Our 4107 croaked and I have a 4108 rebuilt long block
sitting in the saloon awaiting installation. We have a
Thames tranny and the consensus is to get a new
transmission. The mechanic mentioned putting in a drive
saver to extend the shaft to fit the new set-up rather than
buying a new shaft at this time. From photos it looks like
the shaft is around 10' long...heh We could use a bottom
job this year so hauling isn't a huge problem but it would
be kinda nice to have a working engine now.

So what do you all think about drive savers? Strike me I
should just put the money into the new shaft...

Seahag

"Seahag" wrote in message
news:0Mbsi.8328$xi.2815@trndny03...
Our 4107 croaked and I have a 4108 rebuilt long block sitting in the
saloon awaiting installation. We have a Thames tranny and the consensus
is to get a new transmission. The mechanic mentioned putting in a drive
saver to extend the shaft to fit the new set-up rather than buying a new
shaft at this time. From photos it looks like the shaft is around 10'
long...heh We could use a bottom job this year so hauling isn't a huge
problem but it would be kinda nice to have a working engine now.

So what do you all think about drive savers? Strike me I should just put
the money into the new shaft...

Seahag

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. Also, you have a long shaft which will in itself
introduce a litle more flexibility than a very short one if you do hit
something very hard and therefore any shock loading on the transmission will
be somewhat reduced. A new shaft and new outer bearing will give you a good
setup to go with your new motor.

"Edgar" wrote:

"Seahag" wrote:
Our 4107 croaked and I have a 4108 rebuilt long block
sitting in the saloon awaiting installation. We have a
Thames tranny and the consensus is to get a new
transmission. The mechanic mentioned putting in a drive
saver to extend the shaft to fit the new set-up rather
than buying a new shaft at this time. From photos it
looks like the shaft is around 10' long...heh We could
use a bottom job this year so hauling isn't a huge
problem but it would be kinda nice to have a working
engine now.

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

Seahag

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. Also, you have a long shaft which will
in itself introduce a litle more flexibility than a very
short one if you do hit something very hard and therefore
any shock loading on the transmission will be somewhat
reduced. A new shaft and new outer bearing will give you a
good setup to go with your new motor.


Thanks, Edgar. Your reply points out some things we hadn't
even thought about and reinforces my inclination.
This sure isn't what I was planning on doing this year! But
the boat sure looked good out on the creek even under tow

Seahag

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.


..... Also, you have a long shaft which will
in itself introduce a litle more flexibility than a very
short one if you do hit something very hard and therefore
any shock loading on the transmission will be somewhat
reduced. A new shaft and new outer bearing will give you a
good setup to go with your new motor.

We have some friends with drivesavers, basically because previous
owners installed them. I don't see much benefit myself, it's only a
coupling with sacrificial link which, if it fails under heavy load,
will still trash the bearings & packing gland and not do the tranny
any favors.

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!


"Seahag" wrote:
Thanks, Edgar. Your reply points out some things we hadn't
even thought about and reinforces my inclination.
This sure isn't what I was planning on doing this year! But
the boat sure looked good out on the creek even under tow


Pictures! We want pictures!

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...

Fresh BReezes- Doug King

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

"Edgar" wrote:

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!

There ya go...something else I wouldn't have thought about!

Thanks!

Seahag

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

"Edgar" wrote:
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.

If you have to reduce the shaft by a size increment, yes. If it just
needs to smoothed out by a couple thousandths, then it's no big
deal.... more than you can accomplish on a bench with emery paper,
though




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.

Same here, especially under a heavy torque load.


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!

"Edgar" wrote:
The alignment of the shaft is always critical unless flexible couplings are
involved and this is very expensive.

Yep.... that's what I said.

I have seen a few pleasure boats with thrust bearings installed...
it's great, makes the boat much quieter & smoother running.


There always has to be a thrust bearing and it is normally an integral part
of the gearbox except for larger vessels


Correct. But IMHO it doesn't do the tranny or engine any good at all
to use them as the thrust bearing. Especially in a boat that is
maneuvering a lot with heavy reversing loads.


(snipped) 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!


Depends a lot on whether the shaft really needed replacing, doesn't
it? However I am very slow to accuse anyone of this sort of thing,
since I do not have the proper tools to evaluate the situation
myself.... however, out of the several boats passing thru the area
that had work done at this marina, 3 had shafts replaced and no
particularly good explanation given. Another boat at the same marina
wanted to get some electrical work done but rejected their offer to
simply replace battery bank & charge controller.... again with no good
explanation of why this was needed.... kinda raised an eyebrow,
y'know?

Fresh Breezes- Doug King