Hi, we operate some old, low-speed 4-stroke gas engines to generate electricity. We had used 2-cycle gas engine oil for years, because it was convenient; recently we changed to 4-cycle oil and the oil analysis for all engines has been showing high copper, iron, and aluminum ever since. Any ideas? As far as we know there are no failures.

2 stroke diesel engine oil has ash controlled to less than 1%.
4 stroke diesel oil is usually more than this.
There may be a build up of ash causing ring problems.
Suggest the use of low ash gas engine oil, assuming use of sweet gas.
How are the oil results TBN TAN Oxidation, nitration and viscosity.
May be corrosive attack.

main problem is a drastic increase in wear metals: fe, cu, pb, al, si. Could be to the increased detergent activity.

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Tan, nitr, oxid, vis are norm.

High silicon may suggest leaks in the air filter system, resulting in increased abrasive wear.
Increased wear metals suggest both top and bottom end wear.

Look at other engine indicators, Worn Rings will give: Crank case pressure increase or Breather flow and increased iron.

I just lost a medium size diesel engine that was blowing lots of smoke out it's breather and had a long history of high iron. Eventually smoke & pressure got too much and it blew a seal then belched all it's oil = no more engine.

I will sure those metals (fe, cu, pb, al) should came from the engine part. Therefore, the presence of these metal indicates wear on the engine part. However, the trend is more important than metal content itself. If it is raising to fast, then the oil should changed. Otherwise, it could consider normal wear.

Looking at the oil, perhaps you could check and compare the kinematic viscosity between the 2-cycle oil and the 4-cycle oil. Maybe we could find the 4-cycle oil is slightly thinner than the 2-cycle oil. If yes, then this make those metals come from.

Si, should come from the air. It should relating to the air system.

Don't forget to continue regular oil check. Best wishes.