Fuel leaking into oil crankcase

[HTBaggett]

I have Diesel fuel leaking into the oil crankcase on my Yanmar 2GM. Based on input from my mechanic, I have replaced the fuel lift pump with a new one, professionally rebuilt the head with new injectors, had the injector pump professionally rebuilt, and replaced the fuel return to tank line.

Still leaking!

Anyone have any ideas where the fuel is coming from. It takes about 6 hours of run time before the oil/fuel mixture starts coming out at the oil dip stick.

[atoll]

Originally Posted by HTBaggett

I have Diesel fuel leaking into the oil crankcase on my Yanmar 2GM. Based on input from my mechanic, I have replaced the fuel lift pump with a new one, professionally rebuilt the head with new injectors, had the injector pump professionally rebuilt, and replaced the fuel return to tank line.

Still leaking!

Anyone have any ideas where the fuel is coming from. It takes about 6 hours of run time before the oil/fuel mixture starts coming out at the oil dip stick.

if the head was rebuilt/skimmed have you reset the tappet/valve clearance,and also clearance on the decompressor lever.

i had the same problem with a 2cylinder kubota where the decompressor caused the valves to not seal properly,a small adjustment fixed the problem.

[captstu]

There are two typical sources of oil into the crankcase on small diesel engines including the 2GM.

The most common is that the gasket at the base of your fuel pump has developed a leak. Since the fuel pump is operating mechanically by the camshaft, there is a gasket seal the keeps the fuel on the right side and the oil on the left side. The most common way to find that is to remove the fuel pump clean it completely with a paper towel and operate the priming lever on the side of the pub I have a dozen times with a towel covering the base. If the towel on the base is wet your seal is bad.

The second area difficult to find and more difficult to fix. When a diesel engine is operating under load, sometimes part of the fuel injected of the cylinder is not burned until the engine gets up to RPM to take the load.

If this happens over time, for example when you have a dirty prop, or a bottle with excessive drag, the engine is continually running overloaded and trying to inject more fuel to get the power you demand.

This could also be caused by two large alternator load or some similar load that causes the demand to exceed the ability of the engine.

The result is a continual slow flow of diesel fuel into the engine oil until you I’ll lose his lubricating capability of the engine requires rebuilt because it has been severely damaged.

I had twin Yanmar 3GM engines destroyed to the point They required new bearings, new connecting rods, and new pistons. This happened because I fitted too large of an alternator for the engine the support.

Whatever the cause of diesel fuel in your engine oil, you must change the engine oil immediately or you will destroy your engine.

[HTBaggett]

Thank you for the input. I isolated the fuel pump by using a standby electric fuel pump to supply fuel to the engine. Still had fuel in oil, so I’ve ruled out the fuel pump.

As for the load issue you identified, I will need to review that. I have only run the engine while in the slip, both in neutral and in gear(forward and reverse). Unloaded in neutral it comes up to speed immediately. There is a reduction in RPM when I engage the gear, but doesn’t seem to be drastic.

I do not think the alternator is an issue as it’s the same alternator that has been there, prior to the issue started.

[HTBaggett]

Thank you for your input. I have reset the valve tappet clearance. The engine starts immediately, even after sitting up for a couple weeks.

I am unfamiliar with the decompressor clearance. Could you advise how to adjust the decompressor valves?

[Jason Flare]

Just curious. When you installed or used the electric fuel pump did you disconnect the fuel lines into and out of the lift pump and tie them together to bypass the lift pump or did you push or pull fuel through the lift pump?

One time, with a bad lift pump I had to bypass it until a new pump arrived. In my case I was getting air into the fuel system.

[Lepke]

The engine starts fine, so you have good compression. So the rings and valves are sealing normally. I suspect the fuel is coming from a bad seal on the injector pump. Sometimes the shaft gets pits where the seal rubs. So a new seal gets ruined almost immediately. I don't think the engine would run normally with that amount of extra fuel entering the cylinders. Besides, you'd see black smoke if your engine was under extreme load.
On most engines, the only path for fuel into the crankcase is the injector shaft seal or the lift pump diaphragm. It's possible there's a crack in the injector pump housing or if the secondary fuel filter is part of the engine casting, it could have a crack, too.

First I'd talk to the people that rebuilt the injector pump. Then I'd take a compression test to verify the cylinders have a good seal.

[shakey doug]

I note that you mention having the HP fuel pump is it possible to post a list of work carried out & parts used. Main suspects given other work already done would have be bad pump element or bottom delivery valve joint.

[jimbunyard]

Don't know why this stuff seems to run in spells, but I changed 3 gallons of diesel out of a 6.6 Isuzu crankcase yesterday...but that's a story for a different thread.

This is a little strange.

Does the engine run well, with no starting, full RPM or power problems?

If it does, I would make sure that the new lift pump isn't defective, and that it is correct for the application.

As far as I know, the injection pump on this engine doesn't have any rubber seals that seal the diesel injection side from the crankcase. The delivery valves would leak to the exterior, probably the only ultimate source for diesel to get into the crankcase from the injection pump would be the copper gasket (item 6 below), where it would enter the crankcase via either the rack/pinion (14/26) interface, or between the pump body and the guide plunger (18). Re-use instead of replacing the #6 gasket could cause a leak, as could dirt or faulty pump assembly---but the engine probably wouldn't run very well if that is the case.

Seems a case of simplest first (check the lift pump), then bring the injection pump back to the rebuilders. There doesn't seem to be any other real candidates for where that amount of fuel can come from in that amount of time, at least not to my eyes...

[atoll]

Originally Posted by HTBaggett

Thank you for your input. I have reset the valve tappet clearance. The engine starts immediately, even after sitting up for a couple weeks.

I am unfamiliar with the decompressor clearance. Could you advise how to adjust the decompressor valves?

the valve decompressors are located on the side of the tappet cover,and work by holding the exhaust valve/s open when held back,so as to allow an engine to get up to full revs for start up before they are released.

i see in the yanmar manual for the GM series,there is no adjustment possible,pages 72 and 102 for the decompressor mechanism,which works like a semicircular cam in contact with the tappet arm when rotated 90 degrees.

if the head has been skimmed then it may be that the cam is now in contact all the time with the tappet arm in one or both cylinders ,enough to prevent the valve from sealing.

but still allowing the engine to run but causing incomplete combustion in one or both cylinders,the uncombusted fuel washes past the rings and into the oil.

you could try running the engine with the tappet cover removed and if the engine stops making oil then this is what is causing the problem.

the fix would be to remove the decompressor cam and grind back the flat surface untill it is no longer in contact with the tappet arm when not engaged.

the problem i had was because the one of the decompression levers had become bent before i bought the engine,and when i rebuilt the engine i removed the lever and straightend it,then assembled it in slightly the wrong position which caused it to contact the tappet arm.

this allowed the engine to run fine,but caused one of the cylinders to have incomplete combustion which led to fuel in the oil.

i also had the injector pump rebuilt suspecting initially this was the problem.
it was only when i noticed that one of the decompressor levers had tension on it all the time,and no flat spot where it was not in contact that the penny dropped,problem solved after filling the engine 3 times

[jimbunyard]

Well then, experience trumps theory. Go with the decompression lever fix first, and then try the other stuff...

[HTBaggett]

Originally Posted by Jason Flare

Just curious. When you installed or used the electric fuel pump did you disconnect the fuel lines into and out of the lift pump and tie them together to bypass the lift pump or did you push or pull fuel through the lift pump?

One time, with a bad lift pump I had to bypass it until a new pump arrived. In my case I was getting air into the fuel system.

Jason Flare

Yes. Pulled both lines from the lift pump and tied them together and used the electric fuel pump to pass fuel to the engine.

[HTBaggett]

Originally Posted by Lepke

The engine starts fine, so you have good compression. So the rings and valves are sealing normally. I suspect the fuel is coming from a bad seal on the injector pump. Sometimes the shaft gets pits where the seal rubs. So a new seal gets ruined almost immediately. I don't think the engine would run normally with that amount of extra fuel entering the cylinders. Besides, you'd see black smoke if your engine was under extreme load.
On most engines, the only path for fuel into the crankcase is the injector shaft seal or the lift pump diaphragm. It's possible there's a crack in the injector pump housing or if the secondary fuel filter is part of the engine casting, it could have a crack, too.

First I'd talk to the people that rebuilt the injector pump. Then I'd take a compression test to verify the cylinders have a good seal.

Lepke,

Thank you for your input. I did not think of a pitted shaft nor a crack in the injector pump. Not sure I understand the reference to the secondary fuel filter crack, but will check both. Wouldn’t the pro’s who rebuilt the injector pump look for a crack and pitted shaft?

I agree with you that, that if that much fuel is going into the cylinder, I would be noticing a performance issue and a lot of black smoke.

[jimbunyard]

Umm, the pump in the diagram is the pump on the engine if you have a 2gm20. The 2gm10, 15, and 30 have the same style pumps. There is no rotating shaft, nor are there rubber seals internally.

[Jesse]

Faulty return to tank line is a possibility worth checking. I've encountered it twice and both times it was after recent work on fuel system.