1991 Nissan 2.7 Diesel - Valve Problems?

Most probable cause for the blue coloured exhaust gas is

1) Piston rings sticking

2) There is a heavy cylinder liner wear : Scoring /ovality

3) Worn valve guides & or seals which lets oil gets in to the comubustion chamber.

Try troubleshooting all the possible ways ( one by one ) of oil getting in to the comubstion chamber.

Thanks & Best Regards

Suppose the problem is valves. Will a compression test show if the problem is valves?

Hi, Some years ago we had a similar problem with a John Deer tractor.

Mostly used for light duties around the place meant it would be operated at around 750 rpm constantly doing hedge trimming and back hoe work, when we tried to use the machine for some heavy haulage you could hardly see for the smoke.

We called in the local dealer for a quote to rebuild the engine, this old guy turned up and we sent him to the shed to begin his inspection. We could hear a lot of engine reving and huge quantities of smoke issued forth from the tractor shed vent units on the roof.

About an hour later a shout that the tractor was fixed and the bill would be on its way later, as I was on the phone I never got to speak with the guy before he left.

Later talking with one of my men he told me what he had seen the tractor repair guy do. He had removed the engine air filtration unit and wound the old girl up to maximum rpm, he then proceeded to empty a full box of kitchen scouring powder into the air intake, the engine coughed and spluttered belched smoke and carbon vibrated and eventually cleared her throat and roared away with no trace of smoke.

Finnally getting hold of the repair shop guy we had our diagnosis,

Glazed Bores from all that light work, this old tractor has never been touched again to this day and still performs like new. We do however put her through her paces after each light spell of duty.

I dont for one second suggest you try this remedy but the fault could be the same so worth a look see.

Oh almost forgot the bill for this genius £55.00

Only 55 quid for a house call? I'd say you made out pretty good there, even if the labor done did not seem like that much. Most specialists I know want 80 to 90 just to show up ;)

Hi

What is glazed bores?

Glazed bores refers to when the inside of the cylinder bores are polished smooth and glassy. In order for the piston rings to seal in the cylinder, there must be a certain degree of roughness in the cylinder walls. In a diesel this is caused by light loading for long periods of time. ie less than 80% loading. Ind order for diesels to remain happy and avoid glazing they nead to run hard periodically.

Hi

Which scouring powder was used? What was its base?

I would guess it was something like Borax. The scouring powder was used, so it's grittiness (is that a word?) would break the glazing on the cylinder walls.

Hi, Ajax as I recall

Bon Ami is another suitable powder. All of these kitchen cleaners are using very fine pumice powder. But be very careful to use it sparingly. We get glazed cylinders in gensets that run at a fixed fast RPM but light load. Being lightly loaded the engine does not come up to full operating temperature. The cooler cylinders and rings allow more oil to leak past the rings and this oil cooks from the available combustion temps. The resultant hot oil then glazes the cylinder wall. If the engine was hot enough, the rings would fully expand and thus scrape off any oil from the cylinder wall. Blow by and fuel washing down the cylinder wall will also contribute to the glazing material.

Hi, glazed bores are when the cylinder bores aquire a glass like coating from incomplete combustion, this degrades the interaction of the piston rings against the bore surface allowing oil past the ring on the induction stroke and blow by on the ignition stroke

If anybody is watching this space, my problem has solved itself. While driving along at low revs so that the pick-up dont smoke, I got angry. I push in the clutch and then I revved the pick-up long and very hard. Big clouds of smoke and then suddenly nothing. Smoke gone and the pick-up was fine. So what happened?

I think there was a piece of carbon preventing one of the valves from closing properly. I think the high revs dislodged the piece of carbon.

Thanks for getting back to us with an update. All too often, after we are asked a question, the original poster disappears and we never find out anymore about the situation.

The solution was probably along the lines of what I said in post no 6. You have been running the engine too lightly and by, um, getting mad and beating the hell out of it, you broke the glaze and the rings started to seal better. Problem solved.

You may want to lean on it every now and then, as a rule, just to keep it from reglazing.

"solution was probably along the lines of what I said in post no 6."

As well as Exemmet's exellent description in post no 2 and Elnav in no 12.

Sorry E's, I didn't mean to so arrogantly snub you folks like that

Yes IanR, I think you are right. If it happens again I will try the Borax thing. In the mean time I will gun it every now and then.