C3 vs CN
- Thread starter rvich
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If you read a bearing application guide....
In reality, the bearing manufacturers specify that they should be mounted in a steel race/housing. Since they are mounted in an aluminum casting that grows with heat, the added shrink fit , when cold, will cause the outer race to close down on the rollers and prevent assembly or be too tight. The C3 clearance helps accomodate this imperfect application .
In reality, the bearing manufacturers specify that they should be mounted in a steel race/housing. Since they are mounted in an aluminum casting that grows with heat, the added shrink fit , when cold, will cause the outer race to close down on the rollers and prevent assembly or be too tight. The C3 clearance helps accomodate this imperfect application .
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One inspects the tracks and rollers under a strong light and magnification for a decision such as this , so a informed choice can be made .
Rebuild = All New . Overhaul = replace suspect / unserviceable / outside service limit components .
Rebuild = All New . Overhaul = replace suspect / unserviceable / outside service limit components .
rvich
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Let's see if I can articulate this in another manner...
My cases are sitting at Jim Comstock's with no bearings in them. They will be getting new ones despite the fact that I think there is nothing wrong with the old ones. So on to the bearings...
As an example, Old Britts still has some of the CN bearings left. They say they will not restock them once they are gone. This suggests to me that there is the possibility for preferance. There are bikes out there that have been running on CN bearings for over thirty years. They apparently haven't seized up from the tolerances being too tight. I am not an engineer but it seems to me that there must be a sweet spot, the closest tolerance possible without creating excess heat. I don't know if the recommendation to use C3 bearings is to get closer to the sweet spot or if it is the path of least liability.
As Dave says above, if when the cases are cold the fit is so tight you can't assemble the crank into the cases, this is a problem for sure. So I thought I would ask and see what the experience here says.
Russ
My cases are sitting at Jim Comstock's with no bearings in them. They will be getting new ones despite the fact that I think there is nothing wrong with the old ones. So on to the bearings...
As an example, Old Britts still has some of the CN bearings left. They say they will not restock them once they are gone. This suggests to me that there is the possibility for preferance. There are bikes out there that have been running on CN bearings for over thirty years. They apparently haven't seized up from the tolerances being too tight. I am not an engineer but it seems to me that there must be a sweet spot, the closest tolerance possible without creating excess heat. I don't know if the recommendation to use C3 bearings is to get closer to the sweet spot or if it is the path of least liability.
As Dave says above, if when the cases are cold the fit is so tight you can't assemble the crank into the cases, this is a problem for sure. So I thought I would ask and see what the experience here says.
Russ
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Gentlemen,
The reason why Andover Norton switched from standard bearing spec. to C3 was that all bearing manufacturers now work at the lowest possible tolerance within the norm. In the old days they tended to be at the other side of the scale, manufacturing techniques being more "liberal" then.
The problem first became apparent to me with the C2 bearings Triumph specified for the T140 engines (part # 70-2879), in that if one used those lower-than-normal tolerance bearings the crank would not turn as soon as bearing and crankcase had cooled down (I deal in Triumph spares in my German firm, too). I therefore switched to standard tolerance bearings for the Triumphs (part# 68-0625). Shortly afterwards we had the same experience with the Norton Superblends.
Amazingly, I had complaints only from two workshops- Mick Hemmings and my own engine man Rudi Kolano. The others must have banged the too-tight bearings into the crankcases no matter what, or got their C3 bearings from somewhere else- in most cases I tend to think the former. One "Norton Specialist" I asked about it had "never had any problems", neither had any of the British "Triumph specialists". Why did that not amaze me?
We therefore changed our spec for 06-4118 from standard to C3.
Joe Seifert
The reason why Andover Norton switched from standard bearing spec. to C3 was that all bearing manufacturers now work at the lowest possible tolerance within the norm. In the old days they tended to be at the other side of the scale, manufacturing techniques being more "liberal" then.
The problem first became apparent to me with the C2 bearings Triumph specified for the T140 engines (part # 70-2879), in that if one used those lower-than-normal tolerance bearings the crank would not turn as soon as bearing and crankcase had cooled down (I deal in Triumph spares in my German firm, too). I therefore switched to standard tolerance bearings for the Triumphs (part# 68-0625). Shortly afterwards we had the same experience with the Norton Superblends.
Amazingly, I had complaints only from two workshops- Mick Hemmings and my own engine man Rudi Kolano. The others must have banged the too-tight bearings into the crankcases no matter what, or got their C3 bearings from somewhere else- in most cases I tend to think the former. One "Norton Specialist" I asked about it had "never had any problems", neither had any of the British "Triumph specialists". Why did that not amaze me?
We therefore changed our spec for 06-4118 from standard to C3.
Joe Seifert
rvich
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So if the bearings being purchased are old stock, the CN is the new C3, but if you got your hands on old C3 stock, they would be outside of spec? Yikes!
Thanks for the information Joe, it is much appreciated. It sounds to me that if I want precission bearings I should stay away from old stock and buy newly manufactured bearings.
Russ
Thanks for the information Joe, it is much appreciated. It sounds to me that if I want precission bearings I should stay away from old stock and buy newly manufactured bearings.
Russ
http://www.nortonownersclub.org/support ... e-releases
crankcase-superblends-revisited-t6039-15.html#p59523
The FAG Standard Product catalog from 10 years ago lists the range of clearances and, on paper, it's possible to get a standard tolerance C3 bearing that is actually tighter than a C0, (CN). The bearings would be statistical outliers, so the likelihood of ever catching one is pretty slim. It's likely that the tolerance of standard issue bearings probably have improved over the years.
Clearances before installation
C1 5-15microns (for a 30mm ID bearing)
C2 5-30
C0 25-50
C3 45-70
C4 60-85
C5 85-110
15 years ago I installed a set of FAG C3 bearings. No resistance when the cases came together, but there was a notchiness when the crank turned. Took it apart and one of the bearings had marks plowed in the inner race. Replaced it, 20,000mi on it.
crankcase-superblends-revisited-t6039-15.html#p59523
The FAG Standard Product catalog from 10 years ago lists the range of clearances and, on paper, it's possible to get a standard tolerance C3 bearing that is actually tighter than a C0, (CN). The bearings would be statistical outliers, so the likelihood of ever catching one is pretty slim. It's likely that the tolerance of standard issue bearings probably have improved over the years.
Clearances before installation
C1 5-15microns (for a 30mm ID bearing)
C2 5-30
C0 25-50
C3 45-70
C4 60-85
C5 85-110
15 years ago I installed a set of FAG C3 bearings. No resistance when the cases came together, but there was a notchiness when the crank turned. Took it apart and one of the bearings had marks plowed in the inner race. Replaced it, 20,000mi on it.
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Patton,
A club is but a club, i.e. a gathering of enthusiasts of varying knowledge, so I tend to rather listen to professionals.
If two professionals, who have in the past shown they are competent in what they do, and one of them a master toolmaker to boot, tell me (and show me!) that the standard bearing spec has become too tight and if, after they told me that, they have built a great number of engines of which I have ridden some with the C3 bearings which work fine on road and track, I tend to believe them.
I cited the Triumph example to show this is not solely a Norton phenomenon.
I understand that our findings don't make the use of NOS any easier in that only AFTER one has put a bearing on the crank and into the crankcase one will find out how it fits (i.e. if it is too tight). I simply tried to answer a question raised, fully knowing this may present problems to people who have stock of bearings of unknown age.
Experience can sometimes not rationally explained. I know from experience Bosch spark plugs don't work in Brit Bikes (Norton/Triumph) for long, but Champions will go on indefinitely. Then again, Champion spark plugs failed immediately in BMW K100 engines where they were fitted as OE (!), whilst Bosch were indestructible in those engines. There is no logical explanation, but it helps if one knows these things.
Joe Seifert
A club is but a club, i.e. a gathering of enthusiasts of varying knowledge, so I tend to rather listen to professionals.
If two professionals, who have in the past shown they are competent in what they do, and one of them a master toolmaker to boot, tell me (and show me!) that the standard bearing spec has become too tight and if, after they told me that, they have built a great number of engines of which I have ridden some with the C3 bearings which work fine on road and track, I tend to believe them.
I cited the Triumph example to show this is not solely a Norton phenomenon.
I understand that our findings don't make the use of NOS any easier in that only AFTER one has put a bearing on the crank and into the crankcase one will find out how it fits (i.e. if it is too tight). I simply tried to answer a question raised, fully knowing this may present problems to people who have stock of bearings of unknown age.
Experience can sometimes not rationally explained. I know from experience Bosch spark plugs don't work in Brit Bikes (Norton/Triumph) for long, but Champions will go on indefinitely. Then again, Champion spark plugs failed immediately in BMW K100 engines where they were fitted as OE (!), whilst Bosch were indestructible in those engines. There is no logical explanation, but it helps if one knows these things.
Joe Seifert
rvich
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Thanks guys for the information. It makes a lot of sense that if at one time the CN bearings were closer to the 50 micron side of the range, but newer bearings moved to the closer side, this would put the C3 into the same area.
I also appreciate the link the earlier conversation on bearings. I missed it in my search because "C3" is not recognized by the search engine. It is interesting to me that the tech notes are more concerned with premature failure from hammering, which is exactly why I did not want to specify a looser bearing unless I knew why.
Russ
I also appreciate the link the earlier conversation on bearings. I missed it in my search because "C3" is not recognized by the search engine. It is interesting to me that the tech notes are more concerned with premature failure from hammering, which is exactly why I did not want to specify a looser bearing unless I knew why.
Russ
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