Hi all, I am working on my 1957 Venom and have noticed that the advance retard mechanism isn't very positive when it springs back to the retarded position. Here is a link to a short video showing its operation.
So do you think that is ok or could I have a problem with the springs being weak?? Thanks for the help, Stuart.
These mechanisms are very basic things. Don't expect them to be as precise as a modern electronic advance. Your thing looks perfectly normal to me. Fit, it, re-time it, and see how the motor runs, It'll probably be good as gold. Sometimes the springs can relax a bit and cause problems, but in my experience that's pretty rare. Just make sure there's no nasty gunky stuff in there and that it's free to rotate. (That spring-back operation may look lazy, but in operation it'll be more positive). It's really only the fully advanced position you need to worry about anyway... so when you time it, make sure you wedge the bob-weights in the fully advanced position - bob-weights spread out.
Hi. Thank you for the reply. I'm just checking everything as I've had a problem with the Alton electric start that was fitted back when my father used to ride the bike. Last week I tried to start it and it kicked back and sheared 2 teeth of the starter gear. I'm in the process of getting some upgraded parts from Alton but don't want to damage any new parts. At the same time I'm trying to fix an oil leak from the joint in the push rod tube so the head is coming off again. Recently I fitted the new type with an o-ring at the joint and it still leaks which is disappointing considering the cost. The o-ring doesn't seem to be compressed sufficiently to create a good seal?? Thanks, Stuart.
Ah, Alton starter... Obviously that changes things a bit. More at risk than knee or ankle! I wonder if the Alton starter spins the motor quicker than the leg, and consequently advances it too much too early?
Stuarts7, I have had the same experience with a new pushrod tube from Groves. It seems the o-ring they supply with the tube is not up to the job. I remember putting in a fatter viton o-ring to fix the leak. I also remember it took some fiddling to get it seated between the two tubes without cutting it. I think I assembled the two tubes with the o-ring before offering it up to position on the engine. This way I could use small screwdrivers to get the o-ring in place between the two tubes. I didnt have to take off the head, I just removed the studs that the tube mounts to in the head. I remember thinking what a disappointing arrangement it was, but it is now done and no leaks. About the auto advance on your magneto: The advance works between a window of available movement that is limited by bent steel ears that are part of the mechanism. Take time to measure where your advance is occuring. At the advance setting of 38 degrees BTDC, my retarded setting was a few degrees ATDC which made the bike almost impossible to start. The fully retarded setting should be a few degrees BTDC. My fix for this was simply to bend the steel ears on the advance mechanism to get it to the desired window of operation. It was a fiddly job that took several trial and error attempts and careful measuring. Looking at your video, I think your advance mechanism appears to be in a normal condition. The slight stickiness of the springs and cam will be negated by the vibration and movement of the engine. However getting the cams, springs, sliding contacts, etc. really clean will help immeasurably. Fullminator
Thanks for all the comments and feedback. Regarding the pushrod tube from Grove I must say I am disappointed too. Can you remember what size o-ring you fitted to fix the leak? This was going to be my plan and I thought that there may be an imperial size option instead of metric or vice versa that would be a better fit. It isn't apart yet so I don't know what size Grove fitted. I might drop them an email and see if they have any comment or suggestion on o-ring replacement. So the auto advance retard should vary between 38 deg BTDC and 3 deg BTDC. It will be interesting to see what the numbers are before I make any adjustments. Thanks again, Stuart.
I don't know the Groves pushrod tube, but it's not difficult to get a leak-free joint using the old 'string method' with the original tube. I use 'Three-bond' rubbed into the string before turning a few circuits of string around the tube. Assemble it loosely easing the string into the gland nut, and tighten the gland nut after top and bottom stud nuts are tightened, - I let the Three bond dry for a while before finally tightening so it doesn't all squeeze out.
I dont recall what size O-ring I used. I'm sure I just picked one that fit snug on the ID and OD of the two tube dimensions, and fit well in the tubes groove.. It was obvious that the one that Groves supplied with the tube wasn't even close in all three dimensions. I had the original three piece tube with the bike, but I never considered using it as the chrome was pretty bad. I thought it looked to be fiddly trying to get twine to seal it. I thought Grove's advertised two piece unit with a "modern" O-ring would be an improvement. Considering how fiddly this ended up being, perhaps the original design isn't so bad. But as I said, mine is all done now with no leaks. Stuarts7, yes points opening on your auto advance unit, at full retard position, must occur slightly before TDC. If it occurs ATDC the bike will never start. I considered altering my magneto to a Manual advance type, until I realized it could be adjusted by bending the steel ears that the rotation limits against. My Velo is now a good starter and ignition advance seems to be correct. Now if I could only get the #$%@* clutch to operate properly!! Fullminator
Well. Something's wrong with YOUR clutch ain't it. (Note emphasis!) You either have worn parts in it, the wrong parts in it, or it's wrongly fitted/adjusted.
Remember that the Velo clutch was in production for what... something like half a century, successfully, with just a few variations along the way. If there was anything inherently wrong with the clutch, there's no way it would have been in production for so long. Let alone surviving thousands of very fast laps of the Island and other circuits in racing KTTs... Let alone working on the 24 hour record breaker - average over 100mph for 24 hours. No crappy clutch could survive all that.
Back in the day, Velocettes were used, - as daily riders, by ordinary working blokes, not mechanics. They just worked, as did the clutches. The biggest problem with the Velo clutch is the owners!!! :-) LOL.
It's not 'THE' clutch, it's 'YOUR' particular clutch.
Well, I am sure there is something wrong with MY clutch, and certainly not a crappy design problem that causes it to go out of adjustment at will. I mean you offered all that evidence of its proven robustness and things. LOL Seriously, I agree with you about the Velo clutch. It is an oddball that works very well when correct. It is part of the Velocette charm having the oddball that you can confound your riding buddies with. MY clutch's problems stem from once again poor fitting parts. I purchased all new clutch components from Groves. ALL pieces are new. I struggled with springs that were too long. ( I couldn't even get the retaining ring started on the threads.) The clutch now moves out of adjustment at will when the engine is running. I have spent lots of time getting it adjusted, go for a ride, and after about 5 miles the clutch lever at the bars is flopping about with no chance of operating it. Other Velo Fellows have offered that they have heard of certain Velocettes that suffer from this problem. They say it is poor thread fitting on the spring holder, and they always say, "your clutch must be really worn". Again, all the parts are brand new! I have several ideas of how to fix the issue. Some have said they cut a notch across the spring holder threads and place a strip of nylon to act as a sort of nyloc nut. Others have offered that I should buy more spring holders and threaded rings to try to get a good tight fitting one. However I think the next thing I will try is getting the clutch in good adjustment, and then putting blue Loctite on the adjuster ring. This will make future adjustments a problem, but at least it will facilitate riding the bike some. I finished its restoration almost four years ago, and I still have less than 150 miles on it. Very disappointing. I am a Velocette Owner, and I'm sure I am its biggest problem! :-) Fullminator
Apologies if I came across in the wrong tone mate. I understand your frustration, I can only suggest that you pull it apart and meticulously check all the components against the info in Norm's Technicalities. The spring carrier nut should be VERY difficult to get started on the thread, even using a factory-type tool. But I'm sure you don't need more gratuitous advice !!! Hope you can get is sorted soon.
Jools, no offense taken at all! I was trying to be funny as well. I just hope I helped Stuarts7 with the auto advance issue and the pushrod tunnel. Velocette stuff requires us to stick together. Cheers. Fullminator