Like most of us I guess, I have a few second-hand engines with motors that don't turn. Separating the motor from the mechanism is quite fiddly so those that are not being used by the children sit in a box waiting for service.
Yesterday I had a look at such an engine from someone else's collection:
I guess that the motor had become jammed by hard grease and dirt and once free it kept going.
I tried this with another four old stuck engines. Three of them responded.
Hope this is of some use.
(now to change some traction tires and return the engines to the kids.)
