• Mobile App For Android Now Online!

    Download it here. The app is searchable in the Google Play Store under Sailboat Owners.

    Sorry iPhone/iPad users, we are still waiting on Apple. :(

    Click the X in the upper right corner to make this go away

Need 2nd opinion: Cracked piston ring in a Y2GM20F?

May 15, 2015
63
Hunter 280 Everett, WA
Has anyone had a cracked piston ring in a Yanmar 2 cylinder? And if so, what were the symptoms?

Background: For the past year or so I’ve had a slowly worsening smoke exhaust problem that occurs after the engine warms up and approaches cruising rpm. Smoke is a blue and white-ish color, hard for me to tell whether it’s primarily blue or white. Had a mechanic do a compression test and a wet/dry leak down test. Compression was good and the leak down was apparently OK (don't have all the details about this0. The recommendation was to first rebuild the fuel injectors and then the injector pump if the fuel injectors alone didn’t solve the problem. After having all of this done, there’s been absolutely no change in the exhaust...engine still smokes like a chimney. The mechanic is now recommending checking the piston rings, which requires pulling the engine.

Does a damaged piston ring sound like a good next step to go in? Is there any way of checking or confirming this w/out pulling the engine?

If I do have to have the engine removed, what else should I have taken care of at the same time? This is a boat I really like and don’t plan on selling any time soon.

Thanks.
 
Nov 22, 2011
868
Ericson 26-2 San Pedro, CA
Has anyone had a cracked piston ring in a Yanmar 2 cylinder? And if so, what were the symptoms?

Background: For the past year or so I’ve had a slowly worsening smoke exhaust problem that occurs after the engine warms up and approaches cruising rpm. Smoke is a blue and white-ish color, hard for me to tell whether it’s primarily blue or white. Had a mechanic do a compression test and a wet/dry leak down test. Compression was good and the leak down was apparently OK (don't have all the details about this0. The recommendation was to first rebuild the fuel injectors and then the injector pump if the fuel injectors alone didn’t solve the problem. After having all of this done, there’s been absolutely no change in the exhaust...engine still smokes like a chimney. The mechanic is now recommending checking the piston rings, which requires pulling the engine.

Does a damaged piston ring sound like a good next step to go in? Is there any way of checking or confirming this w/out pulling the engine?

If I do have to have the engine removed, what else should I have taken care of at the same time? This is a boat I really like and don’t plan on selling any time soon.

Thanks.
Is the engine consuming oil?
 
May 15, 2015
63
Hunter 280 Everett, WA
No. In the 5 yrs I’ve had the boat, I rarely have to top it off between oil changes. Has always started pretty well and still does. And even now it runs pretty well, except I can feel a change, a slight loss of power or hesitation when accelerating up to cruising rpm 2800. Has ~ 950 hrs.
 
Jan 7, 2014
174
Beneteau 45F5 51551 Port Jefferson
I'm no diesel mechanic but I have worked on a number of gasoline engines. Another source of exhaust smoke in gasoline engines are the valve stem seals. Worn seals can allow oil into the combustion chamber. Could that be a cause?
 
  • Like
Likes: ggrizzard
Jan 7, 2014
174
Beneteau 45F5 51551 Port Jefferson
Pistons usually have at least two sets of rings one for the oil and one for compression. If a compression ring was bad you would get blowback into your engine block and oil coming out of the crank case breather. I think it would be unlikely that you cracked an oil ring. I'd look at the valves or head gasket.
 
  • Like
Likes: ggrizzard
Feb 27, 2004
128
Hunter 335 North East, MD
Another item to consider is a bent connecting rod from a hydro lock situation (ask me how I know :facepalm:)-The engine will seem fine but 1 chamber can't burn all the diesel and it comes out as white/blue smoke- I had this in my 3gm30f- engine sounded fine and didn't consume oil- I found this out after doing all the "easy" things, injectors, mixing elbow etc- Good luck will be interested in your findings
 
May 15, 2015
63
Hunter 280 Everett, WA
I've attached an image below of the smoke I'm seeing. This image was taken back at my slip after taking the boat out and running it for ~ 45 min. Here at the slip I took it from idle to ~ 2000 RPM, which produced the smoke you see. There is no smoke at idle.

Re coolant: I never see any coolant loss. The coolant level in the overflow tank almost always remains the same.

Re exhaust elbows: Is there more than one on a 2GM? The one I know about (below the mixer elbow) was checked when I installed a new mixer elbow last year. Seemed fine then, but I can check it again. Could this by itself account for smoke like this?

Re looking at the valves or head gasket: Would the results of the compression test (which my mechanic said were "good to excellent") have ruled out these issues?

I clearly hear the skepticism here about a cracked piston ring being the culprit. I"m not that engine savvy and my best bet before pulling the engine might be to have another mechanic take a look at it.

Thanks everyone for the advice.

Matt





E8DFE934-0B29-415C-9908-2DF2D6CE893E.jpeg
 
May 15, 2015
63
Hunter 280 Everett, WA
Just saw the bent connecting rod idea--thanks for that--will check it out.
 
Mar 29, 2017
487
Hunter 30t 9805 littlecreek
Another item to consider is a bent connecting rod from a hydro lock situation (ask me how I know :facepalm:)-The engine will seem fine but 1 chamber can't burn all the diesel and it comes out as white/blue smoke- I had this in my 3gm30f- engine sounded fine and didn't consume oil- I found this out after doing all the "easy" things, injectors, mixing elbow etc- Good luck will be interested in your findings
A compression test would have revealed that.
 
Nov 6, 2006
8,866
Hunter 34 Mandeville Louisiana
Kind of a long shot, but ya might want to check out the breather in the valve cover.. If the drainback hole gets clogged, or the separator plate (deflector panel) is cracked or missing, you could have a little oil going from the breather back to the intake manifold, especially at higher rpm.. Long shot.. The compression and leakdown tests should show bad or cracked compression rings but might not show an oil control ring problem..
 

Attachments

Jan 4, 2006
3,147
Hunter 310 West Vancouver, B.C.
I clearly hear the skepticism here about a cracked piston ring being the culprit
The only reason for the resistance to the cracked piston ring theory is that it's about the most expensive repair you can do to the engine short of having it gold plated :eek:.

From your replies that you have no loss of coolant or oil, I just can't imagine it being a cracked ring.

One more thing, do you check the coolant level in the heat exchanger or only in the overflow tank. On my engine, there is so much expandable hose connected to the engine that I don't use the overflow tank. It's always kept dry as it has a bad tendency to spit out coolant at low idle. Heat exchanger tank is kept filled to the neck.

PS .................. did you mention anywhere in previous posts what the smoke smells like ? Not recommended by most doctors, but one good sniff won't hurt.

PPS ..................... is your exhaust underwater ?

PPPS ....................... There is only one mixing elbow:

Mixing Elbow Assembled With Directions 3.JPG

If plugged, it can cause all sorts of problems:

Dirty Sectioned Mixing Elbow.jpg
 
Last edited:
May 15, 2015
63
Hunter 280 Everett, WA
We got more than a sniff of the smoke...on our last cruising trip for the season, my wife and I had to contend with a pretty smokey cockpit for ~ 4 hrs on our way back home under motor power (no wind that day). I would say the smoke smells like diesel fuel primarily.

The exhaust is in fact underwater--I'm curious about what that might indicate?

I've got a mechanic coming Monday to look everything over and render a 2nd opinion. I'll go over w/ him all the points mentioned here.

Again thanks everyone--this is such a great resource.

Matt
 
  • Like
Likes: kloudie1
Jan 4, 2006
3,147
Hunter 310 West Vancouver, B.C.
The exhaust is in fact underwater--I'm curious about what that might indicate?
Mine is as well. Hasn't caused any problems over 20 years and Yanmar reps I've spoke to at boat shows don't seem to think it's of any concern. Mind you, it is dead silent when running which may not be the best thing in a heavy fog:facepalm: .
 
May 15, 2015
63
Hunter 280 Everett, WA
There's a new wrinkle in the situation: When looking over the engine this morning, I discovered the oil level is way over the end of the dip stick, even though I'm almost certain it was right on the mark the last time I checked. I've read that white exhaust is associated with unburned fuel, often from bad injector(s), and this can dump enough fuel into the cylinder to get into the crankcase, diluting the oil and raising the oil level on the dipstick.

This summer I sent both injectors out to a diesel shop to be rebuilt. It was after this that I first noticed the smoke (before that I was trying to fix a very strong, almost overwhelming exhaust odor, but no visible smoke at that point). I assumed the injectors were "fixed" after the rebuild, but is it possible they were somehow rebuilt incorrectly? Or when I subsequently had the injector pump rebuilt, is it possible that the pump wasn't properly calibrated with the injectors?? Really don't know what I'm talking about here, but I'm assuming the pump and injectors have to be precisely coordinated to ensure the correct fuel mixture...??

odaydokay: Thanks for the link...a good article, exceptionally clear in listing all possible causes by smoke color. And I like the illustration of smoke color. After seeing this, my smoke is clearly white, not blue as I thought it might be.
 
Jan 4, 2006
3,147
Hunter 310 West Vancouver, B.C.
I discovered the oil level is way over the end of the dip stick, even though I'm almost certain it was right on the mark the last time I checked.
Any chance you could get the oil analyzed for diesel fuel content ? Tell the lab to look for fuel content only and omit the rest of the analysis to save a few bucks.

I know this is costing you more money over and above what you've already spent BUT, if you get a mechanic in there who is just guessing and going on a wild search on your dime, you'll really learn what spending is all about.

Jumping ahead here, but when you do bring in another mechanic to finally deal with what the problem is strongly suspected of being, do your homework first:

1. Is he a licensed mechanic ?
2. Is he possibly a Yanmar trained mechanic ?

Lots of gumboot mechanics out htere who can cost you a fortune and do nothing but make it worse.
 
Aug 12, 2020
51
Lancer 36 Pago Pago
A faulty thermostat can contribute to white smoke.....a pinhole leak in the diaphram of the lift pump can also cause issues, and raise the oil level; proper troubleshooting is needed to find the actual cause of the smoke, or it gets expensive chasing it around.
 
Mar 29, 2017
487
Hunter 30t 9805 littlecreek
Next curve your high pressure pump can leak diesel into crank case. especially if injectors rebuilding caused more back pressure on seals in pump