Aligning propshaft

[lumphammer]

I understand the basic principles of setting up the engine alignment using feeler guages and rotating the propshaft through 90deg each time. (although my coupling is only about 2in diameter so I'm not sure how precise this is going to be, added to trying to do it while lying on my side on the quarterberth in a small bilge space)

My question really concerns getting the propshaft lined up in the cutlass bearing, which I guess has to be the first stage.

Can I use a dial guage?

Any suggestions gratefully received.

 

[TigaWave]

Just before I go home...If you are fitting a new bearing, then assuming it is a clearance fit in the bearing carrier.

You can check alignment by being able to spin the bearing on the shaft and in the bearing carrier, any mis alignment will not allow the bearing to be slid in and still spin freely.

Once this is achieved with the shaft chocked at the aft end, coat bearing in epoxy and slide back in. Leave epoxy to set and job done.

Have fun I'm off home.

 

[Robin2]

I think Tigawave assumes a ballrace or roller bearing at the inboard end, but I assume you just have a rubber cutless (spelling?) bearing at the outboard end and the connection to the engine on the inboard end. The cutless bearings are not too critical, being rubber. Also they should be a close fit for the shaft so that alignment should be fairly obvious. Being rubber they are going to distort a bit due to the weight of the shaft and the propeller forces.

Assuming, also, that the shaft comes through a water-tight gland, I would try to ensure that the engine alignment allowed the shaft to be centered (approximately - no need for a dial gauge) in the gland to make sure that the shaft does not touch the fixed parts of the gland if the engine vibrates.

HOWEVER ... I strongly recommend using an Aquadrive coupling which does away with the need for close engine-shaft alignment and also ensures that the shaft rotates without vibration.

 

[Saddletramp]

Just a note on the feeler guages. I gave up on that and found it easier to unscrew a bolt until it touched the flange. Then rotate it through 180 degrees. Count the flats you need to turn. See what effect a couple of turns on the legs makes. You will soon get the hang of it. It helps if you think of it in 2 planes vertical and horizontal, especially if you are upside down. When the bolt is just touching the flange all round you are there.

 

[TigaWave]

Sorry Robin2 this method is suitable for any drive set up.

I was assuming a conventional set up of engine/flexible coupling/stern tube with bearing/unsuported shaft/final bearing in P bracket.

Cutless bearings are critical to alignment, even rubber ones. Any misalignment accelerates bearing and possibly shaft wear.

We supply a range of bearings and this is the technique used in nearly all cases, from Armed forces gun boats to antique life boats.

 

[Robin2]

OK, in principle.

However my cutless bearing is an interference fit in the glassfibre tube in which my propshaft runs - I have no P bracket. And there is no scope for fiddling with the alignment of the bearing - only the shaft.

Also, your method requires that the inboard end of the shaft be properly located in order to test fit the bearing, whereas usually the outer bearing is in place and the problem is to match up the inboard end of the shaft with the engine.

 

[TigaWave]

Trust me it works in practice but you have to start out with a clearance fit bearing. Chock aft end of shaft bolt shaft to engine, test bearing in carrier, whether grp or bronze housing. Once it slides in and can be rotated by hand the shaft is aligned.

Used more extensively in Australia, but they seem to be ahead of Europe in a few areas to do with boats.