1-cylinder Yanmar Issues

[agg212]

Hi all,

I've been having some issues with my Yanmar YSM12 (1 cylinder).

The symptoms are as follows:
- Has always been difficult to start
- When under load (forward/reverse): grey smoke in cabin, black exhaust overboard, dies when brought back to neutral, clapping/slapping sound as cylinder thumps
- In neutral, seems to run mostly fine

I've already done the following:
- replaced exhaust eblow/manifold
- checked thermostat
- good waterflow overboard
- checked impeller and looks fine

[Wotname]

Originally Posted by agg212

Hi all,

I've been having some issues with my Yanmar YSM12 (1 cylinder).

The symptoms are as follows:
- Has always been difficult to start
- When under load (forward/reverse): grey smoke in cabin, black exhaust overboard, dies when brought back to neutral, clapping/slapping sound as cylinder thumps
- In neutral, seems to run mostly fine

I've already done the following:
- replaced exhaust eblow/manifold
- checked thermostat
- good waterflow overboard
- checked impeller and looks fine

OK, as you know, this is an old engine and for sure it will have some wear but they are quite robust. From the scant information provided it is difficult to be sure exactly where the problem(s) lie, however here are my thoughts.

Two clues are it is hard to start and grey smoke in the cabin. This suggests to me you have lost some compression and I assume the cabin smoke is from the breather. Maybe worn rings and/or cylinder walls.

First thing though is to do the simplest thing first - check the valve lash (tappet clearance). It should 0.2mm (8 thou ").

If that is OK, either do a compression check or simply pull the head and inspect the valve seats and cylinder wear. The horizontal nature of the cylinder leads to corrosion and pitting on the lower surface of the cylinder.

If you want to dig deeper, you can pull the piston with the engine in situ assuming you have some space on either side. There is a cover on the other side of the head that allows access to the conrod cap and allows checking of the rod bearing wear as well as removing the piston.

One thing to note that while the engine is simple (and robust) and some parts (rings, sleeve, bearings etc) are still available, they aren't always cheap although it pays to search for Asian parts suppliers.

The only weakness with this engine is (IMO) the oil pump. They wear badly and can't be fixed without access to a good machinist, some lateral thinking and dollars. Before spending big money on extensive repairs, I would assess the oil pump first. If it's reasonable, then the rest of the engine is usually worth saving (IMO). Fit a oil pressure gauge (where the oil pressure switch is) and measure pressure hot and cold at idle and above.

Of course you may only have a injector problem and this can be checked by pulling the injector and observing the spray pattern as described in the service manual. Only do this after reading and following the precautions as it can be dangerous (to you) if done incorrectly.

By the way and FWIW, I have recently rebuilt this engine's little brother - a YSE 8; however I'm not a professional diesel mechanic.

[Wotname]

I unloaded a YSM service manual to the CF library today although it probably won't appear to a few days however if you want a copy in the meantime, PM me with an email address.

[GordMay]

Originally Posted by Wotname

I unloaded a YSM service manual to the CF library today ...

THANKS!
CF Document Library Downloads: ➥ https://www.cruisersforum.com/forums/downloads.php

[garyfdl]

Wotname's comments are spot on.

Black smoke with a diesel often means a fueling issue (too much). Check the injector. Gray smoke in the cabin is a leak - somewhere. Possibly a head gasket?

What would concern me the most is the clapping/slapping sound, if that is something new, and assuming it's internal, it probably can't be checked without disassembly. FWIW I had an old Hunter with the 1GM and the "slapping" sound from it was normal.

[Wotname]

Originally Posted by GordMay

THANKS!
CF Document Library Downloads: ➥ https://www.cruisersforum.com/forums/downloads.php

It seems to take a few days for a newly unloaded manual to appear in the Library - I assume there is someone (mod, JanetH, ?) who vets the uploaded file before making it available for the rest of us (???).