Bill,
>From what I've discoverd going down my own outdrive replacement road, some of the 4 cylinder models had the same gearing as the 6's, with the only difference being the prop pitch. Later on, I would say when the short profile drive came to be around 1972, the gear ratio changed for the 4's, the 6's were changed to something different than what we use on our 6's (the 155 fell out of favor, and OMC went to GM's 165hp Chevy inline six) so there are all kinds of combos.
>From everything I've read in both my 1968 Evinrude owners' manual and my old 1970 Johnson manual, the gear ratios between the 120hp four and 155hp six are the SAME GEAR RATIO. The only difference is that the 120hp uses a 14x16 prop and the 155hp uses a 14x18. If didn't read my drive saga before, he's an overview of what I went through and tried out:
Original 1968 5-cap 155hp drive upper gear case shot, no hope for repair.
I decide to try a late (around '74 or '75) 5-cap drive, 120hp, SHORT profile OMC drive. This drive turned out to be too short to operate correctly on my 68 Sportsman, being that it would cavitate (ventilate) very easily. It also over-revved probably due to OMC's later 120hp upper gear case ratio. I ended up selling this drive.
My current drive is a pre-1967 4-cap drive like yours, TALL profile (TALL profile drives were all OMC made pre '72) and it's a 120hp drive. It had a 14 1/4 x 16 prop on it, I changed it to a 14x18 (fit perfectly, no clearance issues, so the lower half might be newer?) and it works spectacularly. I know it's old and some of the upper gear internal parts interchange (you can match a COMPLETE upper unit and a COMPLETE lower unit between years, in that you could take an old four bolt upper gear case and match it up all the way to a 1977 lower gear case) but it works, it was in good condition.
My advice would be to:
Avoid short profile drives, as they are too short to function correctly.
Get a complete tall profile drive, first trying to get a "HP match" to your boat, so try finding a 155hp first. Again, according to our boat's owners' manuals, the gear ratios are the same between 120hp and 155hp, just swap props. You can even use a v8 drive, but then you'll have to start changing prop pitches, but any good prop shop can take a prop 2" in either direction. I guess to simplify, find a drive with reasonably clean oil, a decent ball gear, one that shifts correctly, hang it on the intermediate housing and just enjoy. If you need any help, feel free to ask, as I've been where you are right now. Also, if you find something with the external push pull steering, the internal system can be retrofitted back into whatever you get.
One last thing, if you need a good home for your four-bolt drive, I'd be more than willing to take it off your hands. Since I'm running one right now, I'd love to have a spare.
~Scott
Date: Mon, 13 Jul 2009 06:45:16 -0700
From: bldfw@...
To: omc-boats@...
Subject: [OMC-Boats] Outdrive compatibility
I came across someone selling a full OMC stringer setup from a 4 cylinder boat, both the outdrive and the intermediate housing. I was contemplating picking it up for possible spare parts. Not sure I really need to do it but ya never know. I'm trying to get the guy to give me the model number so I can see what it truly is but haven't heard back yet.
Is there anything I need to be aware of in terms of compatibility with the '65 4 bolt outdrive I have on my V6 -vs- noe for a 4cyl?
-Bill
Dallas, TX
1970 Evinrude Explorer - 155 Buick V6 - OMC Sterndrive
http://www.photobucket.com/evinrude_explorer
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Received on Monday, 13 July 2009
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