1960 Evinrude 5.5 Fisherman Powerhead

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  • William MacNeill

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    #269667

    Hello all.

    I just tore down the powerhead on a 1960 Fisherman as it had no compression in the bottom cylinder. I was surprised to see that the cylinder walls were clean with no scoring and that the pistons were the same. I suspect that this motor had overheated at one time which weakened the rings as when I pulled the lower unit there was an aftermarket waterpump that had a tiny impeller in it as well as the water pasages in the powerhead being caked.  I am going to hone the cylinder walls and install new rings. I see that they come in standard and oversized by .020. I am guessing that the oversized ring is available for if the cylinder was bored. Since I am going to hone it I am guessing that the standard rings are the ones to use. Also looking for a source for the rings as the the part # provided in the parts listing are for a set of 3 #486275 for the standard rings and #486294 for the oversized rings. Both are unavailable.  Looking for clarification and for source for the rings. Thanks in advance.

    Bill


    frankr

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    #269668

    Cylinders must be bored if you are going to use oversize rings.  According to what you said, it doesn’t need boring/oversize.  There is something you aren’t telling us.  NO compression???  Even worn-out rings will produce some compression.

     

    Edit:  Replacement water pump kits have small impellers.

    • This reply was modified 1 year, 3 months ago by frankr.

    William MacNeill

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    #269670

    When I say no compression… Top cylinder was 65 and bottom was 15


    dave-bernard

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    #269671

    check for bad head gasket first.


    William MacNeill

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    #269672

    That was my first suspicion. I did check it and it was not in the best of condition. Replacing improved some compression in the top cylinder but bottom was still low.


    frankr

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    #269673

    Well 15 psi certainly is low or “none”.  65 is borderline.  Were the rings stuck or something?


    William MacNeill

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    #269674

    The rings were stuck. Seafoam and PB Blaster did free them up but compression was not there.


    aquasonic

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    Replies: 634
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    #269675

    If the motor has overheated, you should see signs of overheating such as discolored paint on the cylinder head, and relatively loose cylinder head bolts. A bad overheat will produce scored pistons and brittle heat weakened rings. It doesn’t sound like this motor experienced a bad overheat. If the motor hasn’t overheated badly, then the rings may be salvageable.

    At this point, it may be prudent to take a very close look at the cylinder head. Inspect the head for any tiny cracks, or imperfections. If it passes inspection, resurface the mating surface by lapping it on a plate of glass, or a large, polished floor tile. While you’re at it, inspect the mating surface of the block also. The block can also be lapped if it has gouges or is not flat.

    I believe the standard rings for that motor were used for many years going back to the 1940’s, and into the 1960’s. There are older part numbers that may help with your search. Try PN 378432 or 041333.

     

     

    • This reply was modified 1 year, 3 months ago by aquasonic.
    • This reply was modified 1 year, 3 months ago by aquasonic.

    William MacNeill

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    #269678

    Funny you say this. Some of the head bolts were loose where others were locked on solid. I cannot say there was considerable discoloration but again I do know that the water channels were not able to flow freely due to caked on crud. I did clean up the cylinder head on a piece of glass and got it to be clean all over uniformly. There is an ever so slight wobble to it that is not excessive that could indicate that the head is out of tolerance. The gasket should make up for it and I believe it to be good at this time. There are no cracks in the head or other imperfections that I could identify. The block also looks to be ok. I cannot understand why the part # has not been cross referenced to another set of rings. As you stated they made millions of these motors using the same pistons for decades. I guess it’s part of the fun searching what you need. Thanks for the input and for the part numbers. The 378432 part # is non-existant. I will try the other.  Thanks.


    aquasonic

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    #269680

    “There is an ever so slight wobble to it that is not excessive that could indicate that the head is out of tolerance.”

    This may be the problem, or part of the problem. After lapping, the cylinder head should sit perfectly flat on a large, polished tile or plate of glass.

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