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detonation chewed a piston top?

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  • Engine: detonation chewed a piston top?

    I had some time to tinker a bit with a 62 259 truck engine that someday will go in my Lark. The weather today is around 50 but tomorrow the high might be around 15. I figure that in the next few months I'll take the heads in for repair if all goes well. What I wonder about is the top of #8 piston is damaged to the point where I can see the top ring, I figure the damage is from detonation in the cylinder, I have no idea how many miles are on this engine but what caused the the detonation to go on so log that the piston top to look very much like the lunar surface? The other seven pistons are covered with a slime of oil and some carbon but are all smooth.

    I probably will not get back to this 259 until another nice afternoon or until March/April, no heat in the garage

    Jeff T.
    \"I\'m getting nowhere as fast as I can\"
    The Replacements.

  • #2
    Sometimes it's a simple as a bad spark plug wire crossfiring into that cylinder.

    jack vines
    PackardV8

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    • #3
      Possibly a vacuum leak making that cylinder very lean. I have seen that with one cylinder due to a bad power brake booster and also due to a leaky headlight "motor".
      Gary L.
      Wappinger, NY

      SDC member since 1968
      Studebaker enthusiast much longer

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      • #4
        Have that head checked good. Sometimes anti-freeze mixed in the mix can do that to. Seen it eat the whole side off a piston in very few miles.

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        • #5
          Possibly a vacuum leak making that cylinder very lean.
          Good point. The Stude steel intake manifold gaskets can just rust out and soon there's a huge vacuum leak. Sometimes it's just on one cylinder.

          jack vines
          PackardV8

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          • #6
            Excess oil (from the rings or the valve guides) in that cylinder will also cause that problem.

            Mike

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            • #7
              Originally posted by studegary View Post
              Possibly a vacuum leak making that cylinder very lean. I have seen that with one cylinder due to a bad power brake booster....
              My experience exactly. When I drove my '64 Avanti from California to West Virginia a few years ago I had a cracked check valve on the brake booster. The fitting on the intake manifold was very close to #5 cylinder. As a result #5 piston was slowly burned to where it finally came apart 30 miles from my destination. Damage was significant- crank bearings, cam bearings, cylinder wall (had to bore to .060 over to remove the gouge), oil pump and more. There were aluminum fragments all through the engine. The thumbnail is a very poor picture, but does show what the piston looked like on removal.
              Attached Files
              Paul Johnson, Wild and Wonderful West Virginia.
              '64 Daytona Wagonaire, '64 Avanti R-1, Museum R-4 engine, '72 Gravely Model 430 with Onan engine

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              • #8
                can you post a picture ?

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                • #9
                  If there's ridge at the top of the cylinder wall it can chip off a piece of piston and then it can bounce around in the cylinder and cause damage like this. They make a tool called a ridge reamer to remove this if that's the problem

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