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Thread: 1970 FLH OEM Pistons?

  1. #1

    Default 1970 FLH OEM Pistons?

    Pulled the heads from my 1970 FLH that I am pretty sure has only 7900 miles according to the functioning OEM speedo and the overall bike condition. Motor appears to have never been apart. All original hardware throughout - nuts, bolts etc. Unfortunately someone removed the original paint and ruined it with the fugliest colors I've seen in a long time - krikey! I plan to leave the bike intact and just re-paint with an appropriate 1970 paint scheme. I did a thorough cleaning and rewiring but I thought it might be a good idea to pull the heads while I had easy access to see how things looked. I cleaned the carbon from the pistons and was able to inspect the condition of the cylinder walls and they were perfect. No scoring or scratching and some of the cross hatching is still faintly visible.

    Anyone know if the markings on these pistons would indicate OEM? The piston surface appears a bit "lumpy". Not sure what up with that. Stock bore, 3.437".

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  2. #2
    Join Date
    Jan 2006
    Menomonie, WI


    I would say those pistons are OEM. Jerry

  3. #3


    OEM pistons are far from being smooth on top, have a dimple on the camshaft side and I’ve seen them stamped “A” through “D". However, all the genuine H-D pistons I have hanging around have the letter located along with the oversize stamping (when applicable) on an approximately 5/8 inch diameter raised circle in the center of the dome.
    In one of the pictures, it looks like there’s some evidence of the raised circle having been removed. I know an old timer who said he always did that because he thought they made hot spots that contributed to detonation. He may be right in his belief, but the dimple in it’s place, I can’t explain.
    It looks like one has an “F” for front too.
    I’d be inclined to put the heads back on and ride it.
    Some mysteries don’t need to be solved.
    The drum brake, cone engine bikes are a favorite of mine.

    Last edited by Hercumile; 11-04-2019 at 10:50 PM. Reason: add pictures

  4. #4


    Thanks for that reply,Hercumile. I didn’t plan do do anything more. This was just to lend support to the idea that this was a low mile, first year, alternator shovel. Now I’m fairly certain that the odometer is correct. I’m going to button it up with a new set of gaskets and run it.

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