Yanmar SB 12 Governor arm stuck

[rockin411]

I'm currently not getting fuel through the pump and noticed that it seems that when I move the throttle that it's not moving the governor arm - so the fuel is essentially shutoff. I disconnected the spring and the arm doesn't seem to move back and forth. I'm assuming it should pivot where it attaches? Does anyone have experience with this? Thanks so much in advance!

[rockin411]

Here is a pic form the parts catalog. It looks like there are pins that would keep it from turning but on the other hand i'm thinking it has to move so that it can move the governor on the fuel pump.

https://photos.google.com/search/_tr...E5XQPPWDxuCdnB

https://photos.google.com/search/_tr...8frjp-P62sxgwD

[Wotname]

Not seeing any image in the last post - getting a 404 error on the link.

[rockin411]

Updated the link

[rockin411]

https://www.flickr.com/photos/133520...posted-public/
https://www.flickr.com/photos/133520...posted-public/

[rockin411]

Sorry for the multiple messages but I can't edit/delete for some reason:
The more I look at the diagram I don't understand how the governor arm and governor weight are related? The governor arm goes up to the fuel supply where I think I'm having my problem by it not moving and then it's attached with the spindle that goes into the engine to do something?

[Wotname]

There is a 30 minute EDIT window i.e. you have 30 minutes after you post to carry out any editing. It you need a serious edit that can't be sorted by making anther post, you can contact a moderator and request an edit.

Now onto the interesting stuff - The SB12 governor arm. The attached diagram shows the governor arm (#8) in red, the regulator arm in a green circle, the sliding gov weight sleeve (#12) with blue arrows and main throttle spring in a pink ellipse.

In short, the governor arm should be free to rotate back and forth about say 20 to 30 degrees (red arrows). This in turn causes the regulator arm (green circle) to rotate. To get maximum fuel (starting etc), the regulator arm needs to be fully CW. This means the governor arm has to be full CCW. This is normally achieved with the main throttle spring (pink ellipse) pulling on the governor arm. As the engine rpm increases, the governor sleeve (#14) gets pushed away from the body (by the weights) of the engine causing the governor arm to rotate slightly CW, causing the regulator arm to move slightly CCW, causing less fuel to be delivered by the injection pump. The movement between max fuel to min fuel is only a few degrees.

Regarding the weight assembly (#17) - the frame (#5) rotates with the crankshaft causing the two weights (#6) which pivot on #15 to be 'flung out', as they move, they cause the sleeve (#12) to move away from the engine. The higher the rpm, the further the sleeve moves away from the engine.

If the engine slows down, the main throttle spring pulling against the governor arm forces the sleeve towards the engine.

If your governor arm is not moving, you need to determine if the issue is with the governor weight side or the regulator arm side.

NOTE - if you disconnect the eccentric pin (orange ellipse) which joins the governor arm to the regulator arm, you MUST adjust it properly when refitting. The position of the eccentric pin is critical and a 1/8th of a turn out could make it very very difficult to get a start. The operation manual gives instruction on the adjustment and it does require adjustment every say 500 hours.

If needed, I can post the adjustment method here.

[rockin411]

Thank you so much for the detailed explanation! That actually makes sense to me and that says alot since I didn’t even know the purpose of a governor a few days ago
I believe you helped me with the adjusment of the regulator a few years ago so I’m confident it’s not that. I’d say something is stuck that controls the rotation with the weights as I can’t move the arm at all. It’s locked in the CW position - fuel off. Does this mean I’ll have to do some major disassembly?

[Wotname]

Originally Posted by rockin411

........ I’d say something is stuck that controls the rotation with the weights as I can’t move the arm at all. It’s locked in the CW position - fuel off. Does this mean I’ll have to do some major disassembly?

Probably but not necessarily - depends how lucky you are!
My guess is either
1. the sleeve (#12) isn't sliding
or
2. the governor shaft (#8) has jammed in the needle roller bearings (#9).

1 would be very very unusual while 2 would only be unusual. I suppose there could be a problem with the weight assembly (#17).

The big question to ask is when did this occur? When was the last time everything was OK? What happened between the two events? Without knowing the recent history of the engine, I really guessing here.

ATM, I would be tempted to turn the engine over (decompressed) by hand and feel for any movement or vibration in the governor arm. Then spin it over faster (using the starter motor and still decompressed), apply gentle pressure on the governor arm CCW by hand and tap the arm (gently).

I think #11 is a dust cover and you may be able to squirt some lubricant (WD40 etc) in there to possibly free up the needle roller bearing (#9).

If you can get movement at all on the governor arm, work it back and forth by hand to see if you can free up whatever is stopping it from moving. A small hammer is you friend but do use it with caution. Keep the engine decompressed and keep spinning it over with the starter motor.

Good luck.

[rockin411]

The good news is that i got the governor arm free. Pulled it with a little force and it is now free to rotate. Seems like an internal spring keeps it in the CCW position by default - which means the regulator is CW or full throttle. And the throttle moves it to a more closed position when it's in neutral.

The oil was low when all this started but it had ran fine the day before and weekend before.

The bad news is I can't get it to start. Pulled the injector and it seems to be spraying fine. And I had sprayed WD40 in the intake and that worked(However I used too much and thought I had a runaway engine for about a minute - couldn't get to the decompression lever). I'm really at a loss now. I was thinking about adjusting the regulator again but feel like that would be a waste since nothing really changed there.

[Wotname]

Pretty sure there are no internal springs but I am going on memory here. I might be able to find some of my old photos of the internals later; if so, I'll post here.

I wonder if the governor arm is moving fully CCW. It doesn't take much before there isn't enough fuel getting delivered to prevent a start. However if the injector is spraying OK, then that suggests there is enough fuel getting delivered.

Do you have the hand start (crank handle) option fitted?

If so, can you hear the injector pump 'squeak' when the engine is rotated by hand decompressed as it approaches TDC of the compression stroke. If you can't hear the 'injector squeak', the you might not be getting enough fuel (or you hearing is going south).

[rockin411]

Looking at the parts diagram above, I was thinking #2 was providing weight/spring or something to keep it in the CCW position. Unfortunately I don't have the crank to try to spin itbut when i removed it and installed upside down it seemed fine? I'm thinking about replacing the injector anyway - i think it's original. Are those readily available for purchase?

[rockin411]

The more I think about it I’m convinced it’s a intermittent stuck valve. When I sprayed the wd40 in the intake even that took quite a few efforts to get it to fire. And all my problems in the past have been mostly intermittent where ultimately I didn’t do anything and it just started working either after a few days or weeks

[Wotname]

If the governor arm was stuck (i.e. not moving), then whatever was causing it to stick is very likely to be a big part of the problem. It must be very free to move and it only moves a few degrees in normal operation. Anything that prevents it moving freely will be (IMO) very problematic and could be intermittent. Perhaps some gunk has got past the cover (#11) and into the needle roller bearing (#9).

The only internal photos I have is from the governor weighs and arm for a YSE. It is very similar but not exactly the same as the SB. There are no internal springs in the YSE and I am confident there are none in the SB.

Rather than use WD40, fill a small spray bottle with diesel and mist that into the air intake while attempting to start. If it doesn't fire (and run roughly) while misting diesel into the air intake, you have either a compression problem or blocked exhaust.

BTW, have you checked the exhaust mixing elbow (and exhaust piping) for blockages?

[Wotname]

^^ Forgot to add -

Another reason for failure to fire in the above scenario is low rotational starter motor rpm. To check for this, spin the engine over for 5 seconds decompressed and with the starter motor still engaged, recompress the engine while misting in the diesel from the spray bottle.

If it now fires as soon as the engine is recompressed, then it is likely the electrical aspects of the starter motor circuit is compromised.