Excessive Shaft Movement - Part 2

[sailingjupiter]

Thanks to everyone who replied to my last post on this subject.

I have launched the boat and the new PSS seal is doing its job of keeping water out very well. My problem is as on my previous post, now the stuffing box has been removed the prop shaft is moving around too much. It is banging into the stern tube both at tickover and in gear.

It's making a noise but thats all. I really need to find a way of holding the shaft tight around the inboard end of this area. My own idea for the best way is to fit a cutlass bearing in the inboard end of the stern tube as I think it will push down out of the way of the PSS. This will then support the prop shaft and stop the knocking. Of course I would still neet to work out the best way to secure it from sliding up or down the stern tube. Any ideas on how to do this? I have checked bearing sizes and I think there is one that will fit down the tube and also fit the prop shaft. Its either that or look at something bespoke maybe out of stainless or possibly some kind of nylon type material that would be upto the job.

This is my thought. Can anbody say that this sounds OK or is there a better way?

I realize that the boat will have to come out of the water to do any work. Luckily I have a trailer for my boat and some willing friends at the sailing club to help me...

 

[Tranona]

This is a good idea. Did not suggest it earlier for two reasons that you will need to check. First is that the internal diameter of the tube has to be exactly right for the outside of the cutless, although you could make a sleeve if it is too large. I assume the tube is GRP. You can hold the bearing in place in the normal way with a grubscrew. You will obviously need to drill and tap the tube (and sleeve if needed), and probably a good idea to use two screws on opposite sides. There is no need to use the whole length of the bearing if the tube is not long enough.

However, the potential problem I can see is getting the new bearing exactly in line with the P bracket. Your tube may not be concentric with shaft and parallel. Very difficult to check other than measuring the clearance around the shaft as it goes into the tube, but you will only find out for sure when you fit the bearing. If the shaft turns freely then you can adjust the engine to suit in the normal way. You can't allow the movement to continue as it will cause wear on the cutless in the P bracket, and if you dont get it exactly in line, this may also cause wear.

I have a similar setup on my boat with a 1GM, but my stern tube is a conventional bronze one with an outboard cutless, and originally a white metal bearing and conventional stuffing box on the inboard end. I initially left the inboard bearing out when I re-engined, but had the same problem as you. I had the inboard bearing housing machined to take the cutless (about 3 inches of it) inside and a Volvo seal outside. Replaced the coupling you have with a Bullflex (expensive!) and delighted with the result.

I know you have just bought a new seal and you are limited in choice because of your shaft size, but your original stuffing box is a much better arrangement and it was designed to support the inboard end of the shaft and prevent it hitting the side of the tube! Replacing it gives you quite a major re-engineering job which may give you more bother than the original.

Hope this helps

 

[Heckler]

I suspect that tranona has got it in one, the whole strategic design of the shaft assembly is such that the whole is needed to support the shaft, in my previous life, stuffing boxes also had brass bearing capabilities, you have removed this capability by replacing the seal with one that doesnt have bearing support capabilities.
stu

 

[martinriches]

You could fit a Aqudrive which has a thrust bearing. This would allow the shaft to be supported at both ends .

Martin

 

[TigaWave]

If there is a carrier why not slide a bearing in? if it can rotate by hand in the carrier and on the shaft (assuming the shaft diameter has been checked for wear) then the set up is aligned.

bed it on epoxy and you have a fixed bearing, you could add a grub screw as added security, but if you can ensure you can clean the carrier and have a new bearing epoxy should work.

However I suspect you may have other issues, this ammount of movement will have worn the shaft and/or any other bearings supporting it

 

[PuffTheMagicDragon]

[ QUOTE ]
My own idea for the best way is to fit a cutlass bearing in the inboard end of the stern tube as I think it will push down out of the way of the PSS. This will then support the prop shaft and stop the knocking. .............

This is my thought. Can anbody say that this sounds OK or is there a better way?

...

[/ QUOTE ]

I'm not sure I understand that logic.

If the shaft is banging against the tube it means that something is moving the shaft sideways. If the outer cutless bearing is not worn and if the shaft is not bent, then the cause of the movement is the engine (shot or maladjusted mountings) and / or the coupling (non-concentric: unlikely).
Adding an inner bearing will keep the shaft from knocking BUT it will not cure the cause of the excessive movement. A Bullflex might solve it but I would personally prefer to eliminate the cause; especially if there is not much distance between the inner end of the stern tube and the coupling.

I admit that I might be misunderstanding your plan.

 

[vyv_cox]

Be aware that cutless bearings need a flow of water for cooling purposes. Putting one at the inboard end of the stern tube would presumably mean that there was no water flow, causing it to overheat and fail.

An Aquadrive is a perfect solution but an expensive one. When I had some similar problems I asked my Yanmar supplier, who was able to swap the very soft engine mountings for some harder ones. This didn't totally solve the problem but it helped a lot.