How to seal loose pressure release valve threads?

[Radlan2]

Hi. Here is a solution I read about on another forum perhaps more concerned with the similar unit engine, I have done this and it works though unfortunately I cannot give specific measurements. It is possible to cut an O ring groove in the short threaded part of the PRV which will certainly make an improvement though i cannot say if it makes a leakproof seal. I have a box of odds and ends spare O rings and the one I used was from memory around 0.500" bore and 0.092" (3/32") section. I am only sure of the section as I have just measured the tool I used to cut the groove. I used trial and error to achieve an acceptable fit which would screw in without too much interference which would tear the ring. with a bit of oil I was able to screw in and remove it without tearing the O ring which had to be stretched over the PRV, infact I cannot say that it was an imperial O ring. Sorry to be a bit vague about it but you get the idea.
       Hope this helps
            Chris

[limeyrob]

Reading this thread it struck me: do we really know how a big a problem leakage past these threads is?  Is it that only a few engines leak, or do most leak but unless its severe it doesn't matter?
Assuming these engines left the factory OK (yes I know ) we know many are still working over 60 years on.  I know if at least one A10 that is still in use and has never been rebuilt so the pressure relief valve may have never been disturbed.  If the "factory fit" was OK then the only wear mechanism is dismantling and reassembly and my question would be "how often do these need to be taken apart?"
In my case the engine was in bits and it came with 2 valves, one as standard and one plated (for show) but the plated one was slightly oversize and gave a good fit so that got fitted with some thread seal.  Plating the threads seems a good fix as it maintains the original design intent.

[mikeb]

Rob - i guess any owner will have to decide if this is a problem for their engine or not. when i starting this thread, the local clever people (proper bsa riding actual engineers, not me) concluded it was a probable cause of significant premature engine wear (shells etc). your call - YMMV.

I agree that TT's suggstion of plating the threads would be an elegant solution but I chose to fit a new SRM PRV (much tighter) with some thick loctite goop on the lower threads (cross fingers). I've had more experience plating now so would consider that next time.

I actually like Orabanda's teflon solution as it sounds tested and feasible. Richard - could you post a pic or dimensions or your creation? However for me I had an oil gallery drilled for a pressure switch which would rendeer this diffciult. the switch does suggest i have pressure. (tho weirdly it initally would flicker when hot/idle but now a few years later doesn't - i'd have thought the opposite)

Chris - I'd feel a bit wary about an o-ring as fear I could roll it out and there are few lower threads to cut it in to. Still, if you've tried it, I'd like to see a pic if you have one. I assume it works?

cheers

[limeyrob]

Re-visiting your original post your situation does seem a  bit odd.  I recently rebuilt my engine and had a spare set of cases and spare valve. None were anything like as loose as yours.  I wonder if yours has in the past had some internal corrosion or a very ham fisted mechanic/owner?  The valves are zinc plated and should not react with the ally cases but interestingly (I had a look today) the valve I rejected has lost its plating and is rusty.  The steel in ally would eat away at the ally on an engine that was not being used and kept oily.
I ran an oil pressure gauge on an A65 for years, I seem to recall it released at about 50 psi but with 20-50 oil the pressure hot was usually around 30 psi and would get down to 5 at idle.  I was so alarmed at how low the pressure would get when really hot that I switched to mono-grade oil.

[chaterlea25]

Hi All,
There is a current thread(pun) on Britbike BSA forum on this subject, mostly regarding A65's which are the same as A10's in this respect.  One solution offered is to thoroughly degrease the threads and apply some JB weld to the inner threads then screw in the prv with lubed threads so the JB doesn't stick to the prv.
On a couple of A10 engines I rebuilt I had to get a tap to ease out the threads to fit the SRM prv as these are made to " top limit" on the threads

John

[Sakura]

My fear on the sealant, of any type including JB weld, would be the worry of the relief hole being blocked. I know the application has been stated to be on threads beyond the hole BUT. The only engineering solution, in my opinion, is the machined sealing ring between the PRV and gallery bottom face. Any competent lathe user would knock one up for very little given the dimensions, and digital calipers are very cheap.