I'm trying to eliminate piston rings as a cause of smoke in my 83 240d. It has good compression. Today I pulled my prechambers and looked at the top of the pistons. They were dry. I had run the car to operating temperature just prior to pulling the prechambers. Could I reasonably infer that the rings are sound??
I do not believe it is oil smoke, just wanting to eliminate the rings as suspect. The smoke is whitish gray with a hint of blue. It's all the time.

Did you turn it over & look at the bore?
Does it breath bad?
Does it use oil? If so, how much?
You could have retarded injector timing.

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1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
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1968 Ford F750 truck. 6-354 diesel conversion.
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thanks-
I could not see the bore. Have not driven it enough to establish oil consumption. Timing is good 24*btdc dripped. Chain, valves, egr etc. Hoping that the absence of oil on the piston tops points to no leaking rings.

False hope.

Any oil that is forced up past the rings is oxidized in the combustion chamber. That would be white smoke out the exhaust.

You'll never see any evidence of bad oil rings by looking at the piston tops.

Do you know the mileage on your Engine?

If you believe the Piston Rings may be sticking Soaking in Marvel Mystery Oil may help.
It did on my Volvo that had grey Smoke all the time after it sat a year and I drove it 6 months with a Thermostat that was opening too soon (my compression is also good).

Members have siad that using Synthetic Oil can free up Piston Rings but it takes about 200-300 miles of driving.
Have you done a Valve Adjustment.

Could be your Injectors need to be checked.

Valve Stem Seals? A bit of work but not expensive to replace.

For more details on the above stuff:
DIY Repair Links
DIY Links by Parts Category - PeachParts Mercedes ShopForum

PeachPartsWiki: Do It Yourself Articles - Mercedes Vehicles

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84 300D, 82 Volvo 244Gl Diesel