Crank bearing brands and a clearance question..

Spuddy18 · Feb 4, 2019

Hi all, currently fully rebuilding my 01 650 engine as it was using alot of oil, don't want to do it again anytime soon so it's having the full works, re plated liner, new piston, bushes, bearings, the lot. The whole bike is getting the works to be honest, however I've read a fair bit through various threads on here about main crank bearings, and just wanted to ask a couple of things.

Currently I have skf 6206/c3 ball bearings on the crank, these I am aware are prone to failing. So I'm aware the best thing to do is go for a roller bearing upgrade. No problem. I am however undecided on the brand. Skf rollers are no problem, I understand the ntn's have good reviews on here, however I mainly wanted to know if anyone has run *** bearings before. Couldn't see any mention of them, but they are a premium German brand, and I've been confidently told my 2 of my local bearings suppliers that they are one of the market leaders.

In particular the Nu206ecp/c3.
Any reason why I shouldn't give these a go? Well priced and well rated.

Another question was about gaining myself a suitable amount of crank end float. Has anyone ever machine there engine casings (let's say 0.5mm out of each bearing seat) to allow over 1mm of float, and then use shims to get the ideal spec?
I have a machinist friend confident to do it for me, so just wanted any pointers as to why it could be a bad idea.?! Has it been done before?
There is a slight amount of bearing protruding from the casing when it is installed, so I would only be loosing this to allow myself to easily achive a perfect end float.

Any advice appreciated.
Thanks

bushmechanic · Feb 4, 2019

Nj206 ecp/c4 is what you need not nu or c3

*** have the same problem as skf with the roller end radius

Weed and i have run rollway bearings but they not as good as ntn

The early cases often need machining to allow adequate clearence with rollers. Its not difficult

Spuddy18 · Feb 6, 2019

bushmechanic said:
Nj206 ecp/c4 is what you need not nu or c3

*** have the same problem as skf with the roller end radius

Weed and i have run rollway bearings but they not as good as ntn

The early cases often need machining to allow adequate clearence with rollers. Its not difficult

Thanks, i cant however find a suitable bearing by ntn under that part or code number you suggest. only the skf version.

will the ntn equivalent be a different code?

also, the cn, c3 and c4 specs refer to the internal clearances correct? ad mainly reflect the maximum speed the bearings can cope with. A c3 grade *** or skf in the nj/nu series where up to 14,000 rpm in oil. Surely this way surpasses what i need? negating the need for a c4 spec.
The main trouble is i cant find a c4 rated bearing in the uk, and neither can my bearing supplier.

thanks,

Spencer

bushmechanic · Feb 6, 2019

Hi spencer,

The c rating is a radial clearance. The cases squash the bearing so you need c4 to be correct when installed.

Just use the ntn from ktm. The bearing suppliers can get you bearings for tractors

brand: NTN NJ206 ET2XCS46 this available through KTM, part Number 50330082000

the code ET2XCS46 tell an interesting story

E = bearings with a carburised ring, allot more durable if the clearance run out under thrust loading

T2= nylon cage

X = special radius on the roller rings, same deal as E more durable when things are at the limit

CS 46 means the clearances are precisely set at 46 micron, thats between C3 and C4 ratings.

this is a pretty special bearing.

This is the KTM SMR 560 main bearing.

if you want to know what all the codes mean for NTN go here.

http://www.ntnamerica.com/search.asp?CSERI...E=1.1811&

I picked this up on an all old KTMTalk thread dealing with RFS SMR 560 crank problems, they kill main bearings apparently, the NTN was a factory "fix"

the NTN rollers (50330082000 CYL.ROLLER BEAR.NJ206 ET2XCS46)

Spuddy18 · Feb 7, 2019

bushmechanic said:
Hi spencer,

The c rating is a radial clearance. The cases squash the bearing so you need c4 to be correct when installed.

Just use the ntn from ktm. The bearing suppliers can get you bearings for tractors

brand: NTN NJ206 ET2XCS46 this available through KTM, part Number 50330082000

the code ET2XCS46 tell an interesting story

E = bearings with a carburised ring, allot more durable if the clearance run out under thrust loading

T2= nylon cage

X = special radius on the roller rings, same deal as E more durable when things are at the limit

CS 46 means the clearances are precisely set at 46 micron, thats between C3 and C4 ratings.

this is a pretty special bearing.

This is the KTM SMR 560 main bearing.

if you want to know what all the codes mean for NTN go here.

http://www.ntnamerica.com/search.asp?CSERI...E=1.1811&

I picked this up on an all old KTMTalk thread dealing with RFS SMR 560 crank problems, they kill main bearings apparently, the NTN was a factory "fix"

the NTN rollers (50330082000 CYL.ROLLER BEAR.NJ206 ET2XCS46)

That's excellent info, thanks for that. I'll do some more reading

WArdogG · Feb 7, 2019

I have found a similar NTN bearing, although it's not the very special bearing Bushmechanic mentioned here, I have beaan using these as they are readily available and very resonably priced, and has the correct clearance and a polyamide cage. NJ206ECS46, they are what Pro-X sell for the KTM RFS engine, Pro-X part number 23.NJ206

Spuddy18 · Feb 9, 2019

I've managed to pick up a pair of the ntn bearings as bushmechanic mentioned for £45, so pretty pleased with that.

Now moving on to all the other bearings.

I had some concern about the remaining gearbox bearings etc as when I checked them whilest still fitted in their respective casings, they felt graunchy and bad. They didn't roll smooth at all.
However, once I pressed them out and checked again, they feel fine.
All my other bearings are skf and c3 grade, but am I right in thinking a c4 equivalent of each would allow a smoother bearing movement once pressed into the casings?

Is there any threads on here already discussing this matter?
Thanks
Spencer

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Crank bearing brands and a clearance question..

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