Saving Old Seagulls

I think we're missing the point here, main bearings do not spin when they're new, so spinning must be caused by worn bearings, running dry & grabbing the crankshaft, there is enough energy stored in the flywheel at 4000 revs, & assisted by a running engine to spin 1 or 2 bearings.

How did you measure the ID of the main bearings Art as 2 thou doesn't sound excessive, are you confident in your measurements?
If your using a T bar take 3 readings 120 degrees apart to check for ovality.

There is no point putting tired bearings back in an outboard you plan to use!

Another way a bearing could be spun in the crank case, is by running the motor on 50-1 fuel. Iwas given a century Seagull that was run on 50-1 fuel, luckily it didnt sieze but he stopped the motor when it started making squeaking noises. Didnt damage the crank, but badly wore the bushes.

Charles, I will remeasure the bushes. I did it with an internal mike , verifying across its pins with outside mike. I id not look for ovality. That is quite possible, as the oil groove in the bottom bush is worn away in places.