Lapping flywheel

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  • bobw

    US Member - 1 Year
    Replies: 2116
    Topics: 52
    #269640

    I found a good replacement flywheel for my Johnson FD-12 project to replace the original one with a damaged taper and a couple of cracks in it.   I now need to lap the replacement wheel with my replacement crankshaft and got to wondering how other folks do the lapping process.    A few methods I’ve read about in the past include:

    1. Put the flywheel on the crank and turn it around and around in the same direction for a few revolutions.
    2. Put the flywheel on the crank and rotate it one full revolution in one direction, then rotate one full revolution in the opposite direction.  Repeat a couple times.
    3. Put the flywheel on the crank and rotate it back and forth thru a 90 degree arc, lift it up and turn it 90 degrees from the original starting position and rotate it back and forth thru 90 degrees again.   Repeat until a full circle is completed.
    4. Put the flywheel on the crank with the flywheel and crank keyway slots aligned, then rotate back and forth through a 15 degree arc either side of the crank keyway slot (30 degree total arc).

    Even though the key doesn’t hold the flywheel in place, it seems like the last approach would help to ensure the best mating surfaces for the flywheel in it’s final installed position.  Regardless of what approach is used, I know to protect the upper crankshaft seal area during the lapping operation.

    Anyway, not wanting to start an opinion battle here, just curious what others have done!

    Bob

    1937 Champion D2C Deluxe Lite Twin
    1954 Johnson CD-11
    1957 Evinrude Fastwin 18
    1958 Johnson QD-19
    1958 Johnson FD-12
    1959 Johnson QD-20

    “Every 20 minute job is only a broken bolt away from a 3-day project.”


    Mumbles

    Canada Member - 2 Years
    Replies: 5624
    Topics: 294
    #269641

    Methods 1 and 2 can cut grooves into the pieces. Method 3 is my chosen way.

    Lapping a flywheel is the same as lapping valves by hand.  Back and forth, lift and turn 90°, repeat until and even surface appears. A pencil line is drawn across the new surfaces and the pieces turned slightly to check for contact. The pencil lines should disappear.

    1 user thanked author for this post.

    bobw

    US Member - 1 Year
    Replies: 2116
    Topics: 52
    #269648

    Mumbles – thanks for the input.   Never thought about the comparison to lapping engine valves, but that makes good sense.

    Bob

    1937 Champion D2C Deluxe Lite Twin
    1954 Johnson CD-11
    1957 Evinrude Fastwin 18
    1958 Johnson QD-19
    1958 Johnson FD-12
    1959 Johnson QD-20

    “Every 20 minute job is only a broken bolt away from a 3-day project.”


    Monte NZ

    International Member - 2 Years
    Replies: 235
    Topics: 67
    #269650

    Several years back I successfully lapped a 40 hp Johnson flywheel using  Mumbles method .

    Monte NZ


    Buccaneer

    US Member - 1 Year
    Replies: 6452
    Topics: 958
    #269656

    Not sure if my aging eyes could see the pencil mark very good.
    How about magic marker or bluing, then rotate the flywheel 360?

    Prepare to be boarded!


    Evinrude 25


    Replies: 102
    Topics: 18
    #269681

    Hello, other point is which abrasive grain good for flywheel?

     

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    amuller

    US Member - 1 Year
    Replies: 1049
    Topics: 163
    #270637

    I would use method #3.

    Some Chrysler manual provide a lapping procedure.

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