OK to replace LH Cobra outdrive with RH ?

[rybad]

I have 1989 Four Winns 285 Vista.
Twin 5.7l OMC Cobra Counter-Rotating drives.

My mechanic told me that the forward gear on my port-side (LH) outdrive is blown out. This is the counter-rotating side, and apparently these LH-gear sets are like gold (hard to find). If the mechanic can find the part, he's telling me its going to be $2600 to do the repair.

I found a company here in Michigan that does complete rebuilds of the outdrive for $1995 which doesnt seem like too bad by comparison, plus he does both halves. The problem is that this company said they cant get LH gear sets anymore, and that it would have to be rebuild as a RH drive.

I understand the concept of counter-rotation, and I have to say, if I'm spending upwards of 2-3k, I would prefer that this be done so that it's in the original condition, they way the boat was meant to be.

Having said that, I dont really know how the boat would handle differently. Does anyone have any insight on why this is a good, or bad idea.. considering it looks like I dont have many options.

..Or if anyone knows where I can get the LH gearset parts that would be good too.

Thanks in advance.

-rybad

 

[sethjon]

Re: OK to replace LH Cobra outdrive with RH ?

I'm not sure about the correct answer but I lean toward not doing it. The engineers that designed it did it for a reason and to change it is asking for trouble.

 

[jtmarten]

Re: OK to replace LH Cobra outdrive with RH ?

It will track better in a straight line with counter-rotating drives, I think you'll get better lift as well.
Mine has twin RH drives and does just fine.

 

[HT32BSX115]

Re: OK to replace LH Cobra outdrive with RH ?

Howdy,


If you mean, replace the LH drive with a RH drive (and a right hand rotation engine).. no problem.

Maybe a little problem with steering trim, etc.

If you mean replace a LH drive with a RH drive, keep the LH engine and run the RH drive in REV, you will eventually break the drive.

Most drives were never designed to run "backwards" at high power settings continuously.


Regards,


Rick

 

[rybad]

Re: OK to replace LH Cobra outdrive with RH ?

OK.. Just some clarification on this:

I realize it's not the best solutions to replace the LH outdrive with a RH outdrive. However, it appears that I do not have any option.

I had three different mechanics tell me that they can no longer find the LH gear set for an OMC Cobra 5.7. They also tell me that it's no "big deal" to change the drive, and that most twin engine boats do not have CR drives anyway.

Believe me, I'm not happy about doing this. I'm the type that likes to keep things as original as possible, but like I said, it appears that I dont have any other option, other than to replace the drives with Mercs and conversion kits, and I'm not interested in spending $7-8K.

I guess my real direct questions;

1) does anyone KNOW of any problems with doing this? I was told that nothing on the engine needs to change if I put the RH drive on. The only thing I need to do is make sure I have the correct prop for RH drive (makes sense), but I should be able to bolt it on, and go. (this is what I was told..I'm just trying to get validation on this, as the people that are telling me it's no problem are the ones that stand to loose money if there is a problem, because I wont buy the drive.)

2) Is there any adjustments I need to make on engine? Like I said, I was told by 3 mechanics that I can bolt it on and go. They said that both engines spin the same direction, and that on the Cobra, the counter rotation is done at the gears so I dont need to do anything to the engine (this makes sense, since my delima revolves around these stupid-hard-to-find CR gear sets!)

3) Does anyone know what kind of performance differences I shoud expect? Someone already answered that planning may be slower, low speed control may be harder. I'm not sure really what to expect, especally since my friends all have twin drives that do not have CR and they say they dont have any problems at all. Is this just something I will only notice, only because I once HAD CR?

Again, thanks to everyone who has responded. I truely do appreciate your input!

-rybad

 

[IES99]

Re: OK to replace LH Cobra outdrive with RH ?

I have no dog in this discussion, but having read what most have said here, counter rotation seems like one of those ideas that an engineer came up with that sounds like a good idea but is not really that big a deal. I say that supposing that trim tabs and trim of the drives themselves can probably compensate for the lean inherent in having both props turn the same way.

Thanks for putting up with the interruption.

 

[skiNut]

Re: OK to replace LH Cobra outdrive with RH ?

Somebody touched on this above, and it is something that you NEED to look at. Every boat I have seen with RH / LH setups have a RH rotation engine and a LH rotation engine. YES, the engine itself spins in the opposite direction. These are in hand mated to a RH rotation outdrive, and a LH rotation outdrive.

I do not believe that you can put a RH rotation outdrive on a LH rotation engine. As said above, the drive gears are not meant to run at full spead in reverse, and something will break. On Mercruiser engines, it says the engine rotation on the plastic breather intake cover. I am not sure about OMC engines.

IF both engines are the same rotation, then no, you should not have any problems switching the drive. However in the case of having the same rotation engines, somewhere there is an extra gear that makes the drive turn the opposite direction. I would be very cautious about it and would also be very curious to see where this extra gear is.

As for performance, counter rotating screws is meant to give balance to the boat and prevent cavitation. The torque balances out and the boat tracks better, turns easier, and plains out better because the boat is balanced. With all of the torque now going in the same direction, you can expect to use your trim tabs differently, and one should expect for the boat to react differently when idling and maneuvering in and out of slips/docks, etc. As for cavitation, with counter rotating screws, you are actually "pulling" water from different directions. There is the possiblity that the boat may cavitate easier with both screws turning the same direction. It is impossible to say how much difference you will notice, and/or if it will act the same as someone else's boat that underwent the same retrofit.

 

[HT32BSX115]

Re: OK to replace LH Cobra outdrive with RH ?

If the mechanic can find the part, he's telling me its going to be $2600 to do the repair.

My suggestion?


Pull BOTH drives. Sell the good one and part out the other one.

Get 2 NEW SEI drives (If your LH engine REALLY turns the wrong way, ASK SEI if they have a LH drive)

Do the SEI Kit. http://www.sterndrive.cc/mm5/merchant.mvc?Screen=PROD&Product_Code=9D-116&Category_Code=Cobra


If both engines turn the "right" way, it's a simple job to replace the drive with another "RH" drive.

Good luck.



Rick

 

[jtmarten]

Re: OK to replace LH Cobra outdrive with RH ?

Somebody touched on this above, and it is something that you NEED to look at. Every boat I have seen with RH / LH setups have a RH rotation engine and a LH rotation engine. YES, the engine itself spins in the opposite direction. These are in hand mated to a RH rotation outdrive, and a LH rotation outdrive.

Interesting. None I've ever seen are this way, they all have LH CR lower units with standard rotation engines, and most have been add-ons/swaps. I'm guessing large inboard DD vessels would have engines that counter-rotate.
It's certainly worth checking both engines for rotation before spending a wad on it.

 

[rybad]

Re: OK to replace LH Cobra outdrive with RH ?

Thanks for the info. I am going to DOUBLE CHECK that both engines spin the same direction.

Also.. I have alreach checked into the SEI drive replacement option. It looks like a good way to go. It looks like I could replace both drives, including the CR drive with conversion kits for around $4k .. thats not too bad.

Thanks again!

 

[Lyle29464]

Re: OK to replace LH Cobra outdrive with RH ?

Be carefull on your terminology.

If you really do have left and right hand turn engines the counter rotation is the starboard and the standard turn is the port.

The outdrives would be a left and a right hand turn. You would not want to use the counter rotation term used in your first post.