Categories: Technical

by chris


Re-building an engine, even with an experienced engineer to hand, can be a challenge, particularly when it comes to dealing with rare and unfamiliar parts.

In this case there’s a stub shaft which attaches to the flywheel which marries with a bearing and gear to the J-Type Watermota Gearbox. This short shaft is a two-part assembly. For lack of a better description I’ll refer to the ‘stub’ as the short shaft mounted to the flywheel with four bolts and the ‘bearing’ as the case hardened outer part which meshes with the gearbox.

These two parts should push into each other with probably very little movement, locked by a woodruff key to prevent rotation. I can only imagine this assembly is in two parts to allow different engines and gear ratios to be catered for and perhaps shorten the distance required to pull forward the engine or pull back the gearbox to afford separation.

In my instance, the keyway in the stub was machined larger than the keyway in the bearing with a smaller woodruff key being used. The result was the woodruff key canting between the keyways and slowly destroying both keyways. This also lead to the stub shaft being worn unevenly due to the wedging action of the woodruff key.

Having spoken to Sheridan Marine, they had never come across this issue before although they were aware that various stub/bearing combinations existed. I did ask if they had any replacement units but they only had a box of bits which might get me through the day. The advice was to have the existing assembly machined.

So at the moment, the stub assembly resides with a very good local machine shop and Ford specialist, Scholar Engineering, to cut a new keyway in the case-hardened bearing and weld/re-cut the correctly sized keyway in the stub shaft. After I commissioned Scholar to re-machine the shaft, a fine fellow by the name of Trevor Orman managed to dig up the assembly I needed but as the machinists had already started the work, I was committed. On an encouraging note, Scholar did say the re-machined piece would be like new so will hopefully last longer than me.