flywheel construction

I am building 2 flywheels for Brian Rupnows Thumper Rockerblock i/c engine.I have made the hubs and am starting on the 6" rims which are joined to the hubs with veins at an angle to make fans to cool the cylinder.These fan blades are welded in both the hubs and the rims.The rims finish at 3/4" and I ask for advice on how much to leave on the rims in case of distortion after being welded.

I would have thought 1mm on each surface more than enough as the "blades" are not that thick so you will have to go quite lightly with the welding. Don't know how far you are with the hubs but I would leave the bore undersize and then once the whole flywheel is complete turn OD, one side and bore all at one setting then flip over to skim the other side that way everything should run true. If your hubs are already bored then you may want to allow a bit more on the rim but that will depend on how you jig the flywheel for welding.

Thanks Jason,you have to bore the hub to size as there is a jig to make with a 45 deg, slope to fit a pin of 1/2" so that the slots for the blades can be cut in the hub.I will do as you suggest .The jig for welding will be next after the rims.Thanks again.

Frank

You can still do that, drill it say 3/8" or 10mm for holding on the jig and then once all fabricated it can be opened up to 1/2" at the same setting as finish turning the rim. I'd also suggest boring the 1/2" to fit your crank shaft material rather than reaming.