Diesel slow running

[Guest]

I had a great sail this Sunday on a boat that had a Ford Watermota engine. Considering the engine is 20 years old it runs a treat but when ahead/astern is selected to give minimum revs, the engine stalls. Tickover is set at about 700 rpm (guess as there is no tachometer).

My understanding is that the added load should cause the governor to inject more fuel so that the engine speed is maintained. Am I right and is the problem likely to be the governor? If so is it a case of simple adjustment or something more drastic? Ideas welcomed!

Tom

 

[Guest]

My watermota prop is of the fully pitching variety. If the pitch is to great in forward the blades are nearly in sailing position,if thisis the case it will stall the engine.Try getting full revs in neutral and then gently ease her into gear.

 

[oldharry]

The governor in the injector pump sets the correct fuel/air ratio of diesel to the injectors for throttle setting and speed, but does not compensate for a drop in speed applying a load except to ensure the fuel air ratio remains correct. Either the tickover speed is set too low, or the engine is overpropped, or a bit of both. That is assuming that there are no problems in the transmission causing excessive drag, such as an overtight inboard gland.

Check the shaft is rotating freely - you should just be able to turn it by hand. If all appears well there, set the tickover high enough for the engine not to stall when gear is engaged. If the off load speed is then too high, there is a problem somewhere either within the engine itself (injector timing, low cylinder compression, injectors faulty etc) or the gearbox is part seized and creating excessive load when engaged.

If the engine is overpropped, i.e. over size, or too coarse pitch, then having set tickover to keep running in gear the boat will take off at possibly 2 or 3 knots on tickover, and will be a pig to handle at close quarters manoevering! Solution then is to get on to a Marine engineering expert like Lancing Marine or Norris's for advice on optimum propsizes for that engine and boat.

 

[Guest]

On my diesel(s) they do have a governor as you suggest and the throttle sets the desired RPM which the governor attempts to maintain. As the linkages get older, however, they develop a little slop so the RPM error has to be a little more in order to get it to respond. This results in the often heard cycling at idle - rrumph - rrumph - rrumph as the engine speeds up, the throttle cuts back but not quite soon enough, then overshoots, the RPM gets too low, and the governor speeds it up again.

There is usually not a great deal you can do, depending on the engine. The simplest is to raise the idle RPM a little to cover the slack. Some governors have a "sensitivity" adjustment to improve (or decrease) response but you will need a shop manual to find and adjust it.

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