classic motorcycle forum

It's impossible to say. If someone is desperate for it, quite a lot. If two people are, the sky's the limit....

I would say that few people manage to break even let alone turn a profit on old bikes.....

That looks like a fairly common Sachs engine. Millions around sur le continent.

If this is the standard of stuff on offer so glad I changed my mind about going.

You're always going to get junk wherever you go. Founders Day (and the Banbury jumble) are at least better than the big commercial ones as you often get people clearing their sheds to pay for the next money pit......

Having said that, trudging across miles of fields in the hot sun is less attractive than it once was.

This seat is at one end of a filter housing - the other end of which is a ball valve with a weak sping, which ostensibly allows pressure to build, releasing said ball valve and allowing oil to flow through the engine at pressure. 
 

Not quite - the PRV, as its name implies, releases excess pressure. Under "normal" operation it's closed, making the oil flow through the main and big end bearings. It opens if the pressure seen at these bearings exceeds the design value and in fact that oil is generally used to lubricate timing gear etc.

It's fairly normal for the valve to open with cold (especially straight 50) oil. I would actually consider that to be too heavy for most bike engines - my ES2 and other bikes I've had all seemed perfectly happy on 20W/50 which of course is much thinner at start up. Although some will disagree.

I'm slightly alarmed by the "plenty of silicone" remark - this stuff has a horrible habit of going where you don't want it to.

It wouldn't be a good idea to just increase the spring value. Are new ones available from the Owners Club / Steve Surbey?

Or both......

Some excellent replies there. The only thing I would add would be that I have never come across a 7/16" carb stud on mainstream British bikes - all would be 5/16", BSC (Cycle) on the outer ends, BSW / BSF for alloy / cast iron for the inner ends as said. Normal carb flanges only have 5/16" clearance holes so 7/16" wouldn't go through them anyway.

I agree - please measure in inches not mm. If you have a cheap digital caliper this is perfectly adequate for the purpose.

It seems likely then that your studs have been made to cater for stripped threads in the head (or is it barrel? - side valve?) and are probably stepped. You may be able to helicoil the threads back to stabdard or have inderts fitted depending how much meat is left.

I think this is probably getting more involved than you anticipated. This is invariably the case - a five minute job turns into a major restoration. But stick at it!

Tufnol is essentially the same as paxolin - hard, fabric reinforced phenolic resin (as you can smell when you machine it) as John says. I'm not sure what you're thinking of Rex......

That is true. But not if the top and bottom bolts are kept tight.

I also agree about the re-enactors. We had the misfortune to travel to France via Brittany Ferries a week before the D day anniversary and the ship was infested with them swaggering about in their fake uniforms. I suspect the few remaining real veterans of that conflict view them with some disfavour...