View Full Version : Water in Gearbox!!

03-31-2010, 08:47 AM
I was changing out the oil in my Yanmar 2GM gearbox and was horrified to see about twice the proper quantity, and a murky light brown colour. We had an incident a few months ago where the poor old tub shipped quite a bit of water while we were away, and I reckon it's found its way into the transmission - I guess there is a breather on it somewhere. I can't think of any other way it could have got in there.

I put in new oil, and plan to renew it a few times over the next month or so. Is there anything else I can do to minimise the corrosion? I was thinking of doing a longish run so that it warms right up, and leaving the dipstick for a while out so that any residual water can evaporate out.

Any ideas gratefully received!


03-31-2010, 08:59 AM
Corrosion might not be the main problem but slipping clutch if you do not get it out,
Mix 1/3 oil and 2/3 diesel, fill the box 1/2 full. (forget about dipstick mark).
Start the engine and let it run in IDLE while shifting forward/reverse multiple time to wash out. Do not increase rpm!
Drain completely, fill correct oil-level, do a short run, both ward and reverse, then change oil again.
Hopefully it is ok by now, but keep an eye on it.

04-02-2010, 04:23 PM
You're right about the slipping clutch: a few weeks after this happened (before I discovered the water) I started having problems with the clutch not engaging, and then being hard to disengage. I serviced the Morse control, replaced the cable, and was thinking it was some sort of selector problem. Now I guess it's due to corrosion impeding the movement of the cones on the shaft.

I'll keep flushing it regularly, and start saving for a rebuild, but in the meantime I wondered if there is an anti-corrosion additive anyone can recommend that might help reduce the progress of the corrosion?


04-02-2010, 10:07 PM
Corrosion NOT an issue, but polished clutch system.
Sorry, but a tear down is needed to correct it.

04-04-2010, 09:26 PM
I hear you re polished clutches, but what would explain the difficulty of shifting from forward to neutral? I have to wiggle the lever and force it against considerable resistance to disengage the clutch. It's much less minor when disengaging reverse, but quite difficult in forward. I've already replaced the cable, and stripped and lubed the Morse MV-2 with no improvement..

I appreciate your feedback fella's: the budget only goes so far, so the more I can figure out myself the better things are (especially when I enter budget discussions with the Admiral over the kitchen table).


04-04-2010, 11:34 PM
If not mistaken this is a cone-clutch gear box.
What has happened is probably that the cone surface has been polished and has difficulties in breaking the oil-film.
When it finally breaks the film it gets stuck!
Reverse is probably better as it has not been used that much.
Normally it is possible just to dismantle the box, carefully 'roughen' up the cone and matching gear surface and re-shim the shift fork mechanism.
An old fashioned mech might be able to do the job rather quick and at reasonable price, max 1-2 hrs work at 'loose gearbox', the authorized dealer will probably charge a leg and arm and change whatever he may be able to get of parts!
The alternative is that you get a manual and do it yourself, it is no big deal.

04-05-2010, 12:59 AM
Yes haffiman, it's a cone-type. Your idea about polishing sounds logical, but I'm a bit puzzled , as the vendor's records show the box was overhauled about 18 months (or about 100 hours) ago, 8 months before I bought it, so you'd think it should still be ok!

One question though: according to the manual, the shift cable should be connected to the lever on the box via a sprung clevis. This is presumably to apply a small spring loading to the lever when forward or reverse is selected. Mine however has a solid-type clevis, with no spring. It seems to me that would make cable adjustment critical so as to apply the right force to the cone, and any misadjustment might allow the clutch to slip.

Does this sound logical?


04-05-2010, 01:50 AM
Does not help how many times it was overhauled BEFORE the water ingress.
Running with water/oil only takes a few hours or less to start the problems.
The 'spring loaded' clevis should not be needed. It may 'prevent' people from shifting 'carefully' instead of short and direct. You are not supposed to apply any force on the cone to get it to grip or release.

04-05-2010, 11:36 PM
I've seen people on other forums recommend using a low-viscosity (SAE10) oil to reduce the oil-film effect. Have you sen this?

04-06-2010, 12:38 AM
May be used in cold weather, but will give a harder shifting.
Cone will still be stuck and difficult to get in neutral.
No way around but tear down.
Look for a Volvo mech familiar with the cone systems.

04-09-2010, 02:47 AM
Two flushes with oil, a couple with kerosene, idled as you suggested, then added 10/40W oil and it seems to be OK so far.

old wood
10-12-2015, 10:14 AM
New member, and thanks for the help above!

Am 5 years late here, maybe I should post this elsewhere. Will search.
After 2 years of Freedom! (after an old wooden boat with a Yanmar 12HP single cylinder engine - that I finally gave away) :-) - suddenly find myself with another old wooden boat, this one with a 20-22HP Yanmar 2QM (2QM20?) engine.

On the short trip from the place of purchase (boat belongs to an old friend) over to the harbor, noticed it took the gears up to 30 seconds to engage. Tough s**t when maneuvering in tight places!

Today checked the gear oil - and it was very pink and milky, and the level was about 2-3 cm over the max mark. Really have no history of the boat, whether it has been immersed in water or not, etc.

Am getting rather old and stiff here, but will start by draining then gear box, refill oil, and install a second water pump. Then I may follow lockie's advice above.

And - if "push comes to shove" - I may try taking the box out - work on it over the cold nowegian Winter.