Applying heat to release prop shaft

[Miker]

The cutless bearing and shaft seal on my Bene 260 Spirit are well past their "Sell by" date. I tried to remove the prop shaft last winter but couldn't shift it. Trying to prise open the clamp with the bolt against a metal block wedged in the clamp did not work, only punching a hole in the metal. My crew who seems to know about these things, reckons that "a bit of heat" will soon loosen it. I'm a bit apprehensive, especially as it is my boat.

What I'd like advice on is how much heat will be needed - just a gentle touch with a hair dryer or use of a flame thrower? Also, what area of the boat would be in danger of damage and what would be the best means of protection?

 

[Spyro]

A hair dryer won't do any good you need to apply a lot of heat quickly to the clamp so that the shaft does not get time to heat up. You shouldn't be able to do any damage to the boat unless you point the blowtorch directly at it. If you're concerned protect any exposed parts with something like a piece of canvas or anything flame retardant like a fire blanket. if it's a split coupling you are trying to free up remove the bolts completely and try and hamer in something wedge shaped like the end of a large screw driver to separate the halves.

 

[pvb]

You have a Volvo engine, so do you also have a Volvo clamp, like this?

If so, remove the bolts, reverse them and screw them into the other half of the clamp. Put some flat sheet steel in the slot in the clamp, and tighten the bolts against it. This will gently force the clamp apart slightly. You need only use the two bolts at the prop end of the clamp.

 

[Ruffles]

Are you sure there isn't a roll pin through the clamp and shaft?

 

[Ruffles]

If you're concerned protect any exposed parts with something like a piece of canvas or anything flame retardant like a fire blanket.

I use bits of plasterboard soaked in water. Works well for my attempts at domestic plumbing too.

 

[Miker]

Thanks for the replies. The engine is a Volvo MD2010B. I don't recall that there was any pin preventing the extraction of the prop. We tried the "reverse bolt" method but the metal sheet was not up to the job. Also hammering in an old screw driver did not work and we had great difficulty in extracting it, as we did the punctured metal sheet. Perhaps I should let my crew loose on it with a blow lamp.

 

[Tranona]

Undo the coupling from the gearbox, push the shaft back, insert a spacer inside the coupling to bear on the end of the shaft - a socket will do. Replace two of the bolts (opposite eachother) and tighten up. This will press the shaft out. Much easier and safer than heat. Alternatively if you have enough clearance push the shaft right back and use a conventional puller.

 

[earlybird]

Try heat if you must, but don't have too high hopes. Heating a lump like a split coupling sufficiently rapidly to expand away from the shaft needs a large flame. Assuning the shaft is stainless, it's coeff. of expansion is slightly higher than mild steel, which doesn't help.
My money would still be on jacking the split open using the screws, as suggested earlier.
When you tried, how thick was the metal insert? The fact that you punched a hole with a fairly small screw suggests thin, or very soft material. I'd think 3mm minimum, steel should do the trick.

 

[Miker]

Coming back to this thread belatedly, I'm a bit anxious about putting a socket behind the end of the prop shaft and tightening up on it. Will the gear box casing stand up to the pressure placed on it by the socket? The piece of steel we tightened the bolt on was an old knife blade, only about 1m thick, clearly not up yo the job. I will try again when I can get hold of a thicker piece of steel, first having measured the gap that it has to slide into.

 

[vyv_cox]

I'm not quite sure if you understand what has been suggested. There is a photo at http://coxengineering.co.uk/Aquadrive.aspx but you don't need to make up a separate plate in most cases. Just put a block of some sort, a bolt in the photo shown, between the two flanges after releasing the clamp bolts shown in pvb's photo above. The gearbox casing is not being stressed by this. The shaft will slide out quite easily, assuming there is not an additional fastening such as grub screws, roll pin, etc.

 

[pvb]

The shaft will slide out quite easily, assuming there is not an additional fastening such as grub screws, roll pin, etc.

There's no provision for a roll pin in the Volvo clamp.

 

[Freedom]

The cutless bearing and shaft seal on my Bene 260 Spirit are well past their "Sell by" date. I tried to remove the prop shaft last winter but couldn't shift it. Trying to prise open the clamp with the bolt against a metal block wedged in the clamp did not work, only punching a hole in the metal. My crew who seems to know about these things, reckons that "a bit of heat" will soon loosen it. I'm a bit apprehensive, especially as it is my boat.

What I'd like advice on is how much heat will be needed - just a gentle touch with a hair dryer or use of a flame thrower? Also, what area of the boat would be in danger of damage and what would be the best means of protection?

If your replacing the shaft, just cut the shaft with an small angle grinder. Its much easier to get off when out of the boat. I did the same last winter, wasted a lot of time trying to release the clamp in the boat. The shaft cut through in seconds with a thin metal cutting disc.

 

[Miker]

Thanks again. As I understand it, in tightening against a nut placed between the gearbox flange and the end of the propshaft, is bound to put considerable pressure on the flange. I take it from what you say, that the flange is strong enough to bear it. Tightening against a metal plate looks a neat idea but from what you say, should not be necessary.