Does anyone have a good source for information on rebuilding the yanmar 3GMF? things to look for, what should be replaced etc? This is the engine on my 85 hunter 34'. I havnt been able to find anything helpful on the web.
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Same Engine
Hey Alex,
I have the same engine in my 83 H34. Just curious, why have you decided to do a rebuild?
Good luck with it.
Joe Mullee
Hey Alex,
I have the same engine in my 83 H34. Just curious, why have you decided to do a rebuild?
Good luck with it.
Joe Mullee
To rebuild or not
I'd have to ditto Joe
You normally don't rebuild unless you have a reason to. That will drive the rebuild scope.
IMHO you would have to have something like 6000 hours on a diesel engine before it would need a complete rebuild. I know truck diesels go 300000 miles before rebuild. If you guess that that engine averaged 50 MPH over its life that would mean it ran for 6000 hours.
Now if there is a specific problem I'd just replace the parts that need replacing and possibly some parts that would be cost effective to replace while you have those parts of the engine torn down.
An example is replacing the starter drive gear after you have the starter out to repair the solenoid electrical connections. If the solenoid connections have gone it is a good bet that the gear has been well used and you will have to take it off anyway to get the bendix apart and the solenoid off. Just makes sense to stick a new gear on during the reassembly.
With that said, what are her symptoms?
I'd have to ditto Joe
You normally don't rebuild unless you have a reason to. That will drive the rebuild scope.
IMHO you would have to have something like 6000 hours on a diesel engine before it would need a complete rebuild. I know truck diesels go 300000 miles before rebuild. If you guess that that engine averaged 50 MPH over its life that would mean it ran for 6000 hours.
Now if there is a specific problem I'd just replace the parts that need replacing and possibly some parts that would be cost effective to replace while you have those parts of the engine torn down.
An example is replacing the starter drive gear after you have the starter out to repair the solenoid electrical connections. If the solenoid connections have gone it is a good bet that the gear has been well used and you will have to take it off anyway to get the bendix apart and the solenoid off. Just makes sense to stick a new gear on during the reassembly.
With that said, what are her symptoms?
survey
-Alex
I was told by the surveyor i should last year. some problems i have dont seem any different then other's engines, like the trouble starting in the cold. I have issues when i bring the throttle up the engine runs really rough at certain rpms, once i go just beyond that the engine will level out and run ok. I also have the occasional occurence of when i start her up it sounds like its trying to start on two cylinders. I really just want to make sure im taking care of the engine, and i enjoy the doing the repairs.
-Alex
Alex
I would spend a few bucks on having the fuel system checked out before doing the rebuild. You may that some repairs to the lines, injector, pumps, filters will do just what you want.
The rough running at certain throttle sounds more like fuel/air/timing or errant injector issues than a need for a rebuild. Ask around for someone who knows the GM and it's parts, rather than the yard mechanic.
All the best,
dave
I would spend a few bucks on having the fuel system checked out before doing the rebuild. You may that some repairs to the lines, injector, pumps, filters will do just what you want.
The rough running at certain throttle sounds more like fuel/air/timing or errant injector issues than a need for a rebuild. Ask around for someone who knows the GM and it's parts, rather than the yard mechanic.
All the best,
dave
Take this advice based on how much you've paid for it 
Our Yanmar diesels (I also have a Hunter 34) don't have glow plugs so they will always be rather hard starting in cold weather.
I have been trying to track down the reason for the occasional rough start up. It's a random event which makes it difficult to pinpoint. I've tried to eliminate air leaks so I'm leaning toward a sticking injector possibility.
I'd recommend checking the compression on all cylinders and making sure valve timing is good.
Generally if compression and valve timing are good, it's a fuel delivery issue not a need for an engine overhaul.
As far as the engine jumping around as the throttle is advanced, I have the same problem (especially after the engine is up to temp). I've had the prop shaft checked, the prop balanced, new cutlass bearing, motor mounts removed and inspected, and had the overall alignment of the drive train adjusted. None of these has changed anything.
I still experience the "pounding" until rpm's advance beyond about 1500 after which the throttle can be backed off and the rpm's drop while the engine operates smoothly.
I'm pretty sure the pounding comes from the tranny. The recommended fix is to ensure the gear selector is fully engaging the selected gear. If this is the case, I'm thinking a tranny rebuild is in the future with replacement of the cone clutch.
I plan to live with the problem for a while to see if it gets worse (which it hasn't since I've owned the boat) now that I'm sure all the supporting stuff is fine.
Our Yanmar diesels (I also have a Hunter 34) don't have glow plugs so they will always be rather hard starting in cold weather.
I have been trying to track down the reason for the occasional rough start up. It's a random event which makes it difficult to pinpoint. I've tried to eliminate air leaks so I'm leaning toward a sticking injector possibility.
I'd recommend checking the compression on all cylinders and making sure valve timing is good.
Generally if compression and valve timing are good, it's a fuel delivery issue not a need for an engine overhaul.
As far as the engine jumping around as the throttle is advanced, I have the same problem (especially after the engine is up to temp). I've had the prop shaft checked, the prop balanced, new cutlass bearing, motor mounts removed and inspected, and had the overall alignment of the drive train adjusted. None of these has changed anything.
I still experience the "pounding" until rpm's advance beyond about 1500 after which the throttle can be backed off and the rpm's drop while the engine operates smoothly.
I'm pretty sure the pounding comes from the tranny. The recommended fix is to ensure the gear selector is fully engaging the selected gear. If this is the case, I'm thinking a tranny rebuild is in the future with replacement of the cone clutch.
I plan to live with the problem for a while to see if it gets worse (which it hasn't since I've owned the boat) now that I'm sure all the supporting stuff is fine.
Air in fuel line?
What you are experiencing sounds like an air leak into the fuel line. Make sure all connections are tight. My engine had a leak in the connection from the injector pump to the injectors. The engine would start and run well but as you said not on all cylinders at first. Yanmar engines can take a fair amount of air in the fuel line and still run. After this connection was tightened the engine starts like new. If the rubber lines seem old and the connections are tight you may want to replace the lines.
What you are experiencing sounds like an air leak into the fuel line. Make sure all connections are tight. My engine had a leak in the connection from the injector pump to the injectors. The engine would start and run well but as you said not on all cylinders at first. Yanmar engines can take a fair amount of air in the fuel line and still run. After this connection was tightened the engine starts like new. If the rubber lines seem old and the connections are tight you may want to replace the lines.
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