[phutton]

I would certainly advise using a timing disc, and the method of timing described below requires it. The method is as follows:

1. Attach the timing disc and set the piston at approximately TDC on the compression stroke. (You should be able to rotate the pushrods) and set a pointer at 0 degrees on the disc.
2. Rotate the crank back about 35 then forward to about 30 dgrees. Place a probe into the plug hole (make sure it has a head that doesn't allow it to fall into the cyclinder!) and make a mark on it to record the position. Without moving the crank, mark the postion of the pointer on the disc.
3. Rotate the crank forward until is is about 40 degrees after TDC then rotate it back until the mark on the probe is in the same postion as in (2). Mark the pointer postion on the disc.
4. Rotate the crank back until just before TDC then rotate forward until you are exactly halfway between the two marks on the timing disc. You should now be at exactly TDC.
5. Re-set the pointer to 0 on the disc. Rotate the crank back to the required advance on the timing disc and set the magneto. Timing should be done with the magneto at full advance.

It sounds a bit long-winded but it is the most accurate method, and cancels out the piston top shape.

[paul garratt]

hi there i will shortly be retimming  my sunbeam model 9 series 2, can anyone tell me is the piston flat on the top or curved on the top?. i have noticd that the plug sits in the cylinder head on an angle,so if the piston is curved how do i determin top dead centre?. would a timming disc help?. any bodies help would be appreciated in this matter thanks..