thrust bearing.....what's your take?

[martin]

Most thrust bearings like the ones we use on our motors have quite a low max rpm like under 7000-8000 rpm.

[madmikepags]

there's many ways to think about thrust. how bout if your motor is at an angle with just a J bend? does the thrust push the boat upward? and conversely if the motor is parallel to the hull does it make the boat stay more parallel to the water? just things to think about?? I've used thrust bearings at the strut, mostly because when I started boating the cheaper motors I used, the end bells were just pressed on and if there was any gap the thrust would sometimes push the endbell off the motor. I have also not used thrust bearings on boats and honestly have seen no difference either way??? I like the way the one piece Tamiya thrust bearings look and fit so I do use them on most of my boats.

[rickwess]

When installing the thrust washer at the motor, what is the proper order?

Motor - thrust - spacer - collect

or

Motor - spacer - thrust- collect

[runzwithsizorz]

kevinpratt823 quote;
"Imagine you are pushing the boat with a stick at the motor, as opposed to pushing the boat from the bottom of the transom with your finger......"
flraptor07 quote;
"Bingo, except you are altering the point at which the thrust is being applied."

Ah, an explanation even a dummy like me can understand. However, I was under the impression the use of the bearing was to absorb some of the pressure exerted by the expanding flex? and thus reducing fiction?
Thrust, to varying degrees, will always be there, but once on plane, and at speed is the bearing really having that much effect on thrust? (not pressure). If you had a wire drive, there would be no need at all, correct?
Which U-joint on a cars drive shaft receives more pressure/torque, front, or rear? Is it the same accelerating, as it is at cruise? What if the cars drive shaft were a flex, then which one?
Not trying to be difficult, just trying to understand how the bearings location could really alter the attitude of the hull.

[kfxguy]

I feel a gps test coming on......

[urbs00007]

thrust bearings

kevinpratt823 quote;
"Imagine you are pushing the boat with a stick at the motor, as opposed to pushing the boat from the bottom of the transom with your finger......"
flraptor07 quote;
"Bingo, except you are altering the point at which the thrust is being applied."

Ah, an explanation even a dummy like me can understand. However, I was under the impression the use of the bearing was to absorb some of the pressure exerted by the expanding flex? and thus reducing fiction?
Thrust, to varying degrees, will always be there, but once on plane, and at speed is the bearing really having that much effect on thrust? (not pressure). If you had a wire drive, there would be no need at all, correct?
Which U-joint on a cars drive shaft receives more pressure/torque, front, or rear? Is it the same accelerating, as it is at cruise? What if the cars drive shaft were a flex, then which one?
Not trying to be difficult, just trying to understand how the bearings location could really alter the attitude of the hull.

If you think about it logically, the boat doesnt know if the thrust is at the motor or strut. The only way you can alter the boats running attitude is by angling the strut or raising it up or down. The propeller is pushing the boat from right behind the strut. End of story.

[ray schrauwen]

If your motor has a lot of end play a thrust bearing can help out a lot and you don't have to account for how much end play when setting the gap for the drive dog.

[rickwess]

Can someone please explain the proper way to setup a thrust bearing?

[ls1fst98]

I run thrust bearings on outrunners. They only have a c-clip holding them together and the bearing takes the load off the c-clip. Reason its not needed in aircraft application is the frce is the opposite direction, forcing the motor tohold together. I believe same holds true for inrunners. In car application they get side load. In aircraft its being ulled to he front plate which is supprted by a motormount. The end bell which recieves most of the force is only held on by tiny screws.

[srislash]

When installing the thrust washer at the motor, what is the proper order?

Motor - thrust - spacer - collect

or

Motor - spacer - thrust- collect

You want the thrust washer to have the best footprint for both surfaces (forward and aft)Rick. So provided the spacer is big enough it wouldn't really matter which end it went on. Unless it is being used for clearance purposes.

I will say that after a good run of 4-5 mins at 34,000rpm you will get smoke from them. Hehe

[jcald2000]

The flex shaft does not expand under load it twists tighter.

[T.S.Davis]

You guys that run a thrust bearing at the strut, what do you do with the cable contraction?

Been stewing on this a couple days.

It is an interesting line of thinking that Mike was eluding to. The thrust has to be actually transferred into the body of the boat somewhere. My brain is thinking that transfer happens in one of three places.

At the motor: This would mean that the stuffing tube was relatively straight and there was a gap at the drive dog. This does have a risk of flex shaft whip. There is also a risk of actually knotting up the cable if it's off a tick or if the gap at the coupler is too large. If the transfer is happening at the motor then the pressure is applied at the motors tail bearing or if the tolerances were just right on both bearings. Or....you place a thrust bearing between the motor mount and the coupler. Pressure is then placed on a bearing designed for pressure transfer.

In the stuffing tub: This is either a nice smooth J or S bend. So the transfer happens where the flex smashes itself into the side of the tube as the prop pushes it forward. Makes the transfer between two pieces of metal or against the teflon liner. This is the most common I would guess. Down side, it feels like we get a relatively small pressure point. I don't know exactly what that looks like. It may be that transfer happens the entire length of outside bends in the tube. If you follow. Works 99% of the time though.

At the strut: Requires a thrust bearing or washers at the strut. You still have a J or S bend but only need just enough to stop any flex cable whip. Not sure what happens with cable shrinkage though. Hard to imagine it just doesn't happen.

It's pretty easy to argue that having a thrust bearing or not depends on how you built your boat. Only you are going to know if you have a mild J bend and have thrust at the motor. For anyone to say "you gotta have it" or " you don't need a thrust bearing" isn't really fair. You have to look at the boats build and take your best guess if you need one.

[rearwheelin]

You guys that run a thrust bearing at the strut, what do you do with the cable contraction?

Been stewing on this a couple days.

It is an interesting line of thinking that Mike was eluding to. The thrust has to be actually transferred into the body of the boat somewhere. My brain is thinking that transfer happens in one of three places.

At the motor: This would mean that the stuffing tube was relatively straight and there was a gap at the drive dog. This does have a risk of flex shaft whip. There is also a risk of actually knotting up the cable if it's off a tick or if the gap at the coupler is too large. If the transfer is happening at the motor then the pressure is applied at the motors tail bearing or if the tolerances were just right on both bearings. Or....you place a thrust bearing between the motor mount and the coupler. Pressure is then placed on a bearing designed for pressure transfer.

In the stuffing tub: This is either a nice smooth J or S bend. So the transfer happens where the flex smashes itself into the side of the tube as the prop pushes it forward. Makes the transfer between two pieces of metal or against the teflon liner. This is the most common I would guess. Down side, it feels like we get a relatively small pressure point. I don't know exactly what that looks like. It may be that transfer happens the entire length of outside bends in the tube. If you follow. Works 99% of the time though.

At the strut: Requires a thrust bearing or washers at the strut. You still have a J or S bend but only need just enough to stop any flex cable whip. Not sure what happens with cable shrinkage though. Hard to imagine it just doesn't happen.

It's pretty easy to argue that having a thrust bearing or not depends on how you built your boat. Only you are going to know if you have a mild J bend and have thrust at the motor. For anyone to say "you gotta have it" or " you don't need a thrust bearing" isn't really fair. You have to look at the boats build and take your best guess if you need one.

Perfectly said !image.jpg

[rearwheelin]

I think boats will run looser with a gap which I heard is better for racing. On my quad drive for a test I ran a gap and it mad the boat unstable when exiting corners . It would "break loose" and do unpredictable things. When I closed the gap and pushed the boat with its struts it became very planted and much more "behaved".

[Luck as a Constant]

thrust bearing.....what's your take?

It seems to me all the forward force delivered by the prop is directly transferred to the motor, since the only thing keeping the cable from sliding in and out IS the motor, and therefor, that energy is transferred thru the motor mount to the hull. Essentially the motor is using the mount to drag the boat thru the water...
At the motor makes most sense to me


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