Reply To: Caille Neptune gear case rebuilt

[PM T2]

The original propshaft size is 0.625″ (5/8ths) and I recommend that you make a new one to that dimension and bush the supporting parts in the lower unit accordingly.

I’ve done enough rowboat motor lower units to say that when done correctly, you can rebush the original parts and not have to worry about weakening the original castings.

The exception may be the lash adjustment screw in the nose, depending on how worn it is and if its been carved out already. I have had them so worn out that the threaded part had holes in it from the front end of the propshaft chewing through it. In those cases, I opt to machine a whole new adjuster screw and insert a bushing right from the get go. Alternative is that you can machine a new adjuster screw out of solid 660 bearing bronze and not bother with a bushing. And don’t forget about the little round piece of lignum vitae that is supposed to be up in the front of the adjuster screw and acts as a thrust bearing.

My procedure for repairing the rear lower unit cover is as follows;

To bore out the rear bearing carrier (aka rear cover), use the chuck to grab it around the diameter that fits inside your gear housing and indicate to get it as centred as possible. There isn’t a lot of shoulder there to hold onto, but its enough because you are going to take your time and only take light cuts when you bore it out.This gives you the best chance to bore it out so that the hole you carve is concentric with the locator ring on that rear cover. They use 5/8ths diameter shafts so bore the hole out to 0.750″, then machine a bushing that allows for a 0.001″ press fit into the rear cover. You want about 0.002″ clearance between the new bushing and the new propshaft, but no more than that.

Make the propshaft to original specs, and rework the other parts to make them fit it. I recommend trying to avoid making a stepped driveshaft to accommodate other worn or oversize bushings if at all possible.

Disclaimer – Since its not me doing the work, I won’t guarantee your results, and accept no liability for any wayward results.

Hope this helps.

Best,
PM T2

He's livin' in his own private Idaho..... I hope to go out quietly in my sleep, like my grand-dad did..... and not screaming, like the passengers in his car...