I'm looking for input on what the proper depth of insertion is of the square end of a flex shaft into the square collet on my Zenoah engine? I've read that 1/2" is sufficient, but I have personally experienced the flex shaft reaming out the square collet insert on my Shockwave 55. The flex shaft was factory installed with about 3/8" inserted into the collet so I'm certain that when the engine was up at speed, the shaft wound up and shortened enough to the point that little of the shaft was in the collet causing the reaming problem (I thought the flex shaft snapped as the boat just came to a standstill in the water, but the engine was running smoothly). Your feed back is appreciated.

I also have a question on the purpose of the "Shaft Saver"; a collar that attaches to the flex shaft near the collet. I don't understand how this could possible help do anything for the shaft except stiffen it at the point of attachment.

When you run a shaft that is welded instead of the collet, it prevents the shaft from sliding out of the stuffing tube and lost forever... If you're running an inline prop and rudder, it won't fall out. But if your rudder is offset and the shaft snaps or comes out of the engine collet, your prop and remainder of broken shaft could fall out. Hope this helps clarify things....

I haven't used square drives in a long time, but when I did, I would get as much of the square into the insert as possible. As you said, under load the cable shortens a little bit, so having just a little bit in the square insert could be asking for trouble.

As for the shaft saver, as mentioned it's for use with one piece shaft/flex cables...if the collet (compression type) at the engine comes loose for some reason, the flex and prop are free to slip right out of the stuffing tube/strut and fall into the lake. The shaft saver prevents it from doing so. Not used on square drive setups.

On SQUARE drive set up's the greatest wear induced to the connection area of the drive collet and square end of cable will be when SOFT a/v mounts are in use.
Vibration created by engine makes it shake up & down / back & forth more on soft than hard mounts. NEXT the LONGER the drive cable more the shortening under load further moving the cable in or out of collet pending load.
** So, what we try to have using square drive is fairly stiff mounts so engine position stays relatively consistent and alignment too cable accurate.
Cable movement within square drive collet limited to cables inward and outward movement due to torque loading .. this way wear of the slip joint which is the square cable to square hole is minimized

Scott wrote:
Good point on the mounts!