Thrust bearings

[K F Wheeler]

I'm curious as to how many people run thrust bearings on their prop shafts? I'm talking about bearings that would run up against the out-put end of the strut and ahead of the prop. Or for that matter lower unit? Been out of racing for about 19 years and I don't recall using them back then...
Thanks in advance
Ken W.

 

[Danny King]

Most guys use flex shafts that are clamped by a collet on the engine side. The cable changes length based on load, to a point. Thus making a thrust on the strut tricky. And not many do it.
a flex shaft with a square end that floats in the engine collet is used by some and can be thrust on the strut.
solid drives can be used with a thrust on the strut. But they are just starting to be used. And some thrust on the engine amd some on the strut.

 

[K F Wheeler]

Most guys use flex shafts that are clamped by a collet on the engine side. The cable changes length based on load, to a point. Thus making a thrust on the strut tricky. And not many do it.
a flex shaft with a square end that floats in the engine collet is used by some and can be thrust on the strut.
solid drives can be used with a thrust on the strut. But they are just starting to be used. And some thrust on the engine and some on the strut.

That's pretty much what I thought...

 

[Bradley Maglinger]

 

[K F Wheeler]

Ehhh... One or two...
Scale boat?
Ken

 

[rhomodel]

I use them on my 27 and 30 cc boat: has little balls that run in steel shells. Us square end at the engine output side so that there is no wind-up of the cable.

 

[Charles Perdue]

Sometime when you have a spare minute, this is on a normal cable drive....not a square drive, measure the clearance between the prop drive dog and the rear bearing on the stut, hold the cable collet with a wrench and twist the prop in the opposite direction of rotation about what you think the prop load is (remember that the actual engine torque output for our toy motors is most often measure in inch/oz or inch/lbs of torque) and then check the drive dog/strut bearing clearance again.

This is close to the actual wind-up of the cable length.........

It is much less of a wind up than most boaters think

Charles

 

[Tom Foley]

Of course there is , it is being driven on one end and meets resistance on the other end . The only reason for a square drive is to stop thrust load on the engine . some say driving from the strut but it doesn't matter in my opinion for what its worth .

 

[rhomodel]

I'm not saying the collet is no good: I just find the square drive easier, but then we use a different cable system than you us guys. Stub is 8 mm, not 1/4 inch as you guys use. As for the trust bearing: I used peek for many years but no use the bearings.. Just oil after each run..
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[Daniel's Racing]

It is not cable windup that eats up cable length with round drive.
It is the engine being shoved forward in the rubbers by entire force of thrust.
Inlines can easily eat 1/2" of gap.

 

[Charles Perdue]

I am not trying to tell anyone how to set up their boats. I am just trying to get some of the open minded to think a little about the effects that setups have and not take for fact some of the things they have been told.
I, for one, do not want the entire thrust load of the prop that drives the boat, to push against the engine that I have worked on to reduce friction. All of this load is pushing against smallest bearing in the engine that has the least amount of lubrication.
The square drive is one way to accomplish this, the wire drive is another and there are different ways if you so desire to put in the effort.

Charles

 

[Daniel's Racing]

For sure to each his own. Just different ways to do it and points of view as to why we choose one or the other.

The thrust doesn't push against the smallest bearing in the engine. The mains are the largest bearing.
The main bearings are in the crankcase and usually get all the lubrication they need being it is the wettest area of the engine.

So you would rather put the entire thrust on a tiny bearing at the drive with almost no way to get lubrication to it ? That kinda friction has to be greater drag than little extra push on the main bearings in engine that NEVER fails if you have real bearings not even with the thrust of a inline. Seems to be the easiest and most trouble free way to deal with the thrust is on the engine. Oh sure it would be nice if it wasn't there but when it has to go somewhere the engine is usually the best place IMO.

The gas wire drives push on the engine with a round collet just the same unless you set it up to also incorporate a thrust bearing at the rear too but almost all are fully pushing on the engine.

These were not mine but my buddies at the lake in Pompano.

Pat's Y-6 mono,
This one got a little warm. Melted the shaft while it was on the lake running. Finally stalls the engine when the prop swinging around out of center was too much load for engine to pull.

Daves inline Rico mono,
Shaft seizure. Horsepower is how many twist, torque is how tight the twist are. Lol.

 

[Charles Perdue]

Like I said...my post was about facts for open mined people........

You have a nice day.

Charles

 

[Daniel's Racing]

Yea. ??

I read the FACTS you posted for the OPEN MINDED.

 

[Brad Christy]

For sure to each his own. Just different ways to do it and points of view as to why we choose one or the other.

The thrust doesn't push against the smallest bearing in the engine. The mains are the largest bearing.
The main bearings are in the crankcase and usually get all the lubrication they need being it is the wettest area of the engine.

So you would rather put the entire thrust on a tiny bearing at the drive with almost no way to get lubrication to it ? That kinda friction has to be greater drag than little extra push on the main bearings in engine that NEVER fails if you have real bearings not even with the thrust of a inline. Seems to be the easiest and most trouble free way to deal with the thrust is on the engine. Oh sure it would be nice if it wasn't there but when it has to go somewhere the engine is usually the best place IMO.

The gas wire drives push on the engine with a round collet just the same unless you set it up to also incorporate a thrust bearing at the rear too but almost all are fully pushing on the engine.

These were not mine but my buddies at the lake in Pompano.

Pat's Y-6 mono,
This one got a little warm. Melted the shaft while it was on the lake running. Finally stalls the engine when the prop swinging around out out of center was too much load for engine to pull.

Daves inline Rico mono,
Shaft seizure. Horsepower is how many twist, torque is how tight the twist are. Lol.

Daniel,

This is factually not the case. With a direct collet set-up, the prop thrust is delivered ENTIRELY through the front (small) bearing that is just behind the flywheel. The big bearing serves only to support the pressure of compression and combustion from the rod/piston. Without the flywheel nut in place, theoretically, the crank would simply push out, through the intake opening in the engine, given no other restrictions.

Thanks. Brad.
Titan Racing Components
BlackJack Hydros
Model Machine and Precision LLC

 

[Bradley Maglinger]

Pat's Y-6 mono,
This one got a little warm. Melted the shaft while it was on the lake running. Finally stalls the engine when the prop swinging around out out of center was too much load for engine to pull.

Just curious if he was using roller bearings or teflon?

 

[Daniel's Racing]

Daniel,

This is factually not the case. With a direct collet set-up, the prop thrust is delivered ENTIRELY through the front (small) bearing that is just behind the flywheel. The big bearing serves only to support the pressure of compression and combustion from the rod/piston. Without the flywheel nut in place, theoretically, the crank would simply push out, through the intake opening in the engine, given no other restrictions.

Thanks. Brad.
Titan Racing Components
BlackJack Hydros
Model Machine and Precision LLC

Oh shoot. I thought we were talking gasoline engines. Sometimes I think I am in gas and actually in general.

Even when I ran CMB nitro's they did use the same bearing front and rear but yes I realize other nitro's do not. The small nitro engines often have a tight crank to bearing fit so both bearings are often taking some thrust.
Some small nitro's may not have any front bearing at all. Many of the small nitro's the crank fit in the crank is often tight enough that both bearings are accepting some thrust also as is evident when the bearings come out of cases attached to the crank still.

You can also make custom collars for crank between collet and the engine front bearing or a seal sleeve so the force is on the rear as much as you like or entirely.

Just curious if he was using roller bearings or teflon?

It was standard brass slip fit bushing that most of the guy's running welded stub shaft setup incorporate at the stinger/strut. He ran it completely dry for some time. Hard to believe it could melt the steel while submerged in the passing water.

 

[Brad Christy]

I thought we were talking gasoline engines. Even when I ran CMB nitro's they did use the same bearing front and rear but yes I realize other nitro's do not. The small nitro engines often have a tight crank to bearing fit so both bearings are often taking some thrust.
Some small nitro's may not have any front bearing at all. Many of the small nitro's the crank fin in the crank is often tight enough that both bearings are accepting some thrust also as is evident when the bearings come out of cases attached to the crank still.

You can also make custom collars for crank between collet and the engine front bearing or a seal sleeve so the force is on the rear as much as you like or entirely.



It was standard brass slip fit bushing that most of the guy's running welded stub shaft setup incorporate at the stinger/strut. He ran it completely dry for some time. Hard to believe it could melt the steel while submerged in the passing water.

Daniel,

Nope. There is never any linear force on the rear bearing in a cantilevered crank nitro engine. And you really don't want there to be, as the bearing is not shouldered in the case in that direction, and the bearing could be forced out of its bore.

Not meaning to be argumentative. Just don't want misinformation getting mixed in. I wouldn't want anybody taking it upon themselves to "fix" a problem, causing engine damage.

Thanks. Brad.
Titan Racing Components
BlackJack Hydros
Model Machine and Precision LLC

 

[Daniel's Racing]

The rules are by engine design and non of it is designed the same across the board. Try to stay out of small nitro engine conversations for that reason. Ended up here by mistake. Sorry.

Of course you wouldn't want to push on a bearing in the direction that would try to push it out. If that is what you were saying. I was again referring to mostly gas again at that point.

Any engine using a sealed bearing at the output end you can or most any four bearing engine you can put thrust on outer output bearings. They aren't going anywhere. Not real up on what you can do exactly with the crank bearings on every nitro but when case has a rear bearing as the last thing in the case instead of a seal setup you can push on it's inner race.

The .28 car engines I used to run had output bearing that could take thrust and bearing was shouldered in the case and will only come out towards the end of shaft.

Gas engines with 4 bearings the rear bearing isn't going anywhere. It is either locked in from going past where it sits by circlip or raised portion of the crankcase.

 

[K F Wheeler]

A little bit off topic but...
I've never seen the inside of these gas engines being run in these r/c boats (nitro fan). Are ANY of them running four bearings? If so, why???
Don't recall ever seeing four bearings in anything but four cycle engines. Most where bushings.