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  1. #1

    Default OMC Cobra: Please help or I'm going to blow my brains out!

    ey there forum folks. I'm a newbie here, but I've been a professional mechanic now for 45 years. Bought a 21' Marlin cuudy cabin w/a 305 Chevy & OMC cobra for $400. Trailer & all. The guy had put 1000's into it to end up having to back up all the way to the dock. Got disgusted & sold it to me. That's where my nightmare started. Read all the info I could about these drives. Watched all the Youtube videos. Removed the 1st drive & replaced the gimbal, input shaft, shift cable, etc. (input ujoint shaft was twisted!!) & put it back on to find out the prop shaft was bent. Ok, decided to get good used unit rather than rebuild this one. 2nd unit ended up causing a thumping noise. We lost fwd with it and ended up having to back up to the dock at a lake. Bought a super clean 3rd. unit w/low hours & fresh water use only and decided, ok....its time for me to learn how to rebuild these things. I took the unit apart. Inspected the upper drive. Gears looked beautiful. Perfect tooth pattern. No leaks from the front seal going into the bellows. So, I decided not to mess w/the upper unit other than replacing the water pump seal & large oring. New water pump. Took apart the lower unit & the gears looked great. The area where the dog clutch engages were like new. Nice and square edges. The dog clutch was hardly worn. I decided to install the new updated detent & new dog clutch. Reassembled it w/new propshaft & shift rod seals. Bearings & gear pattern looked awesome. Got it all together & set the shift rod at 8 turns in. I also measured the height as well. 6.904 if I recall. I looked it up. Spoke w/Wayne Koll up in Canada from TC electronics & Marine. He's the one who said 8 turns for the shift rod adjustment. Ran the boat a couple of times new another new cable & it was fine until last night. Was out in Long Beach Harbor net hooping and the drive was going in & out of reverse & fwd no problem. ESA operating properly. Hours later, all of a sudden, after a reverse shift into forward I lost forward. Started grinding like it didn't have enough throw to go into gear. I had reverse though. Out on the ocean, I opened the engine cover w/the engine idling. Removed the shift cable connection & pushed the cable in. Went into reverse & the ESA was working. Tried to pull it into forward and same thing, grinding...no forward no matter how much I pulled the cable out. I believe this boat is cursed. I cannot believe that after 3 drives and having gone into the last one that all my problems are related to the drive. Wayne had mentioned to make sure to use a genuine OMC shift cable because he said there's been issues with the aftermarket ones stretching & then losing forward. This cable is literally 2 months old. This is the last time I'm pulling this drive off. I'm either going to find the reason why this thing keeps having these issues, repower the thing with a Mercury unit, or just sell the boat. I'm done. My mental sanity is at stake here. Any help would be appreciated!

  2. #2
    Join Date
    May 2010
    Location
    DC Burbs/Maryland Eastern Shore
    Posts
    1,931

    Default Re: OMC Cobra: Please help or I'm going to blow my brains out!

    While it can be frustrating, it sounds like you aren't following the procedure for adjusting the lower shift cable properly. I have no idea where 8 turns comes from. You need to do it properly, step by step using the correct tools or else you're gonna continue to have problems.
    Go here:
    http://www.hastings.org/~stuart/cobra/
    Practicing the ancient art of ren-ching

  3. #3
    Join Date
    Apr 2009
    Location
    Long Island, NY,
    Posts
    204

    Default Re: OMC Cobra: Please help or I'm going to blow my brains out!

    The shift rod I never heard of a # of turns, you measure the height with a t square or OMC had a special tool that you use as a guide for this. This is very important since all the other adjustments depend on the accuracy of this measurement. On mine which I’ve owned 18 years it still has the same cable on it (OE) and it was adjusted by a good OMC shop in 2004, was fine till 2013 when the remote adjustment cable changed a bit. I went through the whole adjustment checking the shift cable drag and was able to get it better than even the shop did. It’s been perfect since. I agree with using only an OE shift cable if you can find one. A few points:
    shift cable drag measured with it disconnected on both ends must not exceed 2.5 lbs measured with a fish scale
    the bell crank in the transom mount has to get cleaned out and greased each time you remove the drive and that gasket has to seal well to keep water out
    this is a 2 cable system the remote cable has to get adjusted too
    if the remote control is worn out you could have lost motion in the shift system.
    the key to getting these to shift right is a good shift cable greased bell crank and equal throw on both sides of neutral. That means correct adjustment of both the transom shift cable and the remote cable.

  4. #4
    Join Date
    Mar 2009
    Location
    Portland, Oregon,
    Posts
    12,334

    Default Re: OMC Cobra: Please help or I'm going to blow my brains out!

    Quote Originally Posted by louc View Post
    ........
    the key to getting these to shift right is a good shift cable greased bell crank and equal throw on both sides of neutral.
    You nailed it!

    Whether using Stuart Hasting's method, or another method, the ultimate goal is to place the Dog Clutch sliding sleeve at an equal distance from each driven gear's Dog Clutch engagement teeth while all other components are in absolute neutral.

    While the tool does work in most cases, it was created for an average use on an average drive.

    Not all drives, nor all lower shift cables are going to be the same, nor will all adjustments be made the same, nor will they render the same results.

    Here's a write up that I did several years ago regarding an alternate method.

    Many have used this procedure, and it has always worked for them.

    This is a copy/paste from an earlier response of mine regarding adjusting this lower cable. This works for both the Merc A drive and the Cobra drive.

    This is geared towards the OMC Cobra drives, but the principle is very similar for the Merc A drives.


    The OEM engineers had to choose an initial cable adjustment dimension for average Joe mechanic and average Joe user. Hence the initial adjustment "Tool".

    This gets us close ONLY.... and perhaps may be subject to further adjustment.

    The whole idea is to center the Dog Clutch "sliding sleeve" equally between the two driven gear Dog Teeth while in neutral. The pre-determined dimension (the tool) gets you close ONLY, since each scenario may be slightly different.

    Here is my unorthodox method for a Dog Clutch drive, if you care to try it:

    You can either begin with the suggested OEM dimension, or toss it out the window and begin from scratch.... your call:

    1. With the drive fully down (to counter gravity against the sliding sleeve), have a helper swing the propeller back and forth (right and left) quickly, and in an even pattern and rhythm.

    2. You will be at the engine with the lower shift cable disconnected at the linkage arm.

    3. As you bring the cable towards a FWD gear engagement, note where you just begin to hear the "ratcheting" sound as the sliding sleeve contacts the FWD gear Dog Teeth.

    Note where the cable is in it's travel, and find a way to mark it.

    4. Now move the cable towards a REV gear engagement. The helper will still be swinging the prop back/forth.

    Again, note where you just begin to hear the sliding sleeve contact the REV gear Dog Teeth.

    Note once again where the cable is in it's travel, and find a way to mark it.

    5. When you divide this travel equally, you will have located theoretical Neutral regarding where the sliding sleeve is in relationship to the two "driven" gears.

    This is the goal..... "neutral".

    6. Now connect your lower shift cable up to the rest of the linkage so that this "Neutral" travel adjustment is maintained.

    The spring loaded cam arm will have maintained it's neutral position.

    You may find that the new measurement is slightly different from that of the OEM (or Stuart Hastings dimension for the OMC Cobra drives).

    None-the-less, the sliding sleeve will now be at center of travel while in Neutral on the splines of the propeller shaft.

    Again, this is the goal!

    7. Make your SI or ESA adjustments after first doing the above.

    NOTE: this method works well if all is in good condition.

    If you have a bad cable, bent shifting rod, or any other items that are not working correctly, it will prevent most any method from working as it could.


    Always make your final SI, SA or ESA adjustment with the boat in the water.

    Rick ... aka Ricardo..... AQ series Volvo Penta repair
    Portland, Oregon
    28' SDN F/B w/ twin Volvo Penta 5.7L DP drives

    "Intellectual growth should commence at birth and cease only at death." Albert Einstein

    Please... no PMs! Post your questions on the forum.

  5. #5

    Default Re: OMC Cobra: Please help or I'm going to blow my brains out!

    Quote Originally Posted by o2batsea View Post
    While it can be frustrating, it sounds like you aren't following the procedure for adjusting the lower shift cable properly. I have no idea where 8 turns comes from. You need to do it properly, step by step using the correct tools or else you're gonna continue to have problems.
    Go here:
    http://www.hastings.org/~stuart/cobra/
    Thanks 02BatSea. Yeah. I’ve read that whole article several times when I was doing research online originally when I bought the boat. Great article. And I just re-read it after I posted this & found my problem while having someone move the shifter while I watched the shift bellcrank outside. The dang bellcrank countersink was too deep in the shaft & the rivet in the lever that attaches to the bellcrank was worn & loose. The two problems together caused enough play in the system to cause me to lose forward. I checked the cable adjustment when I took the drive off & it was dead nuts. I replaced both & put loctite on the stainless hold down bolt. Used the cable adjustment setup jigs & the thing worked flawlessly over a period of 6 hours in the harbor. I even made a 4 part short video on how to setup these things properly on YouTube.
    https://www.youtube.com/watch?v=8zcEgZAWqlw

    The 8 turns thing came from Wayne Koll at EC electronics & Marine videos on YouTube. He’s been rebuilding various Outdrives from all manufacturers for 40 years. If you haven’t watched his videos online, I highly recommend them. He’s the only one I’ve found who actually goes in depth in shimming the pinion drive & upper drive using the correct OMC tools to get the correct tooth contact pattern. Here’s the link to his YouTube videos.
    https://www.youtube.com/c/TCElectron...Toronto/videos


    I noticed OMC has two different shift shafts. One with a solid upper (non adjustable) & one that allows you to adjust the upper part that contacts the bellcrank in the tilt housing. My shift shaft is the non adjustable upper. So you can only adjust it by how many turns you screw it in (usually between 7-8 turns to get the 7.156 measurement from the top of the base to the top of the shift rod).

  6. #6

    Default Re: OMC Cobra: Please help or I'm going to blow my brains out!

    Quote Originally Posted by louc View Post
    The shift rod I never heard of a # of turns, you measure the height with a t square or OMC had a special tool that you use as a guide for this. This is very important since all the other adjustments depend on the accuracy of this measurement. On mine which Iíve owned 18 years it still has the same cable on it (OE) and it was adjusted by a good OMC shop in 2004, was fine till 2013 when the remote adjustment cable changed a bit. I went through the whole adjustment checking the shift cable drag and was able to get it better than even the shop did. Itís been perfect since. I agree with using only an OE shift cable if you can find one. A few points:
    shift cable drag measured with it disconnected on both ends must not exceed 2.5 lbs measured with a fish scale
    the bell crank in the transom mount has to get cleaned out and greased each time you remove the drive and that gasket has to seal well to keep water out
    this is a 2 cable system the remote cable has to get adjusted too
    if the remote control is worn out you could have lost motion in the shift system.
    the key to getting these to shift right is a good shift cable greased bell crank and equal throw on both sides of neutral. That means correct adjustment of both the transom shift cable and the remote cable.
    Thanks Lou C for the tips. If you read my response above to 02Batsea I found the problem thank goodness. It was just the bellcrank countersink hole & the lever that attaches to the bellcrank. The rivet came loose and the bolt loosened up because the countersink was worn too deep.

    ive never heard anybody mention 8 turns either on the shift rod before. But Wayne Koll from T.C. Marine & electronics in Canada is actually 100% on that (provided you have a shift rod that doesnít have the 2nd adjustment at the top of the head). I measured the shift rod top to the top of the lower case base & 8 turns put me right at the correct spec. I guess 40 some years of doing nothing but Outdrives heís learned a few things. Lol.

    At either rate, itís fixed & shifting perfectly again. If youíre interested, I actually made a 4 part video which shows what I found on it here.
    https://www.youtube.com/watch?v=8zcEgZAWqlw

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