Yanmar 2GM problem

[sharkwatcher]

I have a problem with the Yanmar 2GM in my Hunter 31. First a little background info: The engine has 1200 hrs, has just had an oil change, all filters (air, fuel) changed and Trans oil changed. The engine starts great and idles smoothly and does not smoke at all and accelerates smoothly. Engine temp is a steady 180 F.

At around 1180 hrs I started noticing the full throttle RPM's decreasing from 3200 now down to 2500. I have not changed the wheel and the bottom is cleaned monthly. I have verified the rpms with an optical Tach, and checked the idle speed (900 rpms) and inspected the throttle linkage and adjustment and can find nothing out of adjustment. Any ideas on where to look next? Any help and advice is greatly appreciated.

[Wotname]

Does it run up to max rpm (>3200 rpm) in neutral?
Have you checked valve lash?
Have you checked for blockages in the exhaust manifold and mixing elbow?

These would be the things I would check next before going to more expensive things (injectors etc)

[captstu]

The 2gm exhaust elbow lasts about 700 hours before these symptoms develop. Followed shortly by a blown manifold and head gasket.

[sharkwatcher]

Originally Posted by Wotname

Does it run up to max rpm (>3200 rpm) in neutral?
Have you checked valve lash?
Have you checked for blockages in the exhaust manifold and mixing elbow?

These would be the things I would check next before going to more expensive things (injectors etc)

It will run up to 3200 in neutral. I have not checked valve lash or the exhaust manifold. I guess those are the next things to check.

[svHyLyte]

The replacement interval on the OEM mixing elbow on the engine is 500 hours. Obstruction will cause the symptoms you describe. The good news is that the replacement is not that difficult. The bad news is that the replacment part is not inexpensive. BTDT...

[NoTies]

Originally Posted by captstu

The 2gm exhaust elbow lasts about 700 hours before these symptoms develop. Followed shortly by a blown manifold and head gasket.

Nonsense.

[Wotname]

^^ I concur with NoTies!

[Wotname]

Originally Posted by sharkwatcher

It will run up to 3200 in neutral. I have not checked valve lash or the exhaust manifold. I guess those are the next things to check.

Yes and although the valve lash is easier, I would suggest the exhaust elbow is the more likely culprit but really both need to be ruled out before looking further afield.

[sharkwatcher]

I pulled the exhaust and mixing U elbow, which was pretty carbon'd up. As soon as I get a replacement, install it and test run it, I'll share the results. Thanks again to all's help and advice!

[NoTies]

Wow, lucky you got on to that before the engine block split in two, the head burst off and wrecked the cockpit sole and the resulting explosion blew your boat out of the water.

[Wotname]

Originally Posted by sharkwatcher

I pulled the exhaust and mixing U elbow, which was pretty carbon'd up. As soon as I get a replacement, install it and test run it, I'll share the results. Thanks again to all's help and advice!

You could, of course try to clean the existing one. At least clean it as much as you can - mechanically poke and prod the deposits wherever you can and assuming it is a cast iron / cast steel, then put it in a caustic soda bath which will help removing the carbon.

If it has salt deposits, use a acid bath (muriatic acid). Just don't get the caustic soda and near the acid bath - that is a BAD combination.

However I get that you might prefer just getting a new one .

EDIT: well done for finding the issue - I'm sure this will be the cause of your engine problem

[Wotname]

Originally Posted by NoTies

Wow, lucky you got on to that before the engine block split in two, the head burst off and wrecked the cockpit sole and the resulting explosion blew your boat out of the water.

You are correct but you forget that is a northern hemisphere issue ; for readers below the equator, you don't have to worry about such occurrences.

[sharkwatcher]

Originally Posted by Wotname

You could, of course try to clean the existing one. At least clean it as much as you can - mechanically poke and prod the deposits wherever you can and assuming it is a cast iron / cast steel, then put it in a caustic soda bath which will help removing the carbon.

If it has salt deposits, use a acid bath (muriatic acid). Just don't get the caustic soda and near the acid bath - that is a BAD combination.

However I get that you might prefer just getting a new one .

EDIT: well done for finding the issue - I'm sure this will be the cause of your engine problem

My game plan is to replace with the new elbow, clean the old one and save it for next time (hopefully, there wont be a next time), assuming I can adequately clean it so it is a worthwhile spare. It's always better to have a spare you don't need, that need a spare you don't have or cant get!

[Wotname]

Originally Posted by sharkwatcher

My game plan is to replace with the new elbow, clean the old one and save it for next time (hopefully, there wont be a next time), assuming I can adequately clean it so it is a worthwhile spare. It's always better to have a spare you don't need, that need a spare you don't have or cant get!

Good plan

[kmacdonald]

Originally Posted by sharkwatcher

My game plan is to replace with the new elbow, clean the old one and save it for next time (hopefully, there wont be a next time), assuming I can adequately clean it so it is a worthwhile spare. It's always better to have a spare you don't need, that need a spare you don't have or cant get!

Yes, a spare will ensure you will never have that problem again.