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Old 06-03-2015, 08:45   #16
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Re: Yanmar diesel smoking/ black soot

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Originally Posted by sailorchic34 View Post
My engine has a piston with three broken rings it did not smoke at all. Used oil like a pig, but no smoke.
I hope you mean HAD, not has?
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Old 06-03-2015, 09:07   #17
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Re: Yanmar diesel smoking/ black soot

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I hope you mean HAD, not has?
Darn blonde moments. Yes Had..... It was a real pig to start too. Now after my up close and personal engine rebuild 2 years ago, it runs great.
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Old 06-03-2015, 09:14   #18
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Re: Yanmar diesel smoking/ black soot

Thats the thing...mine starts up right away...cold or hot. And will stay running.
Why would the smoke go away after it's been running for 10 mins at 2500-3000rpm?



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Old 06-03-2015, 09:25   #19
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Re: Yanmar diesel smoking/ black soot

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Originally Posted by jimbunyard View Post
Exhaust restriction exacerbated by the overheat perhaps?
Could be. Exhaust elbow should be checked.
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Old 06-03-2015, 09:25   #20
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Re: Yanmar diesel smoking/ black soot

It clears up as the engine gets hot and burns more efficiently. If it starts easy, it's NOT rings.
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Old 06-03-2015, 09:26   #21
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Re: Yanmar diesel smoking/ black soot

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Could be. Exhaust elbow should be checked.

Exhaust elbow was removed and soaked in muriatic acid.


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Old 06-03-2015, 09:27   #22
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Re: Yanmar diesel smoking/ black soot

you melted the o rings that seat the injectors and are dumping raw fule into the chamber along with excess air
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Old 06-03-2015, 09:31   #23
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Re: Yanmar diesel smoking/ black soot

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you melted the o rings that seat the injectors and are dumping raw fule into the chamber along with excess air

This makes the most sense. I'm trying to remember if the new injectors came with o rings. But when I get home tomorrow, I'll double check.


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Old 06-03-2015, 09:37   #24
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Re: Yanmar diesel smoking/ black soot

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Then while in gear, it will smoke and soot the entire time.

What are my possibilities? Another ailment is the motor is slow to decelerate and to shut down.
Wouldn't this point to very low compression? Once warmed up it burns fuel more efficiently, but under load the engine slows down due to lack of power and burns the fuel less efficiently?

Also, "slow to shut down", may be burning lub oil and headed for a runaway?
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Old 06-03-2015, 09:57   #25
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Re: Yanmar diesel smoking/ black soot

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you melted the o rings that seat the injectors and are dumping raw fule into the chamber along with excess air
There are no o-rings in the yanmar 3gm injectors, just shims and springs. Same really with the injector pump. The only oring on the pump is sealing the top part nut to the injector body and probably would not cause the smoking.

Here's a test, with the engine idling, pull each decompression lever one at the time and see if the black smoke changes to grey or goes away. If it changes you know that the problem is one injector assembly.

I'm pondering if one or more springs that control the governor tension changed temper and got a little weak.

That the engine starts right up means timing and compression are good.

Hum another test.

Remove the acorn cap over the injector limiter, on the front of the engine. Mark with a black marker the position of the injector limitor stud to the case. Now loosen the lock nut (big nut against the cover, not the small nut at the end of the stud), and turn the injector limiter 1/4 turn clockwise, tighten the long nut and start the engine and see if the smoke is better. If better, repeat 1/4 turn adjustment till smoke is gone.

Note: improper adjustment of the injector limiter can damage the engine. But as your already have excessive smoke, that to me means your getting too much fuel to the cylinders. The injector limiter adjusts that.

If no change is noted, return the injector limiter to the original mark and retighten the lock nut and acorn nut.

It's possible the little roller bearing plate between the governer and crankshaft, lost it's bearings, which would cause excessive fuel input. All that and the springs are access by removing the timing cover, which is easy after the crank pulley is removed, which is not easy. If one of the springs on the governor, lost temper that would cause black smoke too. Adjusting the injector limitor would adjust the temper loss out.
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Old 06-03-2015, 10:01   #26
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Re: Yanmar diesel smoking/ black soot

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Originally Posted by Neo View Post
Wouldn't this point to very low compression? Once warmed up it burns fuel more efficiently, but under load the engine slows down due to lack of power and burns the fuel less efficiently?

Also, "slow to shut down", may be burning lub oil and headed for a runaway?
Pretty much the very first sign of low compression is hard starting. If the engine starts right up, compression is not a problem. Black smoke is overloading either by excessive fuel or a really fouled prop. As he has black smoke at idle its probably not the prop.
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Old 06-03-2015, 10:16   #27
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Re: Yanmar diesel smoking/ black soot

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Originally Posted by sailorchic34 View Post
There are no o-rings in the yanmar 3gm injectors, just shims and springs. Same really with the injector pump. The only oring on the pump is sealing the top part nut to the injector body and probably would not cause the smoking.

Here's a test, with the engine idling, pull each decompression lever one at the time and see if the black smoke changes to grey or goes away. If it changes you know that the problem is one injector assembly.

I'm pondering if one or more springs that control the governor tension changed temper and got a little weak.

That the engine starts right up means timing and compression are good.

Hum another test.

Remove the acorn cap over the injector limiter, on the front of the engine. Mark with a black marker the position of the injector limitor stud to the case. Now loosen the lock nut (big nut against the cover, not the small nut at the end of the stud), and turn the injector limiter 1/4 turn clockwise, tighten the long nut and start the engine and see if the smoke is better. If better, repeat 1/4 turn adjustment till smoke is gone.

Note: improper adjustment of the injector limiter can damage the engine. But as your already have excessive smoke, that to me means your getting too much fuel to the cylinders. The injector limiter adjusts that.

If no change is noted, return the injector limiter to the original mark and retighten the lock nut and acorn nut.

It's possible the little roller bearing plate between the governer and crankshaft, lost it's bearings, which would cause excessive fuel input. All that and the springs are access by removing the timing cover, which is easy after the crank pulley is removed, which is not easy. If one of the springs on the governor, lost temper that would cause black smoke too. Adjusting the injector limitor would adjust the temper loss out.

Thanks sailorchic for taking the time to detail all of this out for me!
I'm pretty sure I'm on the same thought process as you. When I get home tomorrow, I'll do all of this.
Thanks again!!


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Old 06-03-2015, 10:17   #28
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Re: Yanmar diesel smoking/ black soot

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Originally Posted by sailorchic34 View Post
Pretty much the very first sign of low compression is hard starting. If the engine starts right up, compression is not a problem. Black smoke is overloading either by excessive fuel or a really fouled prop. As he has black smoke at idle its probably not the prop.

Yes, always smoking. And I have someone to clean the bottom today.



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Old 06-03-2015, 10:33   #29
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Re: Yanmar diesel smoking/ black soot

I have had similar conditions after overheating with a Perkins and the problem turned out to be the fuel injection pump.

I had my pump rebuilt at Diesel Power and Injection in Miami (305-592-7070), an old established firm specializing in fuel injection pumps and turbochargers.

I suggest you call them and describe your problem and they might be able to tell you it is a fuel injection pump problem or eliminate that as a possible cause of your problem.

They very very helpful and fair in my dealings with them.

Good luck
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Old 06-03-2015, 11:58   #30
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Re: Yanmar diesel smoking/ black soot

Your engine is near death. You have a rebuild or new engine in your near future.
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