wrote in message
oups.com...
So what do you all think about drive savers? Strikes me
I should just put the money into the new shaft...


Depends.

"Edgar" wrote:
I agree. The existing shaft probably has some wear around
the stern gland and outer bearing anyway and unless the
drivesaver leaves the shaft in _exactly_ the same position
(which is unlikely) the wear step will have moved a bit
and then the lip of the worn portions can cause leakage or
bearing problems.

Not necessarily a problem, if you know somebody who is competent with
a lathe.

You need more than that and in the end you will not have saved much if
anything compared to a new shaft. You cannot just rduce the worn area in
diameter because you will need smaller bearings and stuffing box and then
you will not be able to pass the rest of the shaft through such bearings
etc. So, if the shaft is fitted from the outside you will have to turn down
the whole distance back to the engine and then get a new half coupling with
an undersized bore, so it will be quite a costly job. OTOH if the shaft is
fitted from inside the boat you will have to reduce the diameter right back
to the propeller and this will take away some part of the taper on which the
propeller is fitted and therefore may compromise the security of the
propeller fitting.
The usual way to reclaim a shaft is to turn down the worn area and build
back up with sprayed-on metal and remachine to the original size. Metal
spraying is a well established procedure but is dependent on the skill of
the operator and although it looks OK from the outside when finished I am
always suspicious about the adhesion. When they turn the shaft down they
leave a rough surface to assist adhesion but as we know a rough surface can
provide starting points for fatigue failures. So because of all that it is
quite a bit more costly than just finding someone with a lathe and a new
shaft is far preferable IMO.

snipped

A thrust bearing would be a better investment, that way the alignment
of the shaft is not as critical and any shock put on the drive system
will not be carried to the trnasmission & engine. They are expensive
and take up room and require some engineering, though.... which is why
they are far less common!

The alignment of the shaft is always critical unless flexible couplings are
involved and this is very expensive.
There always has to be a thrust bearing and it is normally an integral part
of the gearbox except for larger vessels

snipped

How bad is the wear on the old shaft? If it is still true (not bent or
wobbly) and hasn't worn more than a couple thousandths, it can almost
certainly be slicked up and put back in. We stayed briefly at a marina
that had a racket in new shafts.... he had a warehouse full of old
shafts that he polished up & reinstalled in boats that hit rocks...

Probably not a racket. Someone replaces a 10' shaft and allows him to keep
it and he just holds onto it until someone comes up wanting a shaft that is
shorter. Then he just cuts off the worn bit and machines up a new shaft.
Seahags 10' shaft is a valuable piece of steel or bronze bar and she should
ensure that its value as such is taken off her invoice for the new one!

Fresh BReezes- Doug King