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piston slap

Discussion in 'BSA' started by seattle##gs, Nov 23, 2018.

  1. seattle##gs

    seattle##gs

    Joined:
    Oct 28, 2014
    One winter I put the Atlas away after using all summer. When I brought it out next summer and started it up one piston began to make a lot of racket especially while warming up. As the days went by it increased so I fanally had to pull the cylinders off. One piston was noticably worn. So now I am running into the same problem with an A65. The motor was rebuilt by a reputable shop about a year ago and ran well. This year it has developed the familiar harsh whacking sound. How does this happen all of a sudden?
     
  2. motorson

    motorson VIP MEMBER

    Joined:
    Nov 29, 2011
    My Commando did that in one day by running the timing too far advanced.
     
  3. Fast Eddie

    Fast Eddie VIP MEMBER

    Joined:
    Oct 4, 2013
    Maybe you’re running too rich and washing the bores?
     
  4. seattle##gs

    seattle##gs

    Joined:
    Oct 28, 2014
    perhaps...but my main question is why it seems to develop almost overnight. The A65 has a #3.5 slide
     
  5. Fast Eddie

    Fast Eddie VIP MEMBER

    Joined:
    Oct 4, 2013
    Good question. I don’t know...!
     
  6. kommando

    kommando

    Joined:
    May 7, 2005
    Its called human perception, there is a threshold below which you ignore and above you take notice.

    For clearances in bearings its typically 3 thou, so until there is 3 thou of wear you cannot feel it, above 3 thou you think the world is coming to an end ;)
     
    Paul W. and Fast Eddie like this.
  7. Fast Eddie

    Fast Eddie VIP MEMBER

    Joined:
    Oct 4, 2013
    That makes perfect sense to me.
     
  8. eskasteve

    eskasteve VIP MEMBER

    Joined:
    Sep 24, 2012
    I experienced this same issue years back, probably in the early to mid 80s. Perfect runner when stored, piston slap after a year and a half of storage. I'd oiled down the cylinders and drained all of the fuel so it was stored properly. I shut it down immediately and pulled off the top end. The two compression rings on the right hand side were gummed/stuck in the grooves. Since the barrels were off I did a quick hone and put new rings in. Didn't touch that motor again. I sold the bike about 20,000 miles after the ring thing and I know that it ran well for another 10,000 miles when the new owner attacked it with all kinds of hop up parts.
     
  9. seattle##gs

    seattle##gs

    Joined:
    Oct 28, 2014
    I wonder if pourinf some solvent down the cylinder maybe some gasoline and run the pistons up and down a few times would loosen the rings and get them working again. However, this bike ran without smoking and went down the freeway untill the battery fell to 10.5 volts.
     
  10. Bernhard

    Bernhard

    Joined:
    Apr 20, 2011
    Don't you mean Redex?- it sometimes works, but if the rings are heavily gummed up or engine worn it will not work.
     
  11. oldbeezer

    oldbeezer VIP MEMBER

    Joined:
    Nov 2, 2017
    I don't know if it is still available but Chrysler made a product (we called it "can o' rings") made just for stuck rings. Poured it down the carb...........
     
  12. Bernhard

    Bernhard

    Joined:
    Apr 20, 2011
    I don't know this produce but I would like to try some Berryman 0116 B-12 Chemtool Carburetor/Fuel Treatment and Cleaner, but I am in the UK and shipping costs are prohibitive.
    any body know of any carbon cleaner available in the UK.
    I have included the web site :