Case bearings dropping out easily!

[tony27]

C3 is the internal clearance spec of the bearing & is generally used for main bearings, has more clearance between the balls & races to allow for expansion than a standard bearing

[oldfart]

As above....... C3  is a number/ letter on a  bearing ... it relates to bearings that spin at high-speed thus they have a tolerance built into the race ( were balls spin )  ie   Very low torque. High loads. Heavy interference fits. High temperature. Preloaded

[alexbrown64]

Thats what i love about this place.  Can always get a good answer.  Thanks... i guess the C3 bearings would help but tolerance for centering while machining would still have to be perfect i would imagine and im sure a good machine shop would be spot on with that.

[Tomas]

Tomas, the link you sent had some great ideas on case machining.  It is however, $130 US per side for machining and ring.  This is ok when you have a rare case or due to age they have all become like that as you wont get much change out of $400 AU for a pair including post both ways but it is still a great option.  Simo, can you give me the guys number... i suspect locally it cost more but i could ring him in the new year and discuss options.  I may go with a second set of cases just to have some spares.  Then keep the really worn ones to get machined in the future.  Sleepy, do you know anyone in OZ that does the machining and press fitting?  Here in WA, its over $100 an hour for most workshop jobs so it can become prohibitive unless it is really necessary.  I have all new bearings and seals for the bike which are all OEM (mostly Koyo), exept the mains which are AllBallsRacing but still have "Koyo, Japan" stamped on them.
Cheers,
Alex

Sorry Alex. The link is just to see how it is done. of course it can be done localy for about $150-180 a side. i had mine done for 180 back in Sydney. Greg Ball in Sydney is realy good but a good machine shop or motorcycle engenering shop should be able to do this job.Try Ray Esson in Bayswatter or Robert Cameron in Burswood. You need to set it up on milling machine using oil seal diameter which is concentric with bearing diameter and is not floged out. Also have to check faces to make sure everything is sqare. Diameter should be machined to -0.05 to get good interference fit. Aluminium expands more than steel. It is good to have bore gage or inside micrometer to see what your machinist have done if you dont trust anyone 

[Momus]

The C number refers to the ball bearings internal clearance. It is not a specification for an incrementally different race outside diameter. The standard bearings for 2 stroke mains are C3. CN is the usual fit for non main applications like motor armatures, gearbox shaft support. C3 is looser than CN, C2 is tighter. C4 and C5 are looser again than CN.

These clearances specs are very fine tolerances variations and can easily be overpowered by the amount of press fit interference in the housing.

The YZ cases shown look like at least a resleeve to rectify for long reliable life. If you can get the good used set go for it.

That said, lots of engines have been put together with the garden variety (CN) bearings in worn slip fit housing and a dollop of Loctite retaining compound. If you are not concerned by the possibility of a shorter life or an unexpected teardown this might be the way to go.

[mick25]

So C3 bearings are better to use so they have less of a chance of the whole bearing spinning in the case and wearing it .   Is this why they are used because of more free play they have internal??

[smed]

So C3 bearings are better to use so they have less of a chance of the whole bearing spinning in the case and wearing it .   Is this why they are used because of more free play they have internal??

No, C3 bearings are used in mains because of there extra clearance to allow for heat expansion it has nothing to do with preventing spinning in the cases
I will not use a bearing in a 2T motor main unless I see "C3" stamped into the steel outer race,I have been caught out before,  I fully rebuilt a motor from top to bottom & it only ran for a short time before the mains seized,the donk was carefully run in ,On inspection after disassembly I noticed the lack of markings on the bearings,The boxes the bearings came out of said C3 but I did not check for the marks, I installed a new set of marked bearings & no more probs  

[mick25]

So C3 bearings are better to use so they have less of a chance of the whole bearing spinning in the case and wearing it .   Is this why they are used because of more free play they have internal??

No, C3 bearings are used in mains because of there extra clearance to allow for heat expansion it has nothing to do with preventing spinning in the cases
I will not use a bearing in a 2T motor main unless I see "C3" stamped into the steel outer race,I have been caught out before,  I fully rebuilt a motor from top to bottom & it only ran for a short time before the mains seized,the donk was carefully run in ,On inspection after disassembly I noticed the lack of markings on the bearings,The boxes the bearings came out of said C3 but I did not check for the marks, I installed a new set of marked bearings & no more probs  

thanks smed  I have learnt something new today about bearings

[Tomas]

So C3 bearings are better to use so they have less of a chance of the whole bearing spinning in the case and wearing it .   Is this why they are used because of more free play they have internal??

No, C3 bearings are used in mains because of there extra clearance to allow for heat expansion it has nothing to do with preventing spinning in the cases
I will not use a bearing in a 2T motor main unless I see "C3" stamped into the steel outer race,I have been caught out before,  I fully rebuilt a motor from top to bottom & it only ran for a short time before the mains seized,the donk was carefully run in ,On inspection after disassembly I noticed the lack of markings on the bearings,The boxes the bearings came out of said C3 but I did not check for the marks, I installed a new set of marked bearings & no more probs

would you use oem (suzuki, honda, etc) bearings with no c3 stamped on them? i have two sets of oem crank bearings but non of them have c3 stamped on. would you only find c3 marking on bearings (SKF, etc.)you get from local bearing shop? also some oem bearing are used in various applications.same oem bearing can be used as crank shaft bearing or gearbox bearing.

[smed]

So C3 bearings are better to use so they have less of a chance of the whole bearing spinning in the case and wearing it .   Is this why they are used because of more free play they have internal??

No, C3 bearings are used in mains because of there extra clearance to allow for heat expansion it has nothing to do with preventing spinning in the cases
I will not use a bearing in a 2T motor main unless I see "C3" stamped into the steel outer race,I have been caught out before,  I fully rebuilt a motor from top to bottom & it only ran for a short time before the mains seized,the donk was carefully run in ,On inspection after disassembly I noticed the lack of markings on the bearings,The boxes the bearings came out of said C3 but I did not check for the marks, I installed a new set of marked bearings & no more probs

would you use oem (suzuki, honda, etc) bearings with no c3 stamped on them?
Yes I would use oem bearings with no marks if they were in there original package with correct part numbers ,Sorry yeah, I was referring to aftermarket bearings only

[NSR]

Just for interest, the big end bearings in a Rotax sit in a plastic ring. 

 

[alexbrown64]

That plastic ring must be special stuff... like cutting board plastic or chain roller plastic... Nylon?  Anyway, had a look at my AllBallsRacing main bearings and those boys know their shit as they are good Japanese quality Koyo and they have C3 stamped on them.  I have also had lots of great input from this thread and got a few leads on sorting the problem.  And i believe this will help future members who run into this problem and do a quick search for solutions.
Cheers,
Alex

[Simo63]

Just for interest, the big end bearings in a Rotax sit in a plastic ring. 

When they're not SWiMming all over the combustion chamber

[matcho mick]

not surprised,check the length of the mains  ,double row ducati bevel twins wheel bearings ,or is that just on the drive side main?,