This is my first post on this forum, so I hope it's permitted by the moderator. I was given a 1945/46 WDM20 by a very old friend last year. It hadn't moved since he parked it up in 1989, when it stopped and he couldn't sort it out. After much blood, sweat and tears it's running again, with new tyres/tubes/clutch/cables/etc, and the magneto, which was probably the original problem,fixed thanks to my brother.
It's got a nasty rattle on a fast tickover, which a near neighbour with a number of BSA's thinks is probably a little end starting to go, but I took the tappet chest cover off to check for problems. I've reset the valve clearances as per the book (010/012) and found that the exhaust valve lifter was sitting tight against the collar on the tappet. According to the workshop manual:
The peg on the exhaust valve lifter inside the tappet
chest must always be well clear of the collar on the
exhaust tappet (see Fig. 7), otherwise the engine will
be noisy and the tappet clearances seriously
affected. Failure to check that there is clearance at
this point may result in a badly burnt exhaust valve.
The illustration doesn't give a clearance for the lifter but it seems to be about half that for the exhaust valve, so I tried it at 0.005". The valve didn't lift so I tried 0.003" and it still didn't. I can get more lift by lengthening the cable adjuster but then there will be no clearance.
When I dismantled the cable connector at the lifter lever, the peg was sitting up against the collar on the tappet and roughly horizontal to the axis of the lifter (i.e. about 9 o'clock). I reassembled it so it's below the axis (i.e. at 6 o'clock) as this gave it clearance from the collar and then tightened the clearance with the cable adjuster. However the movement on the handlebar lever at the maximum lifts the tappet only enough to meet the valve stem, which hardly moves. But as previously said, if I lengthen the cable enough to move the valve, it will remove the lifter clearance. Help!
The cable is new from Draganfly and the length seems fine. Any help or advice on setting up the lifter would be much appreciated. I note that others on the forum are running much closer valve clearances but the manual says "the clearances should be regarded as a minimum, especially in the case of the exhaust valve", so I prefer to stick with those for now.
email (option): richard_h_taylor@btconnect.com
Aloha, and welcome!
You will find this forum to be extremely resourceful and full of knowledge, at least I have.
Certainly a good friend indeed to give you such a nice bike!
Have you tried slackening the cable while the bike is running att idle to see if the noise goes away?
Best regards,
Simon
email (option): SimonofSweden
The valve lifter was finally set up correctly after much trial and error. Among other things I moved the lever along the handlebar to get the maximum lift on the peg, so it's now on the bend in the bar where the lever moves through a much larger angle. It looks a bit odd but it works. I may have been stupid when trying the various adjustments, as I only looked for the movement of the exhaust valve but didn't try to turn the engine over with the kickstart. It could be that the very slight movement which I didn't see would actually have unseated the valve enough to release the compression, but I only thought of that afterwards! Anyway it now works as it should and with luck I'll never have to touch it again.
Annoyingly getting the clearance on the lifter right had no effect on the tinny rattle at a fast tickover. It occurs at very specific rpm and comes and goes in a regular pattern. It's like a vibration from a loose component or a thin steel panel, but it definitely comes from the engine. You can make it come and go with the advance/retard lever or the throttle twist grip. Several more people have diagnosed it as the little end, but my brother who had the head off reckoned there was quite a bit of slop in the piston, so it's a winter job to find out whether a rebore is needed.
Meanwhile the bike starts easily, cruises at 50 or so and is happier at about 45 mph. It has now done several longer runs and I'm enjoying a very different biking experience. I just need to sort out the front brake which grabs and may need the drum skimming but that's another story.....
email (option): richard_h_taylor@btconnect.com
Noise sounds like piston rattle when feathering the throttle, nothing at all to worry about if no bad smoking or loss of compression.