1975 Johnson 15 hp rebuild

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    willyboy

    US Member - 1 Year
    Replies: 98
    Topics: 20
    #210805

    I am rebuilding a 1975 Johnson 15, I have it torn down to the bare block. I’ve never rebuilt an engine this ” new”, I mainly stick to the 1920s and 30s Johnson’s which is an entirely different animal. On the bottom bore, the dowel, bearing which is installed from the crank side, is poking thru into the top of the bottom bore. Is this supposed to be poking thru and visible like this? Before taking the crank and Pistons out I had to remove the rod cap screws which were tight. The bottom rod had noticeable slop and movement before loosening the cap screws where the top rod cap had none. Measuring the crank surfaces where the rods ride I found dead even measurements so I’m wondering why the bottom rod had so much slop? I tried to upload a pic of the dowel poking thru into the bore but file upload was too large.I tried asking on our fb page where my pic and video uploaded but my only response was asking if this was my first rebuild. Again, yes on something this new and totally different looking then what I’m used to working on.

    frankr
    frankr


    Replies: 5301
    Topics: 48
    #210824

    Can’t say I know the real answer about the dowel, but I don’t find that to be remarkable. It’s pressed in tight and nothing can leak around it, right?

    We had so much trouble with those engines, that I’ve never seen one run long enough to wear out enough to require a powerhead rebuild.

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    fleetwin

    US Member - 2 Years
    Replies: 3415
    Topics: 51
    #210838

    Sorry buddy, I don’t understand what you are describing about a dowel poking into the bore….
    Why is it that you pulled this powerhead apart? These powerheads are pretty rugged, and don’t wear out or get damaged easily.
    You mention the crank journals measured evenly, how did the bearing/retainers/rod look?
    Perhaps there is wear on the wrist pin side of the rod causing the rod to feel sloppy…

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    willyboy

    US Member - 1 Year
    Replies: 98
    Topics: 20
    #210898

    Can’t say I know the real answer about the dowel, but I don’t find that to be remarkable. It’s pressed in tight and nothing can leak around it, right?

    We had so much trouble with those engines, that I’ve never seen one run long enough to wear out enough to require a powerhead rebuild.

    Thanks for the reply. yes I’m sure it is pressed in tight and nothing can leak around it, just wouldve thought it wouldn’t have come thru on edge of bore like that.

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    willyboy

    US Member - 1 Year
    Replies: 98
    Topics: 20
    #210899

    Sorry buddy, I don’t understand what you are describing about a dowel poking into the bore….
    Why is it that you pulled this powerhead apart? These powerheads are pretty rugged, and don’t wear out or get damaged easily.
    You mention the crank journals measured evenly, how did the bearing/retainers/rod look?
    Perhaps there is wear on the wrist pin side of the rod causing the rod to feel sloppy…

    my description may not have been the best, on the marineengine parts bomb chart this dowel is listed as a dowel, bearing. I decided to tear this one down as the compression was on the low side and judging from the looks of all the orange gasket silicone throughout out the block, someone else has had it completely apart before.the bearings, retainers and rod looked ok. I haven’t checked the wrist pin. thanks for the advice

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    fleetwin

    US Member - 2 Years
    Replies: 3415
    Topics: 51
    #210902

    OK, sounds like someone has had this apart, so be careful here….Why would the compression be low if this had been rebuilt? Were the cylinders scored/pistons scuffed? You will want to measure the piston skirts and cylinder bores carefully before proceeding..Someone may have “honed” the cylinders excessively to get rid of scores instead of boring oversize. When you speak of “dowels”, do you mean the locating pins for the crank bearings in the block journals? This is another thing to worry about, perhaps the crank bearings were never properly aligned during the last rebuild. Misaligning the bearings/dowels/pins will damage the bearings, crank, block, and could have distorted the crankcase halves so they don’t fit together properly anymore.
    I don’t mean to sound discouraging, I just don’t want you to invest money and time into this project only to have it not work out due to “built in issues” left behind by previous work.
    Let me know if you want to email pictures to me if you can’t make them fit here….Don

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