Obsolete Outboards
by Max Wawrzyniak

Start to Finish, Book II:
(Part 2 - Part 3 - Part 4)

Reviving a Vintage Big Twin - Part 1

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(click to enlarge)

As with the first "Start to Finish" series of columns, this series with deal with my taking an old outboard from "as-found" condition to running condition. As of this moment I have just started working on this engine so I do not know exactly how it will turn out; whatever happens, however, will be reported here.

click to enlargeThe subject (victim?) of this series of columns is a 1953 Evinrude 25 HP "Big Twin." I bought this engine 3 or 4 years ago and do not remember how much I paid for it, but I can't imagine that it was more than $100.00 or so. It does not appear to have seen much use.

click to enlargeThis engine is just a bit older than I suggest for "cheap power," but it is in nice original condition and is close-enough to the later OMC engines to still be of relevance to the reader. I intend to mount this engine on a fixxed-up 1956 Crestliner 14 foot "twin-cockpit' aluminum boat that I will be taking to meetings of the Antique and Classic Boat Society, a group that I recently joined.

click to enlargeDay one; The first order of business to to clean-up the engine so that it is half-way pleasant to work on . It is not necessary at this point to get it " spot-less," as working on it will dirty it up again. Since this engine had fairly nice original paint and decals, I used a relatively mild dish washing soap to clean it; my usual degreaser of choice, Castrol Super Clean, would do a better job of removing hardened grease, but would also ruin the decals and paint, so it will be used only sparingly on this engine. I spent about 1/2 hour on cleaning and then put my toys away for the day.

click to enlargeDay Two; I removed about a dozen screws which held on the engine's cowlings (later engines have easier-to-remove cowlings) and set the cowlings aside where they would not get damaged. A compression test with the cylinders "dry" showed about 80 lbs of compression on each cylinder; adding about a teaspoon of 2-cycle oil to each cylinder did not change the readings much, a good sign as a significant rise in pressure with the oil added would tend to indicate problems with the piston rings. Don't ask me what the compression should be on this 50-year-old engine, as I haven't a clue, but the fact that both cylinders were very close on readings is a good sign. Pulling the rope produced the nice, deep-sounding "thunk-thunk" that I like to hear and I would not normally have even bothered with the compression gauge. If you want to use a gauge, get the kind that threads into the spark plug hole rather than the kind that one holds against the spark plug hole, unless you can count on having someone to help you. Pull the rope "briskly" 4 or 5 times and then check the gauge. Make sure the engine is mounted to something solid so it does not fall over (the cart shown was a lously mount for testing compression on.)

click to enlargeNext the recoil starter was removed, and it's mounting screws replaced into their holes so that, when re-assembly time came, there would be no confusion as to which screw goes where (same with the screws that secured the cowling.) Removing the cog from the top of the flywheel revealed the inspection hole that most of these old OMC's have, and through it one could see a very cracked pair of original equipment magneto coils. The one universal weekness of these 1950's OMC engines is that the coils always cracked, but they are not that big of a deal to replace. I was somewhat concerned about removing the flywheel, as it was probably a very long time since it had been removed (if ever) but the flywheel popped right off with the aid of a puller. I would suggest reviewing the magnetos column for info as to how to use the puller.

click to enlargeOnce the flywheel was off, the 4 screws that hold the magneto were removed and the throttle control cable disconnected; this flexible throttle cable is a feature not found on later OMC engines, which have a quick-disconnect bellcrank arrangement.

click to enlarge There is a sparkplug wire "retainer" mounted underneath one of the cylinder head bolts: do NOT remove the headbolt to free the sparkplug wires. Instead, twist this split retainer to open-up a gap in order to remove the sparkplug wires. NEVER disturb a head bolt unless you absolutely have to.

click to enlargeThe whole magento was removed from the engine and placed on my usual workbench (pickup truck tailgate) where I replaced the coils with "used-but-good" coils from my parts piles, and installed new points, condensers and spark plug wires. No rocket science here; see the magnetos column for more info. Something to keep in mind; the "upper' plug wire is usually marked with a little metal band. Be sure to mark your new upper plug wire when it is installed so that you remember which is which, and as stated in the magneto column, install points and condensers on one "side" at a time, while leaving the other side intact to act as a guide.

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Another hint is to carehully note the arangement of the various "gingerbread" items on the underside of the magneto plate, as most of this stuff needs to be removed in order to replace the sparkplug wires. The magneto plates are drilled and taped to fit a number of different engines, and so there are "extra" holes that may not have any application on your particualr engine, but which will serve to confuse you when time for reassembly.

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After about 2 1/2 hours total time, I had the magneto ready to reinstall on the engine, but will hold off a bit until I get some other things done.


continue to part 2.....