OMC Cobra Sterndrive Owner Hints
During one of my numerous phone discussions with OMC Technical Support,
I asked if they had any "hints" or "suggestions" for me, the um, "proud"
new owner of an almost-ten-year-old Cobra.
- I can't find this written anywhere, but OMC recommends the Shift
Linkage be readjusted with the usual fifty-hour (end-of-season)
service. Presumably the Transom Bracket Shift Cable should be
carefully examined, tested for excessive drag, and replaced if
- When filling the Cobra with gear lube, use the middle fill
plug, as shown in the Owners' Manual. Do not fill through the
(bottom) drain plug! If you fill from the wrong port, you will
probably trap a big bubble of air inside the vertical drive, and that
bubble will eventually rise to the top. When it does, the upper
gearcase gears will run dry, and self-destruct. As they say in the
computer biz, "RTFM."
On this diagram (143k), item #53 is the
drain, and item #41 is the fill.
- Don't remove the COBRA badges on each side of the vertical drive.
There is nothing useful hidden underneath, and reinstalling them
correctly can be very labor-intensive.
- Avoid gasohol (more than ten percent alcohol) if possible.
- Modern gasoline goes stale after thirty days. At the end of the
boating season, fill the boat with fresh gas, and add gas stabilizer
(Sta-Bil or similar). A full gas tank is best; there is less airspace
to accumulate condensation. Follow directions on the stabilizer;
excess stabilizer won't help.
- Change the gearcase lube at the end of every season. "Milky" oil
means there is water leaking into the drive; you must get
this fixed promptly!.
- "Fog" the engine before storage. See the Owners' Manual. Any
fogging oil will do.
- If you remove the U-joint or exhaust bellows, note the position of
the hose clamp before disassembly. The U-joint bellows clamp body
should be positioned between one and two o'clock, and the exhaust
bellows clamp body should be at three o'clock. Getting these wrong
will limit the turning radius of the drive, and probably damage
Below are some factoids I've learnt by working on my Cobra, or by
asking OMC Tech Support:
- "ESA" stands for "Electronic Shift Assist." This is a sealed,
transistorized gadget bolted to your engine and wired into the
primary side of the ignition. A microswitch in the shift linkage
enables the ESA, and it intentionally messes up the engine spark.
While the ESA is operating, the engine idles slower, rougher, and
with less torque; this makes shifting easier.
- The ESA seems to be most critical when disengaging a gear
and returning to neutral. The interference "bite" on the clutch dog
combined with the torque of the turning engine and resisting prop make
the dog bite harder to stay engaged. The ESA defeats this by slowing
and weakening the engine momentarily.
- Pursuant to the point above, if your Cobra engages gear easily,
but disengages with difficulty, your ESA is suspect. Test it by
running the engine at idle in neutral, and clicking the ESA
microswitch in the shift linkage (starboard side of carburetor). The
ESA microswitch is the one with the metal arm on it, but you won't
hurt anything if you click them both. If your ESA is working, the
engine will noticably slow down. New-style ESAs have a built-in timer,
and will only munge the ignition for a few seconds.
- If your ESA tests OK when engaged by hand (above), see if it
engages when you shift. Run the engine at idle and study the linkage
while somebody else engages/disengages the drive. Does the ESA
microswitch get clicked on?
- OMC had a batch of defective ESA springs; they were too stiff, and
prevented the ESA from engaging. Diagnose this by watching the shift
mechanism while the engine is running (as above). See "Wrong Shift Interrupter Spring" (120k JPEG),
and/or try "crunching" your spring to weaken it. I bought my Cobra
when it was nine years old, and it still had the wrong spring,
and my ESA never engaged while shifting!
- Bad ignition points can cause the ESA to malfunction. Points are
cheap, and ESAs are expensive; if there is any question about the
points or condenser, replace them first.
- If your Cobra has points in the distributor, OMC makes an upgrade
kit that replaces the points with electronic ignition, and a new
ESA. Ask your local OMC dealer; when I last checked, this kit was
US$200 for my 4.3L Cobra. This is an excellent value; the ESA itself
is about $200, and a Pertronix (non-OMC aftermarket) electronic
ignition kit (no ESA) is US$70-80. Alas, my wife doesn't see this as
- The ESA may have an RPM limiter in it. I have no idea what the
limit might be, and very little interest in pushing my engine that
hard. If any reader discovers the limit, I'd be interested to
- The U-joint bellows is not symmetric. If you examine one, you'll
see the ribs are really one continuous spiraling rib. It has been
deliberately made to have one more rib on one side than the
other. Study your bellows, count the ribs on each side, and place the
"extra" rib on the bottom. When your sterndrive is raised, the
top will be compressed and the bottom will be stretched; you want that
"extra" rib on the bottom.