’57 Evinrude 7.5 fleetwin fuel mix

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    oldemtr

    US Member - 1 Year
    Replies: 10
    Topics: 4
    #194178

    Hi – My first post here, as a guest.
    I’m presently working on the motor in the subject line – Going through the water pump, carburetor rebuild, and ignition tune up that’s usually / always needed to try to bring an old motor like this back into service. Also doing a fuel pump conversion, as it didn’t come with a tank. I think the motor is basically OK, but it’s been parked a very long time

    My question is about this particular motor, that I hadn’t realized when I bought it – Every small hp OMC motor of that era is listed in the factory literature as needing a 24:1 fuel mix, EXCEPT the 7.5, which is supposed to use 16:1.
    This is not intended to be a general opinion type question about fuel mix, but about this specific engine, that OMC specifically calls for using the richer mix – Why ?

    Was there a design flaw in this one, that they tried to help with the richer mix ?
    I do see, that instead of a top crankcase seal, the motor uses an oil slinger – Is that why? Anyone know ?
    Thanks

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    aquasonic

    US Member - 2 Years
    Replies: 360
    Topics: 32
    #194182

    At that time, the 3, 5.5, and 7.5 HP OMC motors all were recommended to use 16:1 mix. The 10 HP and up were recommended to use 24:1 mix.

    The smaller motors were plain bearing. The larger motors had needle bearings on the crank.

    Mumbles
    Mumbles

    Canada Member - 2 Years
    Replies: 4337
    Topics: 428
    #194187

    Einstein-CD-AD

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    oldemtr

    US Member - 1 Year
    Replies: 10
    Topics: 4
    #194193

    OK – This is where I got my info – The only motor listed here, that required 16:1 ;

    gas-mix

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    jeff-register

    US Member - 1 Year
    Replies: 1154
    Topics: 48
    #194196

    On my 53 Evinrude (15-1 mix) inside the cowl it stated to mix 1 qt of oil to 5 gallons of fuel. I carried a 5 GI can & exchanged & filled the remote tank. Always had the same mix & never carried a leaky half full oil bottle. Made it easy + had a filter on the GI can for clean fuel. Used a pair of nylons.
    Never filled in the boat too. Fire scares me.

    frankr
    frankr

    US Member - 1 Year
    Replies: 4715
    Topics: 47
    #194207

    I generally refrain from getting into these fuel mix arguments, and continue to do so. However, if you look hard enough, you can prove anything you want to. For instance the ORIGINAL instructions were for 1 quart of oil to a 4 gallon tank of gas for the 5.5 and 7.5–that’s 16:1

    I also have a 1960 Evinrude factory chart right in front of me with REVISED mixes of 24:1 for 3hp, 5.5hp, while 7.5 remained at 16:1.

    If you really want to get in a fight I also have a 1973 factory chart right in front of me that states 24:1 for 3hp, 5.5hp and 7.5hp —AND is says you can use 50:1 in those motors ONLY if Evinrude/Johnson oil is used. Adding to the argument is the fact that E/J oil from that time is not the same oil as E/J oil of today.

    Let the fight go on, and it will.

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    oldemtr

    US Member - 1 Year
    Replies: 10
    Topics: 4
    #194209

    No fight or argument here – I do understand and have read the many, many posts here on fuel mixes, in general, and I’m not looking for a recommendation on that.
    I only wanted to know if anyone knew WHY the factory specified that particular motor for 16:1, when the others in that same list called for 24:1.
    What was different about the 7.5.?

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    crosbyman

    Canada Member - 1 Year
    Replies: 1401
    Topics: 181
    #194210

    I always heard … read that modern oils are more efficient than the “old SAE30” grade oil mixed at…16/1 so I always mixed 1 liter of TCW-3 to 25 L of fuel on CD and AD’s

    ho well….

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    Steve Martin

    US Member - 1 Year
    Replies: 19
    Topics: 5
    #194218

    Just speculation, but the 7 1/2 was the highest hp motor that had plain bearings so I wonder if they were concerned about bearing load(?)

    • This reply was modified 1 week, 5 days ago by AvatarSteve Martin.
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    kerry

    US Member - 1 Year
    Replies: 348
    Topics: 16
    #194220

    Plain bearing motors need QUANTITY of oil to maintain clearances without burning up from metal to metal contact. Remember, we are talking about 1950’s era manufacturing and mass production. It was hard to maintain a few thousandths tolerance in mass production back then, whereas nowadays a ten thousandth is possible with CNC machinery. People who say modern oils are better forget that those oils were made for modern motors, not 1950’s motors. Better, yes, but only in the ratio the manufacturer recommends. Run a good oil at 16:1 and your motor should be happy for another 60+ years.

    If you have too many, AND not enough, you're a collector.

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    outbdnut2

    US Member - 2 Years
    Replies: 1189
    Topics: 62
    #194229

    I mix 20 to 1 using today’s TCW3 oil in all 16 to 1 and 24 to 1 motors. Yeah, I know I should use a bit more in the 16 to 1 motors, but it’s a convenience thing; mixing a quart of oil to 5 gallons of gas (20 to 1), and not having to keep both 16 to 1 and 24 to 1 cans of gas around…….but……I don’t have a 16 to 1 motor that I run very often, so only running a gallon or so a year, the motors aren’t going to wear out any time soon. If I used one of these motors a lot, including my 7-1/2s, I’d go with 16 to 1. I also use 50 to 1 in 50 to 1 motors, and 50 to 1 in 100 to 1 motors. Some of the early 100 to 1 motors led short lives. When I put a motor on my grandson’s hydroplane (anywhere form 6 to 15 HP), I double the oil because these motors rev to RPMs they weren’t designed to run at. On the hydroplane I sometimes have to go one heat range colder on the spark plugs too.

    Nobody ever killed a motor by using too much oil, and I’m amazed that my PO-15 Johnson at it’s recommended 8 to 1 doesn’t smoke a lot. Racing versions of the Champion “Hotrod” motors use 4 to 1.

    Dave

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    billw

    US Member - 2 Years
    Replies: 1106
    Topics: 38
    #194255

    Just speculation, but the 7 1/2 was the highest hp motor that had plain bearings so I wonder if they were concerned about bearing load(?)

    • This reply was modified 1 week, 5 days ago by AvatarSteve Martin.

    I like this theory. I do know from what I have seen, nothing will throw a rod faster than an AD on a lean oil mix.

    Long live American manufacturing!

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    aquasonic

    US Member - 2 Years
    Replies: 360
    Topics: 32
    #194256

    1963-evinrude-specifications

    After taking a look at the chart that oldemtr provided, a few things became apparent.

    This chart is from 1963 or later. The OMC 7.5 Hp had stopped production in 1958. The other models continued to be produced through 1963, and improvements were being made. Taking a look at the section titled “Crankshaft Bearings – Diameter Clearance” the 7.5 Hp looks to have relatively larger bearing clearance numbers, when compared the 3 and 5.5 Hp. The 5.5 is listed as having “Roller Bearings”, so that may explain why it’s oil recommendation went from 16:1 up to 24:1. I don’t what the justification was for the 3 Hp change from 16:1 up to 24:1.

    As Einstein famously wrote “Don’t forget CD and AD use 16:1” (but maybe not for the 1963 CD)?

    • This reply was modified 1 week, 4 days ago by Avataraquasonic.
    • This reply was modified 1 week, 4 days ago by Avataraquasonic.
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    oldemtr

    US Member - 1 Year
    Replies: 10
    Topics: 4
    #194267

    Thank you, aquasonic – You have satisfied my curiosity .
    That makes total sense, and my bad that I missed the difference in the rod bearings.
    For some of the others that responded, and seemed to be trying to convince me, or something – I have no problem with 16:1 .
    I have a couple British Seagulls that use 10:1, so 16:1 is lean, compared to that :~)
    Thank you, all.

    Mumbles
    Mumbles

    Canada Member - 2 Years
    Replies: 4337
    Topics: 428
    #194269

    The 5.5 horse motors didn’t get needle bearings on the big end of the rod until 1961 so 1960 and older 5.5 motors with plain bearings will need the 16:1 mix. ’61 and later called for 24:1 until 1964 when everything went to the standard 50:1 mix although I think it is safe to assume the ’61 – ’63 motors could use and survive on 50:1 as they are mechanically identical inside as the later 50:1 six horse motors which were built thru 1979.

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