Does anyone use a thrust bearing between prop shaft and strut???

[maddmatt]

Hi, Building a SAW boat and wondering about placing a thrust bearing between prop shaft and strut. After a couple of passes my thrust washer shows some major wear due to the load. I found a perfect sized bearing that will fit the shaft (ID) and not exceed the strut width (OD). I thought about putting on some water proof grease and letting it rip. It would be for speed runs only and maybe not for recreational due to water exposure. I wonder what kind of rpm a quality bearing can handle? I will be spinning it about 45-50k rpm. Anybody know? I also thought it would remove the load from the motor bearings caused by the wear of the thrust washer and also reduce rolling resistance. What do you think about my idea??

[egneg]

Bearings are usually placed between the motor and collet. If you have excessive wear after the strut you don't have enough play due to the compression of the flex shaft.

[Rumdog]

Youneed a gap between the drive dog and strut. The width of the gap should be right around the diameter of your flex cable. The cable shrinks up under load, and this gap will allow it to without binding. No thrust washer, or bearing is needed.

[sundog]

Youneed a gap between the drive dog and strut. The width of the gap should be right around the diameter of your flex cable. The cable shrinks up under load, and this gap will allow it to without binding. No thrust washer, or bearing is needed.

That is, of course unless you have a 2-piece flex/prop shaft with the square end. In that case, no gap is needed and a thrust bearing would be suitable.

[maddmatt]

Hi Guys Thanks for the responses. I do leave a gap which is less than the end of the play of the motor about a 1mm not much. I wanted to put the load on the thrust washer instead of the motor bearing. Just the way I do it.

[Rumdog]

Not a good idea. It will eventually cause cable failure. Thrust bearing shoulg be used between the motor mount and collet.

[RaceMechaniX]

You can run ball bearings in your strut and use these to take up the thrust forces if you are using a square drive system. I would not recommend bearings in the strut for normal collet drives with flex cables as the flex cable will shrink with torque and the stub shaft will have to slide through the bearing bores. I have seen these lead to pulling the bearings out of the strut and causing a destroyed driveline. Wire Drives are an exception although it still a good idea to have a small gap in the strut for wires even if you are using bearings.

Pic is of a ball bearing strut with sqaure drive on the motor end.

[Fluid]

...I wanted to put the load on the thrust washer instead of the motor bearing. Just the way I do it.

The way you do it is risky, as others have pointed out. The cable will shrink under load, and if it is confined between the strut and motor it will cause excess drag, and will fail earlier. Some folks get away with it, but the only way to do it and avoid the shrinking cable problem is to use a square drive. Few FE boats use that.


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