Engine went racing, then kaput

[Deadline]

My 2GM20F went racing twice, so a service tech overhauled the cylinder head and installed new injectors. The engine raced two more times, with smoke everywhere at 4000 RPM for 25 seconds. He had missed the source of the problem, believed now to be the injector pump and/or lift pump.

Got a sample pulled of the newly changed oil that suffered the two latter incidents. An oil test by a machinery lab found 4% fuel by volume, as expected. But it also found 11 ppm of lead. My yard fears the bearings have been so damaged as to require a full overhaul, which means pulling the engine and shipping it to Mack Boring in New Jersey. Three vital questions arise.

1. Is 11 ppm lead in oil significant? I’ve read that new oil already has 4 ppm lead.
2. Why would a soft metal like lead be found on the surface of super-hard steel bearings?
3. Is the lead instead coming from the 4% volume of diesel found in the sample? Or perhaps the Cetane additive?

I attached the chemistry test for anyone who can figure it out. This is a really vexing problem, already expensive and likely to get moreso. Thanks for any advice. Capt. Bill

 

[Charles Erwin]

Diagnose and fix the fuel dilution problem pronto. Once that is done then follow exactly what the lab says to do - take a sample at first run up to normal temperature, sample again at 50 hours then at 100. See whether lead levels change - and make sure the sampler is plenty careful how he goes about sampling.

As to the questions:

If you are curious why 11 ppm is regraded as "elevated" - call the lab and ask. Maybe send them a sample of the oil and/or fuel you intend to use - straight from the container to verify baseline lead content.

Remember, you cannot rely on a one-sample event to conclude lead content is actually out of bounds. There are too many ways sample contamination can occur that have nothing to do with your true motor condition. It is just too early to conclude that anything is wrong.

Charles

 

[kloudie1]

Charles is right on.. Without a good base line, this sample is hard to interpret. The thing that I do get is that it is full of fuel!! I would look very hard at the lift pump diaphragm as the cause. It is unusual (not impossible) for the high pressure pump to leak enough fuel to do this.. is is not unusual for the lift pump diaphragm to do that..
Lead is used in bearings like that because it is soft .. When running, the hard metal crankshaft and the soft lead are separated by a thin film of oil.. These parts do touch when there is no oil pressure or rotation. If the bearings were hard, the crankshaft would be quickly damaged during start and shut-down. Much cheaper to replace a bearing shell than a very expensive crankshaft. I think once you have the fuel/oil contamination corrected, you'll be OK.. Good Luck !

 

[Bill Roosa]

dito what kloudie and Charles are saying. One test does not a sample make. Given that they did not get the first diagnosis right and did not catch it after they "fixed" it I'm thinking I would certainly not be taking their word for 11 ppm being elevated and a sign of bearing trouble.
For the record bearings don't normally fail due to just being spun too fast. As long as there is oil pressure you would have to get the whole engine super overheated to get the bearings to fail. The pistons and cooling system would fail long before the bearings.

 

[Deadline]

Thanks, fellows. I'll get the injection pump and lift pump fixed first, replace the oil and oil filter, and then do the sampling as directed. I also like the idea of sampling the new oil first, very clever. Whew.

 

[Claude L.-Auger]

For the record bearings don't normally fail due to just being spun too fast. As long as there is oil pressure you would have to get the whole engine super overheated to get the bearings to fail. The pistons and cooling system would fail long before the bearings.

Great info here and good advice. Kloudie and Bill are both right with their comments about bearings. FWIW, and without getting too technical, 17 years at Clevite allow me to add that while it does contain lead, Babbitt is the metal most commonly used as the lining for bearing shells of cast iron, steel and bronze. Babbitt metal is characterized by its resistance to galling. Babbitt metal is soft and easily damaged, which suggests that it might be unsuitable for a bearing surface. However, its structure is made up of small hard crystals dispersed in a softer metal, which makes it a metal matrix composite. As the bearing wears, the softer metal erodes somewhat, which creates paths for lubricant between the hard high spots that provide the actual bearing surface. Without that presence of oil, that surface would rapidly deteriorate and of course severely damage the crankshaft.

I concur with Charles, Kloudie and Bill and would proceed with their recommendations before considering full rebuilt. Good luck