Engine and MaxProp problems

[Zen Zero]

I had a lovely sail on a friends boat on Sunday. We bowed out of a windless regata and motored off to find a windier place; which we did after half an hour. My friend said let's see if it happens again as he moved the throttle lever to the upright position and sure enough the engine conked out. It happens quite a lot he says. It's a 30 year old Nanni Diesel 18hp 3 cyl. The cooling water temp gauge starts at 40°C and barely rises above this. It ticks over at just above 700 rpm He tells me he increased the idle speed from 600 recently to see if that would fix the problem.

He says it only happens when he reduces engine speed to idle after half an hour or more of motoring. It doesn't happen when the engine is cold and if he starts the engine again it runs normally.

I can't think what the cause might be.

Another problem this boat has is its MaxProp. Often, but not always, when he engages reverse, the engine struggles and then conks out after a second or two. This happened in the marina after our Sunday sail and fortunately the attendants were at hand to give the boat a shove backwards with their RIBs. Once it was going backwards, it went quite happily into reverse.

I suspect there are two problems 1 with the engine power at low revs and one with the maxprop not unfurling itself properly. But I don't know enough about maxprops to know how to fix it.

Any suggestions?

 

[RichardS]

I can't really see why the Maxprop not unfeathering would cause the engine to "struggle and conk out after a second or two" so perhaps this is the same problem?

Richard

 

[Robin]

Benn over 30 years but had something similar on a Bukh 10 when shutting down, the injector pump 'rack' was sticking below tickover setting on shutting down. If the engine was spun fast by the starter with decompressor lever open it would sometimes restart. One time I bump started it under spinnaker getting it spinning in gear with decompressor open, engine in fwd gear and the starter used simultaneously. Is the engine stop device sticking perhaps?

 

[Zen Zero]

I can't really see why the Maxprop not unfeathering would cause the engine to "struggle and conk out after a second or two" so perhaps this is the same problem?

Richard

Neither can I, but the engine is turning, slower and slower, sounding more and more fatigued until it stops - this all takes less than 3 seconds. I don't know what a MaxProp is doing when it's unwinding itself in reverse but I do believe I have read somewhere else that they require a bit more power to go backwards than forwards. I don't actually know why this is but whatever the reason is, it seems to be a bit wonky on my friend's boat.

 

[Zen Zero]

Benn over 30 years but had something similar on a Bukh 10 when shutting down, the injector pump 'rack' was sticking below tickover setting on shutting down. If the engine was spun fast by the starter with decompressor lever open it would sometimes restart. One time I bump started it under spinnaker getting it spinning in gear with decompressor open, engine in fwd gear and the starter used simultaneously. Is the engine stop device sticking perhaps?

I think the engine power at low revs problem might have something to do with fuel or air supply. I'm not sure how the Nanni handles this, I'll have a look for the manual.

I'm not sure if it could be the engine fighting against its own stop device because it seems to be perfectly ok in all other circumstances.

 

[sailorman]

I would suggest that 600 RPM idle is far too slow, even out of gear & around 850 > 900 RPM at idle would be my guess

 

[earlybird]

I would suggest that 600 RPM idle is far too slow, even out of gear & around 850 > 900 RPM at idle would be my guess

I'd agree. Presumably the Nanni is Kubota based. Beta recommend 850 rpm min. for their Kubota based small engines.