Advice on possible Rebuild of Yanmar 3GM

[Alex 2740]

Hello to all,

Well Nepenthe is now on the east coast of the U.S (Florida) and heading south back to the Caribbean and South America. Before leaving the US again I am considering doing a rebuild/partial rebuild of her 3GM. She has about 7K hours on her today. We’ve been burning about 3 qts of oil every 50 hours or so at mid/higher RPM's (2800-3000) and when we were up on the northeast coast of the U.S. in colder temps (36-60F) she was a bear to start for the colder part of the fall. Exhaust smoke is increasing and is clearly visible most of the time (although not thick). She has become less difficult to start now that we are in Florida with temps 65-80 F but want to make certain not to have to do the rebuild further afield than we need to. FYI Fuel lines/filters and leakage has been checked/and exhaust elbow is new. I plan to have a compression check done next week and will probably rebuild the injectors while were at it just for good measure. The compression test should make the situation clearer for me however the questions that I have in addition to soliciting additional advice are:

1. I did a "benchmark" oil analysis about a year ago and am having a follow up done this week. Has anyone read the results of these and been able to glean any insight into ring deterioration etc..?

2. If I do end up rebuilding the upper half of the engine are there recommendations on what other work I should have done at the same time (beyond the sacrificial components) while I have her heart out e.g. oil pan gaskets, transmission rebuild, etc...)

Alex Lopez
S/V Nepenthe

 

[woodster]

Hello to all,

Well Nepenthe is now on the east coast of the U.S (Florida) and heading south back to the Caribbean and South America. Before leaving the US again I am considering doing a rebuild/partial rebuild of her 3GM. She has about 7K hours on her today. We’ve been burning about 3 qts of oil every 50 hours or so at mid/higher RPM's (2800-3000) and when we were up on the northeast coast of the U.S. in colder temps (36-60F) she was a bear to start for the colder part of the fall. Exhaust smoke is increasing and is clearly visible most of the time (although not thick). She has become less difficult to start now that we are in Florida with temps 65-80 F but want to make certain not to have to do the rebuild further afield than we need to. FYI Fuel lines/filters and leakage has been checked/and exhaust elbow is new. I plan to have a compression check done next week and will probably rebuild the injectors while were at it just for good measure. The compression test should make the situation clearer for me however the questions that I have in addition to soliciting additional advice are:

1. I did a "benchmark" oil analysis about a year ago and am having a follow up done this week. Has anyone read the results of these and been able to glean any insight into ring deterioration etc..?

2. If I do end up rebuilding the upper half of the engine are there recommendations on what other work I should have done at the same time (beyond the sacrificial components) while I have her heart out e.g. oil pan gaskets, transmission rebuild, etc...)

Alex Lopez
S/V Nepenthe

if you have a tranmission/clutch with the fiber clutch plates you might have them checked and replaced if needed.... some times on old engines when rebuilt you will find some othere weeknesses ...you may also want to redo your stuffing box packing as well .....the pan gasket is a given when rebuilding the pistons and cylenders also do a valve job on the cyl head ...while you are at it diong the injectors include the injector pump in that event as well......

regards

woody

 

[Liam]

Alex,
3 quarts of oil every 50 sounds like a lot. How many hours are on the engine?

 

[Bill Roosa]

3 qt/50 hours

If this where a car and you ran it a mid to high RPM (60/80 MPH) you would travel 70*50=4500 miles or an average oil change interval. This rate of oil consumption would indicate that the oil rings are in need of replacing or you have a leak (intake, exhaust valve guide seals etc).
In addition to the valves, rings and other things mentioned I would insure you renew the crankshaft bearings along with the connecting rod bearing renewal. You have to do the connecting rods anyway and it makes no sense to just do half if you are already there anyway.

 

[tommays]

I think if you start taking it apart a 7k hours your gonna end up in a full rebuild as the oil use is on the huge side

 

[Don12364]

The mind boggles at 7,000 engine hours.
If it were a road vehicle averaging 40 mph this would mean 280,000 miles and a rebore, rings and bearings would be about right.
But, on a boat 7,000 hrs at an average of 6 knots means possibly 42,000 miles under engine.
This is like crossing every ocean in the world under engine - twice.

We work only about 2,000 hours a year so it is as if the engine has run constantly whilst you did 3½ years work.
Could you really have 7K on the clock or does it keep on running when the engine is off?

 

[Ray Bowles]

On a diesel engine 7,000 hrs is not unreasonable if she has been run often and at load. If many of these hours are battery charging hours then she will be real tired.
When you go into an engine for piston rings then you really must remove the rods. On a boat engine this required removing the engine. While removing the rods you really should do the rod bearings. Since you are doing the rod bearings then you should do the main bearings and oil pump. So now........we are to the point of a major overhaul.
Doing a valve job is about the only job that can be reasonably done in the boat and that probably is not your oil consumption area unless the valve oil seals are shot.
I think that you are faced with a major engine overhaul as anything less will eventually bite you later for a much greater secondary cost. The other option is finding a low hour used engine and that is an adventure in its own right.
Sorry for this outlook but after spending a good part of my adult life in such repairs I speak from experence.
Ray

 

[redhead78]

If you really like this boat, and plan to keep her, you have to remove the engine to rebuild, it would be worth it to install a new engine. even the weight difference, I replaced and old 30 hp renault 2cyl, and trans,weighing in around 8-900 lbs. new 35 hp enging and trans 370 lbs,and smaller. when you start adding up the parts and things you need to rebuild, triple it and you will still be on the low side with an old/rebuilt engine......my 2 cents, good luck however you choose....Red

 

[Alex 2740]

Alex,
3 quarts of oil every 50 sounds like a lot. How many hours are on the engine?

About 7000 hours

 

[Alex 2740]

On a diesel engine 7,000 hrs is not unreasonable if she has been run often and at load. If many of these hours are battery charging hours then she will be real tired.
When you go into an engine for piston rings then you really must remove the rods. On a boat engine this required removing the engine. While removing the rods you really should do the rod bearings. Since you are doing the rod bearings then you should do the main bearings and oil pump. So now........we are to the point of a major overhaul.
Doing a valve job is about the only job that can be reasonably done in the boat and that probably is not your oil consumption area unless the valve oil seals are shot.
I think that you are faced with a major engine overhaul as anything less will eventually bite you later for a much greater secondary cost. The other option is finding a low hour used engine and that is an adventure in its own right.
Sorry for this outlook but after spending a good part of my adult life in such repairs I speak from experence.
Ray

Thanks Ray, I had planned on pulling the engine to do the work since I can't imagine doing it aboard. I Also appreciate the advice on the ancillary replacement hardware/work that would be needed as well. I will sit down with the Yanmar service providor to hash out the "estimated" costs. I'll grind on the info and try to figure out where to go with this.