Yanmar 2GM blow-back ?

[NickL]

Hello.

I have a 30ft sailboat with a 2GM Yanmar . The boat was built in 1986.
I have used the boat quite a lot in last two years since I owned her and Yanmar generally worked quite reliably.

Last week, however, the engine failed to start. It would crank and eventually pick-up at the highest throttle. Next I know, lots of white smoke around engine. I found oil and presence of water in the air intake. Seems like a blow back.

Mechanic had a look and he found that one cylinder is now not firing properly. There is no change in RPMs when decompression lever is moved for that particular cylinder.

-Checked valves and they appear to be OK and not stuck
-Fuel supply to injectors - OK
- Swapped injectors - problem did not move to other cylinder
- Compression test. About 200 psi (dry test) on one cylinder and ~250 psi on the working cylinder

He is suspecting a stuck piston ring or something more serious but he was unable to tell for sure without having the opportunity to take the cylinder head off for visual inspection.

The engine now starts and it kind of works. It produces random "pops" and engine visibly vibrates when they are heard.

Here is the video taken with my mobile phone. Pings are clearly audible.

https://www.dropbox.com/s/9i4g4jn0zv..._3239.MOV?dl=0

Greatly appreciate if anyone who has had such experience can comment.

[Greatest Lakes]

Stuck ring, maybe glazed cylinder. If you can get some marvel mystery oil into the cylinder, let that sit overnight and I might come loose. Additionally, make sure you don't run at the same rpm all the time or leave it at idle too long. The rings need to be run fairly hard once in a while to function properly and "burn out the carbon". The oil blowby is most likely causing your smoke.

[Compass790]

Compression is way too low if test performed accurately. Not sure what 2GM is meant to be but at least 350 psi
Eg our Ysm8 spec is between 400 & 454 psi.
It will never run well with that low compression, sorry but a rebuild is likely in order but a leakdown test would help narrow down where it's losing compression.
My guess as to what caused the problem would be failed exhaust elbow as that is a common cause of getting water in the cylinder/s
Is the boat kept in freshwater? incredibly clean looking engine.

[skipperpete]

Hi NickL, I agree with the previous posts but having watched your video I’m inclined to suggest a blown head gasket through to the water jacket, or a cracked head...... here’s a thought. Water expands 1,700 times its original volume when it turns to steam and if a small/tiny amount of raw water was present in the cylinder the compression pressure would be greatly enhanced pre fuel injection and would produce a sound not dissimilar to the one in your vid (plus rough running, white smoke and a reluctance to start) I actually saw this happen on a 3HM raw water cooled Yanmar ...... same symptoms as yours but the oil was milky. While trying to diagnose the problem I turned off the seawater valve so as not to hydrolock the engine while dead cranking and the bugger started up, and ran as near as dammit to normal...... turned on the seacock again and the engine started to bog down to idle with a metallic detonation rattle. So that problem was solved but because the raw water had damaged the engine the owner chose to repower with a new Yanmar.
My theory is easy to dismiss, turn off the sea cock and check the lube oil then run the engine (no more than 30 sec or you’re buying a new impeller) it’s also useful to take off the oil filler cap to estimate the degree of crankcase pressure( blow by) while it’s running.
It’s harder to spot a blown head gasket with raw water cooling because there’s no toptank coolant loss or overheating to warn us.
Pete.

[Compass790]

Actually thinking on skipperpetes post i think his scenario is more likely than the exhaust elbow fault causing yr problem.
If so lucky you, ya may have dodged a bullet. If it proves to be the head gasket my advice is to use gasket cement when installing the new one. My favourite is Loctite 518 but there are cheaper alternatives which I have no experience with. You may get howls from people who swear you have to put them on dry but IME you will have no trouble if you use 518 but dry you can get failures.
YMMV
The head is going to have to come off anyway IMO.

[Compass790]

Can you see bubbles in your water injection hose to the exhaust elbow?
Sorry got confused with 2GM20 , yourt style of exhaust elbow isnt as bad as the 2GM20's for dumping water on exhaust valve I'd guess.
Please report back what you find

[billgewater]

My 1GM has decided it has similar problems. Took the head off and saw clear evidence of sea water ingress. Bad corrosion on the exhaust valve and seat.

However, it could even be a cracked piston which I guess would have a similar effect to a broken oil real ring.

Anyway, unfortunately, it does not look good.

I would give thought to replacing the exhaust system with one from HDI who make vastly superior SS ones to the Yanmar product. You may also want to consider putting in a riser on the exhaust system but a chat with an experienced diesel mechanic might help.

[NickL]

Originally Posted by Compass790

Compression is way too low if test performed accurately. Not sure what 2GM is meant to be but at least 350 psi
Eg our Ysm8 spec is between 400 & 454 psi.
It will never run well with that low compression, sorry but a rebuild is likely in order but a leakdown test would help narrow down where it's losing compression.
My guess as to what caused the problem would be failed exhaust elbow as that is a common cause of getting water in the cylinder/s
Is the boat kept in freshwater? incredibly clean looking engine.

Thank you for your feedback Compass790. I agree on the compression comment. I took the mixing elbow off last night and it was not clogged. It had about 1/16th of an inch black carbon build-up on the wall.

The engine has been in fresh water all its life. It has raw water cooling.

Thanks again for your feedback.

[NickL]

Originally Posted by skipperpete

Hi NickL, I agree with the previous posts but having watched your video I’m inclined to suggest a blown head gasket through to the water jacket, or a cracked head...... here’s a thought. Water expands 1,700 times its original volume when it turns to steam and if a small/tiny amount of raw water was present in the cylinder the compression pressure would be greatly enhanced pre fuel injection and would produce a sound not dissimilar to the one in your vid (plus rough running, white smoke and a reluctance to start) I actually saw this happen on a 3HM raw water cooled Yanmar ...... same symptoms as yours but the oil was milky. While trying to diagnose the problem I turned off the seawater valve so as not to hydrolock the engine while dead cranking and the bugger started up, and ran as near as dammit to normal...... turned on the seacock again and the engine started to bog down to idle with a metallic detonation rattle. So that problem was solved but because the raw water had damaged the engine the owner chose to repower with a new Yanmar.
My theory is easy to dismiss, turn off the sea cock and check the lube oil then run the engine (no more than 30 sec or you’re buying a new impeller) it’s also useful to take off the oil filler cap to estimate the degree of crankcase pressure( blow by) while it’s running.
It’s harder to spot a blown head gasket with raw water cooling because there’s no toptank coolant loss or overheating to warn us.
Pete.

HI Skipperete. I am afraid you are correct in your suggestion that I have a blown gasket. When the engine originally failed last week, I found traces of water and oil in my air filter silencer. Also the air filter was ripped apart and piece of it ejected out suggesting severe blow back.

I will be taking the engine out of the boat and cylinder head off. I guess I will find out and what the next steps are.

Appreciate your help and feedback.

[Martkimwat]

When you get the head off, check the exhaust gallery for corrosion through to the oil or water gallery, a pretty common problem with 1GMs and 2GMs at least. They can be repaired by a competent machine shop who can drill/bore out the exhaust and sleeve it with a 5mm wall stainless insert sweated in. I had this problem on my original 1GM10 and it was evident on the second-hand replacement 2gm20. The retailer agreed to provide me with another cylinderhead. Whilst you are at it, replace the original Yanmar exhaust elbow with an aftermarket stainless steel one. A fraction of the price and much more long-lasting. There was a guy based in the US who sold them on Ebay, including UK. Haven't seen his ad lately on UK Ebay but maybe he still sells them on US Ebay. Charged about $100.

[Compass790]

Originally Posted by NickL

Thank you for your feedback Compass790. I agree on the compression comment. I took the mixing elbow off last night and it was not clogged. It had about 1/16th of an inch black carbon build-up on the wall.

The engine has been in fresh water all its life. It has raw water cooling.

Thanks again for your feedback.

I wasnt aiming at the clogging problem I was aiming at the exhaust leaking water back into the head.
Have heard the same issue that martinkimwat talks about as well tho it shouldnt be as severe an issue in fresh water.
Please tells us what you find when you get the head off.