AJS model 20 - Crankshaft Oil transfer

[ajons]

For the attention of all Jampot members (and non members) Technical Problem - Help required.
Details of motorbike = AJS model 20 1953
Problem. Oil is transferring from crankshaft to the primary chaincase. I understand and accept the oil transfer problem when engine is stationary. My real problem is that there is major transfer when the bike is running. Extent of problem = start ona test run with primary chaincase oil level at about ½ inch below bottom of the chain, do 35 mile run at speeds up to max of 50 mph only to find oil comes out of the small inspection cover of the primary chaincase when I opened it. Removing chaincase I found that the clutch had started to be contaminated with oil!!! Another pointer is that this problem only started after I had attended the headlights on rally in Norfolk July 2000. During the run (with lightweight pillion passenger) I had occasionally to run at speeds of 60+mph. That is the only thing that I can relate to that has brought on this problem. Up to then, I had tooled around on fairly long runs at up to 50 mph. with no apparent problem.
Checks done so far.
1 How is oil scavenged from the sump? Is it via a pipe reaching from the return pump inlet down into the bottom of the sump? If it is, then maybe this pipe has broken off and thus the level of oil in the crank / sump has to reach the return pump inlet level before it commences returning the oil. This would give a much higher level overall in the crankcase thereby making the problem???? See also item 2
2 Oil pumps. On start up, the oil return shows full flow return for short period then goes onto the normal spurts and splutters which I believe indicates that the pump has scavenged the sump properly, thus the oil level when on the test run, should be well down in the crankcase and not available to come out along the crank into the chaincase??? See also item 1 above
3 I have purchased the big, red covered book titled AJS motor cycles (single cylinder) & Matchless Twin - covering all motor cycles from 1950. I have checked the oil drain hole in the timing chest and as far as I can see, this is as per the modification shown in the diagram on page 19 of the twin engine section. I have carried out the checks as recommended in this book (se page 21) and the release valve shows no sign of oil transfer; and I guess that if the rings were worn, then back pressure would exhaust via the crankcase relief valve, but as stated earlier there is no sign of oil coming out via the relief valve
4 The chaincase outer is removed at this moment in order to access the spacer behind the primary drive pinion. This is the scrolled version, so oil should be spiralled back toward the crank??When I removed this spacer, it removed quite easdily apart from oil 'sticktion' but I noticed that there were a couple of black marks on the outer edge of the spacer itself. Could it be that this is indication of the spacer 'sticking' in it's housing thus preventing it rotating and doing it's job??
5 I note that the oil is pumped into the Centre bearing area, but how does oil get to the main roller bearings???

I must own to being out of any ideas now and would therefore appreciate any input from fellow bikers in order that I can get out there once again.
Thanking all and sundry in anticipation
Jon Stock ( St. Albans)

[TommoT]

John you seem to have been very thorough in checking all oil related systems. I don't know about the twins, being a "single" man myself, but in these engines the returning oil flow is scavenged from the bottom of the crankcase via a cast in channel and not at pipe! Your problem does sound like the result of overpressure in the crankcase, so maybe you should check the pressure relief valve once again.

Not much of a help but maybe some twin members will tune in!

Tom M. (TM)