Automatic Advance Unit (AAU) overhaul

Previously peter_austin wrote:

Hello Everyone,

I have recently come across a problem that I have never encontered before and would like to sek your advice. I have recently finished rebuilding a 1966 Atlas fitted with the original magneto and while it fired up and ran well, once the engine was stopped it became very reluctant to restart. I eventually removed the timing cover to check the mag timing again and found that the AAU was stuck in the fully advanced position. On removing the said item from the taper the bob weights closed easily and after fitting the unit back on the mag taper where the same problem reoccured each time I decided to replace the springs. The new springs are certainly much stronger than my original springs and snap the bob weights back when operating the unit off the taper, the problem although slightly less, is still apparent when I tighten the bolt to fasten the AAU onto the mag taper. What am I missing? is there otherparts of the AAU that can wear to cuse the problem? any advice would be greatfully received.

Peter Austin

Check that your mag chain is not to tight?

Previously peter_austin wrote:

Hello Everyone,

I have recently come across a problem that I have never encontered before and would like to sek your advice. I have recently finished rebuilding a 1966 Atlas fitted with the original magneto and while it fired up and ran well, once the engine was stopped it became very reluctant to restart. I eventually removed the timing cover to check the mag timing again and found that the AAU was stuck in the fully advanced position. On removing the said item from the taper the bob weights closed easily and after fitting the unit back on the mag taper where the same problem reoccured each time I decided to replace the springs. The new springs are certainly much stronger than my original springs and snap the bob weights back when operating the unit off the taper, the problem although slightly less, is still apparent when I tighten the bolt to fasten the AAU onto the mag taper. What am I missing? is there otherparts of the AAU that can wear to cuse the problem? any advice would be greatfully received.

Peter Austin

hello peter, I had the same prob with my dommie following a rebuild and it took me a bit of time and thought to realise: the AAU is not malfunctioning, it has stopped in the fully advanced position and in reality the bob weight springs are trying to turn the whole engine to catch up with the magneto which of course they are incapable of. When you remove the timing cover dont take off the aau but just rotate the engine forward slightly and you will find that the mag doesn't start to turn until the bob weights are back in the retarded position, ready for the next start. the above assumes the chain tension / alignment is good, if you think about it long enough you will see that it was always thus; your starting prob's are elsewhere I tried Nippon denso spark plugs W22ES-ZU immediate improvement and continued so, even my old '48 ES2 loves these plugs,starts on a tanner as they used to say in the Black country! good luck, Jim Hill

Hello!

Jumping on this thread, since I am experiencing similar issue with the AAU. I'm in the process of setting timing ignition and I am stuck with the aau. When removed from the bike, it has some play, but does not spring back with force. And when placed back on the magneto shaft, it does move even less freely. I have never seen a "perfect setup" so I don't know how much of free movement it should have.

I cleaned the whole aau unit when it was off the bike, and nothing seems to be worn (apart from the locking plate which was a bit bent, as well as the main fastening bolt that had lost some thread).

What can the problem be? Mag alignment (unsure how that can be adjusted)? Tightness of chain? Fastening bolt too tight (if that can happen)? Do I need a new AAU?

I have uploaded a couple of videos of the aau, hope you can see them:

https://we.tl/t-tAE59TxU2H

Thanks for the help.