I'm stumped. My diesel mechanic has done alot of work to try to correct my engine problems, yet the problems remains. Any diesel experts out there ready to tackle this one? My engine is a Yanmar 2GM20F with about 1200 hours (over 10 years). Over several months it became difficult to start, that is, it cranked over for 30 secs or so before starting, and when idling it ran rough, as if just one cylinder was firing. Other symptoms included bluish smoke, which did not go away even after warmed up. I noticed a slight decrease in the oil level over this time. Previous to this, the engine ran fine (no smoking or misfiring) for the 9 months we owned it. We can pin the problem to the #1 cylinder. In listening to the engine a "hissing" could be heard when the air silencer was removed, and the air intake pipe had carbon or soot on its inside. The mechanic's theory was that the air intake valve on #1 was not seating properly, allowing air to escape (the hissing)the cylinder which decreased combustion pressure, causing incomplete fuel combustion (responsible for the smoke and misfiring). This sounded like a good theory. Heres what we've done so far: removed both the fuel injectors, tested them (one was defective) and rebuilt and replaced both injectors. Less smoking resulted, but still some smoke and #1 cyl running rough. So, the head was removed, valves were reground to specs and replaced. When the head was removed, the cyclinder walls and piston heads were inspected visually and the mechanic did not see anything to note. The engine maybe runs a little better, but rough running and smoke remain. So then the hi-pressure fuel pump was tested and turns out OK. So what is next? Is removing/replacing the piston and rings on cyl#1 the next step? Is there anthing to do more before going to the piston/rings? I'm perplexed. Does anybody have suggestions?
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Patrick Ewing
Have you checked the exhaust system?
It happened to me once that my exhaust riser was blocked with soot and none of the mechanics thought to check it. A 15 minute fix cost me lots of time, money and several four hour round trips to Seattle. My engine had similar symptoms to yours with the added complication of reduced engine speed. I am curious to learn what you discover as a fix for it.
It happened to me once that my exhaust riser was blocked with soot and none of the mechanics thought to check it. A 15 minute fix cost me lots of time, money and several four hour round trips to Seattle. My engine had similar symptoms to yours with the added complication of reduced engine speed. I am curious to learn what you discover as a fix for it.
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Doug
Mixing elbo?
I would certainly expect a mechanic (a good one anyway)to check something like a coked up mixing elbo prior to rebuilding the upper end of your engine. Our boat also has a 2gm20f that is about 12 years old. We just replaced our mixing elbo (tried to clean last season while still installed and THOUGHT we did a good job). Upon taking it off and looking into it up-side-down, it is a marvel that any exhaust got through it at all. Good luck. I will be re-visiting this post for sure to see what Gordon has to say. Doug
I would certainly expect a mechanic (a good one anyway)to check something like a coked up mixing elbo prior to rebuilding the upper end of your engine. Our boat also has a 2gm20f that is about 12 years old. We just replaced our mixing elbo (tried to clean last season while still installed and THOUGHT we did a good job). Upon taking it off and looking into it up-side-down, it is a marvel that any exhaust got through it at all. Good luck. I will be re-visiting this post for sure to see what Gordon has to say. Doug
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Gordon Torresen
Response deferred
I would defer to the wisdom of Doug and Patrick. A coked mixing elbow is likely your problem. The symptoms can sometimes come on quite suddenly if some of that coke shakes loose and tries to get out through a passage that is too small. I would look closely at the credentials of the mechanic who suggested replacing rings on one cylinder only.
I would defer to the wisdom of Doug and Patrick. A coked mixing elbow is likely your problem. The symptoms can sometimes come on quite suddenly if some of that coke shakes loose and tries to get out through a passage that is too small. I would look closely at the credentials of the mechanic who suggested replacing rings on one cylinder only.
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Pete
engine troubles
it sounds like you have done alot of major work on a low hours engine I guestion valves and would not think pistons and rings would be needed at 1200 hours besides checking the exhaust elbow I would go over the entire fuel system checking for a possible air leak (ie. loose fitting, filter housing not tight) some of the symptoms sound fuel related to me. Would be intersested to hear Gordon's comments Good Luck! Pete
it sounds like you have done alot of major work on a low hours engine I guestion valves and would not think pistons and rings would be needed at 1200 hours besides checking the exhaust elbow I would go over the entire fuel system checking for a possible air leak (ie. loose fitting, filter housing not tight) some of the symptoms sound fuel related to me. Would be intersested to hear Gordon's comments Good Luck! Pete
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Gene Foraker
Compression?
I am surprised you didn't mention the mechanic performing a compression check on the engine. I can't imagine checking the valves or suspecting the rings without one. The previous advice was good and I would also suggest a compression check and to send the oil off for analysis. That can reveal many problems without spending a bundle.
I am surprised you didn't mention the mechanic performing a compression check on the engine. I can't imagine checking the valves or suspecting the rings without one. The previous advice was good and I would also suggest a compression check and to send the oil off for analysis. That can reveal many problems without spending a bundle.
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Ernie Rodriguez
My experience so far..
On my 3GMD with approximately 3000 hours but only 18 years old I was beggining to have similar symtoms as you described. After replacing the three injectors and not finding any significant improvement in the starting characteristics I ran a compression test on all three cylinders and found that one cylinder had a reading of 160 lbs, one 280 lbs and one 300lbs ( as best I can remember without looking it up). After removing the head I was told by a diesel mechanic that the head gasket was blown. He also recommended measuring the distance above the block on each piston to determine if there was a bent connecting rod. I did this and found that one piston was 14 thousands of an inch shorter than the other two ( but not the one with the low compression reading), therefore indicating a bent connecting rod. I then removed all three pistons and found one piston cracked at the top surface, one piston scorched at the wrist pin area, and one piston with the bent connecting rod. So I now have purchased three new pistons with rings, one connecting rod, two new connecting rod bearings, and three new cylinder wall sleves for the new pistons. Just yesterday I removed the old cylinder wall sleves, and now am ready for the assembly process. I had the cylinder head resurfaced and overhauled. I would definately recommend a compression test on your engine. Hope this helps. Ernie
On my 3GMD with approximately 3000 hours but only 18 years old I was beggining to have similar symtoms as you described. After replacing the three injectors and not finding any significant improvement in the starting characteristics I ran a compression test on all three cylinders and found that one cylinder had a reading of 160 lbs, one 280 lbs and one 300lbs ( as best I can remember without looking it up). After removing the head I was told by a diesel mechanic that the head gasket was blown. He also recommended measuring the distance above the block on each piston to determine if there was a bent connecting rod. I did this and found that one piston was 14 thousands of an inch shorter than the other two ( but not the one with the low compression reading), therefore indicating a bent connecting rod. I then removed all three pistons and found one piston cracked at the top surface, one piston scorched at the wrist pin area, and one piston with the bent connecting rod. So I now have purchased three new pistons with rings, one connecting rod, two new connecting rod bearings, and three new cylinder wall sleves for the new pistons. Just yesterday I removed the old cylinder wall sleves, and now am ready for the assembly process. I had the cylinder head resurfaced and overhauled. I would definately recommend a compression test on your engine. Hope this helps. Ernie
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