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Old 10-05-2020, 08:30   #1
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Yanmar 2GM20F leaky adjustment screw

Hi folks,
my first post here! (long time lurker)

Our Yanmar 2GM20F has an adjustment screw that has been leaking raw water for some time it appears. It is located on the SB/FWD side of the engine.

I looked through the manual, but somehow failed to locate what this screw is for. It was wired to the block, so I assume it is not to be touched frequently.

Any insights? Pretty disconcerting amount of corrosion there...Thanks!
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Old 10-05-2020, 08:43   #2
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Re: Yanmar 2GM20F leaky adjustment screw

That appears to be the injection pump adjustment. Dont move it! Why do you think it's leaking? I see corrosion around it, but that's from salt water. The pump has diesel in it.
The corrosion could be from various things, former work, hose leak, heavy weather/green water getting below into the engine compartment or etc. Is anything wet now?
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Old 10-05-2020, 09:18   #3
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Re: Yanmar 2GM20F leaky adjustment screw

Appears to be possibly a raw water leak somewhere above the “screw” mentioned... Run the engine and observe...
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Old 10-05-2020, 10:24   #4
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Re: Yanmar 2GM20F leaky adjustment screw

Thanks for the replies. It was dry when I found it, but judging from the corrosion it seemed like it was coming from there. That doesnít make sense if it's part of the injection pump of course. I didnít change the adjustment not knowing what it was though the locking wire did snap off being so corroded.

Iíll investigate more and report back!

Thanks for the replies
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Old 10-05-2020, 15:24   #5
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Re: Yanmar 2GM20F leaky adjustment screw

Quote:
Originally Posted by gatorjos View Post
Thanks for the replies. It was dry when I found it, but judging from the corrosion it seemed like it was coming from there. That doesnít make sense if it's part of the injection pump of course. I didnít change the adjustment not knowing what it was though the locking wire did snap off being so corroded.

Iíll investigate more and report back!

Thanks for the replies
Yep I'm with the other 2 posts, definitely not coming from the adjustment screw opening or it would be rusty. Whilst I'm not familiar with the 2gm20 cooling layout it's likely its from a raw water hose drip.
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Old 10-05-2020, 16:21   #6
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Re: Yanmar 2GM20F leaky adjustment screw

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Originally Posted by gatorjos View Post
Thanks for the replies. It was dry when I found it, but judging from the corrosion it seemed like it was coming from there. That doesn’t make sense if it's part of the injection pump of course. I didn’t change the adjustment not knowing what it was though the locking wire did snap off being so corroded.

I’ll investigate more and report back!

Thanks for the replies
Welcome aboard CF, gatorjos.

It is the No Load Maximum Speed Limiter part of the governor - essentially sets the maximum idle speed and is factory set as part of the engine's emission controls. It isn't the end of the earth if it has moved slightly but of course, it is best left alone.

The corrosion is almost certainly being caused by a raw water leak from somewhere in the heat exchanger / exhaust manifold which is directly above the governor housing. It could be as simple as dripping hose but it may be far more serious. Hunt it down!!!
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Old 10-05-2020, 16:28   #7
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Re: Yanmar 2GM20F leaky adjustment screw

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Originally Posted by gatorjos View Post
..........
I looked through the manual, but somehow failed to locate what this screw is for. It was wired to the block, so I assume it is not to be touched frequently.

..........
FWIW

In my service manual, the governor system is chapter 4 and the heat exchanger / manifold is in chapter 8.
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Old 10-05-2020, 18:33   #8
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Re: Yanmar 2GM20F leaky adjustment screw

If youíre lucky itís the raw water hose between the pump and heat exchanger........unlucky would be a leaking heat exchanger end cap, assuming this is a raw water leak and not from, say, the engine hatch or cockpit floor. Click image for larger version

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Old 11-05-2020, 09:07   #9
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Re: Yanmar 2GM20F leaky adjustment screw

I had a similar problem with my engine! The hose from the raw water pump that winds its way up to the heat exchanger was worn out right where it connects to the heat exchanger input port! Mine dripped salt water on the throttle lever where it goes into the fuel injection pump . Right above the engine shut off cable!. My throttle at times is very difficult to move at times and requires extra lubrication!
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Old 11-05-2020, 13:26   #10
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Re: Yanmar 2GM20F leaky adjustment screw

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Welcome aboard CF, gatorjos.

It is the No Load Maximum Speed Limiter part of the governor - essentially sets the maximum idle speed and is factory set as part of the engine's emission controls. It isn't the end of the earth if it has moved slightly but of course, it is best left alone.

The corrosion is almost certainly being caused by a raw water leak from somewhere in the heat exchanger / exhaust manifold which is directly above the governor housing. It could be as simple as dripping hose but it may be far more serious. Hunt it down!!!
I second that. It is a bit hard to find but if you have the Seloc Yanmar Inboards 1975-98 Repair Manual its on page 4-21 of the fuel system. It's wire locked together with the same piece of locking wire with the Fuel Injection Limiter which is on the vertical face below it on the forward face.
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Old 11-05-2020, 15:41   #11
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Re: Yanmar 2GM20F leaky adjustment screw

FWIW, there is _GM & _HM Yanmar service manual available for download in the CF Library (Manuals) area. This covers the OP engine.

https://www.cruisersforum.com/forums...id=1&sort=date
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