RH BPR 4HP Flywheel Timing Marks

Can anyone please help with the formular for establishing firing position BTDC on a 4HP RH BPR.
Thankyou
Brian

Hi Brian, Take out your sparkplug to make rolling over your engine easier. Watch the push rod working your exhaust valve, when the valve is closed your piston will be travelling back down the bore....induction....when the piston is travelling back up the bore it is on the ignition stroke. Watch the big end to find TDC with its position and also check where the gib key is in relation to the piston. The gib key MAY be at 12 o clock or 6 o clock at TDC.
Measure the outside size of the flywheel with a tape and divide the figure by 18 to give you 2o degrees, measure this figure back from TDC and that is near enough your firing point 20 degrees BTDC.

You will probably find timing marks if you look on the flywheel crown........about 6" or so BTDC. This is rough but will give you a start point to fine tune from

Thankyou for your reply, I will give that a try tomorrow as it is realy lumpy
Regards
Brian