Counter rotating drive

[Billd]

I recently purchased a complete counter rotating SE106 drive. Boat originally came with twin mercruiser 260s with I drives; both engines and original outdrives are standard rotation. Replaced port drive with counter rotation drive.
At WOT, port engine is 300 - 400 r.p.m. less than the starboard engine. Placed digital tach on both engines at WOT and confirmed the loss of r.p.m. on the port engine. Checked throttle cable, and the verified that the cable fully opens the linkage on the carburator.

Both props are the same pitch & diameter.

[Technical Support]

Your old lower unit may have been a 17/28 tooth gear set. The new unit is a 13/21. That might account for 100 RPM if you do the math. You should also be checking the props to make sure one of the blades isn't bent. Also the engine may not be making full power.

Tech Support

[Billd]

thanks for the reply. so you are saying the old drive may have different gear set - different from the new SE106? The difference is 300 - 400 rpm not 100.

Prior to installing the counter rotation drive, both engines were within 100 r.p.m. of each other at WOT.

I plan on replacing the props to see if this may be the issue

[Technical Support]

Yes,

They do not make the older style gearset anymore, so the only one you can get is the newer style. Unless the Starboard side has been rebuilt in the last 7 years or so, I would say they have different ratio's



Tech Support

[Billd]

Okay. I'll wait to see if the new props change anything.
the older drive has a 1.5:1 ratio, where the new (se106) drive has a 1.47:1 ratio.