Black exhaust smoke

[mick]

My Sadler 26 has a Bukh 10HP diesel which drives the boat happily all day at about 4.5 knots at about 3/4 throttle. If I get greedy and try full throttle, clouds of black smoke pour out. I'm not usually greedy but there are occasions when it would be nice to have a few more knots. Any suggestions? Thanks in advance.

 

[Guest]

Possibly something to do with the air intake or filter.

 

[lezgar]

Could be:

airfilter blocked
compression poor
low quality diesel
problem with injection pump or injector
thermostat faulty
ventilation to engine room inadequate

 

[pete]

Cause -incomplete combustion of diesel being injected, Is the boat hull badly fouled? if not perhaps you are over propped and need less pitch, a prop supplier will be able to work this out armed with type and displacement of boat,engine size, and gear box reduction.
Good luck

 

[Avocet]

Try getting the injectors cleaned and tested. It only costs about £15 each at any diesel injection workshop. I used my nearest Lucas workshop from the Yellow pages. Diesels often smoke when they're running rich so either you're getting too much fuel or too little air.

 

[Guest]

I get the same thing with my BUKH 20. I can chug along at three quarter throttle and 6knots, with the occasional wisp of white smoke; as soon as I apply full throttle (which I rarely need to do) out comes the black smoke

Last year I had a complete engine overhaul (at huge expense) and it made no difference.

 

[Twister_Ken]

New Bukh does the same

I have a new Bukh 10, installed last year. Only about 30 hours running so far and just first-serviced.

Exactly the same results. Full throttle equal black smoke (not a lot) and no increase in revs. Seems that one is squirting in more fuel than the engine can burn, which leads me to suspect that my prop might be a little too pitched. But as I get satisfactory performance before black smoke, I shan't rush to do anything. Maybe when the current prop reaches the end of its life?

PS - how long do props last assuming no physical damage from hitting things?

 

[johnt]

First point ; A prop can last for anything up to 20 years ! average is 12/15

Now, the main question. I would expect a lot more speed at 75% throttle, 4.5 k on a 26 loa shouldnt take more than 40 to 50% throttle and economical cruise is about 60% power, which should give 5 - 5.25 kn dependant on wind and sea state.

4.5K at 75% indicates that you are slightly underpitched, if so black smoke says that your injector/s need a service.

Full throttle flat water no wind should give you close to 6.5 kn

so start with your injector.

 

[brianrunyard]

According to the Perkins manual, black smoke can be caused by:
1. Restriction in air induction system
2. Fault in atomisers or atomisers of an incorrect type.
3. Wrong type or grade of fuel used.
4. Restriction in exhaust pipe.
5. Engine temperature too low.
6. Fault in fuel injection pump.
7. Timing of fuel injection pump incorrect.
8. Tappet clearances incorrect.
9. Valve timing incorrect.
10. Bad compression.
11. Bad compression.
12. Cylinder haed gasket leak.
13. Valves not free.
14. Worn cylinder bores.
15. Leakage between valves and seats.
16. Piston rings not free or badly worn.

 

[rob]

Mick,
I had a problem until this year with black smoke. From prop. to engine injectors, bad compression etc. was all suspected, but I found the culprit in the end. When I overhauled the engine three seasons ago, I simply didn't replace the fuel injector seating nozzle. This I only found out this season due to having the injector tested, and on assemble found the nozzle not there. It runs fine, with very little black smoke when at full throttle, and giving me a further 3/4kt. This I hope will open other ideas to you.

 

[Guest]

Adding onto this one .... My Sunrider 25 Motorsailer has a 32 HP Perkins 4-99, driving a 13" fixed 3 blader.
So I get white exhaust smoke when engine is first started and then stops once warmed up .... about 4-5 minutes.
Up to half throttle exhaust is clear until engine is working hard against weather / current etc.
3/4 up to full throttle black exhaust smoke and staining of the transom of the boat.

I have been told that compression is low, there may be a hairline crack in the head allowing water into chamber, I have been told that Easy Start over many years has gunged it all up .... the list goes on and on, but the engine keeps chugging away oblivious to all its supposed faults !!!

So anyone out there any ideas what it could be ?