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Old 03-10-2013, 12:47 PM   #1
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The old Bon Ami treatment

I finally got the nerve up to try an "easy" fix on my Cat 3406 with a oil slobber/consumption issue. Some history first: Low hour rebuild, which wasn't broke in properly by the P.O.. Determined the sleeves were glazed after removing the valve covers and exhaust manifold I observed valve guides good and while running the engine without the manifold on(smokey!) I saw oil coming up from the cylinders rather than down from the head.All holes appeared wet. Options here: Lift engine and trans (4000 lbs +-) enough to drop pan for new cylinder packs. (rather not) or try the Bon Ami trick described to me by an old school Cat mechanic. Here's the theory, by introducing a small amount of BonAmi to the intake while running at operating temp the light abrasives in the Bon Ami will clean off the glaze and polish up the rings a bit, and finally help seat the rings. Apparently Cat had a part number for this stuff at one time and was used often to seat rings on rebuilt motors where the rings weren't seating. I figured I really didn't have much to loose, My mechanic friend said I would have little to worry about the stuff getting down into bearings and doing any damage, and I figured if it didn't work, well back to the ring job! So with Bon Ami in hand, I slowly introduced the stuff right into my Turbo, (yikes, Yes i was fighting every cell in my body to do this!) I put in about a table spoon, let it run a few minutes, and then another. I was running about 2/3 engine speed water temp 175.I was pulling hard against my dock lines. The engine never coughed or bogged once. In all I bet I ran a cup of the stuff through there over about an hour. First thing i noticed was a diminishing smoke from un-done breather tube. Well, I ran it a while longer, and then shut her down. The test to see how successful this experiment was would have to be at the next cold start.
The next day I went down to the boat, fired her up, and to my delight the blue smoke that usually chugged out of the exhaust was down to what I would expect as normal for this motor on a cold start. The real sense of victory came when I returned to the engine room and discovered that the oil,usually dripping from the slip-joint at the exhaust side of my turbo was completely gone!!! Yee Haw! I still need to take her out and run the $&#@ out of her to really seat those rings in but so far I'm delighted to report that Bon Ami worked! I would not try this on a modern diesel with the tight tolerances of today but my old 1976 vintage slobbering beast took it well and has saved me a whole heap of work. Bon Ami only and no other cleanser or abrasive should be used. It is made mostly of egg shells I think and advertised guaranteed not to scratch glass!The other cleansers may be harmful to bearings etc.

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Old 03-11-2013, 06:25 AM   #2
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Join Date: Oct 2007
Posts: 14,908
Slobbering will come from glazed or burnished cylinders , with stuck rings.

Using Bon Ami may scratch the cylinder walls enough to hold oil again but does zero to loosten the rings.

The outboard folks have product they claim work well.

Might be worth a try .

"Flitt" insect sprayer with water is great to remove carbon from the cylinder head , but have no idea if it will free seized rings.

I would change the oil and filter after any treatment.
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