Volvo Penta MS transmission bang

[WillieC]

When at dead stop, as at the beginning of a trip, the procedure is to drop the engine to idle, 750-810 rpm. (This MS transmission is connected to the MD17C engine.) Pop it into either forward or reverse, no problem. Gentle shift, no noise, no problem. Throttle up and life is good. The problem comes when maneuvering for docking or stopping.

This may be completely normal but noise is energy and wear and tear. I have observed what is happening, and it has to do with the fact that the as long as the boat is moving, the prop is spinning, whether under power or drifting. So popping it into reverse, even with the engine idled all the way down, the prop and shaft have to immediately stop and start reversing. I would protest myself under those circumstances. As you might imagine, backing and filling and shifting while moving are making me nervous.

The transmission, while under way, makes no other untoward racket. I am considering fashioning some kind of brake for the shaft, but it must not engage while in gear, doh!, and I don't want it too complicated as there is enough going on while maneuvering as it is.

There can't be but two or three of these old combinations still around, but for those similarly equipped, is this bang at direction change normal, or is this indicative of something amiss in the transmission? Previously we had the RB transmission connected to the MD3B engine and it was similar, but not as abrupt.

Thanks for your input.

[Beta Don]

Is that particular transmission known for being a problem? There must be thousands of them out there and it's pretty much guaranteed many Captains are not as careful to wait for the engine to get down to idle before shifting them . . . . especially if they're about to run into the dock! If theirs aren't breaking with the occasional 1500 RPM shifts, yours probably wont either

With your understanding of all things mechanical and your much greater than usual care for it, I suspect the transmission will long outlive you . . . . it's already outlived a couple other owners

My opinion is . . . . you're probably worried about next to nothing AND if you don't quit actively looking for places to spend unnecessary money on that old iron, the Starfleet Commander is going to begin to get jealous! Take her out to dinner instead of rigging up a shaft brake that may end up doing more harm than good!

Don

[dkirsop]

The noise you describe, and the conditions which give rise to the noise, are usually indicative of shaft movement. This can be either internal, such as a gear shaft, or external if it is the propeller shaft. If it is the propeller shaft you can usually see evidence of movement at the stern gland where a small ring of lubricant appears on the shaft as it moves back and forth. If it is internal then usually the problem becomes evident when the transmission fails at the worst possible moment as happened to me 3 years ago.

In my case, the stud holding the rear drive shaft in the transmission backed out and fell into the reduction gear - while I was transiting under the 2nd Narrows Bridge in Vancouver during the time of peak current. This is a high traffic shipping channel. The RCMSARS (Royal Canadian Marine Search and Rescue) provided sterling service in coming to my aid and towing me back to the marina.

Tow of Shame.jpg

I had been under the bridge when the engine quit with a god awful bang. With the current flowing at 5 knots I had drifted a mile before being taken under tow.

[DesertAlbin736]

I wouldn't call that a "Tow of Shame". More like a "Tow of $#^t Happens". At least you didn't have to get towed head-on into 4 foot waves with the tow line rubbing & chafing over top of the bow pulpit cross bar. Don't ask. Another reminder to get my DSC MMSI number via an FCC station license instead of BoatUS so in case of a DSC distress call while in Canadian waters the RCMSARS and RCCG will have access to my particulars. Also why I carry Unlimited Gold water towing coverage with my BoatUS membership.

[DesertAlbin736]

Otherwise I pretty much agree with Don. If it ain't Baroque, don't fix it. Assuming all else is in order I'd only start worrying if the banging noise gets noticeably and progressively worse accompanied by grinding & unusual shaking. That & keep your towing insurance policy up to date. I would also say that if you have crew aboard and a dinghy with outboard, in a pinch you can tow yourself by tying the dinghy alongside the stern quarter (preferably starboard side so you can communicate with the helmsperson) and you drive the dinghy while the Starfleet Commander steers the boat. Works better with more control than a tow line from the bow. We've towed disabled boats that way and it works well, at least in fairly calm conditions.

[Tree]

On a previous boat, albeit with a stern drive the Volvo engine would go in and out of gear with a bang. I put 1250 hours on that engine and transmission without any issues. What I did find out was the drive was on a cone clutch. The clutch does need to “bang” into gear otherwise it would essentially run wearing the taper of the cone out. It was either out or in and you couldn’t “feather” the clutch so to speak.

[WillieC]

Great answers all! If it ain't baroque... kill me now.
And the main problem is it's winter and I have nothing to do but think about stuff.
Beta Don, that's hilarious! Maybe I should take the SC out once in a while and NOT talk about the boat!
Towing insurance? dinghy with motor? What's that?
Dkirsop gave me lots more to worry about, so this query has served its purpose.
Tree, I think these trannies are cones. Not much feathering is exactly right. More likely, any soft slip and slide would probably be more worrisome, indicative of failing friction surfaces.
DA, the mmsi is something I need to do as well. Just read in the BCAlbineers that their A25 group has applied for a common number shared between them all. Our own Mr. Kirsop was instrumental in making that happen. Nice work and a great idea. This last summer I was passed by a group of Little Rocket Men that seemed to think channel 16 was ok for them to use for their happy little conversation. Maybe their plan was to capsize me and thought the CG might want to know where to start looking.

OK, I'll let the tranny noise go. For now. We have bigger things to consider, like how to clean stxray's water jacket short of a tear down.