by Warkton Tornado No.1 » Wed Jan 13, 2021 11:11 am
As far as I understand the various SIII & GP motors that all use similar crankcases/magneto housings of a 'generic' geometry, the appropriate flywheel will always be placed axially in the correct position to function within the flywheel cowling.
Having swapped the flywheel centres for a good flywheel from one type taper to another, apart from nominal differences, I have never encountered any variation as much as the 25 mm mentioned here.
That said, if you know that the consequences of using the new crankshaft will move the flywheel outboard a significant amount, there is something wrong. That scenario is not difficult to prove prior to any assembly of the motor. Just a case of shoving the flywheels onto their mating crankshafts & measuring from fan/flywheel to crankshaft web should prove it. By the sounds of it you have already laid the crankshafts side by side to establish where the difference lie, with all indications being the flywheel side.
If it were my two hundred quid, I'd reckon that'd entitle me to a lot of after sales care & attention, so if you check as suggested & prove your concern, get on to the seller.
Of course, it would be useful for you to let us know the outcome, please.