Engine rotations ?

[tgilmore99]

Maybe a stupid question, but when do you use a reverse rotation motor. How do you know when to use a reverse rotation motor.
I am looking to re-power my 270 Sundancer. It has two 350/5.7L OMC motors. I am having issues so I am looking to replace. On this boat is it proper for both engines to turn the same direction. Would someone mind to answer some of these easy answers. Easy answers to some, unknown to others. Thanks

 

[Daddubo]

Generally on the newer boats the rotation is changed in the out drive or transmission I don't believe any one makes a reverse rotation engineany more.

Maybe a stupid question, but when do you use a reverse rotation motor. How do you know when to use a reverse rotation motor.
I am looking to re-power my 270 Sundancer. It has two 350/5.7L OMC motors. I am having issues so I am looking to replace. On this boat is it proper for both engines to turn the same direction. Would someone mind to answer some of these easy answers. Easy answers to some, unknown to others. Thanks

 

[Air O'Nautical]

If you stand behind your motors do they both spin to the left (standard)?
If one spins the other way you have a reverse rotation motor on that side.

 

[SevenTeas]

In most cases rotation is controlled by the outdrive(if its a sterndrive). With twins it could be interesting if the engines rotated in different directions and real hard to work on them. Watch the belts when the engines are running you should be able to tell if they are rotating the same direction. If your intent is counter rotating props swap one of the sterndrives for a counter rotating model.

 

[fc3]

Right hand (opposite) rotation engines were used in inboard boats. The transmissions did not run in reverse, the engines did. This was common in boats built up to the late 80s early 90s, I think. The older transmissions could not take the engines full output when in "reverse" so the engines were made to run in "reverse." If you don't have inboards, then you don't have a right hand rotation engine.

When Merc designed the second generation alpha, they designed it to counter rotate. The counter rotation is in the lower unit. Counter rotation in the Bravo is, I think, by running one drive in "reverse"

There were some interesting quirks with these engines. The engines turned opposite, so the starter was different and some accessories, like the raw water pump, ran backwards. In was now out, for example. They used gears instead of a timing chain, so the camshaft turned in the usual direction and so did the distributor, but the firing order was different and so was the camshaft. You had to watch when you ordered parts since some substituted left and right and some didn't. Alternators, for example, don't care which way you turn them.

 

[Daddubo]

I know Chris Craft in the 60’s would take a Small block Chevy and make it run backwards. They had their own distributer that went on a bell housing behind the engine. Not sure what they were trying to do maybe torque thrust issues on the wood hull, but those old single screw inboards would only back in one direction.

 

[JJCOTTE]

Right hand (opposite) rotation engines were used in inboard boats. The transmissions did not run in reverse, the engines did. This was common in boats built up to the late 80s early 90s, I think. The older transmissions could not take the engines full output when in "reverse" so the engines were made to run in "reverse." If you don't have inboards, then you don't have a right hand rotation engine.

When Merc designed the second generation alpha, they designed it to counter rotate. The counter rotation is in the lower unit. Counter rotation in the Bravo is, I think, by running one drive in "reverse"

There were some interesting quirks with these engines. The engines turned opposite, so the starter was different and some accessories, like the raw water pump, ran backwards. In was now out, for example. They used gears instead of a timing chain, so the camshaft turned in the usual direction and so did the distributor, but the firing order was different and so was the camshaft. You had to watch when you ordered parts since some substituted left and right and some didn't. Alternators, for example, don't care which way you turn them.

My 87 Weekender has a clockwise and a counter clockwise rotation. But that does allow it to use the same velvet drive tranny for both.