How is it bad advice???
Greenfield mowers are rudimentary at best, granted theres a fair difference in the engineering in a 2000 model than a 70's job. But the design has changed little. Almost all parts are fabricated and the whole basis of the design is about not having to machine a gearset. Even the steering gears on the old ones are cast alloy.
Why go to the trouble and expense of having to remove and strip axles and shafts from the machine to the pont where they can be mounted up in a lathe to be machined only to find that the parts were made to a very opened ended specification to begin with?
When if there is room you could get two new sprockets that make the same ratio, if needed trim the teeth or some diameter off the existing sprocket for chain clearance with a gas axe or plasma and with some careful measuring drill and bolt the new srpockets to the old one.
If you used a motorbike based sprocket you would have something thats hardened, not what at best is probably a mild steel machinery sprocket. You could also fit an O ring type chain, in the end you would have a setup that would thrice outlast the original setup. And when it did wear out is easily replaceable even if you welded it.
Obvioulsy where you to weld it you would do so at your own risk, mixing steel grades can be bad. But it would not make for difficult replacement.
Hence the statement, its not a race car.
