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Black smoke under load


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Hello advice needed. Ive just had a perkins 4108 rebuilt. On start up it gives white smoke....once up to temp it clears  with just a bit of normal exhaust smoke.....however in gear as you pass 1200 rpm to 1800 it gives black smoke....

The boat engineer is coming to check as it has an oil leak behind the timing cover plate. Any advice or ideas please

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Is this only while it is accelerating from 1200 to 1800 rpm or when held steady between those  speeds. I can't see how an overhaul could cause this because it sounds like overloading so an overlarge prop but then it should smoke above 1800 until you back the throttle off a bit.

 

It could be a restricted air inlet but then the same thing applies, it should stay smokey above 1800 rpm.

 

I think it has a hydraulic DPA injector pump and knowing how they work I can't see how that could create smoke (excess fuel) just between those speeds.

 

 

 

 

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3 minutes ago, Tony Brooks said:

Is this only while it is accelerating from 1200 to 1800 rpm or when held steady between those  speeds. I can't see how an overhaul could cause this because it sounds like overloading so an overlarge prop but then it should smoke above 1800 until you back the throttle off a bit.

 

It could be a restricted air inlet but then the same thing applies, it should stay smokey above 1800 rpm.

 

I think it has a hydraulic DPA injector pump and knowing how they work I can't see how that could create smoke (excess fuel) just between those speeds.

 

 

 

 

Max fuel set too high?

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Just now, Leon 12 said:

But once you open the throttle its billowing black smoke 

On a diesel engine, the pump is governed at a set speed. The "throttle" just alters that set speed. On the way from low speed to high the pump is delivering max fuel to try and achieve the new speed. If max fuel is to high then there's insufficient air to burn it completely, hence black smoke.

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I suppose the plunger maximum movement could be set too large but then the smoke should continue after 1800 rpm. In any case the governor valve would control the fuel delivered to the plungers and that is controlled by a non-adjustable spring in the turret. Even the mechanically governed DPA feeds the plungers after the governor valve.

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Just now, Leon 12 said:

No only in gear. Out of gear pretty much nothing 

 

That's overloading - prop fouled or some rare gearbox fault - but it's the stops smoking at 1800 rpm that makes no sense. It should rev far higher than that and if it won't then its very likely an oversized prop.

 

If its been properly overhauled then its not an old engine, its as good as a new one. It might be a bit tight but if so I would expect a low cranking speed.

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All good stuff from the 'team' as usual.  My only remark is that remember you are dealing with fuel and air,  excess/over fuel can also equate to reduced/lack-off air for combustion.  Any air filter fitted?,  Any inlet ducting/pipes with kinks/dents in them.

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Did you replace the packing or tighten your stern gland whilst the engine was out??

If you couldnt check the shaft movement, it could be as simple as the packing on the prop is too tight making the engine work harder than it normally does.

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Just now, matty40s said:

Did you replace the packing or tighten your stern gland whilst the engine was out??

If you couldnt check the shaft movement, it could be as simple as the packing on the prop is too tight making the engine work harder than it normally does.

 

I had that thought but decided not to mention it until more info came to light.

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I purchased the engine . However the head on the engine was not good so they used my cylinder  head.....my head had new valve guides and seals. So i dont know if thepump was redone.....i am guessing not . So apologies  for not thorough explanation.....it has been an ordeal. Icould have got a new engine by the time its sorted 

I bought the engine in good faith off a friend . Nightmare to say the least 

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It's hard for anyone without much technical knowledge to know what is important and what is not so no need to apologise.

 

So its not even certain what this overhaul consisted of apart from fitting your head. See what @Tracy D'arth says about "spray gun overhauls"

 

You should be able to turn the shaft (box in neutral) by hand on the coupling. If not something is wrong.

That engine should  think rev to well over 3000rpm so if it won't out of gear suspect something restricting the air supply or the exhaust (did anyone stuff a rag up the exhaust while the engine was out?) If it revs freely out f gear but not in gear suspect a tight shaft or fouled prop.

5 minutes ago, Leon 12 said:

Starts excellent and sounds really good for a perkins

Would pump timing cause black smoke the higher the revs

Could well do and it might explain an apparent top speed of 1800 rpm. I think pump timing on the Perkins needs a look inside the pump to locat  a circlip and an E marking so you will probably need the manual. (could be wrong from 50 years ago).

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