Crank axial clearance.

hi rabno

i would prepare a crank with the c/b only on it and the rod in situ and then go to work. press the bearings in the cases and then drop the crank in and close it up. check for float now using a rubber hammer to give it a tap L to R and back. use any of the methods previouly mentioned to measure the float.

i would then shim up and take it that i did it right allowing say a tiny amount for error. then rebuild with the desired shim in there. when you pull the crank hard left that side won't expand and move but the RHS moves right and that is where the float and gap will be.

regards

Taffy

taffy so that would work if the TMB ball had a slip fit on the crank ? or does it usually move if you hit it?

what about using an NU206 instead of an NJ206 ?

no inner race lip so don't have to worry about the "float"

FWIW I have seen a tech buliten from Hberg aust for installing the NTN TMB 6206 C3 ball LHS with an NJ206 RHS that says roughly:

press the crank to 59.90mm at the pin remove all shims from RHS of the crank but leave the 0.2mm shim on the LHS and put it together.

sounds like a no brainer but a bike put together at the local (jap) dealer with this tech buliten as a guide died a quick death. IMHO if you press the crank it will flex a bit and get bigger than 59.90 on the first startup. once its found its "happy place" it won't move much anymore but then how do you check the float? the dead bike had zero float and crank width measured 60.18

if the ball isn't a slip fit on the crank you could measure the "width" of the whole crank/bearings/balancer etc as assembled and then use a bore guage sort of thing to measure the distance twixt the bearing mounting flanges in the cases and go for 1mm "float" to be safe. can make a guage out of a long nut and 2 lengths of 3/8 threaded rod with the ends filed to small radius's

another potential problem is (I think) the TMB 6206 C3 has a larger OD as well so the "crush" is higher when installed in the same hole as an NJ206 C3

if we knew the ideal radial clearence as installed for the 2 bearing types then it does away with all the measuring of bearing housings and C numbers. FWIW there is a tech buliten in the DOC that says radial clearence as installed should be 0.04 to 0.05mm for the C3 skf Nj206. also says that if needed the bearing housings can be relieved with wet n dry

not sure if these tech bulitens should be taken as the shiznit in the way of advice but its a start..

HTH

could you edit that bushy and use the following so i can understand you

ball
roller
open roller

it's so much easier to understand that way for other people. me hahahaha! i'm fine (ahem!).

regards

Taffy

rabno

well that's what i have always done. the weak link when hitting the crank ends is going to be the friction between the bearing inner race and the shoulder/journal of the crank. giving it a 'slap' one way measuring, then slapping the other works for me. it also straightens the bearings which is why i can say that i've slapped cranks since 1977.

bushy
the 501 MX i did last year that was a '00 had a 6205 open roller on the right just as you say. it also had a collar on the left that the nut pulled hard on and drew the crank hard left against the bearing.

my "slapping" system works, i just didn't realise that i was the only one that did it?

regards

Taffy

now remember that dowel on the left end of the crank. donchyu dare go near that! use a 10mm deep socket or summink over it to do make the impact.

regards

Taffy

bushy
the 501 MX i did last year that was a '00 had a 6205 open roller on the right just as you say. it also had a collar on the left that the nut pulled hard on and drew the crank hard left against the bearing.

Click to expand...

ahh its a goot idea to have stuff wots not supposed to move tied down properly. if the closed ball isn't tight on the crank the collar seems like a must have if you wanted to use an open roller.. hey thats still confusing

Ive got an idea that when "correct" interference fits are obtained everything can move around when the motor is hot. if anything moves it closes up the float, motor cools and locks everything back in

rev it too hard when its cold with no float and boom

in JBS racings new hardened steel main bearing sleeves the bearings go in from outside the cases not from inside.

Taffy Im guessing that the LHS case needs to be heated to get that ball bearing in there ? I had to near melt this old 550 case to get it out.

hope it goes well rabno

why not simply buy the correct part from husaberg and fit it. this IS what they do on later engines after all!

oil seal, sleeve, ball race left, roller right. sorted. open roller if you don't want to machine the case.

pressing the crank in more than when it came out sounds fine as long as the rod has plenty of space still. no good curing one and moving the problem elsewhere!

regards

Taffy

this has been talked about before here:
http://www.husaberg.org/index.php?name= ... sc&start=0

I think Ive read every thread with main bearings mentioned a few times

even got tech stuff from SKF but except for the one buliten in the doc I can't find any real world info on the ideal radial clearence

skf spec the radial clearence as uninstalled zero load measured for nj206 C3 as 40 -70 microns


if the bearings can have a vairiation of 30 microns in radial play it doesn't matter what the cases measure really, we need to know the ideal radial clearence as installed.

Thomas ? lineaweaver.. JBS .. anyone?

bushmechanic said:

I think Ive read every thread with main bearings mentioned a few times

even got tech stuff from SKF but except for the one buliten in the doc I can't find any real world info on the ideal radial clearence

skf spec the radial clearence as uninstalled zero load measured for nj206 C3 as 40 -70 microns


if the bearings can have a vairiation of 30 microns in radial play it doesn't matter what the cases measure really, we need to know the ideal radial clearence as installed.

Thomas ? lineaweaver.. JBS .. anyone?

Click to expand...

I dont think about this anymore since we have a system that works for our 700cc engine.
For a 450cc moped i would use the OEM settings, and if you would go for something extra use the KTM Ball bearings left casing, but its hard to messure clearence.

For Bullet proof powerful engines i would recomend Ben Ballards modification.
why invent the wheel again, there is enough solutions for the bearing problem.
//Thomas

ah ok so nobodys really measuring radial clearence ? it doesn't matter ?

hey Thomas im not re inventing anything

I used stock OEM KTM rollers in unmodified cases... can't get any less inventive than that.

FWIW I think the miniumum should be 0.04mm radial play

of the 2 in my bike one had 0.02 and the other 0.04, the 0.04 one is in better condition than the tighter one.

with the new bearings i found a variation of 0.02 between the bearings so I put the tight one in the largest case bore to get 0.04mm radial play both sides.

the more radial play you have the greater the capacity of a bearing to accomodate angular misalignment from crank flex

if its not important thats fair enough, I think though that whatever bearings your using you need to make sure they are not too tight when installed at least.

so how is everyone doing that ? simply measuring the cases ?

what's my name dude!!!! LOL!!!

i can tell by simply offering the bearing what it's going to be like. i also press them in sometimes and then have them straight out again. i then do my little trick of honing the bearing house out and have developed a knack for knowing when i've taken enough and a 'nice light press-in' is all that's required.

i'm pleased with it but i had to kill all my customers to stop the complaints! LOL!!!

i have far more trouble getting the crank in and out on the left while testing, measuring and dummy-assembling than i ever do with the case fit. now that's a nightmare!

regards

Taffy

fwiw,i was personally worried about the main bearings poping out.the reason i was worried was, i thought the expansion of the alloy case was greater than the steel from a bearing,but from what taffy is saying it doesn't need to be that tight a fit?
hence like i was showing wildman wal,the crank end float on my bike cold & then again hot,it was no comparison there was definatly more hot.which proves the point, alloy cases expands more than a steel crank.check it yourself.the myth is busted that crank end float reduces when the motor is hot.
radial clearance ...well the c4 drive side roller i have in mine has a lot more than the c3.
i remember sliding one end of crank through the main bearing when it was in the case,then moving the other end of the crank up & down to see how much crank flex it would tolerate,it was something like 20mm,so to my way of thinking its never going to bind with a c3 or c4 bearing..non issue to my way of thinking.
the real problem is the bearing inners move.the fit between the bearing inners & the crank is not always a tight fit.when that moves because of heating/cooling/vibration/whatever, the endfloat can eventually become nil.
i know i measured mine a couple of rides back,.1mm cold/.3mm hot ,scary hey,especially when i cut/ ground the crank spacer down so it had .4mm cold ,when i assembled it.
any reaction ??
..weed