Manual advance system

[Swarfcut]

I'm sure Joe has found "The Cams".... they are the small humps on the inside of the cam ring and can be felt on the unmounted ring. The small rise is magnified by the leverage ratio of the moving points arm so a small movement is turned into the points gap.  Moving the cam ring against the direction of the rotation of the armature and points plate moves the hump and so advances the the position at which the heel rides up the hump.... and opens the points to give the spark...... like MrG says.

Swarfy.

[AlaskaJoe]

Cheers to you both for this clear explanation. I woke up at 2am thinking about this last night and couldn’t wrap my head around it. I’ll sleep better tonight, or more accurately I’ll ruminate on something else. 😎

The last piece of the puzzle now will be setting my timing. I’ve got a tdc tool and am very confident in getting to the point before tdc on compression, but I am less confident in how to move the points at that stage without moving the entire engine and thus losing my point before tdc. Do I need to unscrew and disengage the gear in this photo? That seems to make sense since it’s what rotates the mag.

[Swarfcut]

Ok Joe, theory of setting the timing is easy, doing it simple, getting it spot on first time...... Slim chance.

Here's a quick way to get a rough check of the timing.
First step is to set the magneto at full advance, (slack cable) then bring the crank up on compression and adjust the points gap as you would on a normal contact breaker system. 

 Now reverse the crank and once more turn forwards to the firing point... This changes for model year, different compression ratios and camshafts mean there are various recommended piston heights, and where available crank angles BTDC. All found in published data and on the forum.
 You should now find the points are just opening and that will be good enough to try and get it to start.

If it's miles out then yes the timing gear has to come off the magneto,  using an extractor to avoid damage. Magneto is once again set, turn the points plate clockwise until at full advance the points are about to break. Crank again brought forward to firing point...... And the timing gear pushed onto the plain taper of the magneto shaft.. The hard part is making sure nothing moves as the bolt is tightened.  Plenty more to explore already on the forum of the finer points of the operation.

 Swarfy

Additional. Recommended ignition settings apply to fuels in use years ago. Modern fuels may require slightly different settings to avoid pinging. That drive nut for tacho is a normal lefty loosely thread, original gear is relatively soft fibre.. Treat with care.

[AlaskaJoe]

Cheers Swarfy, I’ll give this a go tomorrow and report back!

[Joolstacho]

Joe, I'll have a go at this. The rotating armature of the magneto is 'locked' with the engine rotation by those gears in the timing cover.
The other, points end, the armature rotates with the engine correspondingly. The camring is independent of the armature and is ground with a thicker section and thinner section, and so if the camring is rotated, (by the advance cable), the 'heel' of the points which is 'riding' on the camring, will open / close the points earlier or later. Advance / retard the spark in relation to the rotated position of the piston.

[groily]

original gear is relatively soft fibre.. Treat with care.

Additional additional: If there's the slightest doubt about the state of the pinion - can't see all the teeth clearly in the pic - Replace!
Shedding teeth out on the road requires dentistry you can't easily do sitting in a ditch!

[chaterlea25]

Hi Joe and All,
Check the timing às found before trying anything else.
Be very careful when installing the points rotor make sure it is engaged in its keyway in the armature before tightening the centre bolt..

A trick that I have found very useful  when setting the timing is to
1 make sure the tapers are clean and degreased thoroughly.
2 put a little chalk dust on the magneto shaft taper, then when engine and magneto are in the correct position use a socket or such to give the pinion a light "tap" so it bites  onto the magneto shaft taper.

John

[AlaskaJoe]

Progress report: she’s a runner!

Unstuck the cam ring, installed new points, adjusted valves, checked timing (was within spec) and it started in the second kick! I removed the sump plate cleaned it all out and installed a new SRM stainless filter for good measure and the oil return is flowing like a champ. Now I just need to wire it up for lights, tune the carb, get new tires, install new fork seals, and I can ride it! Time to go read up on Amal Monobloc carbs…

[Swarfcut]

 Nah.... That will be just fine on the Alaska Highway. Has all the character of a Yukon Truck*

Swarfy
 *A description of vehicles which have somehow slipped through the net of authority and where health, safety and compliance with anything is marginal.

 Swarfy

[Worty]

original gear is relatively soft fibre.. Treat with care.

Additional additional: If there's the slightest doubt about the state of the pinion - can't see all the teeth clearly in the pic - Replace!
Shedding teeth out on the road requires dentistry you can't easily do sitting in a ditch!

I'll second that!!  I had two fibre gears strip and one ATD collapse when the rivets failed.  Lots of debris in the engine and broke a tooth off one of the timing gears (read all about it in Worty's A10 Engine Rebuild thread).  When the well-esteemed Bergs rebuilt my knackered motor, I bought a brand new ATD unit off him for peace of mind.

As with any critical piece of kit, always replace new when you have the chance.  Don't do what I did and trust very old bits and pieces in critical applications.

[Black Sheep]

Replacing the fibre wheel isn't too difficult if you follow Andrew's illustrated guide. My bikes run on alloy ones. There are arguments for both. My Velo runs on a steel pinion since it stripped the fibre wheel a long way from home.

[Worty]

Replacing the fibre wheel isn't too difficult if you follow Andrew's illustrated guide. My bikes run on alloy ones. There are arguments for both. My Velo runs on a steel pinion since it stripped the fibre wheel a long way from home.

I've come to like the idea of alloy wheels, after my ATD woes!!  As I've said, don't rely on knackered mechanisms and fibre wheels that are decades old.  I know new ATDs are expensive, but I'd rate them alongside SRM pumps, etc, a critical component.  Having said that, I still have one of the original mazac oil pumps which is still going strong.

[CheeserBeezer]

Replacing the fibre wheel isn't too difficult if you follow Andrew's illustrated guide. My bikes run on alloy ones. There are arguments for both. My Velo runs on a steel pinion since it stripped the fibre wheel a long way from home.

Personally, I wouldn't use an alloy wheel. The fibre wheel is described as a 'sacrificial component' for a reason. If the armature breaks (and they can) and the mag locks up the back of the crankcase might break off. Back in the day when people took their BSA to the local dealer for a service, the condition of the fibre gear would have been inspected. The reason they strip is because they've been used beyond their service life and the teeth have become sharp and weak.
However, the teeth on a Velocette fibre gear are so fine that it is hard to believe they last more than a couple of thousand miles from new! I, too, would use a steel wheel.

[Joolstacho]

Been running my Velo (which ain't a plodder) for many years with those fine teeth, and rarely heard of failures there. I wonder if the fact that the Velo teeth are finer, effectively 'spreading the load' thereby less loading on individual teeth, therefore fewer failures? (I'd of course bow to your extensive engineering knowledge Andrew).

[Triton Thrasher]

Been running my Velo (which ain't a plodder) for many years with those fine teeth, and rarely heard of failures there. I wonder if the fact that the Velo teeth are finer, effectively 'spreading the load' thereby less loading on individual teeth, therefore fewer failures? (I'd of course bow to your extensive engineering knowledge Andrew).

I’ve met Velocette owners who shout and swear if you remind them of the “bloody Tufnol gear!”