Hi Everyone
Thanks again for all your good advice...much appreciated.

Think I will look into a collar for the prop shaft...I did cut up an old m3 prop and extended it into a 2 piece (see pic) and that seemed to stop the shaft unwinding. I hadn't realised it needed a buffer to stop this.(should've paid more attention in the science lesson)

I'll post the results after the new collar is fitted

Best wishes
Jon

You could simply use some locktite or plain old PVA glue will stop it from unwinding.

Hi Jon
Whoever fitted the propshaft got it wrong. As Lew says you need a proptube with bearings to carry the propshaft which should be long enough to allow for the prop, locknut and thrust washer at one end and a thrust washer, lock nut and connector at the other end. There should be a small amount of play between the thrust washers and the proptube bearings.
This set up takes all the forces from the prop in either direction and prevents any force on the coupling or motor.
If you don't want to reduce the propshaft length then a lockable collar and thrust washer at the motor end as Nick says will also work. You also need to fully engage the splines in the U/j fitting, moving the motor and realigning if necessary.
dave976

Totally agree with flaxybuck, a locking collar is the way to go, but dont forget the clearence, around 15 to 20 thou.

https://www.ebay.co.uk/itm/325238150916?mkcid=16&mkevt=1&mkrid=711-127632-2357-0

Second though after looking closer at the photos. What is restricting the rearward movement of the shaft into the stuffing box? It is hard to tell in the photos.

When the boat is going forward the force on the prop forces the shaft forward. When in reverse the prop is pulling the shaft aft ward. Sounds like our problem.

It looks like you need a collar (with setscrew) that keeps the shaft from working rearward.

Lew
Florida, USA

Thanks Everyone
All very helpful replies, I will work my way through them.

Am I right in thinking that if the locking nut is up against something solid, it can not physically move and therefore remains in situ .
So, if I infilled the gap between the now end of the outer shaft and locking nut ( cut a length of old prop ) this might work as well.
Best wishes everyone

Jon

Make sure the lock washer has some springy give to it so that it functions right. You might try a wider nut so more surface area is against the lock washer, maybe add a second nut (jamb).
Lew
Florida, USA 🇺🇸

Hi Jon
If I were to venture a guess, it would be that the spline fit is a little too loose.
When in reverse the prop thrust is trying to pull the spline connection apart. If there is the slightest amount of play in the spline connection it will "wiggle" itself apart.
The easy solution is to use a thread loc adhesive on the spline joint.
If there is too much play in the connection it will need to be drilled and tapped for a gib screw.
Barry

It looks to me as though you have no locking collar on the prop shaft. This should be placed on the shaft up against the end of the prop tube leaving say 0.5mm clearance.
Good luck😉

Hi Terry
Thank you for your thoughts, I'll have invest in a dog drive ...its a conversion from glow to electric, the outer prop shaft was set when I purchased the already started kit, which I don't really want to rip out .
So, if I infill the inner shaft up to the outer shaft ending, it might work!!
Appreciate your time and help
Regards Jon