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Magneto shaft at standstill
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13-09-2019, 05:31 PM
1926 magneto engine Chummy. Started normally this morning and after one minute stopped. Engine turns as normal but no movement on the magneto. Are the camshafts driven by a timing chain or timing belt? How serious does this look - is it a complete engine tear down or can this be repaired with relative ease ? I would welcome a share your considered knowledge on this problem. Kind regards, William Cuddy
13-09-2019, 05:43 PM
Is the dynamo still turning?
It's gear driven and its either a key that has sheared or a gear has broken. The camshaft gear isn't very robust in my experience Charles
13-09-2019, 05:56 PM
Charles
I have a rebuilt dynamo in a box not yet fitted to the car. The aperture is covered by a plate. Just wondering about the gear and key; is the gear made of metal or is it fiber ? There was no adverse noise or clunk when I tried to restart. If it is a key issue, then the job is not so serious. Just wondering also, how on earth would a steel key sheer. Maybe it is old age ! Thank you for your contribution. Kind regards, William Cuddy
13-09-2019, 06:24 PM
All gears and keys are steel/iron.
You need to check if the cam is turning by one method or another. Charles
13-09-2019, 07:00 PM
The mag is gear driven from the crankshaft with an intermediate gear between the two, and the camshaft is also gear driven directly on the other side of the crankshaft. In my experience the least reliable gear is the one on the camshaft. The keys in the system are on the camshaft, the crankshaft and the drive side of the magneto coupling. The easiest way to check whether the camshaft is turning is to check through a plughole whether any compression develops as you turn the crankhandle.
Robert Leigh
13-09-2019, 07:20 PM
When mine failed the cam gear split near the boss which also broke the crank gear into three parts.
The crank span happily but nothing else moved!
13-09-2019, 09:27 PM
The mag shaft is driven from the crank via an intermediate gear, the mag shaft would turn even if the cam gear is broken.
Sounds like the key in the crank gear, or the key in the mag shaft has sheared. You will need to strip off the timing cover to investigate
13-09-2019, 09:39 PM
HI
There seems to be a bit of confusion here,If the Mag is not turning the problem is between the crank gear and the mag, the camshaft has nothing to do with it. remove the mag and check if the drive is ok by turning by hand this will eliminate or not the mag itself Cheers Colin NZ
13-09-2019, 09:47 PM
Absolutely no confusion from my side.
My mag stopped turning because the cam gear (the weakest gear) broke and as a consequence split the crank gear, giving no drive to the idler gear. Hence my line of thinking. 
13-09-2019, 10:33 PM
one way or another, something not very good has gone on in the timing gear area. Theres only one way of finding out.
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