Gearbox Delay... or not?

[Dazzajon]

I’ve got twin TAMD41b’s with the MS4 gearboxes. Took the boat for a run last weekend, first time in a good few months. All was fine but as I was manoeuvring her back in to the mooring a problem developed with the stb side - at first I though I’d completely lost forward gear.

Anyway tied her up and discovered that for some reason on the stbd side when the shifter was put in forwards gear a delay of 3 or 4 seconds had developed.
before the prop turned. Reverse was fine and the port side was fine both forwards and reverse. I played around for a bit but each time stbd was put in gear forwards still a delay.

Went to try and have another look today, started engine, gear shift to forwards. No problems what so ever. Tried a few times but still no problems.

Has anyone else experienced a similar intermittent problem, and any ideas? I’m wondering if it’s going to play up just when it’s warm, but I won’t be able to check that theory for a few days until I can next take her for a run.

TIA.

[DougR]

The MS4 transmission is a cone clutch design, and typically the symptoms which you are experiencing are indicative of the type of wear that occurs with these designs. When shifting, the cone is moved into contact with a mating gear cup and the engagement of the two parts transmits power to the prop shaft.

The surface of the cone is made with small grooves and channels to allow oil to be wiped/displaced from between the two parts and promote engagement, but as the cone wears, the grooves get worn and become shallower, making it more difficult for the oil film to be displaced and engagement to occur. Normally as this wear process takes place, the application of some throttle allows the cone to cut thru the oil film and engage, but when docking, the application of more throttle gets a bit tricky.

The first thing to check is that the oil level in the gear is correct, and importantly the oil viscosity needs to be correct. Oil that is too high in viscosity aggravates the problem.

The next step is usually the replacement of the cone and lapping the gear cup with a course lapping compound. This lapping process takes the polish off the gear cup and creates a bit of "tooth" to allow the cone to engage.

I'm sure your local VP dealers or other transmission specialists have experience with the process and can resolve things without too much problem.

DougR

[Dazzajon]

Thanks for the reply.

Oil has been changed just to be on the safe side. Old oil looked ok but problem still exists. Just think it’s strange if it’s the cone that it’s only a problem when warm, although...

Since my first post I’ve noticed quite a vibration coming from that side. Didn’t notice it previously as since launch I’ve only been out twice and drove from the flybridge. Vibration isn’t noticeable at low RPM but at cruising speed definitely so. I ran the other engine on its own which was lovely and smooth and then run the problem side on its own and definitely lots of vibration.

Checked the props for fouling with a go pro and nothing there.

When the boat was out the water I had the cutlass bearings replaced so wondering if something has gone wrong with one of these somehow. Other than that really not sure what else could be causing the vibration.

Also wondering if it’s this vibration that’s causing the gearbox to have the delay, especially as that too had no problems last season.