CapeTown73
Well-Known Member
- Joined
- Mar 14, 2007
- Messages
- 180
I posted the information below on a Facebook page this morning, where a few OB boaters were talking about the well-known concerns of the poor durability and lifespan of the standard prop-shaft bushes in our 7.5 lowers. In response, I feel obliged to share my solution for this problem.
About three years ago I asked a good friend here to machine some longer phosphor-bronze bushes (of my own design and which fully replaces the steel K&B screw-in bush assembly), and to make up longer steel prop-shafts. (See my design sheet below from which my friend machined the new assemblies and a further photo lower down of the new assembly parts as I received them.)
The new bush unit (as I receive it) is not yet ready for installation so I then proceed to machine a recess into the front of the new bush so that once the new bush is fully screwed-into the leg, the front lip (with square recess) of the new prop-shaft is in the same position as the original K&B prop-shaft, thereby ensuring that the standard length flex-shaft fits perfectly. I then machine a taper on the rear end of the new bush so that it ends up to match the size of the prop-drive-dog. The new unit is then ready for installation into the lower, and importantly, it now has an extended length of bearing-surface of around 25mm (1 inch). This is almost twice the length of the standard K&B unit and phosphor-bronze is tons more durable than the original soft Lead-Teflon bushes in the K&B assembly!
However, there is one further very important requirement to ensure the long life of the new bush, and that is to have good lubrication!!! So I made up a pressurised oiler system which ensures continuous oil (castor-oil) delivery to the full length of the new bearing surface. See the images below which show how this sealed/pressurised setup works. The main requirement is for the oil to remain under pressure all the way down the lower, past the flex-shaft, and along the prop-shaft with the only ‘escape’ being where the prop-shaft protrudes out of the rear of the bush against the prop-drive-dog.
The end result in my boats has been excellent!!!
I installed two of these new units into the lowers on my son’s and my boat over two years ago and they have ‘lived’ through at least 20 to 25 race days, with each race day consisting of 4 heats of 2 minutes milling + 5 minutes of racing AND AFTER TWO YEARS, THERE IS ABSOLUTELY NO NOTICEABLE WEAR ON EITHER OF THE SETUPS!!!! And I run 7.5 Novarossi’s in both boats so we’re pushing respectable power and revs through both prop-shaft assemblies!!!
So in my opinion, there is a good solution, but it does require a bit of additional work on your boat to make it happen!
I hope this info is of value to you. (THERE ARE A TOTAL OF 5 RELATED IMAGES/PHOTOS BELOW!)
Kind regards,
About three years ago I asked a good friend here to machine some longer phosphor-bronze bushes (of my own design and which fully replaces the steel K&B screw-in bush assembly), and to make up longer steel prop-shafts. (See my design sheet below from which my friend machined the new assemblies and a further photo lower down of the new assembly parts as I received them.)
The new bush unit (as I receive it) is not yet ready for installation so I then proceed to machine a recess into the front of the new bush so that once the new bush is fully screwed-into the leg, the front lip (with square recess) of the new prop-shaft is in the same position as the original K&B prop-shaft, thereby ensuring that the standard length flex-shaft fits perfectly. I then machine a taper on the rear end of the new bush so that it ends up to match the size of the prop-drive-dog. The new unit is then ready for installation into the lower, and importantly, it now has an extended length of bearing-surface of around 25mm (1 inch). This is almost twice the length of the standard K&B unit and phosphor-bronze is tons more durable than the original soft Lead-Teflon bushes in the K&B assembly!
However, there is one further very important requirement to ensure the long life of the new bush, and that is to have good lubrication!!! So I made up a pressurised oiler system which ensures continuous oil (castor-oil) delivery to the full length of the new bearing surface. See the images below which show how this sealed/pressurised setup works. The main requirement is for the oil to remain under pressure all the way down the lower, past the flex-shaft, and along the prop-shaft with the only ‘escape’ being where the prop-shaft protrudes out of the rear of the bush against the prop-drive-dog.
The end result in my boats has been excellent!!!
I installed two of these new units into the lowers on my son’s and my boat over two years ago and they have ‘lived’ through at least 20 to 25 race days, with each race day consisting of 4 heats of 2 minutes milling + 5 minutes of racing AND AFTER TWO YEARS, THERE IS ABSOLUTELY NO NOTICEABLE WEAR ON EITHER OF THE SETUPS!!!! And I run 7.5 Novarossi’s in both boats so we’re pushing respectable power and revs through both prop-shaft assemblies!!!
So in my opinion, there is a good solution, but it does require a bit of additional work on your boat to make it happen!
I hope this info is of value to you. (THERE ARE A TOTAL OF 5 RELATED IMAGES/PHOTOS BELOW!)
Kind regards,
