another generator question

[chris piazza]

Hi all,
Got a 15kw Onan with a 4cly Cummins in it. A while back the gen was using about a quart of oil an hour. Traced the problem to the rear injector pump seal. Took the injector pump off and replaced the O-ring and this fixed the problem. Now there is another problem. When I start it up I get a lot of blue smoke that mostly clears up after about ten minutes, also a slight amount of fuel sheen in the water. Is this a bad injector? I don’t have an IR gun to check cly temps. Is this a timing problem? I did note that when I took the pump off the O-ring sits in a grove on a plunger that is pushed in and out via a lobe on the camshaft. In thinking back maybe it got turned so this would make the timing off of the injection of the fuel? It is not burning any oil at all now; I have let it run under load twice for about a total of six hours with no consumption at all. Any suggestion would be a big help.

Chris
Superior Nights 53C

[Avenger]

Remote diagnosis again, yippie. Based on the type of injection pump I think you're describing, would I be correct in thinking that this is an older Onan? The pump would have a ring gear around the base and be operated by a cam in the engine if it's what I'm thinking of. If that's the case it's an Onan engine, despite what Cummins will tell you.

The timing on these is set by a button that is underneath the follower, it's retained by a clip so it's pretty unlikely that you lost it. Turning the gear on the other hand could cause a problem. But frankly if you're off one tooth with the gear install you would have running problems all the time i.e. smoke, hard starting, and being unable to carry full load. I'd be more inclined to think that you're on the right track with a faulty injector. It can be hard to tell, but if it's fuel the smoke will actually be white, whereas burning oil will have a blue tint. If it's fuel you may be able to isolate the bad cylinder by carefully loosening the injector line at the injector when the engine is running (yes, fuel will spray out, have a rag handy, and keep your fingers away from the fuel that's spraying out) Do this on one cylinder at a time and have somebody watch the exhaust. What you're doing is shutting the cylinders off one at a time, so if your observer notices a change you've isolated the problem cylinder. If you're really interested, you can swap that injector with another, then do the test again and see if the problem follows the injector. If the same cylinder is still the problem it's an engine issue. Or, you could just pull the injectors and take them to a fuel injection shop and have them tested.

If you can't pin the problem down to any one cylinder it may just be time for new injectors or valve stem seals. I'd start with trying to isolate it to one cylinder, we can get more involved if that doesn't work, let us know how you do.

[67hat34c]

that sounds like valve guides.

[chris piazza]

Thanks for the info. I have done that procedure before to check for a bad injector on a truck that I had (Ford, International diesel) but it’s a lot easier to hear the bad injector at idle than when the genny is running at 1800. It’s got near 2900hrs on it and I am sure the previous owner (who was horrible with preventive maintenance) didn’t do anything with it. I probably should change them all or at least have them checked. Being that it’s a 1979 I was also concerned about the timing but don’t have a service manual to refer to find out how to check it or set it.

Chris
Superior Nights

[Avenger]

Yeah, I was only thinking that you might be able to observe if the smoke clears up when you crack one line. As far as checking the timing I could explain to you how to flow time it, but it will take longer to type it here than either of us has time for. If you really want to take a crack at it PM or e-mail me and I can fax or e-mail you some pictures and descriptions that will help clarify it.

One simple thing you should be able to do to check that you got the gear in correctly is: Bar the engine to the PC or INJ mark on the flywheel, remove the valve cover and make sure the rockers on #1 cyl are free, this is compression stroke on #1 and see if the timing slot in the pump gear lines up. There is a small screw in the mounting flange of the pump on the side opposite the throttle linkage, you can use a piece of .125 brass rod as a timing pin, or you may be able to check visually, with a good penlight and small mirror. Using the timing pin you'd need somebody to slowly bar the engine while you have the pin inserted in the screw hole. Stop turning the engine when you feel the pin drop in and check for the flywheel mark.

Lining up the mark on the flywheel and pin in the gear slot is how the pump is installed. Actual final timing is best done by flow timing as mentioned earlier. It is unlikely that this has changed if nobody has tampered with it but if you've got everything else right it wouldn't hurt to check it. Be sure you didn't lose or change any of the shims under the pump mounting flange, these set the correct gear clearance, and changing them will affect timing as well.

One thing I'm still puzzled on, how you changed the O-ring on the tappet and fixed an oil consumption problem. The only purpose for the o-ring is to retain the tappet when the pump is off the engine. You must have inadvertently done something else that stopped that.

[Nonchalant1]

One thing I'm still puzzled on, how you changed the O-ring on the tappet and fixed an oil consumption problem. The only purpose for the o-ring is to retain the tappet when the pump is off the engine. You must have inadvertently done something else that stopped that.

Happens all the time........"I inadvertantly fixed it". When something's not working right, sometimes I just take it apart, look at all the parts, don't see a problem and reassemble it, and voilla....it's fixed!

Doug

[chris piazza]

Ok your way over my head now. The previous owner had a mechanic on board before who said the oil consumption was caused by the rear injector oil seal (o-ring) this is what I replaced. It made sense to me because the seal prevents oil from the crankcase from entering into the injector pump and than into the fuel. Also the old o-ring was completely gone when I removed the pump. However there is what I call a ring gear that surrounds the plunger that may have been turned before re-install, this is what I think screwed up the timing. I guess I will take one step at a time and change the injectors first.

[Avenger]

Happens all the time........"I inadvertantly fixed it". When something's not working right, sometimes I just take it apart, look at all the parts, don't see a problem and reassemble it, and voilla....it's fixed!

Doug

I can't even count the number of things I've "fixed" that way. I think I'm going to call it "Daylight Therapy." It's amazing the healing that a little exposure will do.

the old o-ring was completely gone when I removed the pump. However there is what I call a ring gear that surrounds the plunger that may have been turned before re-install, this is what I think screwed up the timing. I guess I will take one step at a time and change the injectors first.

Maybe you're referring to a different O-ring than I'm thinking of, as long as it worked it doesn't matter.

The thing I described with the timing pin will verify that you got the gear position correct when you re-installed it and it really isn't hard to do. Feel free to ask if you need more info. Good luck!