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July 4th, 2014, 05:35 AM   #81
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A great read Bushmecanic ! Many thanks for taking the time !

From all this reading there rises another question which is not directly connected to the mains but to the different mass of the 550 and 628 crank.

Why on earth is the 550 crank mass higher than the 628 ? I thought that usually the bigger the engine (longer stroke) the heavier the crank ?
>"550 crank and rod 4.75 kg 32mm pin rod length 123mm
628 crank and rod 4.5kgs 35mm pin, rod length 136.2mm<"

Would it be a good idea to lighten the crank of the 550 and then (of course) rebalance it ? I would think that by doing this the 550 will have less Gyroeffect and less stress on the mains ( I run roller bearings on both sides with the pin for the big end welded )

Just a humble thought.....

Best,
Heimir Bardason
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July 4th, 2014, 08:50 AM   #82
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Has anyone heard if the DCR crank modification? I took my bike to Dave Clark Racing a few years ago to get some work done and he did the modification on my bike. He told me at the time he used to tear every bike down that he sold, which was a lot, and do his modification before leaving is shop.
I think he mentioned new roller bearings and an extra oil seal somewhere to help the end float.
i think i just nodded my head and smiled

I guess it would be interesting to know the details in the context of this thread
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July 4th, 2014, 03:45 PM   #83
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yes I forgot to include that one phillis .. thanks!

Ive not seen one but its described in johns original thread

as far as I can make out from reading the posts there the DCR mod is the 610 crate engine NTN TMB ball on the drive side with a collar between the drive gear and the main bearing (basically a sleeve that fits over the 30mm part of the crank). then a bigger ID seal is used over that sleeve on the drive side, I think an Nj206 was used on the other side.

the idea is to hold the crank over to one side so it cant drift around when hot and change the axial play

same idea as most jap bikes except that the bearing itself is not mechanically retained in the case, its just a very very tight fit so in theory it can still move.

almost the same situation as below.

Originally Posted by bushmechanic View Post
the first one that was popular was the use of a KTM crate engine deep groove ball bearing on the drive side and an NJ 206 on the ignition side.

many jap bikes use this idea but they fasten the ball bearing to the cases and also to the crank so the crank cannot move.

they also have about 2mm room between the rollers on the roller bearing and the lip or.. no lip at all so the rollers never contact the lip in these bikes

in the husaberg the ball bearing is just a stupdly tight fit in the cases and on the crank but the crank is not actually locked in position and can move.. you wouldn't know about it though till the roller bearing failed.

it is also very difficult to measure the space between the ends of the rollers and the nj roller bearings lip... you still need the same amount of room for the crank to expand because the axial loading is shared by the 2 bearings and the NJ bearing still gets squashed into the lip

it has worked for some people but i have seen it fail in 20 hours
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July 4th, 2014, 03:52 PM   #84
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Originally Posted by HeimirBardason View Post
A great read Bushmecanic ! Many thanks for taking the time !

From all this reading there rises another question which is not directly connected to the mains but to the different mass of the 550 and 628 crank.

Why on earth is the 550 crank mass higher than the 628 ? I thought that usually the bigger the engine (longer stroke) the heavier the crank ?
>"550 crank and rod 4.75 kg 32mm pin rod length 123mm
628 crank and rod 4.5kgs 35mm pin, rod length 136.2mm<"

Would it be a good idea to lighten the crank of the 550 and then (of course) rebalance it ? I would think that by doing this the 550 will have less Gyroeffect and less stress on the mains ( I run roller bearings on both sides with the pin for the big end welded )

Just a humble thought.....

Best,
Heimir Bardason
your humble Viking thoughts are always worth posting up Heimir

welded pin very good idea

the 550 crank is a full circle crank probably done this way because followed convention at the time and was cheaper and easier than having a specific pork chop forging done like the 80mm crank in the 628. also many old school people don't like the feel of a fast revving engine with little inertia.

plenty of pics of similar KTM 525 cranks that have been lightened here

Balancing an 80mm 650 crank

the thing to watch is the shape created by the forging at the center of the crank is a weak point if you cut too much off. I think you could at least get it down to about 4kgs pretty safely check the pics I put up later in the thread.

edit: the easiest and arguably the safest way is to put it in a lathe and turn down the OD of both webs, this does not change the balance factor and has maximum effect in reducing mass moment of inertia.

apparently the minimum amount of metal between the pin and the OD is about 6mm, go for 8-9mm

Last edited by bushmechanic; July 4th, 2014 at 08:40 PM.
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August 4th, 2014, 01:35 AM   #85
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I hope you don't mind if i add a bit to your thread. I Found some of this info on a fellow KTM/BERG site

Crank Main bearing codes / part numbers
the crank mains bearing code is:

NJ206ECP/C3 doesn't matter what brand, they look up the SKF reference then cross match

real important though to get ECP/C3 match

EC = Optimized internal design incorporating more and/or larger rollers and with modified roller/end flange contact

P = Injection moulded cage of glass fibre reinforced polyamide 66, roller centred

C3 = Radial internal clearance greater than Normal


I gave up trying to use the online timken bearing part number finder, bloody useless................

Over the counter OPTIONS

another bearing to look at:

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)

last longer in the berg engines than the SKF.

IMHO its because the roller end radius on the SKFs is too sharp and their clearance range is too tight and varied. they spec C3 but some can be very tight and still fall within the C3 range whereas the CS46 on the NTN means they're sposed to be all 46 microns clearance which is nearly C4.

NTN also list a CS42 clearance option which might just be "perfect" for the SX-F engines

NTN NJ206 ET2XCS42


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August 4th, 2014, 02:12 AM   #86
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thanks Gav

i would add that for over the counter bearings do not use a std SKF NJ206ECP/C3. people have had bad experiences with them

the only SKF we should consider is the OEM part which is specially hardened and has a radial clearence spec of 58 microns

most other over the counter STD recognized brand NJ206 bearings have been used with good results but it is better to use C4 not C3
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August 8th, 2014, 12:10 AM   #87
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OK where can I get a NTN NJ2206 (wider than the std 206) with the appropriate designations?

I looked and settled for the SKF EPC/C3 but would use the NTN if I could find one.
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August 8th, 2014, 02:13 AM   #88
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dunno Spanner

I used brass cage max capacity "rollway" nj2206 beacsue weed had used them

they were C4

i used one of the skf nj2206s C3s for a while but took it out cause it looked like it was having a hard time compared to how the rollway C4s were handling it
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October 10th, 2014, 11:33 AM   #89
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crank spread root cause

I owned a ktm 450sx 2006 (old engine) same crank used for the husaberg
I have tried everthing to set this issue
As it is said previously my spread was 0.15 mm after only 4hours
I have placed a new crank in the crankcase , run the motor for few hours and checked the spread and see that it was already of 0.15mm

I tried also following things
- weld the pin
- replaced the roller bearing with ball bearing

None of these solutions gave good results
My engine always made noise after 17hours in any case

The only solution found was to sold the bike (

I have rebuild the engine if this bike 5 times

For me the problem can come from the interface between crank and pins which is not strong enough

Or the rigidity if the crankcase also not too strong

But in any case the change of the roller will set this problem

The root cause is the ktm engineer

Last edited by ptitloup13; October 10th, 2014 at 11:46 AM.
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October 10th, 2014, 03:10 PM   #90
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Hi pitloup

thats disappointing for sure.

did you try 1mm crank axial play with c4 nj206 rollers ?

or a new crank? (pin fit will be tighter with brand new crank)

im curious what crank axial play you were using with the 5 failures

with the 450 you could also have removed about 1kg from the crank, reducing the spreading loads significantly.

Last edited by bushmechanic; October 10th, 2014 at 07:44 PM.
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