2 cylinder Yanmar 3YM20

[awol]

It started with white smoke, but only occasionally, then a trail of diesel behind the boat and, finally, a sump that was at least 2 litres above the full mark. The injectors were "acceptable" but there was zero compression on No3 cylinder and so I was left with the choice of an engine out (not enough room to lift the head off) in a port 150nm, as the shite-hawk flies, from my home anchorage, or something else.
The something else was to isolate the No3 injector by taking the feed from the injection pump and T-ing it into the tank return. Apart from a bit of engine wobble at tick-over, fixed by increasing to 900rpm, the engine appeared smooth. Made it home yesterday having motored over 20 hours (including the Crinan Canal) and the donk appears not to have suffered.
The question is - can I carry on with a 2/3YM20 until the seasons end or do I need to incapacitate the boat now?

 

[awol]

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[yotter]

Not sure about the Yanmar but if it was a 3 cylinder VP like the MD2030, I would be careful not to get raw cooling water in No.3 cylinder through the exhaust valve, this might(?) happen if there is not enough exhaust going down the exhaust elbow to discharge the coolant when cranking before the engine starts. If it is starting slowly then a mitigation may be to shut the inlet seacock then open it just after the engine starts. Just a thought really.
Angus

 

[Bilgediver]

I take it that the diesel diluted sump oil has been removed? I this found its way into the other cylinders you could have a runaway engine. Which could only be stopped by choking the air supply.

 

[scottie]

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You will not be comfortable with it till you sort it

 

[awol]

Old oil removed, flushing oil used, then a new fill; filter changed; and now it is so clean it is difficult to see the level on the dip-stick.
As for comfort - I don't want to use the engine at all and started home with the idea that it would probably cope with pontoons and, if necessary, anchorages though I did need it for battery top-up. The oft prevaricated solar panels have moved up the buy list! The winds, of course, did not play fair and I used it much more than I intended, apparently without ill effect. Another couple of months seems doable if within reach of home.

 

[LittleSister]

I see no one has actually answered your question - 'can I carry on with a 2/3YM20 until the seasons end or do I need to incapacitate the boat now?' - so in that absence here's my three 'aporth.

I am certainly no expert, I would emphasise, but I can't think that continuing to use it, with the fuel supply to that cylinder shut off, in itself would cause significant harm. That it has run 20 hours without obvious ill effect is encouraging.

I do wonder what has caused the not just low but 'no compression'. Can this really be just wear? Are the rings broken, for example, in which case continued use may further damage the No. 3 cylinder walls?

I think yotter's concern about back-filling with water is misplaced, or at least exaggerated. The exhaust from the other 2 cylinders will be sufficient, I think, to prevent backfilling from the exhaust elbow to the engine, and the duff cylinder itself will be pumping air out of its exhaust valve. (Of course the normal precautions in the event of an engine not starting promptly would apply.)

Bilgediver's point about potential for diesel having migrated past the piston into the lube oil is a good one. I suspect if this was happening to any harmful degree this would have made itself known during the 20 hours run. That said, I think if you are continuing to use use the engine for the time being it would be worth draining some or all of the lube oil and inspecting it for diesel contamination. [p.s.- your post No. 6 hadn't been posted when I drafted this.]

All in all, my inexpert guess answer is 'Yes, you can carry on', and if in your shoes I would be tempted to do that. Be it on your own head, though!

 

[38mess]

Gardener engines can shut one cylinder off without harming the engine. I reckon yours will be fine

 

[LittleSister]

Pretty much any fuel ignition car/motorbike will shut off the fuel on the over-run, though that is of course short-term. I believe some larger modern car engines (6 & 8 cylinder?) shut off the fuel to some cylinders for economy when cruising along (e.g motorway driving) for extended periods.

How well that will translate to a relatively agricultural engine with water-cooled exhaust and suspect rings i don't really know but, as I said above, I guess it'll be fine.

 

[scottie]

generally all if favour of it will be ok however
Ask a professional and the answer very quickly changes to no if you expect me to pay for getting it wrong

 

[Bilgediver]

Old oil removed, flushing oil used, then a new fill; filter changed; and now it is so clean it is difficult to see the level on the dip-stick.
As for comfort - I don't want to use the engine at all and started home with the idea that it would probably cope with pontoons and, if necessary, anchorages though I did need it for battery top-up. The oft prevaricated solar panels have moved up the buy list! The winds, of course, did not play fair and I used it much more than I intended, apparently without ill effect. Another couple of months seems doable if within reach of home.

As a matter of interest have you checked the tappet clearance. I have seen the clearances reduce on a friends boat and if no clearance the valve may not seal.

 

[awol]

generally all if favour of it will be ok however
Ask a professional and the answer very quickly changes to no if you expect me to pay for getting it wrong

The one who pays for getting it wrong is ME!

 

[awol]

As a matter of interest have you checked the tappet clearance. I have seen the clearances reduce on a friends boat and if no clearance the valve may not seal.

It's a possibility - engine clearance top (and port) is minimal and I never got that far. My guess is a burnt valve and I have just procured a bore scope to investigate though I have a suspicion that I may avoid the nausea of once again removing injection and return piping to remove the No3 injector (and replacing without a leak) until the engine is out.
Another winter "must do" is to put a fuel cock within the engine compartment - the present one is at the bottom of the tank at the bottom of the cockpit locker just, and only just, within finger-tip range after removing the contents.

 

[awol]

Boat ashore so I pulled the engine forward to remove the cylinder head. The compression problem was very obvious - 2 pistons oscillating up and down when the crankshaft was turned - the third was stationary at the bottom of its stroke with about half an inch of diesel (remember injector has been isolated for about 20 hours of running).
Next move was to lift engine into the cockpit and remove the sump. How I didn't hear anything I don't know but I didn't! There is a small crack in the sump, a little scarring on some webs but at first glance no serious damage.

 

[footsoldier]

I think someone up there likes you! It could easily have been a catastrophic failure, a long way from home.

 

[awol]

Now I'm costing replacement bits - e.g. conrod price - both genuine Yanmar parts - €63 to £335 !!!! Not all European companies will deliver to UK. It appears a 3YM20 uses same bits as 3TNV70 engine used in John Deere etc excavators, mowers, etc. but these are mostly USA. China is also a source for non-Yanmar lool-alike parts. Hours of internet fun!

 

[Bilgediver]

Now I'm costing replacement bits - e.g. conrod price - both genuine Yanmar parts - €63 to £335 !!!! Not all European companies will deliver to UK. It appears a 3YM20 uses same bits as 3TNV70 engine used in John Deere etc excavators, mowers, etc. but these are mostly USA. China is also a source for non-Yanmar lool-alike parts. Hours of internet fun!

Looks like you hydraulic locked a cylinder. This could require checking the exhaust system. Etc.

Do you have a high level exhaust elbow as this might be needed.

 

[Stemar]

Does Yanmar make their own engines, or are they based on Kubota or someone, like the Betas? My brother-in-law has a sit-upon mower with the same engine as the Beta 20. The only real difference apart from the marinising bits is that his is blue and mine is red. When I needed new sumps last year, they came in a fetching blue shade.

 

[Tranona]

Yanmar make their own in these sizes and are a direct competitor to the others like Kubota, Mitsubishi Shibauru/Perkins who all make a range of engines in both marine and industrial form.

 

[awol]

Looks like you hydraulic locked a cylinder. This could require checking the exhaust system. Etc.

Do you have a high level exhaust elbow as this might be needed.

One of my thoughts as well. The small end has sheared across the oil holes; both big end bolts have broken, one lost its head, the other sheared at the top of the thread but both were loose in the sump; the small end bearing had been beaten into a strip; the piston skirt had been chewed on both sides and, of course, the conrod is twisted and bent.
The motor had just reached 1000 hours and its predecssor, a 2GM, had well over 4000 hours, both on the same exhaust set up. The exhaust mixer, not the high rise version (I'm not sure I have the clearance), seems intact at first glance.
I don't suppose anyone has a scrap 3YM20 or a 2YM15 lying around?