From: Charles Ping
Date: 03 Mar 2002
Time: 18:38:48
Remote Name: 213.122.8.112
As far as I recall there were 3 flywheel types - 1 1/8" crank ones that had a smaller taper for the small crank, early 1 5/16" ones that were identical except for the bigger hole for a larger diameter taper and ones designed for rear facing starter motors that has the ring gear integral with the flywheel. I've been told that a good machinist with a big lathe can convert the first type to the second type but it has to be accurate (and cutting the keyway would be fun). The third type is not usable in your "vintage" engine. I think that your 5/16"UNF holes are red herring and a modern conversion. Longbridge wouldn't have used UNF! I'm pretty certain that they're all 1/4BSF. I'd never weld a cast iron flywheel. Cast iron doesn't weld well and you don't want a flywheel coming apart at 3000 rpm! The bits of metal stop at nothing be it cast aluminium, steel floor or drivers ankle. The zero option is to make a new one out of a thick bit of steel - the racing chaps do this with aluminium.
Charles