Yanmar 2gm hard starting and stalling on lower RPM

[Yanman511]

Hello

motor will only barely start with full throttle, anything bellow is impossible to start. When ramping down the RPM with running motor to about 70% it starts to run unstably and lowering even more the motor will stall completely. The injection pump was removed at some point to be renovated, also I have checked the fuel is not the issue by running it directly from clean source with clean fuel, still same issue. Valves should be okay, smoke is quite white when running.

Also when the injection pump was removed I did not measure the old shims thickness and they were replaced by some standard gasket material, so the timing is possible off. Could this be the issue for hard start and running bad at low RPM and do anybody know what would be the standard thickness for the shims? I have bought new set of shims that come in 5pc and they are different thickness.

Thanks for any help.

BR
Fabi

 

[Ralph Johnstone]

Welcome to the site @Yanman511.

A little clarification here will help to tell just where you are at this point.

The injection pump was removed at some point to be renovated, also I have checked the fuel is not the issue by running it directly from clean source with clean fuel, still same issue. Valves should be okay, smoke is quite white when running.

Also when the injection pump was removed I did not measure the old shims thickness and they were replaced by some standard gasket material,

Did you notice your starting problems immediately after you "renovated" the injector pump ? Was it you who did the work or someone else ? If you did the work and used standard gasket material for the shims, I'm going to say that you now have more than a few problems.

The shop manual I have is for Yanmar mechanics and advises them against disassembling the injector pump.

However, they do advise Yanmar mechanics how to overhaul the pumps if disassembly is unavoidable.

Seloc's Yanmar Inboards1975-98 Repair Manual is for general nonprofessional mechanics who can follow complex instructions. Its advice on the injector pump is DO NOT TOUCH.

If, as I suspect, you disassembled your injector pump without a manual and used standard gasket material instead of Yanmar shims to reassemble it, I think you're pretty much out of luck. My best suggestion at this time would be to approach a well known, certified, marine diesel shop and ask them to take over and do as they suggest. Get a quote first as this will not be cheap. They may suggest a new pump but whatever, will require that they install it for any type of very limited warranty. Good luck with this and next time RTFM of which I think this will prove to be an excellent reason why.

 

[SycloneDriver]

How did it run before the pump was removed?

Difficult starting and light colored smoke would suggest that the timing is retarded.

 

[Yanman511]

Thank you @Ralph Johnstone ! The pump itself was only removed by me and actually it was fixed and renoveted at a qualified diesel shop with long experiance (+40) years of renovating pumps and diesel engines. They told me about this shims thing there and I knew I screwed up since the old ones broke when removing so I threw them away without taking any measurements.

 

[Yanman511]

@SycloneDriver actually the were multiple issues and I thought the pump was the main issue. It was very difficult to start, took longer and longer to crank and after a while it did not start at all anymore. I removed the pump at first to have it fixed, the diesel shop that fixed it said there were some issues with it, some part where completely stuck that should move sideways. Anyway when putting the pump back it did not fix the issue, so I removed the pistons to see that 2 rings were burnt to the piston. I replaced all rings on both pistons and also the bearings on the rods. After that I got it running but only with the described method of starting with 100% throttle and then stalling when lowering to lower than 60-70%.

But timing is very likely not correct. I just wonder if there is some standard measurments for the shims settings that I could try.

 

[Ralph Johnstone]

The pump itself was only removed by me and actually it was fixed and renoveted at a qualified diesel shop with long experiance (+40) years of renovating pumps and diesel engines. They told me about this shims thing there and I knew I screwed up since the old ones broke when removing so I threw them away without taking any measurements.

There may be a glimmer of hope yet. I know that I would not be touching the pump but given your situation, you may find some words of inspiration in the Yanmar Service manuals which can be found in Owner Resources/General Downloads :

 

[Yanman511]

Thanks @Ralph Johnstone I appreciate it I will give it a try.