I have been putting in a few miles on a recently recommissioned 1930 Model 18. This is actually a '31 model, with the magdyno behind the cylinder. The bike is running well but in use the magneto drifts forward resulting in a slack & rattly magneto drive chain. I have tightened the single fixing bolt which clamps the mag platform between the engine plates but it still drifts after a few miles. I think the bolt remains tight but the clamping action is not effective. Has anyone else experienced this, and found a way to stop the mag moving?
Where is the wear ?
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Sounds logical
Thanks Richard. The mag has to come off again anyway so I will look more closely at the platform and inside faces of the engine plates. A hardwood wedge might allow me to put off that job for a while though. A higher priority task is removing the forks to check the condition of the headstock bearings.
Cheers, Ian
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The other thing..
.. that happens is that the big countersunk screws under the platform (which can't be accessed without getting the mag off) come loose. I used the chunk of wood trick on my 16H back in the 1970s but I thought I'd invented the trick!
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There must be wear either in the mag platform or the engine plates that will need to be built up in order to cure the problem. If they're run loose then they soon deteriorate.
If you don't want to miss the summer riding season then a hardwood wedge pushed down between platform and crankcase was apparently the War Office solution.
In normal use, it shouldn't move.