Low Compression?

Discussion in 'General Harley Davidson Topic' started by twicecam, Sep 5, 2008.

  1. twicecam

    twicecam Active Member

    I am working on a 75 shovelhead,I did a compression test and both cylinders are reading 65 pounds, is this too low? The battery shorted out on the seat last weekend and right before it died it backfired , so I pulled the push rods out and did the compression test agin and it was the same readings.Does anybody have any ideas??
  2. Fossil

    Fossil Active Member

    My first Harley was a 1975 FXE. Loved that bike. You need to give the experts on this forum a little more information. Like how many miles on the engine. Any recent work or tuning. Do you have a good shop manual. Did you notice it was smoking while riding? Any way hang in there and as there are some really experienced guys on this forum that will jump in. Fossil
  3. silentflyer

    silentflyer Active Member

    Stuck rings? pull the plugs, pour some Marvel Mystery Oil in both jugs, let it sit for 24 hours, then crank it over with the plugs out, then reinstall the plugs and fire it up.
    If that the problem it will break them lose. Works great in aircraft jugs especailly if it has not been run in a while. Worth a shot before you pull the jugs.
    If it is carbon under the valve seats, pull the plug and rig a old drilled out spak plug to a air hose and put about 80#'s of air on the jug, if you hear it leaking back into the crank case, ring problems, if the "hiss" is in the intake/exasust, valve seat problems . I have fixed leaky valves by pulling the plug, feed some small nylon rope into the jug with the piston near TDC, remove the valve spring/retainer/keeper and then chuck the valve stem (carefully) in a drill and spin it. If it is carbon or crud on the valve or seat, it will break it lose. Put it back together and fire it up. Again works, on aircraft jugs, and they are very similar to HD jugs, just about 3 times as expensive.
    If it flys,floats or flirts, it is cheaper to rent it....applies to Harleys also......