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Thread: Is this detonation damage?

  1. #1

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    Is this detonation damage?

    This is a small bore continental that has 87 hours since major overhaul. Plugs were wet with oil, consumption was 1 quart every 2-3 hours and compression was 20. Borescope showed a few lines in the cylinder but when I pulled the cylinder it was seriously scored and the cylinder in front of it had the exhaust valve leaking and was orange. At first I thought carbon buildup but now I am thinking detonation damage. What says the tribe? Tim

    oh and these were new superior cylinders
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  2. #2
    Cub Builder's Avatar
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    Detonation damage will leave the top of the piston looking like it was sand blasted clean, then beat with a small ball peen hammer. The last engine I tore down that had serious detonation, the rings still looked good, but the top ring groove was seriously eroded around the top ring on the piston. Your photo looks more like galling, like the engine was assembled with +.010" pistons in a standard bore cylinder. FWIW, that doesn't look like the markings I see on a Superior O-200 piston, which is what I am assuming you have there. Looks more like the Continental piston.

    Additionally, unless you hopped it up with high compression and/or loads of advance, it's darned hard to get a small Continental to detonate.
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  3. #3

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    They are superior pistons, I cleaned up the other one next to it with ultrasonic and blasted with walnut shells. When I put it together today, I verified piston part numbers, weighed them, checked ring gaps iaw the superior service letter. I may try to see what superior says. The engine was rebuilt by a shop in Oklahoma and has leaked since day one...

  4. #4
    Steve Pierce's Avatar
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    Looks like piston slap to me, lots of cold starts maybe. Is the cylinder a new Superior? What did the bore measure and different depths of the cylinder?
    Steve Pierce

    Everybody is ignorant, only on different subjects.
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  5. #5

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    New superior cylinder. I did not check the bore on this on, the owner wanted me to install other ones so I did those first. I should be able to get some more pictures later today. First priority is put the engine back together. The airplane is kept in a heated hangar. So if it was cold started, I don’t know how probable it was. Tim

  6. #6

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    Saw pretty much the same thing on a C85 last year, looks like standard pistons in oversized cylinders.


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  7. #7

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    looks like someone put connecting rods in wrong to me, so that the squirt holes arent pointing to the opposite cylinder if its a 90 or 0-200.
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  8. #8

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    They are superior pistons, I cleaned up the other one next to it with ultrasonic and blasted with walnut shells. When I put it together today, I verified piston part numbers, weighed them, checked ring gaps iaw the superior service letter. I may try to see what superior says. The engine was rebuilt by a shop in Oklahoma and has leaked since day one...

  9. #9
    8GCBC's Avatar
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    Looks similar to chrome rings on chromed cylinders. What does the screen show?
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  10. #10

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    Quote Originally Posted by tempdoug View Post
    looks like someone put connecting rods in wrong to me, so that the squirt holes arent pointing to the opposite cylinder if its a 90 or 0-200.
    i verify that the squirter is pointed at the piston
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  11. #11

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    Quote Originally Posted by 8GCBC View Post
    Looks similar to chrome rings on chromed cylinders. What does the screen show?
    it’s a filter, I have not got it cut yet. Now I am fighting pushrods, I have only found 2 lengths and I thought there was 4 part numbers. Exhaust valve is not closed with the rocker installed.

  12. #12
    windy's Avatar
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    Probably the engine was assembled by the little trolls there at Ogden. Nuff said.


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