On the Subject of Prop Shafts

[Aeolus_IV]

Have just got the boat onto the hard standing (just in time for this gale, good timing eh?), and have a couple of questions about prop shafts and cutlass bearings.

I'll start with the bearing, or rather the residue of bearing which had bonded intself to the shaft. At the point in the shaft which would be in the bearing the shaft had a thin layer of very hard black substance bonded to it. This wouldn't clean off with spirit so have to carefully scrap it off. Underneath this the shaft had a slight coppery colour to it. This has all clean off very nicely with some metal polish, so you cannot tell now where the bearing was. The bearing itself looks OK and normal to me with no obvious wear.

I'm assuming that this is not normal, and that the bearing was either too tight at some point, or didn't get sufficient water lubrication while in use. What is the forums opinion and experience?

Now for the stern glad, or rather, evidence of wear on the shaft from the stern gland. Here the shaft has been polished by the stern glad around the shaft. Cleaning the shaft with metal polish shows that I cannot polish the shaft as well as the stern glad. But also that the surface of the shaft in this area is now slightly uneven. I doubt that I could see the unevenness, but I can feel it. The stern glad is a simple grease and packing one - in the time we've had the boat (a couple of years) it has never leaked and I've never tightened up the packing, only ensured a continious supply of grease while the engine is running.

Again, is this normal, or is there a problem I should be sorting out while I have the chance?

Thank you in advance,
Jeff.

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[charles_reed]

Leave well alone - sounds as though at some time the cutless has run hot enough to melt the neoprene bearing.

If there is no leak past the gland don't bother, when it's reassembled you might get a seepage, but the probability is so low that it doesn't justify the cost of a new shaft.

What I usually do is to have the shaft made over-length and then change the bearing area by cutting a little bit off at the gearbox end

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[Aeolus_IV]

Charles,

Thank you for your comments - I hadn't thought of having the shaft made up longer than necessary, next time I need a new shaft I'll remember this.

As for the cutlass bearing I think I now know when this happened. I had some rubbish wrapped around the prop reciently, didn't know this untill the boat was lifted out (I remember the engine hiccupping for no obvious reason). The stripper had done its job but there was a remanent wrapped between the p-bracket and the stripper, so probably cutting down the water flow through the bearing.

Regards, Jeff.

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[Col]

Some shafts have a taper both ends, and you can double it's life by swapping end for end.

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[brianhumber]

Like others suspect you had restricted flow through weed/floating debris. Measure any wear down on the shaft and fit new bearing. Countrose of Leeds make these and they did supply special undersized diameters on request . If your bearing has been hot enough to melt the surface a) your clearance is bigger and the bigger the clearance the faster the wear rate and b) it may have weakened the bond between rubber bearing and bearing shell housing. This has happened to me after picking up a pot rope in the Little Russell.

Stern gland - sounds as if you have roughened up the packing if the shaft is uneven. I was taught when I first when away sea to keep 1 drip per minute from these packing glands. Heat is generated from the contact between shaft and packing turns and the water carries this heat way. Pumping full of grease will allow the centre of the bearing to get hot, the packing then 'grips the shaft' and tears the shaft surface which forms ridges.
Used to own a yacht where this had happned and ran it allowing about cupful of water throug evey six hours with quarter turn on the greaser after every finished with engines. This stopped any ingress while the shaft was stationary but not enough to cause further overheating.
You have brought back many memories of struggles with sharpened welding rods to extract burnt out turns of packing- happy days!

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[Chris_Robb]

I would go along with Charles. Certainly leave the gland alone if it has not been leaking. Just pleanty of grease. It is worth double checking that it is not running hot, especially if you tighten it a little.

With the Cutlass bearing it is worth cheacking of there is any play. It sounds like the black deposit was probably the overheated remains of a plastic bag!

At least you haven't got crevis corrosion on the shaft. this would result in high wear of the cutlass bearing. Had that last year so had to change the shaft.

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[Aeolus_IV]

As this shaft is only a year old I'd rather not replace it yet, its not that big, so not that expensive - but any unnecessary cost should be avoided. Now that the shaft is clean I'll take it back to the boat and offer it up and check the play in the cutlass bearing. The wear is a little uneven which could indicate that P-bracket, shaft and gearbox are not quite in line - we'll see.

All part of the fun.

Regards, Jeff.

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[charles_reed]

Cutless bearing

I'd replace it whilst the boat is out of the water - for the cost of a new one it's really not worth taking the risk. A worn cutless is the quickest way to getting shaft wear.
Get the old cutless out and borrow a micrometer to measure the shaft diameter (0.01mm) can make a difference, and the ID of the housing.
I'd second getting a replacement from Countrose, they're actually in Perry Bar, telno 0121 356 7220, ask for Keith Reddings or Andy Markham. They'll make one up to exactly fit at little over the price for inferior over-the-counter one.
They'll also advise on the bearing & backing material - there's much more to cutless design (it's actually one of the more esoteric areas of tribology) than the average marine engineer appreciates
Unless your in the biz they'll not sell to you direct but Les Hill of Lake Engineering in Poole will usually do the honours and give you a discount.

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[Aeolus_IV]

Re: Cutless bearing

Had pretty much concluded that a new cutlass bearing would be required. Just need to get the old bearing out of p-bracket. Should be "fun".

Thanks for your help, Jeff.

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[wiggy]

I tried to extract my cutlass with a homemade extractor, hours of effort for no result. In the end removed rubber poart easily with a screwdriver and hammer then broke the case up (laminated thing) carefully with the same screwdriver and hammer, it took about half an hour!!!!!!! Try Lancing Marine (Brighton) for replacement the are great with advice.

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[charles_reed]

Re: Cutless bearing

Don't mess - if it won't drive out after removing the grub-screws and applying a little judicous heat to the outside, with an hot-air gun, take an hacksaw to the damn thing.

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