Engine stalls when engaging forward

[Stemar]

A friend has a little 24ft motor sailor with a Yanmar engine which starts and runs fine in neutral and astern, but stalls when put into ahead. He's had the gearbox refurbed by the local Yanmar guy, to no avail. The gearbox turns fine by hand, in gear with no noticeable difference between ahead and astern, likewise the shaft and prop. Yanmar guy has been back and checked things over, but the best he can come up with is to increase the idle from around 750 rpm to 1200, which helps, but it still stalls quite often.

Any ideas?

 

[fredrussell]

Prop too big or something wrapped around it?

 

[PaulRainbow]

Because of the design of the prop, putting the engine ahead imposes a bigger load than putting it astern, plus the reduction ratio is likely to be different, which would account for it only stalling when putting the transmission ahead.

Increasing RPM to 1200 is a total bodge, don't do it.

Could be lots of things, dirty fuel filters, blocked exhaust elbow, dodgy injector, low compression etc

I'd check the fuel system first, then the elbow.....

 

[roaringgirl]

I had similar symptoms on my Yanmar. It turned out to be the lift pump on the way out.

 

[scottie]

Try disconnecting the alternator if it’s a 1GM as the initial load can cause this to happen
Reduction ratio may be different in reverse just to cause problems

 

[jamie N]

Try disconnecting the alternator if it’s a 1GM as the initial load can cause this to happen
Reduction ratio may be different in reverse just to cause problems

I'd strongly disagree with this scottie, for a couple of reasons. Once excited, the alternator won't cease 'charging' when the exciter is disconnected, and will only disconnect when the lead to the battery is disconnected, which is very bad practice when the engine's running as it can very easily destroy the diodes in the alternator.
I do start my engine with the alternator 'unexcited', and once it's running and 'happy' switch the exciter in, and commence charging the batteries, as it lessens the load during starting I believe.
I believe that the OPs issue isn't with the alternator, and would more likely be with the throttle cable set-up, if it's a single 'handle' unit. If it's a separate gear shift and throttle, then it wouldn't fail like that I'd think?

 

[rowlock]

Investigate the drive train moving forward in the hull. Engine mounts past their prime and shaft slipped fwd in half coupling can be problematic examples. A propeller is trying to move forward when ahead is engaged. If it can without taking the boat with it the boss can come up against a P bracket or outer bearing. Face to face friction of these is sufficient to stall a small engine.

 

[scottie]

I'd strongly disagree with this scottie, for a couple of reasons. Once excited, the alternator won't cease 'charging' when the exciter is disconnected, and will only disconnect when the lead to the battery is disconnected, which is very bad practice when the engine's running as it can very easily destroy the diodes in the alternator.
I do start my engine with the alternator 'unexcited', and once it's running and 'happy' switch the exciter in, and commence charging the batteries, as it lessens the load during starting I believe.
I believe that the OPs issue isn't with the alternator, and would more likely be with the throttle cable set-up, if it's a single 'handle' unit. If it's a separate gear shift and throttle, then it wouldn't fail like that I'd think?

I say this From experience and am not suggesting that it be a permanent option but as a short term option to see if it works,however I note that you are in the practice of doing what I am suggesting for the same reason ie to reduce load but on a longer term
I would agree that the control ser up be checked

 

[Refueler]

I'd strongly disagree with this scottie, for a couple of reasons. Once excited, the alternator won't cease 'charging' when the exciter is disconnected, and will only disconnect when the lead to the battery is disconnected, which is very bad practice when the engine's running as it can very easily destroy the diodes in the alternator.
I do start my engine with the alternator 'unexcited', and once it's running and 'happy' switch the exciter in, and commence charging the batteries, as it lessens the load during starting I believe.
I believe that the OPs issue isn't with the alternator, and would more likely be with the throttle cable set-up, if it's a single 'handle' unit. If it's a separate gear shift and throttle, then it wouldn't fail like that I'd think?

I agree here ....

I have seen single lever control malfunction .... when engaging gear - the throttle part is incorrectly installed and literally shuts off engine.

My single lever - had a quirk for a while where the cable connection inside was faulty ... and occasionally throttle failed to respond or reduced when lever put ahead.... only when it completely failed - did it become obvious.

For OP situation .... I would see if operating throttle direct on the engine while someone engages gear works OK ... needs two people of course.....

 

[Rappey]

I saw this engine and what was happening. It has twin helm stations.
It has a brand new lift pump, fuel filters and systems all have great flow. Its not fuel related.
You can go from neutral to reverse on tickover then rev the hell out of it . It works under load as it should.
The moment you put it in forward it instantly stalls out.
Managed to put in in forward with some rpm then instantly opened it up and it worked but the moment you lowered the revs in gear it stopped dead before tickover rpm was reached.
Next time I met with the guy he told me a yanmar service agent had taken the gearbox away, did something, charged lots and it was refitted.
Now it went into forward and the gear shift lever on the gearbox jammed in forward and could not rotate the gearbox shaft when it was back out of the boat.( Don't know if it stalled going into forwards)
Not sure what the current situation is but he is getting badly let down by the yanmar service agent who does not bother to turn up at agreed times.
Not totally sure but I think each helm has twin levers as in one for gear shift, one for throttle..

 

[coopec]

Have you had a look at these links?

Engine Stalling When Shifting To Reverse - Cruisers Forum
https://www.cruisersforum.com › forums › engine-stalli...

21 Sept 2019 — Do the easiest thing first, make sure the throttle lever is sitting on the idle adjusting screw near the injector pump with the gear control in ...
3HM35 Yanmar stalls under load. What next? - Cruisers Forum 4 Mar 2014
Starts, Idles, then Dies + Stalls on Takeoff - YM 1GM10 14 July 2009
Yanmar 3gm30f - Occasionally sputters and dies on start up 5 Jan 2016
engine stalls when put in gear - Cruisers & Sailing Forums 22 July 2013

yanmar engine stalls in forward gear - Google Search

 

[Bilgediver]

I saw this engine and what was happening. It has twin helm stations.
It has a brand new lift pump, fuel filters and systems all have great flow. Its not fuel related.
You can go from neutral to reverse on tickover then rev the hell out of it . It works under load as it should.
The moment you put it in forward it instantly stalls out.
Managed to put in in forward with some rpm then instantly opened it up and it worked but the moment you lowered the revs in gear it stopped dead before tickover rpm was reached.
Next time I met with the guy he told me a yanmar service agent had taken the gearbox away, did something, charged lots and it was refitted.
Now it went into forward and the gear shift lever on the gearbox jammed in forward and could not rotate the gearbox shaft when it was back out of the boat.( Don't know if it stalled going into forwards)
Not sure what the current situation is but he is getting badly let down by the yanmar service agent who does not bother to turn up at agreed times.
Not totally sure but I think each helm has twin levers as in one for gear shift, one for throttle..

The first point as another poster has just mentioned is that it seems this engine DOES NOT HAVE THE IDLE SETTING ON THE ENGINE governor case SET CORRETLY

This means that idle is being arrived at the random positions of the twin helm station Teleflex system and so it is not surprising that there is a problem.

It is important to check from time to time that the idle and full speed screws limit the speed arm on the engine correctly and are adjusted to take control of the idle setting and not rely on what can be random indications from the Teleflex.

I would suggest checking that the engine speed lever goes to the correct position ahead and astern when using both helm positions. and takes the speed lever to both full speed and the slow speed setting when using both throttle controls. Have one person moving the throttle and communicating to another who is watching that the speed lever moves to the setting point for both the high speed and slow speed setting.

 

[neilf39]

I had a rope twisted round one blade of my prop. Was fine in reverse but when in forward it stalled as the rope then tangled on something. Came loose again in reverse. Needed to rotate at a certain speed so was fine when turning the shaft by hand but not under motor. Ended up going on the drying grid to work out what was happening.

 

[ChromeDome]

Got me thinking about the in-gear start prevention switch on the gearbox.
Mercruisers use this also to cut out the ignition for a second when engaging gear to prevent the clonk from dog clutch engaging. If not properly adjusted will kill the engine when engaging gear.

Admittedly might be irrelevant for the OP, though.

 

[Stemar]

Quick update - my friend changed his engine mounts, and that sorted the problem, so it seems that going ahead caused the engine to twist badly out of alignment. Who'd a thunk it?

 

[ean_p]

Quick update - my friend changed his engine mounts, and that sorted the problem, so it seems that going ahead caused the engine to twist badly out of alignment. Who'd a thunk it?

Try Mr Rowlock in #7.........

 

[scottie]

Thanks for outcome although a rather roundabout way to find failed engine mounts