
VOC Member
I did the same thing on my Rap many years ago. The rear exhaust nut was held in place by a combination of baked silicon and muffler putty. A new exhaust nut and a LOT of patience fixed it.
 

chankly bore

Well Known and Active Forum Website User
Non-VOC Member
.Bronze insert. They have never failed.Cheers F5AB/2A/7945 (ex Sven Kallin machine) In my opinion,any other repair is questionable because some head castings have little material for o/s threads and putty and other stuff is useless.Welding can affect the strength of the head in this important area.Join your local Section,and you will get a lot of help!
 
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wmg73141

Well Known and Active Forum Website User
Non-VOC Member
More than 50 years ago, I had this problem on my Comet – exhaust thread completely gone – I bored the head out to take a thin walled shrunk in threaded insert made from duraluminium – I’ve still got the old girl and the repair is still good today.

I would however strongly recommend shrink fitting an insert rather than press fitting because well documented experimental work on shrink fits vs pressed fits has shown that a shrink fit has something like three times the ''grip''.

Such work requires a cryogenic source; liquid Nitrogen is the obvious choice but if not available then a mixture of solid CO2 (Cardice) in Acetone is also pretty cold (-77°C) and might be more easily obtained.

A lot of work? Maybe, it certainly requires more facilities than the average owner will have so farming the job out would seem to be the way to go. However, this method has the merit that it imposes almost no thermal stress on the cylinder head, is all but invisible and it worked!
 
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