Angular contact bearing for collet setups?

[RaceMechaniX]

Guys,

Has anyone considered or tested using an angular contact bearing instead of a deep groove ball bearing on the output side of a nitro motor to cope with the thrust forces from a collet drive? I have noticed that the front bearings on the 67/80/91 motors don't last more than a weekend or two worth of racing when used with a collet drive compared to a square drive set-up where the bearings last considerably longer. I can't convert everything to square drive, but wonder if using an angular contact bearing would work? In theory, yes but what looking to see if anyone has input.

Tyler

 

[Mark Bullard]

It is a good thought. But that kind of bearing needs to be loaded which it would get when the boat is in the water. But it would not be a steady load. It may try to throw the balls out the front when the motor unloads. We had a 800 hp 900 rpm pump motor with a stack of three 7238 thrush bearings or angular contact bearings for the pump thrush. The city had a main break with this motor pumping a lot of water. when the pump unloaded it lifted the rotor which pick the bearings up. not a pretty site. Balls everywhere destroyed the shaft and done a lot of damage to the end housing that cares the bearings. Lot of machine work and lots of money to fix that one.

 

[Grimracer]

Strange.. on my 67s I have never lost a front bearing on a fixed drive...

Wonder whats going on..

Grim

 

[Joe Warren]

Mark is Dead on. a deaccelerating prop pulls on the shaft & Tries to unwind it.. unloading the angle brg that was happy running loaded. Smaller Shafts brg ID & hsg with bigger OD bearings are the answer. You need Bigger Balls to solve the problem. a larger bearing dont roll as many times in one revolution as a smaller bearing

 

[Ron B.]

If you are going thru bearing that fast your bearing supplier is selling you low grade bearings! T9H retainer with a C3 fit.

 

[Michael Costanzo]

If you are going thru bearing that fast your bearing supplier is selling you low grade bearings! T9H retainer with a C3 fit.

this^^^ never killed bearings in the big motors even when i was way lean on set up.hell even the boca bearings that every one said were **** lasted quite awhile with no issuses.

 

[RaceMechaniX]

My problem may be compounded with insufficient axial rotor clearance. With a new front bearing there is no contact from the rod on the rotor, but after several heats there is enough play that the rod is thrusting against the drum. This builds a lot of heat in the motor!

I believe there is minimal risk of the angular contact bearing losing its balls since the crank is captured by the rear bearing on the other end. The entire crank would have to shift several millimeters for this to happen and the balls would be captured by the inner wall of the crankcase. I have thought about adding a thin wave spring to maintain a minimal level of preload, but we'll see if I have room.

@Ron, the bearings are TH9/C3 fit bearings from a good vendor so I don't think that's the issue.

 

[Charles Perdue]

Hello Tyler, I may be able to help you a little on your problem. I use a sintered brass thrust washer between the drive dog and the strut. I then try to wind up the flex cable as tight as I can by holding the engine flywheel and twisting the prop by hand, then measure the distance required to clearance the thrust washer to split the thrust load between the thrust bearing/strut and the engine. This measurement is usually somewhere about .018 to .020 spacing between the drive dog, thrust washer and the strut.

This is the system that I used on the early BOSS boats on up to the boats that I build now. The also helps prevent the flex cable from pushing out against the inside of the stuffing tube on the outside of its arch, this helps reduce the drag similar to the square drive. NEVER had a problem with this system.

Maybe this will help you some....

Charles

 

[John Beardslee]

My problem may be compounded with insufficient axial rotor clearance. With a new front bearing there is no contact from the rod on the rotor, but after several heats there is enough play that the rod is thrusting against the drum. This builds a lot of heat in the motor!

I believe there is minimal risk of the angular contact bearing losing its balls since the crank is captured by the rear bearing on the other end. The entire crank would have to shift several millimeters for this to happen and the balls would be captured by the inner wall of the crankcase. I have thought about adding a thin wave spring to maintain a minimal level of preload, but we'll see if I have room.

@Ron, the bearings are TH9/C3 fit bearings from a good vendor so I don't think that's the issue.

Hi Tyler,

We also used to shim the end play to the flywheel collet as well usually between .001-.002 to prevent cramming the disk. We also tried the angular contact bearings years ago and at that time they didn't seem to be the answer, Jerry or Mike Betke may be able to chime in with more detail on their experience as well.

Thanks, John

 

[dave roach]

I would check the two bores between the two bearings in the case.You mite have a mislinement on the two bores taking out the bearings.

Dave Roach

 

[RaceMechaniX]

Tha

Hello Tyler, I may be able to help you a little on your problem. I use a sintered brass thrust washer between the drive dog and the strut. I then try to wind up the flex cable as tight as I can by holding the engine flywheel and twisting the prop by hand, then measure the distance required to clearance the thrust washer to split the thrust load between the thrust bearing/strut and the engine. This measurement is usually somewhere about .018 to .020 spacing between the drive dog, thrust washer and the strut.

This is the system that I used on the early BOSS boats on up to the boats that I build now. The also helps prevent the flex cable from pushing out against the inside of the stuffing tube on the outside of its arch, this helps reduce the drag similar to the square drive. NEVER had a problem with this system.

Maybe this will help you some....

Charles

Thanks charles, I will likely try this and possibly adding a wave spring between the drive dog and strut to give a little more safety factor on windup shrinkage.

The other option is having Dave Ripey make stub shafts with a square end at the right length and using a simple collar to keep the shaft from going out the back.

Thanks for all the replies guys.

 

[dwilfong]

Well The VAC .91 has the same bearing in it and thy don't last long. When I built the VAC 1.05 out of a VAC .91 with a RS 1.01 P/L in it thy failed in only a few runs. Wonder why?????????

Well I have run this eng now with the same bearings for some time. Even broke a rod in it and patched the block. But the new bearings are like new still.

Full complement ceramic hybrid bearings thy carry twice the load of a normal bearing. Problem solved...............

Wonder what Jeff is running in his 1.05........

 

[Mark Bullard]

So which way are you wanting to put them in. I assume you were going to place them so that the flex shaft would push against loading part of the bearing. If this is so the outside part of the bearing under the flywheel will have very little to hold the balls in place when the bearing unloads.

You may not have enough clearance on your rod. Also what is the bearing that you are using behind the crank. If I remember right your motor may be running a 6002 bearing. There are two different widths. One is 9mm and the other is 10mm I think. But if you have the wide one installed you have very little rod clearance if any and this will also load the front bearing which will cause it to have a very short life.

And lets not get started on ceramic bearings again. They are not for our motors.

 

[RaceMechaniX]

The 67/80 and 91HR/VAC all use the same bearings. 6000(10x26x8mm) up front and a 6002(15x32x9mm) in the rear. I would have to think a 10mm rear bearing would cause massive connecting rod misaligning so that's going to be mistakenly put it.

If I used an angular contact bearing on the front side, with the thrust force facing inwards towards the rear crank that means the the inner race would have to move towards the collet for the balls to become loose. I think there is little risk as the rear bearing and crank throw prevent the crank from moving outwards towards the collet.

First I need to pull the motor apart and check the rod to drum clearance and get that sorted.

Tyler

 

[Steve Anderson]

Hello Tyler, I may be able to help you a little on your problem. I use a sintered brass thrust washer between the drive dog and the strut. I then try to wind up the flex cable as tight as I can by holding the engine flywheel and twisting the prop by hand, then measure the distance required to clearance the thrust washer to split the thrust load between the thrust bearing/strut and the engine. This measurement is usually somewhere about .018 to .020 spacing between the drive dog, thrust washer and the strut.

This is the system that I used on the early BOSS boats on up to the boats that I build now. The also helps prevent the flex cable from pushing out against the inside of the stuffing tube on the outside of its arch, this helps reduce the drag similar to the square drive. NEVER had a problem with this system.

Maybe this will help you some....

Charles

Charles,

Is your .018 to .020 spacing the set clearance without the flex cable wound up?

I don’t understand how you determine how much of the thrust load is shared between the engine and the strut. Are you saying .040 or more clearance is 100% to the engine and .000 is 100% to the strut so .020 is shared 50/50?

 

[Daniel's Racing]

There is a lot more than just wind up to add up when figiuring how far forward the drivedog will be shoved.

You have wind up, you have the back and forth zizag path the cable takes under load and you have rubber engine mount deflection. Problem is none of these can be measured nor are they ever the same. Making contact in the rear is usually the surest way to rip a welded stub type of cable apart.

 

[Mark Bullard]

Tyler, What your trying to do is run the bearing backwards. This will not have good results. By looking at the picture the side your looking at is the thrust load side of the bearing. So to install you would face that side into the crankcase. This way it would take the load from the flex shaft. But as you can see at looking at the other side it is possible to have the balls come out the front.

 

[Steve Anderson]

Tyler, What your trying to do is run the bearing backwards. This will not have good results. By looking at the picture the side your looking at is the thrust load side of the bearing. So to install you would face that side into the crankcase. This way it would take the load from the flex shaft. But as you can see at looking at the other side it is possible to have the balls come out the front.

Mark,

How can the balls come out without there first being a huge axial shift to the races?

 

[Steve Anderson]

delete

 

[Terry Keeley]

I remember the Betke's played with NDH angular contact bearings years ago, maybe they'll chime in.

I could see where running one on the front (small) bearing might help if you're taking the shaft thrust on the motor. They're obviously better with axial loads than regular bearings.

I don't know why people say they're having problems with bearings in the VAC 91, I've got a bunch of runs on mine now with no problems. I do check the end play of the flywheel on my motors every 25 runs or so (front bearing clearance) and if it's greater than 0.008" or so I replace the bearings, otherwise I usually replace them after 100 runs or so.