Secondary cutless bearing?

[Dieselram94]

Just wondering if anyone has seen or installed a cutless bearing in the stern tube just behind the stuffing box? If so how was it done? Off the shelf part? Custom machined part? Or perhaps a bearing on some sort of a mount between the stuffing box and the transmission?

[SamNassar]

I am in the process of installing 3 cylinder Yanmar and I have found that the engine/transmission needs to have a completely steady shaft/coupling. I “fixed” the shaft with intermediate flange bearings,2, , one just forward enough of the Albin stuffing box for its removal, the second bearing mounted to the aft face of the engine box. For me, the key alignment fixture for the shaft was a bushing I made that fits perfectly in the stern tube ID and very close tolerance to the 1” SAE shaft. So one shaft bearing is the cutlass bearing in the keel, next forward is the mentioned bushing, then the flange bearing in a cross bulkhead fabrication glassed in last is a second flange bearing on the engine box. The flange bearings are not a slip fit on the 1” shaft but a hone of some sort will remove the 0.001” or so so they slid easily.
I found that with the shaft so well supported, and the engine mounts adjusted, I can push the shaft from outside the boat and the shaft will be aligned with all 4 bearings and start into the coupling bolted to the transmission. I am confident that a feeler gauge level of accuracy can be achieved.
After all the fabrication is complete I contemplate sliding the flange bearing from the engine box back to the intermediate bulkhead and bolting it there for storage/backup.
Of course after the alignment of the bearings is done, the bushing needs to be removed and the Albin stuffing box installed. My goal for all this is to eliminate any side loading of the stuffing box.
I hope this helps
Sam

[WillieC]

I installed a second bearing in the bronze/brass stern tube just behind the PSS installed by a PO. The PSS didn’t support the shaft at all where the original traditional shaft seal may have provided some support. None of them preclude proper shaft/engine alignment. Having a verified straight shaft counts as well.

Since the shaft was 30mm and the tube was not much bigger I scratched my head trying to come up with a match. Machining a stock cutlass didn’t seem too practical and would have run the bill up. My thought was that there wouldn’t be much brass left anyway.

Anyhoo, I discovered that the all rubber cutlass for certain Benetau sailboats fit the bill. 30 mm bearing surface and OD close enough for the stern tube. I was concerned about it spinning since it wasn’t an interference fit in the tube so I put 3 daubs of epoxy (JB weld I think) and put it all together. I didn't want a permanent installation in case it didn't work at all. A little heat would release it. I propped it up slightly to make it center as close as I could then adjusted the engine mounts for alignment.

Previously I had assumed in my ignorance that 1/4” shaft wobble and the associated syncopated rhythm section from all that misalignment was normal. What an improvement.

Edit: Don't neglect motor mounts. Who knew that 40 YO oil saturated originally vulcanized rubber and steel parts might not be to spec? Boats...such a learning curve.

[Dieselram94]

Thank you for the replies! My A25 is running a Perkins 4.108 with a zf transmission, a brand new 1.25” stainless steel shaft with a brand new cutless bearing (Bind) and a brand new stuffing box and flange. It runs very true, but I’m concerned that the motor will not stay in position without shifting around as I had to elongate several of the mount holes ( stud holes for the motor mounts to fit through) to actually get it to line up. Also at certain rpm’s the motor vibrates a fair amount and that adds to my concern of holding it tightly enough in alignment. Last thing I want to do is have the shaft contact the stern tube and wear into it. So I was wondering if a secondary cutless or a flange bearing would make sense to ensure no contact with the stern tube would be possible.

[Dieselram94]

I am in the process of installing 3 cylinder Yanmar and I have found that the engine/transmission needs to have a completely steady shaft/coupling. I “fixed” the shaft with intermediate flange bearings,2, , one just forward enough of the Albin stuffing box for its removal, the second bearing mounted to the aft face of the engine box. For me, the key alignment fixture for the shaft was a bushing I made that fits perfectly in the stern tube ID and very close tolerance to the 1” SAE shaft. So one shaft bearing is the cutlass bearing in the keel, next forward is the mentioned bushing, then the flange bearing in a cross bulkhead fabrication glassed in last is a second flange bearing on the engine box. The flange bearings are not a slip fit on the 1” shaft but a hone of some sort will remove the 0.001” or so so they slid easily.
I found that with the shaft so well supported, and the engine mounts adjusted, I can push the shaft from outside the boat and the shaft will be aligned with all 4 bearings and start into the coupling bolted to the transmission. I am confident that a feeler gauge level of accuracy can be achieved.
After all the fabrication is complete I contemplate sliding the flange bearing from the engine box back to the intermediate bulkhead and bolting it there for storage/backup.
Of course after the alignment of the bearings is done, the bushing needs to be removed and the Albin stuffing box installed. My goal for all this is to eliminate any side loading of the stuffing box.
I hope this helps
Sam

Any pictures? Very interested to see this set up.

[SamNassar]

The glassed bulkhead is adhered to the hull with chopped strand bondo
I purposely left a small gap between the bulkhead and the hull after I positioned the bearing on the bulkhead with the shaft aligned. With that procedure done, I used the bondo to hold the bulkhead properly. I would not have been able to align the bearing by measuring etc. I used the same method for the engine box bearing alignment.
The bearings are aligned such that I can push the shaft through all the way and into the coupling from outside the boat with no problem
Sam