Pop shaft end play

Greetings, When I pulled our boat this fall I checked the cutlass bearing for wear. Although it felt great, I noticed that there was a polish mark forward of the bearing indicating that the shaft is moving fore and aft in the bearing.

It appears to be about 5/8 of an inch. The boat is new to us this year and I am still new to higher HP applications, but this seems to be excessive. While chasing other problems, I've run the engine at full load in both forward and reverse. So I'm not surprised to see shifting, just not this much. The engine was replaced a while back before we had it. The original was a Perkins 6.354, 135 hp. It was replaced with a Perkins T6.354.4 turbo 240hp (I wish it was the 135). The transmission is a Velvet Drive 2.1 to1 ratio.

My first suspicion is shifting in the engine mounts. Secondly, lash in the transmission. Either one is not good. The engine sets in a formidable steel welded cradle bolted to the stringers. Actually I was pretty impressed with the installation. So I don't expect movement there.

There is absolutely no vibration or noise until I reach 2,200 rpm and then there is a rumbling and lots of other noises that I attribute to the boat trying to go on plane and pushing a huge bow wake. I wonder too if doubling the hp is the cause of the noise and shifting by exceeding the limits of the previous engine installation. In which case just don't throttle up max. Our Heritage West Indian 36 tops out at close to 12kts with the new engine.

Looking around the yard I see other inboard boats with this shifting but not as pronounced. Any Ideas? Thanks, Ted

Some motion is normal, but 5/8" is a LOT. Usually see 1/8-1/4".

Check for a loose shaft to shaft coupling fit, shaft may be moving in and out of coupling. Check for axial play at gear output flange.
Check for loose mounts.

" It appears to be about 5/8 of an inch."


"There is absolutely no vibration or noise until I reach 2,200 rpm and then there is a rumbling and lots of other noises that I attribute to the boat trying to go on plane and pushing a huge bow wake."


On your installation does the shaft run straight from the prop to the trans coupling or do you have a universal and/or thrust block along the path in-between?

I wonder if the mounts were upgraded when the 135 engine was swapped for a 240? Maybe the extra thrust is overloading the mounts? Or maybe the mounts just need to be replaced.

But definitely confirm there is no play else where in the drive line. Axial play in the gear should be easy to check for.

I've rebuilt several of the BW VD's. Never felt any endplay over maybe 1/16".
I would treat this as a serious issue, that is, don't drive until fixed. It COULD be a loose nut that holds on the output flange. Reverse will allow the flange to move aft. It could also be a slipping shaft clamp, that was not properly dimpled to take the setscrews.
A good test is to do an in-water forward and then reverse, while watching what moves.

More on the VD. Please report the series number. The 72C, for instance, had a 2.1 ratio as an option and is rated at 205 diesel HP at 3200rpm. The 73C, larger, but didn't come in a 2.1.

The movement could be loose engine mounts. It could be a poor fitting coupling.
The engine mounts may not be likely but worth checking. A poor fitting coupling may be more likely.
Both can be checked by watching. In the case of the coupling put a felt pen mark on it so any movement is clearly highlighted. There should be none as you shift between forward and reverse. A stick or tape can be used to check the engine itself.

I have had to turn the set bolts so the ends matched the taper angle of the dimples. If the angles are not close there can be movement which will get worse as wear occurs.
Use some Loctite, blue 242, [NOT RED 262] to secure the bolts once set. You might also drill the heads and safety wire them.

C lectric said:

. . . . set bolts . . . You might also drill the heads and safety wire them.

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Absolutely. IMHO this is should not be optional.

You might also drill the heads and safety wire them.

Click to expand...

Can someone provide a picture of this? I can't visualize it.

Remember the danger of spinning shafts while you are observing....

I had an issue with a loose coupling and after a couple of years of hand wringing, so my shipwright and I decided to pull the shaft and have a good look around. We discovered that the coupling was indeed loose. We had a tapered bore coupling and the set bolt was not functional as it wasn't engaging the set hole in the shaft. As above we drilled the set bolt and wired it so it will not loosen off again.

Xsbank said:

Remember the danger of spinning shafts while you are observing....

Click to expand...

In 2008 my old T-shirt got caught on the shaft coupler while I was wearing it. In an instant I was pulled on to the shaft as my head slammed into the transmission. The T-shirt was ripped off in about 1/100 of a second. From the pictures you can see the burns and bruising that resulted as the T shirt was ripped off. Every time I look in the mirror I have a permanent reminder of how stupid I was and also how lucky I am. Needless to say we have a changed a few procedures.

Ouch!! And that was dang lucky. Spinning shafts are a real hazard and can maim or kill you in an instant.

I always (???) look at what I am doing around spinning stuff and ask myself where I am going, what am I going to do, and how could I get caught in it. Screw up occasionally, but so far have been lucky.

There are pages and pages of lawyerese written about safety. 90% is BS. Working around heavy spinning hardware is real.

Thanks for the reminder.

Hello Everyone, Sorry it took so long to get back. Thanks for the ideas. Naturally the coupling is near impossible to reach. But, ya gotta do what ya gotta do.... Actually that would be great to be the source of the problem. At least I can do that without the boat yard.
The shaft is one piece. straight line with no supports other than the cutlass bearing, which is in good shape and the engine coupling. The shaft is about 6 feet long. Next time I'm up I'll take a look at the coupling. The boat is out of the water for the winter here in Ohio. Cold too.... Thanks for your input. I'll post back when I find out what's wrong. (when it warms up a bit).

Did you do a push-pull test of the prop? Literally have one person push and pull axially on the prop while you are inside checking for movement.

If the observation is merely a polished spot on the shaft, could it be an old wear mark that is due to a new shaft location due to the repower? As in the shaft has moved forward in the cutlass bearing due to a dimensional change?