Author Topic: Advance retard unit fit on magneto  (Read 160 times)

Offline Rudgeman

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Advance retard unit fit on magneto
« on: 23.08. 2019 16:54 »
Hi again,
               First run of the SR last weekend - 50 miles two up around the Worcestershire countryside at the Rudge rally. It proved quite a challenge keeping up with 90 year old Rudges on the back roads and two of the blokes riding them were 90 years old !

Two problems presented themselves, the first of which I've made a start on. The atd was stuck on full advance. It pinked like hell at low revs and was fine at high revs.

I've started working on it. One of the pins is wobbly, the springs look stretched, and the rivet heads are too proud and the weights are fouling on them. Nothing I can't fix.

However, I have noticed that when tightened up on the shaft there is 2mm of axial play on the baseplate and gear. Pushed towards the mag the front of the fibre gear is 1.5mm pround of the cam gear. I can then pull it out to make it 3.5mm proud. This doesn't seem right to me.

So - is this common, or should I be fixing it ? The way I would go about this would be to put a 1.9mm spacer between the baseplate and the fibre gear. I might make a new ring for the other side of the gear to better align it with the cam gear.

Any insights you could offer would be greatly appreciated.

R

Offline Swarfcut

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Re: Advance retard unit fit on magneto
« Reply #1 on: 23.08. 2019 18:02 »
Axial movement of the fibre gear relative to the taper centred  carrier is controlled by the position of the retaining collar, pressed onto the  carrier. Usually the two parts are flush or the collar very slightly proud.The rivets under the  weights are flush, hence your problem. Looks as if someone has had it apart and not assembled it with the care and attention to detail it needs, and left it a bit too loose in a futile attempt to clear the rivet heads. You may find more evidence of misguided modifications when it is apart. Have a look on the excellent Priory Magnetos Website, there is a section on DIY  refurbishment, 5 to 10 thou endfloat  between the gear and shaft is recommended.

 Swarfy.

Offline Rudgeman

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Re: Advance retard unit fit on magneto
« Reply #2 on: 24.08. 2019 18:44 »
Thanks for that swarfy, good advice. I hadn't thought of Priory magnetos, and I have bought bits from him before.

I'll order a rebuild kit from him on Tuesday and take it from there.

Brill forum, thIs,

R