Runaway Diesel..... why?

[flyawa]

A bit of background: This engine was purchased from a shop that said they had rebuilt it and then it smoked so the customer refused to take it. It was cheap so I bought it. It sat for several years and then I got a car that needed an engine so I put it in. It did not have the baffle over the cam so I figured that might be the smoking issue. I did have a hard time with the timing because it had the wrong flywheel on it. I found TDC with a wire through the #1 injector hole, and timed it till it ran well. It has run well for abourt 15000 miles and on a long trip it was running well and at about 70 MPH it suddenly began issuing a hugh cloud of smoke and when I stepped on the clutch the engine went to full RPM. It would not shut off with the key so I killed it with the brakes as it rolled to a stop at the side of the interstate. I took the head off and fully expected to see a hole in a piston or some such. The cylinders seem normal. The #2 and #3 pistons had marks from a valve hit (exhaust) but the valves do not seem damaged. There is a fair amount of lateral play at the pistons. Would enough oil get past the rings to cause the runaway? There was a small bit of oil in the breather. Not enough to run on I would think. Any ideas anyone? I guess now would be the time to take the engine all the way down for rings etc. It had great oil pressure and ran really well, got nearly 50 MPG, but did use about a quart of oil every 500 miles. Really did not smoke much unless you really stood on the accelo. Head seems fine and valves seem fine and tight in the guides.

[flyawa]

Forgot to mention that it's a 1.6 NA 1981 vintage

[rdezsofi]

Excess blow by = runaway engine. Oil is fuel, after all. Could have some broken or worn rings, bad valve guides/seals, etc, etc.

[JSWTDI09]

Excess blow by = runaway engine. Oil is fuel, after all. Could have some broken or worn rings, bad valve guides/seals, etc, etc.

This is a possibility, but so is a failed turbo. Bad turbo seals can cause the turbo to pump motor oil into the intake. As stated above oil is fuel. A runaway diesel is basically an engine running on it's own motor oil. The only question is where is that oil coming from. It can come from blow-by or the turbo, but the end result is the same. It is burning it's own life blood (motor oil).

Have Fun!

Don

[flyawa]

Thanks for the ideas.

Not turbo version so that is ruled out.

Valves seem tight in the guides. I'll put new seals on them.

Haven't got the rings out yet so will get back on that. Seems strange that would occur suddenly.

[Rockerchick]

Well sudden in the sense that the runaway happened suddenly, but if its been sucking down that much oil, it was pretty much just waiting to happen.

[flyawa]

OK, after some time away from it I've gotten back on the project. Got the pistons out and the rod bearings are fine. The piston rings have an end gap of nearly 1/4 inch. (This engine supposedly was rebuilt).

Question is still unanswered. Why the runaway? Would enough oil get past the rings to cause a runaway? Could a malfunction of the injector pump cause a runaway?

Ordered the parts to go back together but wish an obvious reason for the runaway could be identified. Your input appreciated.

[rdezsofi]

How was the head gasket, right near the oil passage????? That could blow into a cylinder, supplying the necessary 'fuel' for a runaway.

[flyawa]

Head gasket was fine.

I'm just having a hard time understanding how gradually worsening rings could make such a sudden and hugh oil burning event. That towering cloud of oil smoke was really impressive.

Six lanes of traffic were completely obscured for a couple of minutes. As it began to clear most of the cars had slowed and pulled off. (including a KHP unit)

[flyawa]

Got the engine back together and it started right up.

New rings, bearings, and checked the head over. Everything is new or in spec. Have only about 5 miles on it. It's smoking more than I'd like to see. Could be just old fuel in the exhaust system after the runaway, but Usually a fresh engine clears up quicker than this one seems to be. Installed an Oil pressure gauge. What should warm OP be? It starts at 75 lbs and drops to 25 when warm. It's always only had an idiot light so I'm not sure what it should be developing. The old sender was the wrong one. It turned the light on when the engine started and went out after shutdown. Backwards, but I learned to live with it. I'd put a temporary gauge on and found good pressure so just ignored it. Watched for light out as a warning. Now with the permanent gauge on I'll see what it runs at long term.

[Glegor]

OK, after some time away from it I've gotten back on the project. Got the pistons out and the rod bearings are fine. The piston rings have an end gap of nearly 1/4 inch. (This engine supposedly was rebuilt).

Question is still unanswered. Why the runaway? Would enough oil get past the rings to cause a runaway? Could a malfunction of the injector pump cause a runaway?

Ordered the parts to go back together but wish an obvious reason for the runaway could be identified. Your input appreciated.

the rings were way too small for the bore if they had a .250" gap...

that is the problem, if indeed the rings DO have that much gap. theres no way that engine was rebuilt if it had 1/4" ring gaps.

[damac2004]

i got a 1.6 na motor in my jetta right now with turbo bits on it and high volume oil pump and i peg 100 pounds on gage on first starts with 15/40 oil

i have my gage on the side of the head.

as it warms up i see about what you do at idle. and it rises accordingly with rpm after that. i have seen it peg again when reving the heck out of it.

my last engine was lower for sure even with new intermediate shaft bearings and oil pump. haven't torn that engine down yet but it burned a good amount of oil and it would smoke white out the pipe when sitting still, that i don't think was related to timing at all.

[Glegor]

i got a 1.6 na motor in my jetta right now with turbo bits on it and high volume oil pump and i peg 100 pounds on gage on first starts with 15/40 oil

i have my gage on the side of the head.

as it warms up i see about what you do at idle. and it rises accordingly with rpm after that. i have seen it peg again when reving the heck out of it.

my last engine was lower for sure even with new intermediate shaft bearings and oil pump. haven't torn that engine down yet but it burned a good amount of oil and it would smoke white out the pipe when sitting still, that i don't think was related to timing at all.

any good 1.6 will PEG a 100# gauge.. my diesel makes enough oil pressure that it balloons out the bottom of the filter yet.. you need a 150psi gauge to not peg it when its cold.. these things make LOTS of oil pressure.

[rdezsofi]

.25 inch end gap? That would give you low compression....a lot of blow by into the crankcase, as well as a lot of oil consumption into the cylinder on the down stroke of the pistion prior to compression.

I don't know where anyone could find rings with that much gap....but there is your answer for the runaway.

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[flyawa]

Thanks for the replies. It must have been the rings that allowed the runaway. Could not find any other problems.

The engine now has about 300 miles since the rebuild and the smoke has stopped and it does not seem to be using any oil. It is gradually getting more power as it breaks in. Probably reducing friction as it wears in. It does have a puff of black smoke on start up and a few seconds of white/gray smoke as it misses for a moment. As soon as the miss stops it clears nicely. What would the miss be? Any ideas? It starts instantly even when cold. It stops instantly when shut off too showing that the compression is high.

Thanks for the input.

[Glegor]

Thanks for the replies. It must have been the rings that allowed the runaway. Could not find any other problems.

The engine now has about 300 miles since the rebuild and the smoke has stopped and it does not seem to be using any oil. It is gradually getting more power as it breaks in. Probably reducing friction as it wears in. It does have a puff of black smoke on start up and a few seconds of white/gray smoke as it misses for a moment. As soon as the miss stops it clears nicely. What would the miss be? Any ideas? It starts instantly even when cold. It stops instantly when shut off too showing that the compression is high.

Thanks for the input.

dude, its got 300 miles on it, its not gonna start good till its got atleast 3000 miles..

the miss is because its cold as hell, and its rings arent quite sealed up. you can give it the SLIGHTEST amount of throttle, and it smooths right out, huh?

it MAY be that an injector is not atomizing good enough at idle when cold.

[Rockerchick]

I dont recall feeling a miss on starts after our rebuild, but I wasn't driving it as much. We still always blip the pedal on startup though just to wake it up on a cold start

[rdezsofi]

If you don't pull the advance lever when cold....it will miss a bit. If you are pulling the lever, you're timing may be slightly retarded.

Exhaust.....it will take a while to burn off any oil residue from prior to rebuilding. Till then...no way to know the source. An hour on the freeway should speed up the process of cleaning out the exhaust....

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[Glegor]

I dont recall feeling a miss on starts after our rebuild, but I wasn't driving it as much. We still always blip the pedal on startup though just to wake it up on a cold start

all the VW diesels that i have re-ringed/rebuilt, have had a SLIGHT miss at idle for a few seconds upon cold start.

retarded injection timing probably had quite a bit to do with that tho..

the miss went away as the miles went on the engine..

[Rockerchick]

Yeah ours is at .95. Seems to like that timing setting a lot better than the .9 we started with.

[rdezsofi]

My '86 1.6 NA, rebuilt 51,000 miles ago....started it today without the cold start lever pulled just to see. Yep, a random miss to the engine when accelerating, went away within a mile of driving off. (Was 67 degree's this morning.) With the cold start/timing advance lever pulled, and pushed in at the end of the street when taking off...there's no miss.