bronze propshaft repair

[gag]

I had to cut a rusty collar off a bronze prop shaft but because of the awkward access I managed to score the shaft with the angle grinder. The mark is about 1/32 deep and 5/16 long by 1/8 wide , on a 1" bronze shaft. What is the best repair to carry out in situ? Braze , silver solder or what? Any advice appreciated.

 

[nedmin]

Is it running where the cutless bearing is? if it is I would solder it,try and get some "plumbers metal" fairly high lead content,its what you use for wiping joints thats if its still available, use flux and smooth down to shaft size.trouble is you would need so much heat for the others you mentioned.if you run in clean waters ie the sea you could smooth the edges and you would get away with it .where I boat in heavy silted estuary waters the cut would hold mud and grind the bearing.If you use solder you would need a gas torch,make sure the area to solder is clean.The advantage of solder is that you wont damage the shaft with the heat needed to run the solder.Dont use emery cloth to finish as the lead will hold bits of abrasive,I would scrape it, a stanley knife would do if your careful.

 

[gag]

The groove I made is 1" inboard of the stern gland , with access restricted but possible. I am told the collar was a belt and braces arrangement if the taperlock at the engine end let go in reverse. The collar would stop the prop pulling back into the rudder. Unfortunately it was made of steel and had to be cut off to allow the stern gland nut to be undone. There is some free space around so not too risky re fire. Its a wooden boat.
Thanks.

 

[nedmin]

I would use a couple of jubilee clips next time put the tighteners opposite for balance.

 

[vyv_cox]

If I understand your post correctly the damage is not in an area that runs in any bearing? I would not attempt to weld, solder or any other process that involves heat. You will not remove a stress raiser by filling the cut up with another metal. The heating may cause metallurgical changes to the bronze.

The shaft is almost certainly plenty strong enough to transmit the power but leaving a stress concentrator in place runs the risk of generating a fatigue fracture. I would blend the damage carefully with a small grinding stone or a file, removing any sharp corners. This will lower the stress concentration factor.

 

[nedmin]

If its clear of the bearing I would leave well alone,I thought it was where the cutless ran thats why you were worried,At the depth your talking about soldering wouldnt give you any stress from heat problems,as to get the solder to run you would spread the heat round the shaft especially on bronze.

 

[gag]

Thanks , everyone.
I will leave the shaft , only smoothing out the mark.
Will SS jubilee clips react with the bronze?
Local engineers also say better not to heat the propshaft because of possible warping of shaft.
All the best.

 

[vyv_cox]

Rather than adding stainless steel hose clips, can you use your shaft anode to do two jobs? Mine is on the forward side of the P-bracket, where it would prevent the shaft from being lost if the coupling bolts came undone. Don't put it in contact with the P-bracket, leave a gap of 10 mm plus to allow cooling water through the cutless bearing.

Alternatively, can you fit the hose clip inside the boat? This is the more normal way to prevent shaft loss.

 

[nedmin]

I assumed he would put the hose clips inboard.

 

[vyv_cox]

Yes, you could be right. Odd that the previous device corroded so badly though.