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I'm glad someone else has heard about Bon Ami.
I was allowed to rebuild a Jag engine in the shop of a dirt track racer.
During a break I was listening, picking up tips from the guys who hung out there and sure enough just like DrEntrophy says, Bon Ami was often added to a fresh race engine that had no time for break in before a race.
I tried it once in a Porsche 356sc engine that smoked and spit sparks out the tail pipes on a freshly rebuilt engine.
Now, that was no help at all. After tearing the engine down, I found broken rings on one of those pistons and the jug was shot from the scoring. Very expensive those were. And, no, I wasn't the one who rebuilt that one..just the new owner.
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No, it was about 7 years old. I eventually had it repainted the original white and sold it a bit later. Can you believe I bought it for 1800 ? I don't remember what I sold it for but it wasn't much more.
 
Since Bon Ami has been mentioned, I'd like to clarify that there are two different kinds of Bon Ami. By far the most common variety says on the can not to use it on glass ... this is NOT the one you want. The kind that says "safe for use on glass & mirrors" (which ISTR is labeled "cleansing powder" rather than "cleanser") is the correct variant for helping rings to seat.
https://www.bonami.com/products/

But the symptoms sound rather similar to something that Steve Hedke at British Pacific says he has seen several times now on freshly rebuilt motors : severe ring wear. A local club member had less than 10,000 miles on a rebuilt TR4 motor, and the ring gaps were discovered to all be over .030". His theory is that ethanol is washing down the cylinder walls on 'wet' starts; and recommended adding top end lube (eg Marvel Mystery Oil) to the fuel.

I've read elsewhere that TCW3 outboard motor oil is a good substitute (and a whole lot less expensive) for MMO. A lubrication engineer claimed it will actually improve fuel mileage as well ... I bought a gallon but haven't tried it yet.
 
That ethanol theory is a good'n Randall. One more reason to hate th' stuff.
 
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