OMC Cobra Stern Drive Tech Info Part 4

Written by Stuart Hastings
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OMC Cobra Shift System Adjustments for "KW-RG" (1986-1991) Clutch Dog Models - Stuart's Transcription

Here is the legendary how-to-adjust-your-Cobra-shift-linkage document what your dealer never told you, or didn't know


     This was transcribed by hand from an OMC Service Bulletin labelled "KW-SHIFT.WPS" and dated "10/17/96". There may be transcription errors, formatting errors, and/or other misteaks. OMC may have superseded this with an improved, more foolproof procedure. Misapplication of this procedure may cause expensive damage to your sterndrive. Information deemed reliable, but not guaranteed.

     With the foregoing in mind, trying to adjust your sterndrive linkage with no knowledge of this procedure is probably even worse for your sterndrive.

     I'm not saying that marine technicians are incompetent! Marine Technicians are like any other group of people;they want to do it right, they just don't always know how. Put yourself in their shoes; you're a competent, hardworking person that's familiar with MerCruisers(tm) or whatever else. Customer Joe Anxious brings his boat in for some whiny problem with shifting, it's got a wierd shift linkage you've never seen before, and Joe desperately wants his boat back NOW. He is on vacation NOW, and the boat must be fixed immediately! Every hour is precious!

   What would you do? You'd give it your best shot; alas, that might well be a shot in the dark, because the Cobra shift linkage isn't very similar to anything else.

     I am providing this information to the Web as a public service, in the belief that it will help other Cobra owners get the best service from their sterndrives.

     I'm telling you that this procedure worked great on my Cobra. Remember that "It worked for me!" is just a testimonial, the weakest form of evidence. Just because I think this information is accurate, helpful, true, etc, doesn't mean it will solve any of your problems, or that it won't cause you problems. Free advice is usually worth what you pay for it.

Just 'cause I'm a great guy doesn't mean I know what I'm talking about.

     If you are mystified by technical terms used in this procedure, you probably shouldn't attempt this adjustment. If you're motivated to answer your own questions by reading the OMC Cobra Service Manual, or referring to pictures in other documents stored on this site, you have just re-qualified yourself. This is not difficult, just fussy.

     If you are uncomfortable doing this work yourself, I humbly suggest you make a printed copy of the orignal OMC documents page 1 and page 2, and take it to the shop where you have your boat fixed. Give the technician a copy of the OMC document to keep; they'll be grateful for this useful information, your sterndrive will probably shift better, and Cobra owners that come after you will also benefit from this knowledge.

     Although the procedure below is divided into five steps, I personally didn't pay close attention the first time I tried to follow it, and I unintentionally skipped over some critical steps. (Don't worry, I didn't damage anything!) For best results, I humbly suggest the reader divide each of the five steps into individual sentences, reading and performing the work described by each sentence,in order.

I sincerely wish you the best of luck with your Cobra.

Happy Boating,

Stuart E. Hastings

End Disclaimer



References: SB#4051, 4052, 4096, 4099, and Appropriate Service Manuals

A. Remove outdrive, replace the transom bracket shift cable if outer jacket is ribbed. Use the appropriate service manual.

"KW-AR" Models(1986-1987) will use Cable Kit #986955 superseded by 987662. This kit will supercede the shift system up to a "GD-RG" style system.

"GD-ME" Models(1988-1989) will use replacement cable #986654 superseded by 987661.

B. Disconnect the remote control shift cable and the transom bracket shift cable at the engine shift bracket. Also, disconnect the throttle cable at the carburetor.

Note from Stuart: OMC is saying "unhook all three control cables from the engine."

Once all your cables are freed from the engine, test the long cables that connect your shifter (single or dual lever box at helm) to the engine. Since you just freed the engine ends, the shifter should shift very easily. If it doesn't, remove the cables from the shifter box and test the box and each cable individually. If any cable is bad, replace both; they're cheap (about US$30 each). If your shifter box is stiff, it may need cleaning and lube, or something inside may be bent or broken. Either way, shifter boxes and cables are much cheaper than gearsets.

All of these parts must be in good working order before you adjust anything else; any problems with the shifter or cables can indirectly destroy your Cobra gearset (US$1000 plus labor). I respectfully suggest you make sure that your shifter and cables are working smoothly and easily before proceeding.

C. Perform the transom bracket shift cable adjustment. Use only the 914017 alignment plate to hold the bellcrank at the 90 degree position. Always use the new 915271-M tool to hold the 7 9/16" dimension. "PW" (1990) and newer models may have a collared retainer nut on the aft end of the shift cable core wire, leave it off!

Note from Stuart: OMC demands that this adjustment be made using two of their special tools see Recommended Tools for adjusting the Cobra shift linkage below.

Recommended Tools for adjusting the Cobra shift linkage

I found the previously OMC-recommended procedure in the OMC Cobra Service Manual: see 11 - 16 below

Cobra Service Manual 11 -16

and 11-17 below.


     This "obsolete procedure" requires only a straightedge, ruler, and some wrenches, although it would go faster if you have a helper. When I last performed this adjustment, I had to climb into and out of the boat five or six times; I've decided that's O.K. since I'm only adjusting one boat. If I worked at a marina, I might feel otherwise.

     The intent here is to adjust the distance between the hole in the cable end and the cable jacket. The adjustment is simple if you have the sterndrive off. Examine picture #83 in 11-16 above; if your dimension "D" is 7 5/8 inches (+/- 1/32 inch!) when in Neutral, you need adjust nothing. Of course, if you have just replaced your transom shift cable, you already have the sterndrive off, and you can adjust this yourself easily.

It is critical that the transom bracket shift cable move freely for its full range of travel and throw after all torquing operations are completed!

     Cable drag cannot exceed 2 1/2 pounds when measured with a spring scale, and less drag is preferred. Check the drag in both directions, full travel!

Note from Stuart: With the outdrive removed, the bellcrank picture 13 below

installed, and the TBSC unhooked from the linkage next to the carburetor, the TBSC (Transom Bracket Shift Cable, the "red one") should slide with 2.5 lbs (about 1,1 kg) force in either direction. If yours is stiffer, either you need a new TBSC, or perhaps your bellcrank is bent picture 12 below,

or your "retainer" was tapped crooked (see below).

This is important. Please don't skip this crucial test. 2.5 pounds (1,1 kg), and no more! If yours is too stiff, loosen the retainer and retest. If it's still stiff, remove the retainer and bellcrank and retest. If the cable by itself is too stiff, it is bad and must be replaced. This is crucial for the durability of your gears.

On Stuart's Cobra, this cable drag was about four pounds (1,8 kg). The problem was a defective "retainer" see part "R" in picture 11 above; the threaded hole in the retainer was not perpendicular (square) to the faces of the retainer. In simpler words, it was "tapped crooked." This is impossible to see by examining the retainer itself; you must thread the retainer onto a suitable length of threaded rod (such as the end of the transom bracket shift cable) and see if the retainer hangs square from the rod.

The replacment retainer I bought for US $12 was less crooked, but not truly square, so I carefully ground down my original defective retainer with a file. This reduced my cable drag to almost 2.5 pounds (1,1 kg). If you try this, you must have a length of suitable threaded rod installed in the retainer so you can check squareness as you work. Does anyone want to buy an unused, slightly crooked retainer :-) ?

D. Return the shift bellcrank to a 90 degree setting. Check the outdrive to make sure it shifts freely into both gears, then return the outdrive to the central neutral detent (SB #4096). Remove the front anode and check the shift rod height. "PW" and newer models can have the shift rod height set without removing the upper gearcase. Shift rod height is a critical adjustment!

Note from Stuart: See picture 15 above

    OMC demands that this measurement be made with their special tool, but I personally don't understand why this can't be measured with a small carpenters' T-square, or equivalent.

If your Cobra used to shift normally, and has only recently developed a shifting problem, it's unlikely that this setting could have changed.

     Install the Outdrive. Refer to the Appropriate Service Manual. (KWB-WXS models with the 983900 transom bracket do not use the nylon spacers on the aft trim/tilt pivot rod). If you are working on a KWB - ARY model (1986-1987). (sic) You must install the adaptor kit on the engine shift bracket. This consists of a new shift lever, special anchor blocks, and assorted hardware. KWB-ARY dual station systems will also require a new engine shift bracket lever & pin #913264.

Note from Stuart: Your shift lever should look like picture 19 below.

If your shift lever looks like picture 18 above, you have the "old one" and you should upgrade it (ask your OMC dealer). This adjustment procedure assumes that your shift lever is up-to-date.


"5 Steps of the Engine Shift Bracket Adjustment"

1. Forward Overstroke Adjustment

Center the cable anchor located in the angled slot on the top of the shift lever. Install the remote control shift cable, control box in FORWARD GEAR FULL THROTTLE. Pull out on the casing guide to remove any slack. Ajust the shift cable trunnion to center the forward (fixed) overstroke cam with the switch button on the overstroke switch.

2. Forward Gear Engagement

Install the transom bracket shift cable, control box is still in forward gear full throttle. PULL OUT ON THE TRANSOM BRACKET SHIFT CABLE TO FULLY ENGAGE THE CLUTCH DOG WHILE SOMEONE ROTATES THE PROPELLER. Make sure you pull back on the shift cable to remove all the end play from the system as you adjust the black barrel trunnion. When installed correctly and all slack is out of the system the load lever will "rock upward stiffly" and "rock downward easily"but should always center itself!

3.Reverse Gear Engagement

Shift the control box into REVERSE GEAR FULL THROTTLE, loosen the 7/16" nut in the angled slot at the top of the shift lever on the shift bracket. PUSH DOWN on the shift lever while someone rotates the propeller to FULLY ENGAGE THE CLUTCH DOG. While holding down on the shift lever, remove all slack from the remote control shift cable by pulling its casing guide to the rear of the boat. Be careful not to preload the system. Then tighten the 7/16" nut securely. When adjusted properly, and all play removed, the load lever will "rock downward stiffly" and "rock upward easily", but will always center itself.

4. Reverse Overtroke Adjustment

Adjust the reverse overstroke cam to center itself with the switch button on the overstroke switch (3/8" nut). The control box is still in reverse gear full throttle. "PW thru RG" (sic) models will probably not have a reverse overstroke cam.

5. Throttle Cable Adjustment

Install and adjust the throttle cable. Control box should be moved into the forward gear idle position, then half-way back to neutral. Tension on the cable should be only enough to positively close the throttle plates. Excessive tension will cause the shift system to bind. (Unit should shift no harder with the cable installed than with it removed).

Now run the unit and check for smooth positive shifting, also check for proper operation of the ESA system by making the running checks at the engine shift bracket! Service Kits are available to upgrade the ESA module to the latest pulse pattern, time duration and RPM limits (SB #4099).


Part 4 How To Adjust Your Cobra Shift Linkage

Part 3 OMC Cobra Stern Drive Tech Info

Part 2 Problems with the Cobra

Part 1 OMC Cobra Stern Drive Tech Info


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Recreated with the permission of the Author for CBOC


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