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Compression for flat 6

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  • Compression for flat 6

    I am pulling the 185 flat 6 out of my 55 Champion to overhaul over the winter and find a small coolant leak. Small in that I see it when I change the oil after extended sitting but not enough to cause white smoke while running. I am going to check compression for reference before I pull it, but what is acceptable compression for a 50 year old un-touched flat head?

    All feedback and any helpful hints on pulling this engine are appreciated.
    Thanks, Chris

  • #2
    Pull all the plugs out before you check compression. Then squirt a little shot of light weight oil in each cylinder just before you test it.
    Spin the engine over 5 or 6 times to get the compression gage to stabilize. I'm just guessing here because alot depends on how the engine's been treated thru the years and whether or not it's run much of late, but I'd say 110 to 125 per cylinder. And I wouldn't be distraught if it were higher or lower so long as they're fairly close as a group. I think the rule of thumb is anything more than a 15% spread is cause for concern. But since you're gonna overhaul it anyway...........
    Just be sure you have that head magnafluxed. That could be where the coolant leak is or it could just be a bad head gasket.

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