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[WDCO42]

Hello Dave, don't give up with you G, you have eliminated quite all the susceptible causes of your problem ! Have you dismantled the breather, that is on the left side of the engine, and tested it ? It seems there is no breathing on you engine, and the air escapes where it can : the drive side bearing.... When your engine runs, do you see oil returning to the front oil tank ? You could normally see it after a while. Please let me know that
Claude

[DM]

Hi Claude,

I think I've talked myself into splitting the crank cases to delve a little deeper.
Yes there is air and oil coming from the breather, I have just re-routed it into the primary drive case to catch the oil. As fare as returning oil to the front tank, no it isn't, that is to say if you mean the oil return just below the filler cap/neck. I did replace the bearing and spring and blow air through the system. The only breakthrough is that the oil flow to the head is vastly improved.
I am of the same opinion that there must be a blockage somewhere which in turn is forcing air/oil out where it shouldn't.

[WDCO42]

Hello Dave, it's a good thing you keep the G, she is a fine bike, and a real joy to ride. Maybe have I found the solution : you say that the head lubrification has been vastly improved, so you return pump system works correctly, as it is the same circuit ! the trouble comes after the head oiling system : the by-pass ball bearing... I had a look at the oiling " picture " (my vocabulary is a bit poor) : if there isn't enough oil pression to push the ball, all the oil goes to the head. So your problem is : or your ball spring is too strong, or you have tightened it too much, or your non return valve plug is blocked (as you have changed the spring and the ball, I opt for the second option). In the manual, it is said that the pression to puhs the ball up is between 30 to 40 lbs/square inch (psi ?), so around 2.5k/cm2. That could explain why the oil can't be properly scavenged, as there is only one way for the oil to escape (except you drive side roller.. Sorry, joke), instead of two... Try to unscrew the plug and let me know, please.
Hope it will help you. Claude

[WDCO42]

Hello Dave, have you found the cause of your troubles ?

[DM]

Hi Claude,
No not fixed yet, although I'm desperate to sort the problem I have been working on one of my other less temperamental bikes.
To answer your question ref unscrewing the return bolt thus releasing tension on the ball bearing spring, this I did and yes there was more oil return, but not enough to stop the oil evacuation via the final drive sprocket.
The position of the return bolt would spew oil vertically towards the cap if the oil returns at any greater rate, can I assume that oil returns to the tank via another rout also?? another question, if oil return flow is restricted with these engines will the oil always push past the piston rings and drive sprocket? or is my problem not a common one?
Onwards and upwards as they say.

[WDCO42]

Hello Dave. I assure you that this isn't a normal problem with those engines. I have my Co for more than 20 years, remade the engine several times, had at least 3 other ones remade, had several endemical troubles, but nothing like your's.
So, you have at least some scavenge to the front oil tank (it is normal after a rebuilt or an oil change that the oil level goes down, but you should see it going up quickly to its original level, is it the case ? If not, some oil way partly clogged in the front return system, or a bad timing cover gasket (I had one once with a missing hole), or a poor pump disk sealing), you have some breathing (even if I'd make the duck nose pipe mod if I were you), you haven't poored more than 2 liters of oil in the tank (engine dry), your valve timing is supposed spot on, as you bike starts 2nd kick, rests the piston's area... Is it an Hepolite one ?(there was a real interesting post where Bullet Whisperer said that he put 250 AJS rings on his new pistons, so he was assured that they were real NOS Hepolite ones, and not some Khiber Pass production) ? Did you make a rebore ? Have you controled the rings gap ? For me, assuming that the oil level isn't going up the drive side bearing area because of a poor scavenge reason, as the drive side bearing arrangement is quite impervious (did you check the outside thust washer had the correct thickness or wasn't tight fit on the crank spindle ?)there must be a holly high crankcase pressure to get such a leak by the drive sprocket... Let me know you inquisitions results, I'll make some voodoo rites until you have answered.
Claude