LIFE: Part 2

For a while we have been puzzled.

We would start the port engine and put it into gear. And all would be well.

Then we would stop for whatever reason.

And then we would put it into gear again – and nothing happened. It seemed like the prop wasn’t turning. Indeed occasionally that was the case. But in most cases the prop shaft was still going around.

Yet we were doing just 1.5 kts instead of 3.5 kts, using just the one port engine. And the same would happen in reverse – just no power when we try to maneuver.

Finally we figured out that the clutch must be slipping.

The workshop manual had a whole list of possible causes, but most seemed to do with oil pressure. I guess that the clutch needs oil that is not too thin, and not too thick, in order to work correctly. The gearbox case does specify SAE 30 oil, but a lot of people seem to think that Automatic Transmission Fluid would do the job better. That is most specifically NOT the case. Well, we didn’t have ATF in it, but we did wonder if perhaps the mechanic in Antigua had put the wrong grade in, and that now, when the oil heats up, it would get too thin and no longer work.

The mechanic who took a quick look at it started muttering about replacing the cones for about $1000. Hmm, not keen on that idea.

In any case we were well overdue for a transmission oil change (oops – mea culpa), so I bought the correct grade of oil, changed the oil twice, in order to totally rinse out the old oil, and then filled it up with ‘Genuine Yanmar Transmission Oil – SAE 30’ just to be absolutely sure we had the right stuff.

That was four days ago.

Well, since then we have not had any problems with it slipping. And today we gave it a very good workout which would previously have caused us problems.

So, it looks like it was all fixed with some fresh oil!

Phew.

Update November 2013

Once we were tucked up in Ragusa, we decided it was time to take a proper look at this. Over the summer the clutch has mostly behaved itself, but there were still times when it was slipping.

Further research had revealed that this is actually quite a common problem, caused by the cone on the clutch becoming too polished. The cause of this is too much idling with the clutch out of gear (as when sitting at anchorage charging batteries). It is for this reason, plus the knowledge that idling isn’t good for diesels in general, that we always try to put the engine into reverse gear when charging. This pulls the boat gently back on the anchor, puts some load on the engine, and works well except in the lightest of zephyrs when one then ends up going around the anchor in circles.

Anyway, fixing the clutch is, supposedly, a simple job. Take it apart, lap it down with some carborundum paste (like lapping engine valves in their seatings), and then put it back together.  Except that someone in the past had locktited everything together ,so we just couldn’t get the housing off the clutch.

We called in a mechanic who understood the problem. He took it to his shop, took it apart, and ground down the cone. However, he said that this was not the first time it had been done, and that next time around we are going to need a new replacement unit.

He also told us to use ATF oil instead of the normal 30 SAE. This rather surprised us, but he did seem to understand the problem with these units, so I guess we will give it a go. He said that we should do this because of the worn-down state of our cone. Another Yanmer mechanic confirmed that we should do that.

It turns out that this fixed the problem and all is working well now.

How to Remove the Gear Box

The photo below shows the marine drive assembly. You will see that there is a big chunk labelled Torque Limiter. Not many boats have this, but ours does. The intent was to prevent over-torquing the marine drive when first putting it into gear. It contains a number of discs that operate rather like a clutch – they will slip if too much torque is applied which should also protect one from damaging the gear box with a prop wrap.

Anyway, to take the gear box off, first empty the oil from it.

Then you have to disconnect the torque limiter from the gear box. You do that by undoing the 4 stainless bolts (next to the letter A) of which you can see three above. There are also some bolts on the forward end of the torque limiter, by letter B. Do NOT undo those, as that will take the limiter apart, and you will then have a real struggle getting it all back together again.

Once you have taken out bolts A you have separated the prop shaft form the torque limiter.

You will see inside a big bolt with a huge slot in it. This has a LEFT HAND THREAD. Use something large, like an old U-fitting from a turnbuckle, or some piece of stainless steel plate, that will fit nicely into the slot and onto which you can get some leverage. Then, holding the torque limiter still with a vice grip wedged in, turn that bolt clockwise to undo it. That will separate the torque limiter from the gear box.

Now it is just a matter of removing the blots from around the rim of the gear box, and disconnecting the morse cable controls.

If you need to service the torque limiter itself, read the scarce and hard to find torque limiter_service manual (pdf).

 

 

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