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Hey Oldtimers, I'm thinking about the Bon Ami trick

Discussion in 'The Hokey Ass Message Board' started by alchemy, May 24, 2011.

  1. alchemy
    Joined: Sep 27, 2002
    Posts: 9,331


    We've got a flathead powered car that has a recently rebuilt engine that drinks oil. Even tried a fresh hone and new rings again. Same thing. It's been driven 1,500 miles since the rebuild, probably 800 after the re-hone. Isn't really smokey, just needs oil added maybe a quart every two tankfulls.

    I'm thinking of trying the Bon Ami or Comet down the carburetor trick this weekend. Has anybody done it? I need details.

    I've heard of just sprinkling it down the carb with the engine running, and I've also heard of mixing it with gas and dribbling that down the carb. Or maybe should I mix with water and dribble that down? I'm thinking the gas mix is not the best bet in case a little blows out of the cup and lands on the generator right there in front of the carb.

    Here's the engine particulars: 99 Merc block bored 3-3/8" with solid skirt three-ring pistons. Has a tall Weiand intake with two 97's on top.

    So, how did you do it? What mix did you use, what RPM, and how much? I will change the oil after this operation.

  2. Never done it myself,,,but a Buddy that should know,says it's a last resort at Catapillar,,,,Bon-Ami is the stuff to use
  3. I'd be tearing it down to find out what the problem is....
  4. porknbeaner
    Joined: Sep 12, 2003
    Posts: 34,595


    We always use a soda straw and blew it straight into the cylinder through the spark plug hole.

    It always worked for me that way.

    You got chrome rings?
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  5. Larry W
    Joined: Oct 12, 2009
    Posts: 566

    Larry W
    from kansas

    How is the valve stem clearance and ring clearance?
  6. gas pumper
    Joined: Aug 13, 2007
    Posts: 2,842

    gas pumper

    If the oil usage is too high, then the spark plugs will be loaded with the burned residue. If the plugs look good, let it go and get more miles on it.

    A quart every two tanks is not really that bad for vintage engines.

    Visible blue smoke is bad, but none or just a haze you can see at night in the headlights of the car behind you is not bad.
  7. 48 Chubby
    Joined: Apr 29, 2008
    Posts: 1,016

    48 Chubby
    Member Emeritus

    Two things come to mind here.
    First off modern machine shops are not set up to use torque plates on flat heads
    Modern ring sets are great but require precise fitment.

    And 1 quart every other tank full ain't way out of line on a fresh flat head.

    Reguardless of old wives tales pumice (the abrasive in cleanser) down the intake is not good for any engine.

    Patience Grass Hopper give it some time.:)
  8. JohnEvans
    Joined: Apr 13, 2008
    Posts: 4,883

    from Phoenix AZ

    Back in the 60s when I was running a 3/8X 3/8s flattie I found those 3 ring pistons had so much taper built into them that in a few thousand miles I was blowing lots of smoke and using oil. The orignal design of those were for racing so low oil use was not a factor. I finely went to some 4 ring std style pistons. You using modern 3 piece oil rings? If not try a set that has those in it. Use ONLY Bon Ami drizle in 2-3 teaspoons dry at about 2000 RPM. The Bon Ami trick was even recomended by Cat Tractor Co.
  9. I vote with the "have patience" crowd. They'll seat in better and better as you rack up some miles.
  10. 40FordGuy
    Joined: Mar 24, 2008
    Posts: 2,907


    When that engine was assembled, were the O-ring seals installed on the outside of the intake valve guides ? If not, it'll suck oil up between the guides and the block. It's an oft overlooked item. New ones are available from various sources.
  11. 40FordGuy
    Joined: Mar 24, 2008
    Posts: 2,907


    Ps; I wouldn't dump anything thru an engine.......... 4TTRUK
  12. If they are chrome good luck gettin them to seat, If they are cast time will be on your side.
  13. Ole don
    Joined: Dec 16, 2005
    Posts: 2,911

    Ole don

    Before you try the Bon Ami, try this. If you know the piston fit in the cylinders, less than three should seal. Warm it up good, and wind it out in first and second gear to valve float. That helped one of mine years ago. About 65 in second and it finally sealed up. If your pistons are at .004 to .010 clearance, it may never seal.
  14. alchemy
    Joined: Sep 27, 2002
    Posts: 9,331


    The machinist is a respected local guy who has been building flatheads and four-bangers for decades. He retired his regular business and still has a waiting list for the Model A engines he builds out of his home shop. I trust his machining and the tolerances.

    The pistons have regular cast rings. Not the new modern thin ones, and not chrome rings. I've also assumed he installed the seals on the intake guides.

    To all the guys saying "have patience", for how many miles? Isn't 1,500 enough to seat the rings?
  15. alchemy
    Joined: Sep 27, 2002
    Posts: 9,331


    Wind it out and hold that speed for how long? A few seconds or a few minutes?
  16. Ole don
    Joined: Dec 16, 2005
    Posts: 2,911

    Ole don

    Wind it out as far as it will go, then shift. Really rev it up, it may seal.
  17. patman
    Joined: Apr 30, 2007
    Posts: 507


    Sounds like you should be asking him what he recommends. Throwing grit into a new engine on purpose sounds like a bad idea just on general principles. If you were him, which conversation starter would you rather hear? "I think it's using too much oil", or "I thought it was using too much oil so I ran some Bon Ami through it". At least let him give you his 2¢ before you decide to go for a no-turning-back fix.
  18. Ole don
    Joined: Dec 16, 2005
    Posts: 2,911

    Ole don

    For you younger fellows, this is how a Cat 14 A engine was broken in. That is a mid fifties D8 dozer, 1246 cubic inch inline six. At overhaul time, you put in sleeves, pistons, rings, and bearings. The rings are hard chrome plated for long life. When the motor is started, it is let idle at different RPM's while the hood and belley pan are put on, a good two hour job for two guys. The engine is run up to governor speed, and it should be smoke free by then. If not, one can of Bon Ami sink cleanser is cut open, and dumped into the two cupped hands of one guy. With the air cleaner off, the other guy gets up on top and as he opens the throttle wide open the first guy shoots his hands near the intake and it goes POOF right through and makes a dust cloud out the exhasut. After that, no more smoke. Put it to work for another ten years.
  19. kwoodyh
    Joined: Apr 11, 2006
    Posts: 642


    30 w (API SA) non-detergent next oil change and 1000 miles? It might be the modern oil is too slick for the engine?
  20. porknbeaner
    Joined: Sep 12, 2003
    Posts: 34,595


    Cast rings shouldn't be a problem seating at all. Usually where you run into a problem is with Chrome Rings when the bores are not properly honed.

    @ 1500 you may be right on the edge of breaking in or you may actually look for a different plce for your oil to be going. Like a leak? I know you'd think you would notice a leak.

    Anyway just something else to think about.
  21. hotroddon
    Joined: Sep 22, 2007
    Posts: 16,120


    back in 1976, I had a Porsche 914 that we had a 1914cc motor built for. The rings wouldn't seal. Took it back to the engine builder and they fired it up and help it at about 2,000 RPM. They then poured Ajax down each of the carburetor throats (it had Weber 48IDA's on it). I about had a heart attack. They said "if it doesn't work, we'll pull it out and rebuild it again". Damn if it didn't quit smoking and no more ring problems.

    Honestly if you haven't got a decent seal in 1500 miles, I think there is a good chance that you could have glazed the cylinders. More miles isn't going to break the glaze. So it's either pull it apart and re hone it, probably with new rings or try the abrasive trick.
    Last edited: May 24, 2011
  22. kwmpa
    Joined: Mar 14, 2006
    Posts: 1,241

    from Pa

    Last rebuild I had done it took 3000 miles to seat the rings....after that all was right with the world...last time I heard the guy had put like 10,000 miles on it with no issues or major oil consumption
  23. Larry T
    Joined: Nov 24, 2004
    Posts: 6,951

    Larry T

    I wouldn't do it to a fresh engine. If it's working on the piston rings and cylinder walls, it's also working on the valve stems and probably enough is getting by to "lap" the piston skirts too.
    I'd drive it a few thousand miles more. If it doesn't stop by then, you'll probably be able to see where the problem is when you tear it back down.
    Larry T
  24. I'm alchemy's brother and the car belongs to our father.

    Here's an easier to read summary of what's been done:

    - The engine, as a whole, has 1500 miles since a full rebuild.
    - The builder came back @ 700 miles post-rebuild and re-honed the cylinders.
    - The engine has 800 miles post re-honing.

    Personally, I'd be hesitant to pour a gritty material down an expensive pair of carburetors and in to a relatively expensive to re-build engine. I'd consult pops about whether he wants to risk having to do another rebuild of the short block, or just live with the excess oil consumption. Given how little the car gets driven each year, I suspect he'd lean towards the latter.
  25. NOTHING else will work except Bon-Ami....we used it on our sprint car to reset worn rings, it would keep the oil smoke away for a 50 lap race.
  26. railroad
    Joined: Feb 3, 2010
    Posts: 242


    Have you run a compression test? What oil are you running? What did things look like at 800 mile hone? I would let the engine builder advise me, before bon ami.
  27. Just remember:Bon-Ami and Comet are two completely different animals. Bon-Ami is about the consistency of talcum powder-Comet is GRIT.
  28. steel rebel
    Joined: Jun 14, 2006
    Posts: 3,135

    steel rebel

    Years ago a neighbor had a Monkey Ward rebuilt flathead installed in his 50 Ford. It burned oil for a few thousand miles. He took it back a few times and they just said give it time. Sure enough after a few more thousand more miles it broke in and he put a lot of miles on it.
  29. randydupree
    Joined: May 19, 2005
    Posts: 610

    from archer fl

    Cat sells Bon-ami in a can with a cat label,yes,it works.
  30. davidwilson
    Joined: Oct 8, 2008
    Posts: 597

    from Tennessee

    put some harley oil in it - 70w

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