Had an issue last weekend

[David W]

While motoring back after a romping sail (7 kts in 2 - 4 ft swells) in our 1978 Crown 34, running the 2QM15 at about 21-2200 rpm when suddenly the rpm dropped to about 1500 and we started belching black smoke. I looked down and the throttle lever was in the same position.

I throttled back to idle, all seemed normal and the smoking stopped. I gradually ran it back to cruising rpm. No problem, provided I wanted to provide a smoke screen for a platoon of Navy commandos.

So back it off to where it stops smoking and we putter back to the dock at 3 kts.

Today, my mechanic came out. She fired up just fine, we let her warm up a bit. He pulled the throttle cable pin at the engine end and put it into forward gear. He climbed down into the cabin and open the throttle wide open. NO SMOKE...

But we did find that the mixing elbow was cracked in a few places. He attempted to pull just the elbow but had to pull the exhaust manifold as well because the elbow was just too stubborn to remove.

The hose end of the elbow was bit blocked, maybe 25-30%. He thought maybe the rough sailing had loosened some carbon which eventually blocked the elbow and was held in place while we were still running. Once the engine down on Sunday, it was loose enough that it came out when the engine was re-started by the mechanic.

In any event, I haven't got the manifold and elbow back but am curious about if and then how I would go about de-carboning the engine without tearing it down. The mechanic didn't feel the amount of carbon in exhaust port in the head was too bad.

Any thoughts from the interweb mechanics?

 

[mklein@iowatelecom.net]

There are a lot of products specifically made to decarbon an engine. Rislone poured slowly into the intake. Also Seafoam poured slowly into the intake. A poor man's way is also to simply slowly pour a little water down the intake, carefull to not completely choke out the engine, followed by some automatic transmission fluid.

 

[Ed Schenck]

You'll get less carbon buildup with the engine running closer to maximum rpms. Then I heard that someone replaced the elbow with a stainless model. That would probably never coke up. But "platoon" of Navy commandos?!

 

[Don12364]

I figure thus:-
Engine running OK at 2200.
Revs suddenly drop to 1500.
Governor tries to restore original engine speed and injects vast amount more fuel.
So black smoke due to partially burned fuel.

Why?
Engine suddenly came on high load.
Look at prop for rope, plastic sack, fishing gear or even tangle of netting or weed.
May have dropped off now?

You didn't mention if the mechanic tried running full speed whilst in gear.

 

[David W]

I figure thus:-
Engine running OK at 2200.
Revs suddenly drop to 1500.
Governor tries to restore original engine speed and injects vast amount more fuel.
So black smoke due to partially burned fuel.

Why?
Engine suddenly came on high load.
Look at prop for rope, plastic sack, fishing gear or even tangle of netting or weed.
May have dropped off now?

You didn't mention if the mechanic tried running full speed whilst in gear.

Yes, we did put it gear. Also I can clearly see my prop so when we got back to the dock last Sunday I had a good look for anything wrapped and I could see nothing. But your logic makes total sense, especially when it performed like just fine when the mechanic was there.

 

[David W]

Anyone use Rislone, Seafoam etc. on a diesel?

You'll get less carbon buildup with the engine running closer to maximum rpms. Then I heard that someone replaced the elbow with a stainless model. That would probably never coke up. But "platoon" of Navy commandos?!

According to the material I have on the engine; original brochure, owners manual and service manual, the max rpm is 3000. She will cruise happily at 2400 rpm (80% of max) when the bottom is clean but she's it been two years since the last haul out & re-paint. I have have zincs changed every year tho'.

 

[David W]

Would anyone use these on a diesel?

There are a lot of products specifically made to decarbon an engine. Rislone poured slowly into the intake. Also Seafoam poured slowly into the intake. A poor man's way is also to simply slowly pour a little water down the intake, carefull to not completely choke out the engine, followed by some automatic transmission fluid.

I've heard of this on a gas engine but not on a diesel...

Anyone every try using Rislone, Seafoam or a bit of water to de-carbon a diesel?

 

[zeehag]

had that happen-- mine sukked in the air cleaner/filter-- check that also.

i would first check the air cleaner and all other possibilities before pouring some gunky stuff into my diesel tanks.....

 

[David W]

Air cleaner? Check!

had that happen-- mine sukked in the air cleaner/filter-- check that also.

i would first check the air cleaner and all other possibilities before pouring some gunky stuff into my diesel tanks.....

Air cleaner is in its proper place so I think I'm good there.

 

[zeehag]

if no more black smoke, mighta been a bit of carbon from cylinders, combined with the elbow being in a gonna fail soon mode and mebbe injectors. if no mo smoke-- do nothing but improve that which wants to try to fail-- elbow. that will make smoke even intermittently. mine did before replacement.

 

[David W]

My fingers are crossed!

if no more black smoke, mighta been a bit of carbon from cylinders, combined with the elbow being in a gonna fail soon mode and mebbe injectors. if no mo smoke-- do nothing but improve that which wants to try to fail-- elbow. that will make smoke even intermittently. mine did before replacement.

Hoping a new elbow will do the trick. They are also going to clean the exchanger; the poor 2QM is probably getting some much overdue serious maintenance. I've no idea how many hours are on it... I'm putting in a hour-meter next!

 

[Winkfish]

I've heard of this on a gas engine but not on a diesel...

Anyone every try using Rislone, Seafoam or a bit of water to de-carbon a diesel?

I use Seafoam religiously on my gas outboard, never had a diesel. But if I recall correctly, the label indicates it can be used on diesel engines as well. I'll double check when I get home this evening.

 

[zeehag]

2qm is a righteous lil engine--- i hope you have it rebuilt instead of exchanged.....they are awesome..mine i had rebuilt and is wonderful! i had it done when i bought ericson and is still perfect!

 

[David W]

Thanks @WinkFish

I use Seafoam religiously on my gas outboard, never had a diesel. But if I recall correctly, the label indicates it can be used on diesel engines as well. I'll double check when I get home this evening.

I'm interested in trying something when I get the manifold back from the shop.

 

[Winkfish]

I'm interested in trying something when I get the manifold back from the shop.

This is from Sea Foam's web site. You can use on diesel engines.

http://www.seafoamsales.com/how-to-use-sea-foam-motor-treatment.html

 

[sailaway78]

I have to think

You have another problem. You stated that the mechanic opened the throttle wide open at the dock, while in gear. If it didn't smoke at that time, just don't think that is right. I have run my 3GM like that a couple of times. Mine will only turn up 21 or 2200 wide open throttle, tied to the dock. And it smokes something terrible. Have a friend with a 2QM, and it does exactly the same. It should not be able to rev up to max tied to the dock, and if it can't rev up with throttle wide open, it will smoke.

 

[David W]

You have another problem. You stated that the mechanic opened the throttle wide open at the dock, while in gear. If it didn't smoke at that time, just don't think that is right. I have run my 3GM like that a couple of times. Mine will only turn up 21 or 2200 wide open throttle, tied to the dock. And it smokes something terrible. Have a friend with a 2QM, and it does exactly the same. It should not be able to rev up to max tied to the dock, and if it can't rev up with throttle wide open, it will smoke.

I wondered the same thing and asked him. We were both in the cabin hunched over the engine. He had the governor arm pinned both in gear and out of gear. Max rpm for the 2QM15 is 3000. Out of gear it topped out at ~2900 indicated (Faria/Yanmar tachs tend to read ~100 rpm low) with virtually no smoke. In gear it went to about 2600 rpm indicated with some smoke at first then it tapered off to a very small amount of smoke.

Like your friends QM, at the dock previously I was leaving soot on the water (smoke on the water ) at about 2000 rpm. I normally cruise at 2200 rpm. Using the popular "cruise at 80% of max rpm" gives 2200 rpm which is my normal cruising rpm which pushes us close to hull speed (6.2 kts) with a clean hull.

The previous owner had written "cruise rpm = 2000" in the original manual so I suspect it went a long time running like that as I also ran her at that speed. One day when I had to make time and I ran it up to the point where it smoked and then backed off till it stopped. Lo and behold, 2200 rpm and far smoother as well.

In discussion today with the mechanic, the elbow was quite restricted as was the manifold. As anyone with a 2QM series engine knows, exhaust manifolds are no longer available. Luckily the shop had pulled a 2QM that was seized but had a great manifold. So $300 later I have a new manifold and elbow Well it's still at the shop waiting for a gasket...

I'll upload pics when she's done!

 

[Bill Roosa]

Sounds like you dropped a cylinder due to a valve sticking. This results in no compression (or engine shake at higher RPM BTW) and raw fuel being pumped into the exhaust where it is promptly set on fire by the other cylinders resulting in lots of black smoke as there is not much O2 in the exhaust. The valve unsticks and things are all back to normal.
There are a couple of causes for this:

Heavy carbon buildup flaking off and sticking between the valve face (exhaust usually) and cylinder head. I do mean HEAVY buildup BTW.

Mechanical problem in the valve train (those normally are not "self healing" though).
A bent pushrod can “self heal” as it rotates and only gets stuck in one position

Something like an air filter piece getting sucked in the intake and hanging up on a valve.
Inspect the air filter and cover very closely for missing pieces.

 

[David W]

Thanks for the heads up

Sounds like you dropped a cylinder due to a valve sticking. This results in no compression (or engine shake at higher RPM BTW) and raw fuel being pumped into the exhaust where it is promptly set on fire by the other cylinders resulting in lots of black smoke as there is not much O2 in the exhaust. The valve unsticks and things are all back to normal.
There are a couple of causes for this:

Heavy carbon buildup flaking off and sticking between the valve face (exhaust usually) and cylinder head. I do mean HEAVY buildup BTW.

Mechanical problem in the valve train (those normally are not "self healing" though).
A bent pushrod can “self heal” as it rotates and only gets stuck in one position

Something like an air filter piece getting sucked in the intake and hanging up on a valve.
Inspect the air filter and cover very closely for missing pieces.

I'lll give it a good look before we button her up!

 

[David W]

Saw the old elbow today

I'lll give it a good look before we button her up!

Dropped by the shop this morning where I saw the old elbow and manifold. The elbow to manifold gasket surface was corroded thru in several places. The thermostat was essentially stuck shut.

The most revealing part was that the manifold end of the elbow was almost completly blocked with carbon; perhaps only 25% open. The new 'used' manifold looked great. Should be. In by the weekend.

I'll update everyone when she's back together!