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 appropriate.
• 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 something.

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 essential (yet).
• 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 know.
• 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.