The pulley on the right looks to me marginal if the hole is to be bored to the size of the left one. Measure the diameter of the bottom of the smallest pully wheel to see if it is bigger than the proposed bore. I would not be happy with less than 2mm, 0.080" wall thickness after boring.

If you're just expanding it 6mm, you might as well just bore it out, just make sure to set it up running true.

Nowt wrong, I would think, with filling the ‘space’ and machining to match the profile of the pulley. That might mean machining away and fitting a new piece (likely by brazing) or filling the gap with braze and machining.

The latter might slightly alter the balance, but I doubt it would be noticeable.

You could kill two birds with one stone perhaps?

Measure the overall length, and the groove spacing of the original pulley, and the OD of the shaft on the replacement motor..

For the moment, we will assume that the shaft is exactly 0.750" diameter

Bore out the original pulley to 1.000 or 0.875" (Whichever you choose ) ensuring that the bore is square to the faces of the pulley.

Measure the bore accurately

Turn away the damaged groove

Turn up a new pulley with just one groove, the same as the largest diameter groove with the piece missing, but with a "nose" to make it so that the O A length is the same as the original pulley, and that the groove spacing will be the same as the original..

Turn the OD of the "nose" to 1.001" or 0.876" (i e a thou bigger than the new bore in the original pulley, and bored to 0.752". )   This should give a close but sliding fit on the 0.750" shaft of the new motor.

It is easier to turn an OD to match a hole than to bore a hole to match an OD.

Put the new long nose single groove pulley into the freezer and leave for 24 hours..

After 24 hours, heat the oven to Gas Mark 6,. You are looking for 5 – 600 degrees

"Cook" the remains of the original pulley for at least an hour, to ensure that it is REALLY hot.

Place it in the oven, small groove down, preferably

Have a copper/hide mallet to hand, or a hammer (At least 2 lb ) and a piece of wood; in case you need it.

You will also need another piece of wood or ply on which to put the original when it is removed from the oven. , and placed on the floor.

Remove the new single groove from the freezer and wrap in a towel to keep it cold, while you remove the original from the oven.

Place the original on the ply, small diameter down and quickly unwrap the new long nose groove, and drop it into the remains of the original pulley.

Hopefully it will drop easily into place. It it does not, assist it with the copper/hide or the the 2 lb hammer with the piece of wood between the hammer and the pulley.

You need to be quick about this so that the original does not cool, or the new piece warm up too much.

When everything has cooled to the point where it can be safely handled, admire your modified pulley and fit it to the motor.

Hopefully, once the motor and pulley are installed and aligned., the D W will be ready to function with a long belt life and the full designed range of speeds.

(Straight edge across the face of the motor pulley and of the pulley that it is driving. )

The "Heat and Freeze" technique works, or did for me when fitting a 1" diameter bar into a reamed 1" hole in a cast iron base..The 0.001" interference has left the bar securely in the cast iron base.

HTH

Howard

Edited By Howard Lewis on 29/10/2021 06:34:39

Just thought of an alternative and maybe easier way!

Measure length and groove spacing of the damaged pulley

Bore / ream the damaged pulley to 3/4"

Turn a single groove pulley to replace the damaged area, and bore out to say 1.5" diameter.

Measure the bore accurately..

Reverse the damaged pulley, and machine away the broken groove to leave a central spigot, 0.001" larger say than the bore of the new single sheave.

Heat and freeze as before , and hopefully you will be back in business!

Howard.

What HP is your newly acquired motor?

Fatter shafts normally mean higher HP or a much older motor.

Too much power can temp over stressing little mills that aren't light industrial built.