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November 28th, 2013, 11:54 PM   #11
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bearing codes

there is a lot of discussion in the main thread about bearing codes heat treatment and special steels

what it boils down to is that the only skf roller bearings you should consider using are the ones used as OEM parts, a standard SKF nj206 c3 or c4 is not good enough (aparently)

IMHO though you should not use SKF NJ seires bearings at all.. just use NTN or nachi or rollway.. they all have nicer roller end radii. the advantage of the skf (if any) is that they have 58 micron clearance vs 46 for the NTNs.

FWIW the ktm crate engine ball bearing is also a "special" TMB (transmission deep groove) bearing although many ktm engine builders have had great success with nachi and koyo C3 ball bearings
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November 29th, 2013, 12:05 AM   #12
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Re: Definative main bearing thread

so its simple when you understand the problem really comes from the crank not so much the bearings

As far as I know adequate endfloat + NTN rollers have been good enough for everyone worldwide who has tried them in a stock build, the same is not true for the SKF bearings. this is even the OEM skf bearings with the code NJ206ECP/C3HVC058.. they are not as good as the NTN used as OEM bearings in some years of the RFS with code NJ206 ET2XCS46

beyond that there are many other things you can do to improve on the standard arrangement
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November 29th, 2013, 12:59 AM   #13
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Re: Definative main bearing thread

Bushmechanic, you're a legend mate!

I think you just described why I have hundreds of chrome looking metallic flakes on my strainer the last couple of of oil changes... and what to do to fix it. Greatly appreciated!
Thanks from bushmechanic
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November 29th, 2013, 01:08 AM   #14
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Re: Definative main bearing thread

Hi Bushie

Great tread, with a very good documentation, thanks

In my old 400-02, I've been using 2 ball bearings SKF ETN9 C4, without a problem, what do you think about that solution ?

Also, what do you think should be my axial play ?

Thanks

ZAGA
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November 29th, 2013, 03:38 AM   #15
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Re: Definative main bearing thread

Originally Posted by zaga
Hi Bushie

Great tread, with a very good documentation, thanks

In my old 400-02, I've been using 2 ball bearings SKF ETN9 C4, without a problem, what do you think about that solution ?

Also, what do you think should be my axial play ?

Thanks

ZAGA
I think if it works for you then it is very good, you are smart enough to have it setup right IMHO

the axial play if its working.. then its good no? .. RFS builders use 0.2-0.3mm on that setup but they use a slip fit between the crank and the ID of the bearings, either by honing out the bearing ID or polishing the crank down. this is done so the crank can't pull the bearings out of their bore and wear out the cases and also so that if the bearings move on the crank when they are hot it cannot be locked without enough end float when it cools back down.. it greatly reduces the axial loading on the bearings.

with the C4 clearance this could be less of a problem but is still something to consider.

check how the bearings can be pulled inward out of the cases

Originally Posted by Bushmechanic
Interesting experiment i tried to retain the outer race of an Nj2206 with an alloy plate





you can see its cracked. the outer race of the bearing has been pulled
out of its bore by 1.5mm and with enough force to break the retainer.

I find this interesting as there is no easy way to apply a force to the outer race
in this direction. there is a lip but it can only push the bearing into its bore not
out



also I was running 0.8mm crank endfloat so for the outer race to move any
more than 0.8mm out of its bore means there is some extraordinary flexing
going on.

im guessing that at TDC on the exhaust stroke the piston and rod pull hard
enough on the crank to make it flex inward and at the same time apply enough
radial force to the rollers to let them lock up and pull on the outer race.

in any case because of this experiment and so I can measure the axial play
properly Ive honed out the ID of the spherical roller about 2 thou in total
to be a 1/2 thou slip fit on the crank.
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November 29th, 2013, 04:09 AM   #16
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Re: Definative main bearing thread

Hi

My endfloat is 0,3 so it should be in range, a friend mechanic told me it could be even more without a problem.

Thanks

ZAGA
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November 29th, 2013, 01:29 PM   #17
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Re: Definative main bearing thread

yes your right I reckon 1mm is pretty safe

regardless of the type of bearing used the crank still needs the same amount of room to expand

well.... the ACs and the spherical rollers don't need any axial play but the cases do
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November 29th, 2013, 07:29 PM   #18
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Re: Definative main bearing thread

Originally Posted by Kye
Bushmechanic, you're a legend mate!

I think you just described why I have hundreds of chrome looking metallic flakes on my strainer the last couple of of oil changes... and what to do to fix it. Greatly appreciated!

Kye this a drain plug after 1 main failed in a 550



if the mains are ok just a few flakes can also be the bigend
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November 30th, 2013, 01:26 AM   #19
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Re: Definative main bearing thread

JBS kit on my 710 husaberg,
I run 22206 crank bearings, welded pin crank
2005 special crank

welding of the pin is cracked after 25 hours!!!!
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November 30th, 2013, 02:22 AM   #20
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Re: Definative main bearing thread

Kye this a drain plug after 1 main failed in a 550

Whoa! Yep, well I reckon that is what my drain plug would look like if I had a magnetic one (must throw one of those on the shopping list).

I had no idea these cranks flexed so much!
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