Have you ever heard of a "Bon Ami" ring job?

Dear Car Talk

Dear Car Talk | Oct 01, 1998

Dear Tom and Ray:

Have you ever heard of a "Bon Ami ring job"? I have an oil- and gas-guzzling
1984 Dodge Van with a 318 V8. I had a compression test done which revealed two
or three cylinders with compression below 100. An old-timer friend of mine
suggests using Bon Ami. He says it's an "old-time used-car-lot trick." He told
me to take a shot glass full of Bon Ami (it has to be this brand of scouring
powder because it doesn't scratch) and slowly pour it into the carburetor while
the engine is running. My friend, Old Gene, explains: "The Bon Ami will dry up
the oil in the cylinders for a few strokes, thereby causing the rings to burnish
and reseat themselves." Gene claims I will see higher compression, more power
and less oil burning for about the next 10,000 miles. Have you guys heard of
this and will it work, or is it an urban legend? -Steve

RAY: Heard of it? We practically invented the Bon Ami ring job, Steve! When my
brother was just starting to work at the garage, I gave him a nice easy job one
day. I said to him ,"Go over there and clean out that carburetor." Next thing I
knew, he was trying to save time by pouring Bon Ami down the throat.

TOM: I don't know if the customer's car ran any better, but I guarantee you he
had the shiniest carburetor in town!

RAY: We'd have to classify the "Bon Ami ring job," as mostly a myth, Steve. It's
one of those things that you try when you have absolutely nothing else left to
lose. Like letting my brother work on your car. When the engine is junk anyway,
why not pour a shot of Bon Ami in there, right? Heck, why not squeeze some of
Old Gene's Dentu-Creme into each cylinder? It can't make things any worse, can

TOM: Well, it can, actually. Drying up the oil is just about the worst thing you
can do to an engine. In fact, engine manufacturers go to great lengths to make
sure you never run the cylinders without oil. Why? Because they know it ruins
the engine.

RAY: In theory, the Bon Ami trick sounds good (this is the key to all lasting
urban legends). You "rough up" the rings and get them to reseat themselves,
forming a new, tighter seal. But in reality I wouldn't count on it. More likely,
you'll rough up the rings and they'll stay roughed up.

TOM: And you don't even know if bad rings are your problem, Steve. Your lousy
compression may be caused by bad valves. And we know for a fact that Bon Ami
won't do anything for your valves (except, or course, remove the soap scum).

RAY: If you eventually determine that your rings are bad (by doing a "wet
compression test"), and if you're going to rebuild the engine or junk the van
soon anyway, then sure, go ahead and try the Bon Ami. Just don't be surprised if
you get 10 more good miles instead of 10,000.

TOM: And don't forget to put the Bon Ami back under the kitchen sink, so it's
there next time your wife goes to look for it. Otherwise, you might find
yourself in the embarrassing situation of having to confess to her exactly how
you ruined the family car.

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