Counter Rotating a motor.

[mannyq]

How does one convert an outboard to counter rotating, besides the right prop, when the boat has twin outboards? Can the motor be run in reverse to accomplish that?

 

[marinegrh]

Re: Counter Rotating a motor.

do you have 2 standard rotation gear cases, or are you just curious

 

[lakensea]

Re: Counter Rotating a motor.

It is a different gearbox assembly.

 

[mannyq]

Re: Counter Rotating a motor.

I'm may be buying a boat and both engines are identical. I've read that there is a benefit to counter rotation on twin engines to cancel out torque. <br /><br />Lakensea, how do the gear boxes differer?

 

[JasonJ]

Re: Counter Rotating a motor.

I have often wondered why a person couldn't put a left hand prop on and modify the shift linkage so the motor shifts into reverse but actually pushes forward. I know that in reverse the linkage is set up to not allow full throttle while in reverse, but I am sure there is a way around this. Unless I am mistaken, a counter-rotating lower unit has the same gearing, it is just the shift mechanism in the lower unit is shifting into the "reverse" gear instead of the "forward" gear. The gearing itself is identicle to a standard rotation lower unit, it just swaps what is forward and what is reverse. I would imagine any mods to be done would be inthe control box because that is where the throttle limitation takes place. Maybe even going to a control box that has seperate throtle and shift, then you have full throttle regardless of gear selection. If there is a throttle limiter in the two stick box for reverse, it could be eliminated. Anyone ever hear about anyone doing something like this?

 

[seahorse5]

Re: Counter Rotating a motor.

Back in '85 and '86, the Johnson and Evinrude counter-rotation outboards had the motors run the opposite direction. Then they came out with their counter-rotation gearcase.<br /><br />You cannot run a regular gearcase in reverse with a left hand prop to go forward for any length of time. The thrust bearing on the reverse gear is not made to run continuously under load and will disintegrate after a few hours of high speed running. The clutch dog lugs are also not cut to grab as well as the forward gear ones.

 

[mannyq]

Re: Counter Rotating a motor.

Just a blank question then from a mechanical standpoint?<br /><br />If the reverse thrust bearing takes the load when in reverse with a standard prop as it PULLS, wouldn't the thrust still be towards the front bearings since the reverse prop now PUSHING against the drive bearinq? <br />In other words, the primary thrust bearing will always be under load when when you're in reverse with a reverse rotation prop? Yes/No?<br />As far as the clutch dog goes, I could see a problem there.

 

[Bradster941]

Re: Counter Rotating a motor.

If shaft end is clockwise, how is counter rotation achieved in the gearcase?<br /><br />Is it a dual gear system like on the duo-props?<br />If so is the gear case body the same as standard rotating?<br /><br />Good question Helios, glad you posted it.

 

[seahorse5]

Re: Counter Rotating a motor.

The pinion, forward, and reverse gear teeth are angled for quiet operation and can handle higher torque loads. The angle forces the pinion gear up against it's large roller thrust bearing. Forward gear is forced agaist a full diameter thrust bearing, and reverse gear has a small diameter needle bearing to take its thrust. whenever an outboard is running, all 3 of the gears are turning. Since in most instances, reverse in not used for any long periods of time and not at full throttle, there is no need for a big thrust bearing in a regular gearcase. <br /><br />Stop by a dealer and ask to see a forward bearing with its good sized rollers and about 4" in diameter and compare it to the 2" diameter reverse bearing with its small needle bearings.<br /><br />A counter-rotation gearcase uses a tapered roller bearing in the aft gear that is encased and also uses a 2 piece prop shaft, since the propshaft thrust turning the propeller is in the opposite direction of the back gear thrust during normal operation.

 

[mannyq]

Re: Counter Rotating a motor.

Other than cancelling the torque, any other benefits or should I just leave things alone? Is it just a matter or replacing the gearset and bearing?

 

[Hooty]

Re: Counter Rotating a motor.

Seahorse speaks with straight tongue. If you look at a set of regular gears and a set of counter-rotating gears side by side, there's a big difference.<br /><br />c/6<br />Hooty

 

[captweed]

Re: Counter Rotating a motor.

Don't even think about it,he's exactly right.The forward gear in a rt. hand rotation is in the nose with heavy bearing,Left hand forward is toward the prop with heavy bearing.I have seen someone try to reverse shifter and prop,burned up.

 

[airman]

Re: Counter Rotating a motor.

I have no idea if this applies to any outboards at all but Volvo outdrives are built with equal sized gears and clutches for both directions. All you do is flip the shift linkage over for ****er-rotation. Very handy - only one spare leg for a twin engine boat.

 

[seahorse5]

Re: Counter Rotating a motor.

The Volvo upper gear unit where the shifting takes place, has a huge thrust bearing on each of the gears, so it does not matter which gear is "selected" as forward. Both gears are also identical, unlike outboards.