Interesting bearing thought for main bearings.
11-15-07, 09:00 PM
#1
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Interesting bearing thought for main bearings.
Heres a thought I had the other day about replacing main and rotor bearings in our engines, now I'm not a bearing expert or engineer so feel free to tell me I'm stupid.
I pressed a set of main bearings out of a set of stationary gears yesterday and have been thinking of multi-peice e-shafts as well. I thought of replacing the journal bearing that normally presses into the stat gears and rotors with large roller bearings. Similar to this:
Obviously something thinner and wider, but something that could press into the stat gears and rotors. Then machine 5 sections for an e-shaft.
The first section would get pressed into the roller bearing in the front stat gear with your regular sized front shaft with key-way for the front cover assembly sticking out. On the inside part of the engine the front e-shaft section would be tapered and splined to accept the front rotor section of the eshaft which would be pressed into the roller bearing inside the rotor.
Heres a very crappy paint drawing:
Thats just the front section of the engine, if it continued to the rear, there would be 5 e-shaft sections all coupled together by tappered splines. Including a main bearing in the center iron to prevent e-shaft flex.
Doing this you'd need to machine a complete new e-shaft but it would not have to have a perfect finish on it since the bearings would just be pressed onto the seperate sections.
Now obviously I haven't thought this right through because I dont really know what to do for oiling these bearings or how to hold the e-shaft all together (maybe a bolt down the center of it?)
But anyways....I'd like to hear other opinions on this idea. No harm in putting it out there!
I pressed a set of main bearings out of a set of stationary gears yesterday and have been thinking of multi-peice e-shafts as well. I thought of replacing the journal bearing that normally presses into the stat gears and rotors with large roller bearings. Similar to this:
Obviously something thinner and wider, but something that could press into the stat gears and rotors. Then machine 5 sections for an e-shaft.
The first section would get pressed into the roller bearing in the front stat gear with your regular sized front shaft with key-way for the front cover assembly sticking out. On the inside part of the engine the front e-shaft section would be tapered and splined to accept the front rotor section of the eshaft which would be pressed into the roller bearing inside the rotor.
Heres a very crappy paint drawing:
Thats just the front section of the engine, if it continued to the rear, there would be 5 e-shaft sections all coupled together by tappered splines. Including a main bearing in the center iron to prevent e-shaft flex.
Doing this you'd need to machine a complete new e-shaft but it would not have to have a perfect finish on it since the bearings would just be pressed onto the seperate sections.
Now obviously I haven't thought this right through because I dont really know what to do for oiling these bearings or how to hold the e-shaft all together (maybe a bolt down the center of it?)
But anyways....I'd like to hear other opinions on this idea. No harm in putting it out there!
11-15-07, 09:15 PM
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Five points to build error?
I think you could go with the same idea used in 2-cycle engines and other equipment. The inner bearing race is the shaft itself. You could then use a 2-piece shaft.
I think you could go with the same idea used in 2-cycle engines and other equipment. The inner bearing race is the shaft itself. You could then use a 2-piece shaft.
11-15-07, 11:05 PM
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http://www.fc3spro.com/TECH/HOF/eshaft01.jpg
http://www.fc3spro.com/TECH/HOF/eshaft02.jpg
Do you really want to machine it smaller there to have it be able to fit into the pressed in end sections? That'll be a weak area in the rear, those pics are of the front, but it shows that the shafts aren't indestructable and they can and will shear off at that point
A better idea would be to use the shaft as a race and press in the bearing into the stat gear, if you can get one thin enough and use this with a pre-existing 2-piece eccentric shaft. You'll be seriously limited by the tight gap between the componenets, as it's designed to only accomodate the thickness of the bearing, and not seperate races and rollers. That sort of bearing with very skinny rollers is called a needle bearing by the way. I've heard them being referenced for use in really high rpm engines for the rotor bearings, but have no info on this.
Besides, you forgot to think about the most important thing, what is this meant to accomplish and can it be done in a simpler, easier, or already existing way and why will someone be willing to pay to have it done?
http://www.fc3spro.com/TECH/HOF/eshaft02.jpg
Do you really want to machine it smaller there to have it be able to fit into the pressed in end sections? That'll be a weak area in the rear, those pics are of the front, but it shows that the shafts aren't indestructable and they can and will shear off at that point
A better idea would be to use the shaft as a race and press in the bearing into the stat gear, if you can get one thin enough and use this with a pre-existing 2-piece eccentric shaft. You'll be seriously limited by the tight gap between the componenets, as it's designed to only accomodate the thickness of the bearing, and not seperate races and rollers. That sort of bearing with very skinny rollers is called a needle bearing by the way. I've heard them being referenced for use in really high rpm engines for the rotor bearings, but have no info on this.
Besides, you forgot to think about the most important thing, what is this meant to accomplish and can it be done in a simpler, easier, or already existing way and why will someone be willing to pay to have it done?
11-16-07, 12:13 AM
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Why reinvent the wheel when its not broken? Sorry I don't see any reason for them. In the intermediate housing to eliminate flex ok, but I just dont see a use. Cool thinking though.
11-16-07, 01:53 AM
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I can see wanting needle bearings with the idea to reduce friction for maybe more power and to possibly help fix wear or spun bearing issues with really high rpm's. But the shaft is supported by the oil pressure anyway, so there's not much friction to start with (it'll be small compared to that of the seals) and the bearings don't seem to be a problem for high rpms in particular (There's competition bearings that are meant to handle the high speeds better), or at least I don't see people complaining about them.
Good for you for thinking outside the box though.
Good for you for thinking outside the box though.
11-16-07, 05:57 PM
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I assumed you wouldn't, but I still think you would have a hard time keeping total clearance of all the pieces added together to an acceptable level. I also believe there would be strength problems. And how do you fasten them at assembly without excessive pounding, pressing, or beating of press fit pieces if you plan on no clearance between the pieces?
Actually I'm intrigued by the idea. I'm sorry if you thought I was scoffing at it. With a center bearing, 2-piece shaft, and using the shaft as the inner race it surely seems possible.
Actually I'm intrigued by the idea. I'm sorry if you thought I was scoffing at it. With a center bearing, 2-piece shaft, and using the shaft as the inner race it surely seems possible.
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11-16-07, 06:31 PM
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I can see wanting needle bearings with the idea to reduce friction for maybe more power and to possibly help fix wear or spun bearing issues with really high rpm's. But the shaft is supported by the oil pressure anyway, so there's not much friction to start with (it'll be small compared to that of the seals) and the bearings don't seem to be a problem for high rpms in particular (There's competition bearings that are meant to handle the high speeds better), or at least I don't see people complaining about them.
Good for you for thinking outside the box though.
Good for you for thinking outside the box though.
So you guys think using the shaft as the inner race would be better than having a full bearing that just presses onto the shaft and into the stat gears/rotors? Hmmm well theres a thought... Maybe that way it could just be a 2 peice shaft instead of multiple.
Those pictures from above of the broken e-shaft are probably partially because of a bearing failure or excessive clearance. With a needle bearing design that shouldn't be a problem....or would it? Like I said, I'm not engineer or bearing expert so I'm just thowing ideas out there.
11-16-07, 08:05 PM
#9
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Maybe we need to concentrate on the source of the problem and beat the drivers who over-rev the engines 
. Seriously though, some nice solid drivetrain mounts and some good solid shifter bushings should help reduce such occurances.
I think you'll HAVE to use the shaft as a race, not that it's a good idea to do so due to wear, but the severe space restrictions would seem to necessitate it, if one will even fit in the first place. It's a nice hard, smooth surface though which is good though. From what I've heard the mating surfaces for the bearings on the other side aren't exactly perfectly smooth, so you'd need a race there. Either way you could press the races on prior to the assembly of the motor and assemble the bearings while you're building the engine, then there's no need to do a 5 piece e-shaft or anything crazy like that.
The e-shaft picture was more to show that having it narrow down a bunch in there in order to fit the one splined bit into the other isn't a good idea as it'll severely weaken the part and that they're not exactly indestructable now. A hard drag lauch could probably shear it right off at the back of the engine. A needle bearing could fail too if the loads are high enough, it may not seize, but it could still be damaged.
Even if you can get the bearings to survive, if you over-rev it to, say 15k, then it should probably get looked at anyway because who knows what else might have been damaged right?
. Seriously though, some nice solid drivetrain mounts and some good solid shifter bushings should help reduce such occurances.I think you'll HAVE to use the shaft as a race, not that it's a good idea to do so due to wear, but the severe space restrictions would seem to necessitate it, if one will even fit in the first place. It's a nice hard, smooth surface though which is good though. From what I've heard the mating surfaces for the bearings on the other side aren't exactly perfectly smooth, so you'd need a race there. Either way you could press the races on prior to the assembly of the motor and assemble the bearings while you're building the engine, then there's no need to do a 5 piece e-shaft or anything crazy like that.
The e-shaft picture was more to show that having it narrow down a bunch in there in order to fit the one splined bit into the other isn't a good idea as it'll severely weaken the part and that they're not exactly indestructable now. A hard drag lauch could probably shear it right off at the back of the engine. A needle bearing could fail too if the loads are high enough, it may not seize, but it could still be damaged.
Even if you can get the bearings to survive, if you over-rev it to, say 15k, then it should probably get looked at anyway because who knows what else might have been damaged right?
11-16-07, 10:18 PM
#10
spoon!
There's a problem here though, and it ties into why they use journal bearings. Using small diameter needle bearings like that, the velocities get silly really quickly. It's going to be a pain in the *** to keep them from just starting to skid, and because of the stress levels on them... they're going to wear to the point where they do that pretty quickly. And be more susceptible to over-rev.
That and the shaft is one of the things that's going to keep the rotors from skewing and contacting the irons, so doing anything to reduce the cross-sectional area of it would be counter-productive.
That and the shaft is one of the things that's going to keep the rotors from skewing and contacting the irons, so doing anything to reduce the cross-sectional area of it would be counter-productive.
11-16-07, 10:36 PM
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There's a problem here though, and it ties into why they use journal bearings. Using small diameter needle bearings like that, the velocities get silly really quickly. It's going to be a pain in the *** to keep them from just starting to skid, and because of the stress levels on them... they're going to wear to the point where they do that pretty quickly. And be more susceptible to over-rev.
That and the shaft is one of the things that's going to keep the rotors from skewing and contacting the irons, so doing anything to reduce the cross-sectional area of it would be counter-productive.
That and the shaft is one of the things that's going to keep the rotors from skewing and contacting the irons, so doing anything to reduce the cross-sectional area of it would be counter-productive.
11-16-07, 10:57 PM
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I have worked with engineers in the past who have worked with the formula one setups and have personally seen how cam roller bearings hold up in NASCAR cup engines at 4,500 rpm. Kenku is right you are going to increase performance at a sacrifice of longevity. After one race our cam roller bearings looked like a bag of *** and needed to be replaced. They would probably handle over-rev very well if the usage on them is within a certain limit, after that the amount of abuse they could take would be significantly less.
A roller bearing has less load bearing surface area. This increases the rate of wear at the points of contact. This is also why if you tear into a mazda pickup truck transmission and an RX-7 transmission of similar years you will find the truck has bushings and the RX-7 will have roller bearings instead. This is because the bushings can take more load and will last longer with the loads the truck would put on them.
Also a perfectly smooth surface is not always ideal, to keep the rollers working properly you will actually need a slightly rougher RA finish, otherwise the needles stop rolling and will skip across the oil eventually causing galling and bearing failure.
For these reasons it would never be economical and only have practical use on race circuit cars where frequent replacement would be acceptable.
A roller bearing has less load bearing surface area. This increases the rate of wear at the points of contact. This is also why if you tear into a mazda pickup truck transmission and an RX-7 transmission of similar years you will find the truck has bushings and the RX-7 will have roller bearings instead. This is because the bushings can take more load and will last longer with the loads the truck would put on them.
Also a perfectly smooth surface is not always ideal, to keep the rollers working properly you will actually need a slightly rougher RA finish, otherwise the needles stop rolling and will skip across the oil eventually causing galling and bearing failure.
For these reasons it would never be economical and only have practical use on race circuit cars where frequent replacement would be acceptable.
11-16-07, 11:20 PM
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Well obviously there'd need to be a more detailed study into this before any action is taken to make sure such things don't happen. Then the bearings would need to be selected based on sound engineering practice. Generally I don't see it happening, and don't see it being that helpful in making an engine live longer or better survive stratospheric revs, other things will break instead.
Just stick with a 2 piece shaft and lightened rotors (less force) then add some competition rotor bearings, some windowed mains, keep the oil pressure up and do the oil loop line to ensure good pressure to the front bearing (better support the force) and it should survive quite well. Having that center bearing will help reduce the incidence of spun bearings by keeping shaft flex in check so the shaft doesn't **** sideways in the bearing and it'll spread the loads out on a larger area, both of which will help to keep the shaft from making hard contact on the bearing.
Just stick with a 2 piece shaft and lightened rotors (less force) then add some competition rotor bearings, some windowed mains, keep the oil pressure up and do the oil loop line to ensure good pressure to the front bearing (better support the force) and it should survive quite well. Having that center bearing will help reduce the incidence of spun bearings by keeping shaft flex in check so the shaft doesn't **** sideways in the bearing and it'll spread the loads out on a larger area, both of which will help to keep the shaft from making hard contact on the bearing.
11-17-07, 10:50 AM
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It's been done. For reasons mentioned above, it doesn't work well. Back in the day, SCOOT used to do this but I don't think anything ever came of it. Journal bearings are highly reliable, and won't send needles through the engine if they fail...
11-19-07, 02:38 PM
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^Interesting picture Aaron, is that a picture from Scoot?
So your saying that the roller bearings could possibly increase the performance because of less resistance? But wouldn't last very long...
I have worked with engineers in the past who have worked with the formula one setups and have personally seen how cam roller bearings hold up in NASCAR cup engines at 4,500 rpm. Kenku is right you are going to increase performance at a sacrifice of longevity. After one race our cam roller bearings looked like a bag of *** and needed to be replaced. They would probably handle over-rev very well if the usage on them is within a certain limit, after that the amount of abuse they could take would be significantly less.
A roller bearing has less load bearing surface area. This increases the rate of wear at the points of contact. This is also why if you tear into a mazda pickup truck transmission and an RX-7 transmission of similar years you will find the truck has bushings and the RX-7 will have roller bearings instead. This is because the bushings can take more load and will last longer with the loads the truck would put on them.
Also a perfectly smooth surface is not always ideal, to keep the rollers working properly you will actually need a slightly rougher RA finish, otherwise the needles stop rolling and will skip across the oil eventually causing galling and bearing failure.
For these reasons it would never be economical and only have practical use on race circuit cars where frequent replacement would be acceptable.
A roller bearing has less load bearing surface area. This increases the rate of wear at the points of contact. This is also why if you tear into a mazda pickup truck transmission and an RX-7 transmission of similar years you will find the truck has bushings and the RX-7 will have roller bearings instead. This is because the bushings can take more load and will last longer with the loads the truck would put on them.
Also a perfectly smooth surface is not always ideal, to keep the rollers working properly you will actually need a slightly rougher RA finish, otherwise the needles stop rolling and will skip across the oil eventually causing galling and bearing failure.
For these reasons it would never be economical and only have practical use on race circuit cars where frequent replacement would be acceptable.
So your saying that the roller bearings could possibly increase the performance because of less resistance? But wouldn't last very long...
11-20-07, 09:54 AM
#18
I am an engineer at a company that designs and builds mud pumps for drilling. Our pumps go up to 3000 hp. We use roller bearings everywhere. We have a couple of competitors that use babit sleeve bearings. We tested a competitors pump vs one of ours in terms of mechanical efficiency. Ours tested at around 95% mechanical efficiency and the competitor without the roller bearings tested at around 75%. An oil temperature test showed where this energy was going. Our oil stays literally a few degrees above ambient temperature. It's amazing. We also aren't running through a hot internal combustion engine so heat is different from a car engine. The competitors oil temps were at about 180 degrees. Their oil is used as a bearing. That's what it does in a babit "bearing".
Bearings make a huge difference. Keep in mind we are turning at 120 rpms and not thousands so this doesn't mean that rollers are a good solution for a car engine. I've looked into using them but I am most worried about longevity. The rollers would be very small and would be turning very fast. Our oil is used to cool rotors too so oil temps would likely not change appreciably even if rollers worked good. I'm still willing to try it though just to see what would happen.
One problem has been finding a bearing that wouldn't require machining down the e-shaft. If you just press out the bearing from a stationary gear, you don't have much clearance. You need more. I just miked an e-shaft and got a usable diameter of 43.16 mm where the bearing rides. This may vary slightly shaft to shaft based on wear. 36 mm is as small as you can machine down the shaft for bearing room and still have threads for the e-shaft nut on the back. You can't really do much on the stat gears as they are fairly thin already. I pressed out a bearing and got 46.85 mm. That leaves us a little bit over 10 mm of room for roller bearing thickness.
I found a roller bearing in 2 widths. The relevant one is 20 mm. You'd need to use 2 of them side by side for a total of 40 mm. They have an inner and outer race and measure 37 mm inner and 47 mm outer which is within our machinable area on the e-shaft. That's the skinniest ones that I can find that have a decent load rating. These will give you a 100,200 psi static load rating. That's alot. The dynamic load rating however is 56,400 psi. Again that sounds like alot but I have yet to calculate what the dynamic load of the engine is at peak rpm. It may or may not be enough. Even if it is, you need a safety factor. For production pieces we shoot for 1.3:1 on things like belts but much higher on bearings. We like nearly 10:1. When our pumps fail it's usually a bearing that does it. Keep in mind that with our high safety factor, that's usually nearly 20 years down the line! I'll have to figure this all out in regards to a rotary someday. I deal with the same thing for pumps everyday.
Even with a bearing that will fit, you will have to machine the eshaft. That means rebalancing the rotating assembly. That's doable though. My biggest concern is internal engine clearance. I have yet to figure out how to set e-shaft play. For a good roller bearing to work and be reliable, it needs to be pressed on tight. If it's not, it may still work but wear will go up. If it is pressed on tightly, assembling the motor would be next to impossible and you can't set end play.
There is alot to think about with rollers in car engine. We don't have these concerns on mud pumps which makes things easier for us.
Bearings make a huge difference. Keep in mind we are turning at 120 rpms and not thousands so this doesn't mean that rollers are a good solution for a car engine. I've looked into using them but I am most worried about longevity. The rollers would be very small and would be turning very fast. Our oil is used to cool rotors too so oil temps would likely not change appreciably even if rollers worked good. I'm still willing to try it though just to see what would happen.
One problem has been finding a bearing that wouldn't require machining down the e-shaft. If you just press out the bearing from a stationary gear, you don't have much clearance. You need more. I just miked an e-shaft and got a usable diameter of 43.16 mm where the bearing rides. This may vary slightly shaft to shaft based on wear. 36 mm is as small as you can machine down the shaft for bearing room and still have threads for the e-shaft nut on the back. You can't really do much on the stat gears as they are fairly thin already. I pressed out a bearing and got 46.85 mm. That leaves us a little bit over 10 mm of room for roller bearing thickness.
I found a roller bearing in 2 widths. The relevant one is 20 mm. You'd need to use 2 of them side by side for a total of 40 mm. They have an inner and outer race and measure 37 mm inner and 47 mm outer which is within our machinable area on the e-shaft. That's the skinniest ones that I can find that have a decent load rating. These will give you a 100,200 psi static load rating. That's alot. The dynamic load rating however is 56,400 psi. Again that sounds like alot but I have yet to calculate what the dynamic load of the engine is at peak rpm. It may or may not be enough. Even if it is, you need a safety factor. For production pieces we shoot for 1.3:1 on things like belts but much higher on bearings. We like nearly 10:1. When our pumps fail it's usually a bearing that does it. Keep in mind that with our high safety factor, that's usually nearly 20 years down the line! I'll have to figure this all out in regards to a rotary someday. I deal with the same thing for pumps everyday.
Even with a bearing that will fit, you will have to machine the eshaft. That means rebalancing the rotating assembly. That's doable though. My biggest concern is internal engine clearance. I have yet to figure out how to set e-shaft play. For a good roller bearing to work and be reliable, it needs to be pressed on tight. If it's not, it may still work but wear will go up. If it is pressed on tightly, assembling the motor would be next to impossible and you can't set end play.
There is alot to think about with rollers in car engine. We don't have these concerns on mud pumps which makes things easier for us.
11-20-07, 10:26 AM
#19
spoon!
rotarygod, do you have a part number or anything? I seem to recall that once when I was looking out of curiosity I couldn't find anything applicable, but that was a while ago. I'm kinda tempted to try experimenting.
11-20-07, 11:32 AM
#20
I forgot which catalog I saw it in. It's either timken, NSK, or URB. We deal with each of them (except our bearings are several feet in diameter!). I need to go figure it out again. I remember inner and outer diamters and the fact that they are needle rollers. That shouldn't be too hard to locate again. Keep in mind that you will have to turn down the eccentric shaft on a lathe to make them fit and do very minor lathe work on the stat gears. Just a few thousandths though.
If the problem of assembly and setting internal clearances can be solved, then it would also be possible to use rollers on the rotors as well. One problem at a time. I suspect this is why we don't see them. It's a pain in the ***!
If the problem of assembly and setting internal clearances can be solved, then it would also be possible to use rollers on the rotors as well. One problem at a time. I suspect this is why we don't see them. It's a pain in the ***!
Last edited by rotarygod; 11-20-07 at 11:46 AM.
11-20-07, 12:27 PM
#21
spoon!
Yeah, I've got a lathe and shitloads of spare 12A e-shafts, which is why I was pondering it. Like I mentioned before in the thread, running numbers through my textbooks say that it isn't going to last but... well hell, textbooks are an inexact representation of reality anyway.
I have to wonder if they'd seal well enough to have any oil flow to the rotors.
Probably not worth the trouble, but hell it's just time and tooling.
I have to wonder if they'd seal well enough to have any oil flow to the rotors.
Probably not worth the trouble, but hell it's just time and tooling.
11-20-07, 12:48 PM
#22
Oil cools the rotors so you still need to have that. You also need to have a hole in the outer race of the rollers to get oil flow into the bearings. Although they aren't babit bearings, they do need lubrication.
If you could use a 3rd main bearing as the Guru shaft does, your bearing stresses go down as you now have more bearing area. That would make a difference in lifespan but creates other issues of course. You'll be limited to only one 20 mm bearing in the center though. You wouldn't get 50% more bearing but it's still more.
I am skeptical about longterm use. I have no doubt that it will work in the short term. Another issue with bearing life is engine rpm. Higher rpm's hurt bearing life. Rollers will probably work fine up to a certain rpm cap. I don't know what that is though. This rule holds true with all bearings though. More rpm's means less longevity. More power at a lower rpm is easier on the engine than less power at a higher rpm. Within reasonable limits of course.
I'll eventually try to calculate this all out to see what it "should" do on paper. Real world results can vary. That's why people test! I don't know when I'll get to it though. It's not really a priority.
If you could use a 3rd main bearing as the Guru shaft does, your bearing stresses go down as you now have more bearing area. That would make a difference in lifespan but creates other issues of course. You'll be limited to only one 20 mm bearing in the center though. You wouldn't get 50% more bearing but it's still more.
I am skeptical about longterm use. I have no doubt that it will work in the short term. Another issue with bearing life is engine rpm. Higher rpm's hurt bearing life. Rollers will probably work fine up to a certain rpm cap. I don't know what that is though. This rule holds true with all bearings though. More rpm's means less longevity. More power at a lower rpm is easier on the engine than less power at a higher rpm. Within reasonable limits of course.
I'll eventually try to calculate this all out to see what it "should" do on paper. Real world results can vary. That's why people test! I don't know when I'll get to it though. It's not really a priority.
11-20-07, 01:14 PM
#23
spoon!
I'm rather more than just skeptical about long-term use, but a lifespan of (to pull numbers out of thin air) 5-10 hours with a 9500rpm cap? For some purposes that might be enough to be useful if the efficiency gains are statistically significant.
11-20-07, 04:59 PM
#24
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Yeah this is the kinda info I like to hear, someone who deals with stuff like this. Thanks rotarygod. I talked to a couple bearing companies like NTN here in Canada and they told me the highest rpm roller/needle bearing they make is for 10,000rpm....then the cage that holds the needles in place break and would cause the same damage as in the pic Aaron posted above.
11-21-07, 01:06 PM
#25
I've found bearings that can go as high as 11,000 that fit the needed size range. The problem is the load ratings. I can't find a heavy duty needle roller that will fit in this space. I can only find standard duty bearings. I doubt highly they would live long. I'm still looking. Next time our bearing guy stops by, I'll ask him if can find anything.