1986 omc cobra outdrive sounds like the it's shifting in and out of gear when going forward?

Question

when i start out driving it will make a kind thuding noise even after it planes out almost sounds like it's shifting in and out of gear then it will smooth out and go away as a long time engine guy i know that this is an outdrive problem not an engine miss but it almost acts like one but its definatenly in the outdrive any help would be appreciated

Answer 1

Ozy is correct, there was a gear change in the lower unit. It was done to all except the 3.0l with the small V-4 outboard lower unit. The change was the engagement area of the forward gear and clutch dog. At first it was 3 deg then went to 5 deg undercut. With this a shift interrupt switch and module was added to assist with shifting out of gear. It's improvement was to assist with the clutch dog and forward gear pulling into each other and prevent them from slipping apart and slamming back into gear.

Now, is your issue the slipping in gear. You will need to locate the plate where the shift cables meet on the motor. If it has 2 switches there, you should have the updated gear set. Run the boat in the water and watch the cables, if when the noise happens and the cable moves, your clutch and forward gear are releasing, this forces the cable to move. If the switch is activating, this will also cause the engine to miss by dropping a cylinder.
Check the oil in the lower unit, if it has metal flakes in it, it my be too late for an adjustment and the gears and clutch dog will need to be replaced. You may want to take to a service shop for the adjustment, Cobra's are a little tricky.

As far as the slipping prop hub theory, sorry, once a hub starts to slip under load it will let go till it cools off again.

Answer 2

Omc Cobra Outdrive

Answer 3

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RE:
1986 omc cobra outdrive sounds like the it's shifting in and out of gear when going forward?
when i start out driving it will make a kind thuding noise even after it planes out almost sounds like it's shifting in and out of gear then it will smooth out and go away as a long time engine guy i know that this is an outdrive problem not an engine miss but it almost acts like one but its...

Answer 4

Cobra Outdrive

Answer 5

Make sure its not the prop hub slipping under the stress of reaching plane. This could cause a in and out thudding do to pressure changes to the U joint, similar to the sound it makes putting it in gear. If it doesn't make that sound or have that feel in a hard turn then disregard this answer. Good luck ............Yes Mercman you are correct when the prop is just about shot. But in this case the lessening of stress brought about by the boat being on plane, brings "that cooling" effect much more rapidly on a hub not so worn out. A prop hub is designed to slip once in a while in till it reaches it's fatigue limits. It could be on it's way out ? It's nice to see you and the Capt. in the same question again. It's probably not the prop but you got to start some were.( Frank, why don't we just rebuild the carbs so this doesn't happen again?) Bump-N the idle KILLS !

Answer 6

Prepare to spend about a $1000.00. We had it in ours. It's an 89 OMC Cobra and did exactly what you have described and after $1k it runs great. The better 1/2 thinks they were called plate gears...and he has described them as if you were to put weights(dumb bell style) on the pole and they all mesh together if you can understand that...that is what they look like. Hope that can help you. Go luck from one water lover to another.

Answer 7

Spun Hub TroubleShooting

Put a mark on prop shaft nut or washer at 12 o'clock and a mark on prop or prop hub above the same spot but on other side of rubber part of hub. I use a nail or screwdriver to scatch it.
Drive the boat - when it slips - stop and see if align marks are different.
If the marks have moved apart - then time for re-hub or new prop.

If same problem persists and marks are alligned - I would first check my shift cable.
First - with engine off and key out - shift to foward and carefully unhook shift cable. Push the linkage and see if there is more travel to insure complete foward is engaged. If you felt it move to more engaged then you need to adjust your cable throw.
(you could try this in the water but very carefully)
If no movement I would venture your clutch dog has been compromised.

Answer 8

That happened to my fathers 90 omc cobra,I believe it was the drive gears .There was a new design set of gears.Call the local omc dealer and he should know the parts you need.We thought it was cable adjustment cause it only happened under a moderate load.

Answer 9

It will fit. There where some minor changes, That should not interfere with it being used as a replacement. I'm always careful about buying any boat with a "rebuilt" anything. Only do so, with the provision that an in the water test ride be completed before the deal is final.

Answer 10

Ok, I've had some experiance with one of these...LOL !!! I have one on my bench as we speak... The Dogs on the gears were a little on the soft side and they wore...To save some money you can take the gears to a machine shop and have then put a 5 degree undercut they can match your shift dog too .. but make sure your shift module is working or you wont be able to get ot out of gear comming into a dock.. it momenterally stumbles the engine to assist you in geting out of gear..the worst part of this job is removing the snap rings in the lower Hsg....