Drive Saver: Yay or Nay

[Tom.B]

After being on the hard for 3+ months, we developed a vibration in the boat. Bess noticed it first and I wrote her off as crazy since we had not been on the boat in a while and she had just lost her Mojo (and to her affinity for things that vibrate ). Well, last weekend when I was running the motor up to temp in the slip, I had a chance to take a look at the prop shaft (and it was making a funny noise). When I looked at the stuffing box, it was wobbling around about a 1/2" each direction. That, we then knew, was the source of Bess' mystery vibration. (apologies followed )

Since I was not 100% sure what was going on, we got a professional from the local boat yard to come have a look. Turns out that the Drive Saver - that red urethane disc between the transmission output and the shaft collar, had slipped off of center. Primarily due to the previous owner's use of flat washers between disc and plates.

The tech mentioned that he prefers NOT to use Drive Savers. Most notably because we are a single screw with a protected prop. "They cause more problems than they fix.", he said. The validity of that is a bit suspect because, as a tech, he only sees the BAD things that happen and may not see all the props and/or transmissions saved by them. Anyway, I am getting off the point.

After he removed the washers and reset the Drive Saver in place, all seemed somewhat back to normal. And like all things boating, good news always comes at a price. The shaft still had a slight wobble to it. He broke out the dial gauge and we do, indeed, have a bent shaft. Withing the part of the shaft he could get to, we are out by .012". Spec calls for .010" as a max, so we are just barely outside of that, but we can't see the entire shaft and could be way off down the tunnel. He has recommended that it CAN wait a little while, but we need to do it in the Fall at the latest. Considering that our 2" drop Velvet drive is no longer made, but can be rebuilt, we will probably do it mid-summer before the shaft start destroying the transmission beyond repair.

So I guess you are wondering what my question is? Well, since we will be ordering a new shaft, should we plan on replacing or removing the Drive Saver? I don't know. The little voice says to use it, but at $500 to replace, that seems like a lot for hunk of polyurethane that a 15-year marine mechanic doesn't recommend.

Tom-

 

[Phil Fill]

Its fix so why change? Besides a new shaft is going to cost a couple of grand. plus the cost of installation and the yard.

 

[Nomad Willy]

Tom B,
I'd remove the shaft and have it straightened. Don't watch them do it. No shaft is straight. Some are just straighter. When you buy a new shaft you need to have it straightened. Find a shop that does a lot of boat shafts. Get a new "shaft saver" and carefully inspect your coupling/s, intermediate bearings, stern bearing (cutlass) and any other related hardware that requires shaft removal. The Shaft Saver is not something I'd recommend for general service but it's OK. It's not a flexible coupling but a weak link to protect the shaft when you hit something w the prop like a rock. Install everything carefully according to manufacturers specs.

If you really want to get rid of the Shaft Saver get a cutoff piece from the shaft shop and properly mate it w a coupling and have all cut to size. Couplings are fine. Get the type that are basically tubular and clamp w many socket head cap screws. I thought of them as Mickey Mouse band aids until I used one.

 

[Brooksie]

Have them on my boats and never had a problem. They do serve a purpose but are not a substitute for a good alignment. I would continue with one. I don't understand where the PO put the washers, but did that ruin the Drivesaver? By all means have the shaft straightened if it can be and it sounds like it can.

 

[Tom.B]

I am totally planning on doing the majority of work myself. Shaft removal and re installation doesn't look like rocket surgery to me. However, I will probably bring in the pro to just make sure it's lined up correctly when it goes back in.

John, the washers were on both sides of the Drive Saver on every bolt. I have the manual for it and there are no washers shown at all. So how the PO decided to put them in is beyond me.

Thanks for the tips. The yard said they don't like to straighten shafts (actually send them out to be done), but if I can find a place to do it, I will go that route for sure.

Tom-

 

[Tom.B]

NICE!

How to Straighten A Propeller Shaft - YouTube

 

[Nomad Willy]

Oh yes ......

Shaft runout varys greatly w length.

Find a good shop Tom.

 

[psneeld]

...have no clue how he could have done an accurate shaft straightness alignment with it in the boat as shafts sag....that's why alignments are just a guess on most boats...I'd go with a new drivesaver if I were you unless you are willing to go through buying a new shaft or having a machine shop try to make an inset/longer coupling.

If most of the problem went away when the drivesaver was redone...why think it is also a shaft problem?

 

[Tom.B]

After he re installed the Drive Saver, the prop still had a small wobble to it, so he suspected a warped shaft.

I specifically asked if an out-of-alignment engine would cause it to do that. He said no. He was 99% sure it's a bent shaft. Yes, he acknowledged the measurement *could* be off a bit because it's in the boat, but that it's usually a pretty good indicator.

The current plan it to possible do a short haul over the summer. Pull the boat without blocking it and pull the shaft to check for straight. If it's straight, re install and drop back in the water. If not, block it up and spend a week or so fixing it.

 

[psneeld]

an out of alingnment engine will cause wobble....but what you have in mind is probably a good route...

 

[CPseudonym]

Call local machine shops Tom. Any machine shop worth its salt can straighten the shaft.

When is the last time the prop was off the shaft? Everything properly torqued?

Just a couple outside the box questions is all...

 

[Tom.B]

an out of alingnment engine will cause wobble

That's what I thought too, but AT the transmission end, it reads almost true (or within spec anyway). Back three feet from there, it's out by the measured .012". Does that mean anything?

 

[Tom.B]

When is the last time the prop was off the shaft? Everything properly torqued?

Since before I bought it 4 years ago and I am guessing at least a year or more before that.

Had a diver on it too last weekend. He checked, double-checked, shook and spun the prop. Gave the in-water gear two thumbs up.

 

[CPseudonym]

Our boat had a small vibration starting at about 2,000 rpm when we purchased it. I'd been running around since the purchase at 1,800, basically choosing to live with it until I could dive and inspect the prop for nicks or dings.

Tuesday I took it out and ran it up to 3,500 for 2 miles and no vibration at all. Made me wonder if the packing had taken a set during the last year of limited use? Ran the rest of the day at 2,200 with no vibration

It just went away???

 

[psneeld]

That's what I thought too, but AT the transmission end, it reads almost true (or within spec anyway). Back three feet from there, it's out by the measured .012". Does that mean anything?

Not sure...have to start someplace with a known or a strong assumption.

On the surface it sounds like the shaft could be bent...but how all of a sudden?

Assunimg that everything was OK before the drivesaver slipped...something sounds fishy.

Do you align the coupling to the drivesaver or the drivesaver to the tranny flange?

 

[Tom.B]

On the surface it sounds like the shaft could be bent...but how all of a sudden?

Assunimg that everything was OK before the drivesaver slipped...something sounds fishy.

I know that it got out of keester big time while on the hard. I understand boats change shape when they are out for a while and may not always go back to 100% correct. So I believe the weak point was the drive saver connection that slipped during haul-out. Now, as for the current, post technician, wobble we see *COULD* have been there all along. I never noted it when I had adjusted the stuffing box in the past. Did it wobble before? Yea, maybe, but I am not sure. So it may not be all of a sudden. We could have hit a log in the river on our way home, but I would THINK a prop hit that could bend a 2.5" piece of hardened steel would be pretty noticeable. I mean it's a pretty small wobble now and apparently something we can live with for a little while.

Your second question I didn't understand fully.

Tom-

 

[Nomad Willy]

Any machine shop can beat on a shaft but only a good one that does lots of boat shafts can straighten it.

Straightening boat shafts is part science but mostly experience and skill.

I know this because I worked at a good one for 14 years.

 

[psneeld]

I know that it got out of keester big time while on the hard. I understand boats change shape when they are out for a while and may not always go back to 100% correct. So I believe the weak point was the drive saver connection that slipped during haul-out. Now, as for the current, post technician, wobble we see *COULD* have been there all along. I never noted it when I had adjusted the stuffing box in the past. Did it wobble before? Yea, maybe, but I am not sure. So it may not be all of a sudden. We could have hit a log in the river on our way home, but I would THINK a prop hit that could bend a 2.5" piece of hardened steel would be pretty noticeable. I mean it's a pretty small wobble now and apparently something we can live with for a little while.

Your second question I didn't understand fully.

Tom-

Not sure of your setup...but I'm guessing an outer cutlass, and inner cutlass, shaft coupling, drivesaver, tranny flange.

If the inner cutlass is worn you can have a lot of shaft whip depending on length...but that's not what it sounds like to be out so close to the tranny. ...plus you would probably hear some noise from it. If the engine didn't really go anywhere and just needed a minor alignment after readjusting the drivesaver...and everything else is squared up...then the shaft would be uspect especially if even a rough runout showed it...but the runout is not very important while the shaft is in the boat as stressors could just have it deflected.

 

[Marin]

A few years ago we had one shaft straightened and one replaced. We also chose at this time to get rid of the stock but too-small shaft couplers and replace them with bigger, heavier-duty, split couplers which do a much better job of helping to keep the shafts in alignment.

While we never considered shaft savers, I have heard several negative things and owner reports about them but never any positive ones. In one case a prop strike broke the shaft saver as advertised but the shock still sheared two engine mounts.

So based solely on what we have heard we would never bother with them. The investment we made in the new, big split couplers, however, was well worth it.

 

[Besslb]

Not sure of your setup...but I'm guessing an outer cutlass, and inner cutlass, shaft coupling, drivesaver, tranny flange.

Does this help??

 

[O C Diver]

From the original post, is it safe to assume that before this episode started everything was running straight and true?

If so, then everything (prop pitch balance, shaft is straight, cutlass bearings don't have excessive wear, transmission output bearing doesn't have excessive play, motor and transmission mounts aren't warn or loose fasteners, etc.) was correct and something(s) has changed.

If it were me, I would plan on pulling and blocking. Then pull the shaft and have it checked, drop the prop off at the prop shop to have it checked, and finally go through everything listed above before reassembling. Remember, if you stop after finding the first problem, you may not have found all the problems.........but then in this case you already know that.

Ted

 

[FF]

The drive saver is not made to make yp for a crap shaft , only to "save" the drive train when you go over a log or sea land box at speed.

There ARE mechanical systems that will accept some shaft wiggle , but its far cheaper to just do the shaft right in the first place.

 

[Ben]

the Drive Saver - that red urethane disc

we are out by .012". Spec calls for .010" as a max, so we are just barely outside of that, but we can't see the entire shaft and could be way off down the tunnel. He has recommended that it CAN wait a little while

The little voice says to use it, but at $500 to replace, that seems like a lot for hunk of polyurethane that a 15-year marine mechanic doesn't recommend.

Tom-

Hi Tom,

1. I'd get the cost to true the shaft. .002" out of tolerance should be true-able. Plus once trued, your shaft might likely be within .005"

2. You need your own machine shop. Figure you probably have anyway. You could pull the drive saver, get the material ID, and make your own with a decent lathe and drill press. You just need the fine dimensions which you can measure with precise calipers anyway. Seems like the drive saver "may have" (quotes because that's my guess) disguised your shaft wobble for a while.

It sounds like the shaft is your primary issue, but close enough to fix.

A bent shaft is no laughing matter.

 

[psneeld]

Maybe I missed it...was the engine ever aligned after the drivesaver was recentered?

 

[Brooksie]

The Drivesaver had washers on bolth sides you say... If it is the correct Drivesaver, it has a spigot on one side and a recess on the other to match up with the transmission and coupling recess and spigots. This centers it. One set of bolts are socket head cap screws and the heads fit into recesses in the Drivesaver the other set of bolts are hex head and are exposed. Washers, if thick enough, could prevent the spigots and recesses from engaging properly. Removing the washers and reinstalling the Drivesaver is not an alignment check so your "bend" could be due to angular misalignment but I doubt it because the Drivesaver should have handled this. Nonetheless, a basic "feeler gauge" alignment check should have been performed with the Drivesaver out to check for angular misalignment and coupling runout. While at it you should check that the hex head bolts haven't been replaced & are grade 5 (3 lines on the heads)

 

[Tom.B]

Maybe I missed it...was the engine ever aligned after the drivesaver was recentered?

No, but the tech said that the engine's alignment would not make the shaft act the way it is.

I have video of the before re centered wobble that I will post once I get an after video.

 

[Marin]

My only experience with this sort of thing is as a boat owner and yard customer, not as a DIY mechanic. But from what I have gathered over the last 14 years is that engine alignment is REALLY important and it can slip out fairly easily.

The yard we use automatically checks engine alignment when a boat is relaunched after being out for a week or more for bottom paint or other things. All boats, not just the wood ones they work on. Just sitting in the blocks and braces can change the alignment. Doesn't automatically change it, of course, but the potential is always there. So their normal procedure is put the boat in the water, let it sit overnight, and then check the alignment in the morning.

An out-of-alignment shaft can create several other problems besides just vibration, like uneven or prematurely worn cutless bearings. And the vibration can, in turn, cause the alignment to drift out even more over time.

I would be very suspicious of the expertise of a driveline mechanic who told me that a vibration problem was not due to engine alignment unless he actually checked it and found that it was, in fact, correct. Simply assuming alignment is okay is not a good assumption to make in my opinion.

 

[Tom.B]

The Drivesaver had washers on bolth sides you say... If it is the correct Drivesaver, it has a spigot on one side and a recess on the other to match up with the transmission and coupling recess and spigots. This centers it. One set of bolts are socket head cap screws and the heads fit into recesses in the Drivesaver the other set of bolts are hex head and are exposed. Washers, if thick enough, could prevent the spigots and recesses from engaging properly. Removing the washers and reinstalling the Drivesaver is not an alignment check so your "bend" could be due to angular misalignment but I doubt it because the Drivesaver should have handled this. Nonetheless, a basic "feeler gauge" alignment check should have been performed with the Drivesaver out to check for angular misalignment and coupling runout. While at it you should check that the hex head bolts haven't been replaced & are grade 5 (3 lines on the heads)

They are Grade 5 bolts. I checked that already

The rest of the Drive Saver is as you described with the exception of the washers that have now been removed. No feeler gauge alignment was done. I may get to that eventually. Any tips on performing that? Are we mating the coupling to the transmission plate without the Drive Saver and reading the gap? I'd need an adapter of some kind, right? Or are the coupler and trans plate the same bolt pattern?

Tom-

 

[jleonard]

I don't care for drivesavers. I prefer to get the alignment and straightness correct then there should be no problem.
I have made and installed solid steel spacers (I have one now) and you could do that to make up the space of the drivesaver if you choose to remove it.
No problems at all with doing that.

 

[Brooksie]

They are Grade 5 bolts. I checked that already
The rest of the Drive Saver is as you described with the exception of the washers that have now been removed. No feeler gauge alignment was done. I may get to that eventually. Any tips on performing that? Are we mating the coupling to the transmission plate without the Drive Saver and reading the gap? I'd need an adapter of some kind, right? Or are the coupler and trans plate the same bolt pattern?
Tom-

Yes, remove Drivesaver, push the 2 couplings together (no bolts) and check all around couplings w/ feeler for same* reading. Then turn the shaft 180degrees and see if the widest opening moves. If it does, your shaft is bent and/or the coupling face is not true (90 deg) to the shaft both jobs for the machine shop.

*Same= less than .001/ in. of coupling diameter.