Advice please re purchase of 1958 7.5hp Johnson

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  • Monte NZ

    International Member - 2 Years
    Replies: 304
    Topics: 89
    #219184

    Hi All. A friend of mine has offered me the above motor and as I’m not familiar with this model Johnson, I was wondering if there are any things to be aware of and can be a problem. As we suspect it hasn’t been run for a long time, I would expect the coils, spark plug leads etc will need to be replaced and the water pump to be checked and more than likely a new impeller fitted.

    Unfortunately there is no history on the motor. It doesn’t appear to have any signs of salt corrosion, including under the hood. The paintwork appears to be original and is pretty worn, which is to be expected after 62 years. The gearbox skeg is worn down and is smooth indicating that it may have been used on a river with sandbars. The prop is also smooth. The motor appears complete except for the Medallion on the front of the hood. Pulling the motor over by hand indicates good compression, but a compression gauge will be used to check and by the way, what compression figure would be necessary to get reasonable performance?

    It will be interesting to see what the gearbox oil is like. The motor doesn’t appear to have roughly treated going on appearances.
    I believe that model has a shock absorber device on the drive shaft and wondered if this could be troublesome.

    Many thanks in advance for your comments.

    Monte NZ


    billw

    US Member - 2 Years
    Replies: 2071
    Topics: 66
    #219185

    My two cents: The shock absorber is probably okay if the engine turns over fairly easily and has “bounce,” that is, backs off a compression stroke on it’s own, when pulled over. These engines like to put connecting rods through the side of the crank case if run on 50:1 mix. Some say 24:1 is okay; I say why risk it….run at 16:1. Keep in mind you will need a pressure-type; twin hose fuel tank for it, or you will have to convert it to a fuel pump; single line system, which isn’t as easy to do on a 7.5, as it is on some bigger models.. They are good running engines, when right.

    Long live American manufacturing!

    • This reply was modified 3 years, 5 months ago by billw.

    fleetwin

    US Member - 2 Years
    Replies: 4737
    Topics: 46
    #219187

    Like Bill says, the powerhead is suspect if it has been running on anything less than 16:1. The problem is you have no history on the engine so you just don’t know. Compression readings are one thing, but they won’t be affected much by leaner oil mixes, but the rods sure will be. You might try removing the recoil and the little inspection plate over the flywheel, then have a look at the coils. Seeing old/cracked coils may actually be a good thing, means it is a relatively low hour motor that probably has not been run on today’s leaner oil mixes.
    As for the gearcase, I would definitely crack the lower drain screw. Milky or watery oil means trouble, and that shock thing is always suspect, especially on this engine that appears to have been used to dredge clams.
    You mention that the engine is not in particularly great cosmetic condition, normal wear for its age. So, with all that said, I surely would not pay much for it. Needless to say, it will need all that work you mentioned to make it a reliable daily runner…


    crosbyman

    Canada Member - 2 Years
    Replies: 3588
    Topics: 326
    #219193

    Great… I just went POOF again 🙁 🙁 I wish we would have a list of POOF edits so we could work around them there is obviously a listing of words to POOF us out so let’s publish the list

    btw great motor……. lots of utubes I sent before being poofed

    Joining AOMCI has priviledges 🙂


    crosbyman

    Canada Member - 2 Years
    Replies: 3588
    Topics: 326
    #219196

    here is a word version to bypass the edits

    Joining AOMCI has priviledges 🙂


    crosbyman

    Canada Member - 2 Years
    Replies: 3588
    Topics: 326
    #219192

    Try for $75-100 cdn (eqv) which is what I usually pay they are great motor assuming they got TLC converting to pump is not difficult and to change the impeller you need to pull the head which is also easy to do

    figure about $100-125 CDN in parts with your free labor ………. you will have a great motor. here are a few links yo get you going (very addictive hobby)

    http://www.youtube.com/watch?v=ga1Cjymj6ms&feature=youtu.be
    https://www.ebay.ca/itm/1-5-40HP-Outboard-Engines-Ignition-Coil-For-OMC-Johnson-Evinrude-584477-582995-/203046524200?hash=item2f46841528

    http://www.marineengine.com/parts/johnson-evinrude-parts.php?year=1958&hp=7.5&model=AD-12
    http://www.youtube.com/watch?v=EY2HrEdp5vg
    http://www.leeroysramblings.com/johnson_magneto.htm
    http://www.pochefamily.org/outboard/Coils.htm
    https://www.vintageoutboard.com/collections/johnson-evinrude-water-pumps-impellers-lower-units/products/18-3001c-impeller-kit-for-johnson-evinrude-5-5-hp-and-7-5-hp-1956-58
    http://www.youtube.com/watch?v=tA0u62hciwY

    Joining AOMCI has priviledges 🙂


    amuller


    Replies: 1055
    Topics: 163
    #219224

    IMO, the biggest liabilities of these otherwise nice motors are:

    Need to remove powerhead to work on water pump. (Because there isn’t a provision for disconnecting the shift rod otherwise.) Some say this isn’t a big deal. Maybe so. But it surely discourages changing the impeller/inspecting the pump.

    The “shock absorber” in the drive shaft. (This was before rubber slip hubs in the props.) This can separate some, putting a lot of pressure on internal parts. Or the spring can break. You get to inspect this while doing the water pump work.

    Need for lots of oil in the fuel. There are tons of opinions about how much is enough. I think the official OMC guidance for a ’58 was 20-1. People above are saying use16-1. Not even OMC itself consistently gave sound guidance on mix ratios.

    The pressure tank system isn’t ideal but but will work fine if the special tank is in good shape.


    crosbyman

    Canada Member - 2 Years
    Replies: 3588
    Topics: 326
    #219227

    amuller… ain’t that the whole fun of it during winter confinement aside from the shock absorber of course 🙂

    my buddy runs his 5.5hp I sold him on 24/1 TCW/ and swears by it but he uses it for trolling only aside his 40 Honda I warned him about 16/1

    the conversion to pump ain’t bad either if the tank is missing or rusted out

    Joining AOMCI has priviledges 🙂


    amuller


    Replies: 1055
    Topics: 163
    #219261

    Well, I wasn’t trying to discourage anybody, just mentioning the issues as I see them. I have a 5.5, a ’62 I think. Servicing it ate up more time than I was expecting, but the results have been good. I’ve been running it at 24-1 but I know opinions vary.

    Also have a pressure tank ten hp that needs attention. It’s from the year that went to the smaller gearcase. Hope to get to it this winter. Don’t have a 7.5 but would be open to one.


    crosbyman

    Canada Member - 2 Years
    Replies: 3588
    Topics: 326
    #219268

    I had a 7.5 along side my 75 ETEC for a while (nice ratio 50 years apart ) used it for trolling and back-up in case th big guy konk out 5 miles out

    I think it consumed equal or more gas than the 75 🙁 The ETEC burns about 2 cups / hour trolling

    Joining AOMCI has priviledges 🙂

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