Obsolete Outboards
by Max Wawrzyniak

"Big Twin" Tiller Conversion

As I keep mentioning, I feel that OMC-built outboards of from 3 hp up to 40 hp, made from about 1955 until the early 1970's offer an excellent value for the seeker of cheap outboard power.

One of the many qualities to which I attribute this value, is the ease with which most of these outboards (with just a few exceptions) may be converted to both tiller-control as well as remote control. The various bits of hardware necessary for remote-control operation of these engines was discussed in the columns concerning remote control of shift and throttle, and remote control of steering, so that aspect has already been covered.

Virtually all OMC engines of under 25 hp (and also some very early '70s 25's) came from the factory fitted with a tiller, so no additonal parts or work is required for tiller control of these engines. Unless a previous owner has removed the tiller when one of these engines was fitted with remote controls (OMC recommended leaving the tiller in place), you will get the tiller with the engine.

The "Big Twins," however, were available either with a tiller or without a tiller (for remote control only) so if one wants tiller control over one of the latter engines, a tiller must be mounted.

Converted a "non-tiller" big twin to tiller control is no big deal; these remote-control engines usually came fitted with an engine-mounted "flipper-handle" throttle mounted on the forward Port side of the engine. Sometimes this was referred to as a "warm-up" throttle, for use when starting the engine from the engine, and not from the remote control location. The warm-up throttle is simply removed from the engine, and a tiller bolted-on in it's place.

But first, one must acquire a big twin tiller. These are common swap-meet items, and also are sometimes seen on ebay. Lastly, one can often be pruchased through dealers of used outboard parts. I consider a reasonable price for a complete big twin tiller to be around $30.00 to $50.00. However, the more "convienient" it is to obtain, the more expensive it will most likely be, and I have heard of price quotes of $100.00 from the used parts resellers.

A couple things to keep in mind; first of all, make sure what you are buying is a big twin tiller and not a tiller from other models of engines. The only other style of twist-grip-throttle tiller used on OMC engines made during the time period in question is much shorter than a big twin tiller, and the big twin tiller bolts on to the engine in a different manner than the other style of tiller. Also, the interior throttle shaft is visible from the underside of a big twin tiller, but is totally enclosed within the tiller housing of the other OMC tillers.

Be advised that two different styles of "cogs' where used in big twin tillers. Twist-grip-throttle tillers used on all OMC engines from this period all operated in the same manner; the rotating twist-grip throttle was coupled to a internal shaft in the tiller itself. this shaft has to have a flexible coupling at the "hinge point' of the tiller (where the tiller folds unward) and this flexible coupling is accomplished by having inter-locking "cogs," on the shaft in the tiller, and also on the throttle shaft extending into the motor itself. I refer to the two different styles of cogs used, as "pointy" toothed cogs (used up until 1956) and "ball" tooth cogs (used after 1956). It really does not matter which style cog you use, as thery are interchangeable, but you do need to have two of the same style cog. Also, the "ball" tooth cog
will be seen to have one extra-large tooth and one extra-large "gap:" in other words, they can engage in only one relative postion. Attempting to force engagement with one cog rotated out of alignment may damage the cogs.

I mentioned the throttle shaft extending into the engine; a complete tiller will include this shaft, which should come with the cog needed to engage the cog on the tiller. The other end (aft end) of the throttle shaft may or may not
come fitted with the pinion gear that engages the vertical throttle shaft; this same pinion gear is already on the engine and it is not necessary to get that piece as well. You do need to get the shaft, though, as the "flipper handle" is permanently attached to the shaft already in a "remote control-only" big twin and can not be used with the tiller.

Finally, you should try to get the attaching hardware for the tiller , which will consist of a bolt and nut, a dished-and-notched lock washer , and a very thin friction washer.

Step one to making the conversion is to de-grease the engine so you can see what you are working on. I de-greased the example engine in 10 degree F weather where the water was freezing on the engine (and on me). Such is
my dedication to this column.

Next, one can remove the large bolt that holds the throttle "cover' or "cowling" on. The cover itself can not be removed until the "flipper handle" and shaft are removed, but get the cover loose anyway. Note that in the photos, the big bolt is accessed from above; on some engines you need to go in from underneath to get to the bolt. Next, remove the small set-screw from the pinion gear at the aft-end of the throttle shaft on the motor proper. Remove this screw entirely, as it passes through a notch in the shaft, and loosening it only (as it appears would work) will not work. Guess who, having not made this conversion for several years, forgot about that when trying to remove the gear from the shaft.

Then have a look at the shaft from underneath. Some of these engines will have a "stop" mounted on the shaft that limits it's maximum rotation. This "stop" which looks like a small lever, will be pinned to the shaft and will need to be removed in order to remove the shaft. Not all engines have this "stop." Use a hammer and very small punch to remove the roll pin which holds the stop on.

At this point, you can withdraw the shaft from the engine. The pinion gear will be loose so watch that it does not get lost. Also, there may be small plastic bushings that support the shaft where it passes through the webs of the castings; don't lose them.

You are halfway done. Insert the throttle shaft for the tiller into the engine and attache the pinion gear to it's aft end. Note that the shaft and the gear have a "flat' on them for alignment. Then one simply bolts the actual tiller on, being sure to line-up the cogs correctly. The very thin washer goes between the tiller and it's mounting boss. Also note that a nut is used on the mounting bolt; one was not used on the cover that was orignally there.

I wish to emphasise that the tiller controls both the throttle and the steering of your engine, so make sure the lock washer is used on the mounting bolt, and a bit of Locktite would not be a bad idea, either. Frequent checks of the mounting hardware during the first few hours of operation are are also warranted.

Make sure that the throttle mechanism operates smoothly. The most common problem that I have seen is for bushing wear on the throttle shafts to allow the hinge-point cogs to sometimes "skip". Although the proper fix is to replace the little plastic bushings through-which the shafts pass, I have on occasion managed a reliable fix by adding a shim between the cogs and the webs of the castings (through which the shaft passes) by inserting either a very thin washer or sometimes even a twist of copper wire. If you try shimming, however, be carefull that you don't shim too much, or the tiller may not "hinge down" all the way to it's stops.

You will probably want more steering friction with a tiller than was used with remote steering. These engines are fitted with steering friction screws in different locations. However, as I felt the friction available to be inadequate, I have often run these engines with bungee cords running from the engine to each side of the boat, such that the engine will self-center if the tiller is released.

It is also possible to fit these engines with lanyard 'shut-offs" simliar to modern outboards, and I would suggest that one look into that as well.

Removing the necessary hardware and mounting the tiller should take you no more than an hour or so, and the tiller can also be used in conjunction with remote controls, giving you 'two-station" control of your boat. Just keep in mind that a control "failure" could casue injury or worse to you or someone else, so be sure the tiller is securely mounted and that the throttle function works smoothly, and as mentioned, a lanyard safety "shut-down" (to be the subject of a future column) is also not a bad idea.

Three "big twin' tillers of varying color and grip style- all are interchangeable. To the left is the "throttle shaft" that you also need, fitted with a "hinge point" cog on one end, and the pinion gear (which you should already have) at the other end.

The underside of a big twin tiller; note that the internal shaft is visible. The shaft is not visible from the underside of other twist-grip OMC tillers. The throttle shaft is sitting in it's relative position.

The big twin tiller is on the left; the green tiller on the right is of the style that you do NOT want. The internal shaft is not visible from underneath; it is also shorter. HOWEVER, the hand grips ARE interchangable with the grips on the big twin tiller, as are the "hinge point" cogs

Our "victim" engine; an early '60s Gale 25 hp. I have always
liked the style of hood on these 60's Gales. Not that it has
anything to do with the price of rice in China.

On the right in the photo below is the "flipper handle" of the warm-up throttle. this will be removed and the tiller mounted in it's place.

The throttle handle, to the left, is attached to a horizontal shaft which runs to the right and ends with a pinion gear, which engages another gear on a vertical shaft. The throttle cable for remote controls attaches to a lever on the gear on the vertical shaft (click to enlarge).

looking underneath the engine, one can see the throttle shaft connecting the flipper handle to the pinion gear towards the right (click to enlarge).

In the center of the photo a wrench can be seen in place on the mounting bolt for the cover to be removed. Note that this hardware is SAE and NOT that silly metric stuff (click to enlarge).

The cover has been loosened and is just sitting on the throttle shaft; a screwdriver is being used to remove the set screw that holds the pinion gear to the throttle shaft. Note green sleeve of parka; 10 degrees F and I am working on a Duckworks column. (click to enlarge)

The parts removed sitting on the stern of the Larsboat; the fliipper handle and shaft; to the imediate right of the shaft is the pinion gear and it's set screw; the throttle cover or cowling; the mounting bolt for the cover and the lock washer for the bolt.

This is what the engine looks like after removing the above parts. (click to enlarge)

This is what we are installing; the tiller with it's retaining bolt, nut, and washers; also the throttle shaft. Note the "ball" tooth cog on the tiller with a big gap in the teeth on the bottom.

The throttle shaft for the tiller has been inserted and the pinion gear attached to the aft (right) end. The shiny brass teeth of the cog can be seen to the left. Note that the shaft and the pinion gear have "flats" for alignment (which you can not see in this photo)(click to enlarge)

Bolting on the actual tiller. Be sure to align the teeth of the cogs at the hinge point, and don't forget the lock washer. If your tiller falls off and you kill someone, don't blame me. I told to to check it frequently for several hours of operation.

Make sure the cogs engage properly; you may need to replace bushings or slightly shim them if the cogs "slip" ( "jumps teeth"), but if you shim, don't shim so much that the tiller will not go all the way down. If your cogs are really worn, you may need to replace them.

A photo taken in 1994 of a 1959 Evinrude 35 hp that I mounted a tiller on, painted with a couple spray cans of Tempo "polychomatic blue," and ran on the Mississippi River for a summer. Still have the engine but have not run it in years.

A parts diagram showing the tiller and related parts, and.....
(click to enlarge)

...a parts diagram showing the "flipper handle" warm-up throttle and related parts. (click to enlarge)