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Black smoke under load


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Pause for thought......

 

When revving the engine out of gear .no black smoke ....

 

In gear at 1200 rpm onwards increases in black smoke.....

Surely if timing pump problems  it would smoke the same in and out of gear....

The engine mounts are set up for the old engine .......if this new block  has been placed directly  onto  the engine mounts but no realignment done would this cause any problems . The prop does rotate by hand but if slightly out would it explain.????

 

Would it smoke the same  out of gear the as much as does in gear......my non mechanical brain says it should?????

 

Any thoughts ???

 

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I expect black smoke as the revs are increasing sharply off load, that's because for a time the engine is overloaded as it gathers speed. But continuous black smoke under moderate steady load does suggest over propping or excess mechanical friction.

 

We craned a boat out once with a plastic garden chair stuck in the skeg, no one knew it was there but that would cause some drag. Nothing on the prop, they had checked it. 

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Hmm, odd. If it has had new pistons bearings etc. it might just be (very) tight, new big end shells on an oval crankshaft  or something but that's really digging into the unlikely. If it revs freely out of gear then that is not it. Its the black smoke under load that's a mystery, some sort of severe misalignment is possible but you would see that. Is the coolant connected up and circulating properly ?  that is only relevant if its on the verge of seizing though. When I put a bigger prop on my boat I could tell as the engine note dropped when in gear, it was working harder. Does the Perkins sound as though it is working harder than before? If everything seems ok I would suspect the pump but as I avoid anything to do with them then its over to the specialists.

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1 minute ago, Leon 12 said:

The engineer said it is tight as its had new shells in ???

Does that make a difference

No engineer that I know would build a "tight" engine.

With the correct size of bearing shells on a crank ground to the correct size and finish and bores and pistons correctly sized and honed, the degree of stiffness to turn is minimally more than a run in engine, certainly not enough to be described as tight.

Any increased drag would disappear very quickly with normal running. 

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Well, the crank would have been worn and instead of the bearing surfaces being round they would have been very slightly oval, regrinding the crank to, say, 10 thou or 20 thou smaller would have returned it to being circular but a different, slightly smaller, size of bearing shells would have been fitted. If new shells were fitted but the crank was not removed and reground they would be clamped really tightly around the crank .  Multiply that by 4 cylinders and you will get a real braking effect on the engine.  Its unlikely though as if it revs freely out of gear and the starter spins the engine over OK then thats not the problem, usually common problems are common as they say and really tight shells are not common but some 'reconditioners' have been know to cut corners.   Edited to add , Tracy D'arth is spot on., posts crossed.

Edited by Bee
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I remember Perkins engines in Seddon buses. When the engines were rebuilt they were tight. So tight they needed 24V to start them. The mechanics tried everything including machining metal off brand new parts. After about 12 hours running they were fine. They never did get to the bottom of it and it was only those engines that had this problem, Leyland and Gardner engines were rebuilt without issue.

Edited by Sir Nibble
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I once had a set of shells for a BMC that were definitely thicker than the package said and those did creat a tight engine. The crank had been reground and we measured it several times to check it was right. In the end I reverted to traditional methods a scraped the shells - the only time i ever scraped bearings.

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I think the engineer neant until the rings seat properly  ....will keep you updated 

I think the engineer neant until the rings seat properly  ....will keep you updated 

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