Yanmar 2GM20 Injector pump delivery problem

[broken pete]

Hi everyone,
I would really appreciate your input on the following problem. I recently rebuilt my 2gm20f, everything was frozen from the pistons to the injector pump (including the injector nozzles). engines were left for 8 years and was not in a good shape.

So now everything is freed up, cleaned up and rebuilt she starts up reasonably well however I am getting black smoke on acceleration and she does not increase RPM very easily. There is a noticeable delay upon accelerating, she gets there but not as fast as it should be.
I believe the smoke is as a result of excess fuel because the cylinder head and all the exhaust system has been cleaned up and de-coked.
The injectors have been stripped apart, cleaned up and I have given them brand new nozzles.

I have totally stripped apart the injector pump, cleaned it up and rebuilt it because the rack was frozen.
I have a feeling the fuel delivery is too much now but I have no idea how to adjust this. The workshop manual talks about an adjustment screw and a eccentric screw but I am now out of my depth.
Can anyone with some experience here help me out?

Many thanks in advance

[skipperpete]

Originally Posted by broken pete

Hi everyone,

I would really appreciate your input on the following problem. I recently rebuilt my 2gm20f, everything was frozen from the pistons to the injector pump (including the injector nozzles). engines were left for 8 years and was not in a good shape.



So now everything is freed up, cleaned up and rebuilt she starts up reasonably well however I am getting black smoke on acceleration and she does not increase RPM very easily. There is a noticeable delay upon accelerating, she gets there but not as fast as it should be.

I believe the smoke is as a result of excess fuel because the cylinder head and all the exhaust system has been cleaned up and de-coked.

The injectors have been stripped apart, cleaned up and I have given them brand new nozzles.



I have totally stripped apart the injector pump, cleaned it up and rebuilt it because the rack was frozen.

I have a feeling the fuel delivery is too much now but I have no idea how to adjust this. The workshop manual talks about an adjustment screw and a eccentric screw but I am now out of my depth.

Can anyone with some experience here help me out?



Many thanks in advance

This is a big ask for the forum because of the numerous possibilities. For a normal diagnosis, a mechanic usually asks what work has been recently done on the engine and tries to eliminate that work as contributing to the current or actually being the current problem. In this case it's everything❗️but I'll start the ball rolling🤢
First and easiest is to ask if the decompression lever is causing the problem, have you run it with the valve cover off ?
There is a thing with injector pumps called phasing and calibration. Phasing is getting each element of the pump to cause injection at the correct point of the cycle but not in the same way as injection timing. On a 2GM, one pump element could be out of phase to the extent that the cylinder it serves could fire so late.... or early that it caused the engine to basically act as a single cylinder. Calibration is simply getting the pump to deliver precisely the same amount of fuel to each cylinder and again, if one element is out of cal the engine runs as a single cyl or as an overfuelled twin on one cylinder.
What's the compression like?
Are the precom chambers installed correctly?
Take the heat exchanger/ exhaust manifold off and run it to see which cylinder/s is smoking.
Give more info about what you actually did and how you did it to enable the forum to come up with a fix.

[broken pete]

Ahh ok, i can clarify a few things. The engine is running well and firing on both cylinders. When running she sounds nice (well as nice as a 2 cylinder engine could sound). There is no problem with the valves or the decompression levers that push against them.
The cylinder head has been stripped down, pressure tested, new valve seats, new valves and the head has been very lightly skimmed.
The engine has good compression from I can tell by turning the engine over by hand.

I did remove the swirl chambers/pre-combustion chambers. I have cleaned them up and changed the insulator and protector/washer on it. I don't believe these engines have injector seats, it looks like the top of the pre-combustion chamber acts as the seat? am i a right about that.

Unfortunately i cannot check which cylinder is producing the smoke because the cylinder head has one outlet, the exhaust channels in the head mix together before it meets the heat exchanger. If there were a noticeable noise from one cylinder it would help diagnosis, but they sound the same :/

I understand there is an adjustment screw at the front of the injector pump, I wondered if anyone has experience adjusting this?

[a64pilot]

To me it sounds like retarded timing.

However it’s my opinion the the pump and injectors ought to go to a shop that can bench test them, as I’m sure you know there is a cracking pressure that must be right with injectors and there are similar things on a pump that require setting that pretty much requires test equipment that it’s not likely you have.

But smooth running, but slow acceleration with black smoke and likely down on power sounds to me like timing.

It’s not just too much fuel, that’s not possible. Add fuel and the engine accelerates, fuel delivery is of course how a Diesel is throttled, but obviously when that fuel is injected is very important.

[skipperpete]

Well done saving the life of the 2GM and thanks for all the information about the repairs. I totally forgot that the 2GM has only one shared exhaust outlet. The screw on the front of the case is the injection limiter and the workshop manual says unscrewing the limiter will increase smoke. If you do adjust the limiter, measure its protrusion before moving it so you can wind it back to original.
Heres a pic of the precombustion chamber parts.
Also try cracking the injector lines at say 1,000 rpm and see if the smoke is isolated to one cylinder or shared equally

[Compass790]

Did you get the rack mark on the injector pump in the right place?
Do you have a workshop manual? It should tell you how to adjust the injection limiter in that. If you don't have a workshop manual check in the CF library.
Otherwise pm me your email & I can send you a PDF
Is the compression good?

[Richard Kollmann]

The shim plate thickness under injector pump affects fuel flow to each cylinder. The adapter fitting's torque where injector line is attached to pump will also alter fuel volume to that injector, this is why two wrenches are required to hold adapter from moving when removing or installing injector line.

[broken pete]

thankyou for the replies, yes the matching mark on the rack were spot on, I took my time building the injector pump and was very careful to ensure I followed the manual.

great idea to crack the injectors one by one whilst the engine is running, I will try this tomorrow morning when I have help again. Hopefully this will either isolate the smoke and tell me which cylinder is responsible or make no difference. That would point the finger more in the direction of timing.

unfortunately I am in Trinidad, finding a good/reliable workshop to properly test the injector pump is not straightforward. This is why I have done so much myself upto this point.

Skipperpete, I have not needed to touch the no load limiter, do you think I should try adjusting it or leave it be?

Thanks guys

[svthreecheers]

Originally Posted by Richard Kollmann

The shim plate thickness under injector pump affects fuel flow to each cylinder. The adapter fitting's torque where injector line is attached to pump will also alter fuel volume to that injector, this is why two wrenches are required to hold adapter from moving when removing or installing injector line.

Sorry Richard but the shims under the Inj.Pump are for setting the injection timing not the fuel settings.

[skipperpete]

Originally Posted by broken pete

thankyou for the replies, yes the matching mark on the rack were spot on, I took my time building the injector pump and was very careful to ensure I followed the manual.

great idea to crack the injectors one by one whilst the engine is running, I will try this tomorrow morning when I have help again. Hopefully this will either isolate the smoke and tell me which cylinder is responsible or make no difference. That would point the finger more in the direction of timing.

unfortunately I am in Trinidad, finding a good/reliable workshop to properly test the injector pump is not straightforward. This is why I have done so much myself upto this point.

Skipperpete, I have not needed to touch the no load limiter, do you think I should try adjusting it or leave it be?

Thanks guys

A64pilots suggestion regarding the injection timing is good advice, especially since you're already familiar with removing a delivery valve to perform the check.
With both the governor adjuster screw settings it's wise to follow the service manual because you need to see the rack position marks and slavishly follow the steps but, it's ok to randomly adjust the screws ..... ONLY if you can RETURN to the original setting by measuring the length of the setting screw with a vernier caliper or other accurate measure before you start.
The no load rpm is about 3750 and should be ok at the factory/ original setting however, this is the hi idle of a healthy engine and should not be adjusted until the smoke issue is resolved.

[wannacat]

Just wondering, you did drain , clean the tank, fuel filters and are using fresh new diesel fuel?

[Richard Kollmann]

Originally Posted by svthreecheers

Sorry Richard but the shims under the Inj.Pump are for setting the injection timing not the fuel settings.

Think about it if timing is off flow is too early or too late on both cylinders. One cylinder's flow off can be a single cylinder pump adapter's incorrect torque adjustment. At 2000 rpm trip one compression release at a time to isolate the cylinder. Then adjust adapter torque to reach best matching rpm fuel.

[jakkum]

The shims.
Yes, they change the timing

I bought a cat with two 1gm10s.
Both ran good, but one was always more difficut to start and had a lot of diesel knock.
I loosened the nuts a little bit so the pump would rise slightly before it injected , injected later!!!
Problen solved. Ibought a little plastic bag with pumpshims at a yanmar workshop and the mechanic told me that yanmar would add shims to the pump on engines shown on a show
Of course you could never see the smoke, but they ran very quiet.
Theformer owner of the cat had left an open billfor needless work done on that engine thatnever hadgot cured.
Mycost? €5 or so.
Injection too late? Smoke possible.

[skipperpete]

Is the 2GM fitted with a higher output alternator and/or a smart regulator? Even the original hitachi alternator will create a lot of load at low rpm if the regulator fails and the result can be slow acceleration and black smoke . To prove or disprove this possibility just remove or loosen the belt and run the engine briefly. The coolant circulating pump will not be working so you have about a minute or two to complete the test before the temp starts to climb.

[broken pete]

Originally Posted by jakkum

The shims.
Yes, they change the timing

I bought a cat with two 1gm10s.
Both ran good, but one was always more difficut to start and had a lot of diesel knock.
I loosened the nuts a little bit so the pump would rise slightly before it injected , injected later!!!
Problen solved. Ibought a little plastic bag with pumpshims at a yanmar workshop and the mechanic told me that yanmar would add shims to the pump on engines shown on a show
Of course you could never see the smoke, but they ran very quiet.
Theformer owner of the cat had left an open billfor needless work done on that engine thatnever hadgot cured.
Mycost? €5 or so.
Injection too late? Smoke possible.

This is a dam good idea and an easy test. I will give that a go.