Author Topic: main bearing shimming  (Read 1094 times)

Online sean

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main bearing shimming
« on: 11.07. 2020 20:57 »
anyone ever figure out the factory method for end play on the main bearing not enough room under the bearing when fitted to get a split bearing puller under without destroying the cage .....looks like I am going to have to hone the inner race out of a new bearing and keep it in my tool box to get the end play correct .
measured .005 end play before I split the cases but that was a Hoffman bearing the new one is an nsk 206w so I would imagine there will be a difference and the hoffman bearing had 3000 miles on it .
origional shim was .010......... ordered a shim set from Baxter cycle but they all measure .004 and the ID of their shims is really sloppy almost 3/16 too big  .
Sean
TIA
have a good day

Online RDfella

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Re: main bearing shimming
« Reply #1 on: 11.07. 2020 22:02 »
There is no engineering reason for the bearing being anything other than a push fit on the crank - ie you should be able to pull it off without force. If not, relieve the crank slightly with emery tape.
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Online chaterlea25

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Re: main bearing shimming
« Reply #2 on: 11.07. 2020 23:18 »
Hi Sean,
Have you tried using a really thin steel wedge ?
I ground a chisel to a very shallow taper to start the bearing moving on a Rudge engine
I have a Huntmaster crank on the bench currently and need to fit 30 thou shim behind it
The engine was put together without shims ?? *eek*
It was also assembled without the cork on the top hat breather and apparently was running away happily until it was hit by a Transit van *doh* :( :( *cry*

John
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Online sean

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Re: main bearing shimming
« Reply #3 on: 12.07. 2020 00:59 »
measures up to a 1 thou interference fit between crank and inner race id... pretty much destroyed the origional one
 pulling it off with a split brg puller but I was planning on replacing it anyway so I wasnt too concerned .
I would measure the shoulder but the crank is in the freezer dont think there is enough room to get anything between the bearing and crank without damaging the metal cage .....probably should have bought the one with the nylon cage and taken it apart .

Offline Swarfcut

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Re: main bearing shimming
« Reply #4 on: 12.07. 2020 08:54 »
Back in the day the bearing type chosen was the familiar NF type, rollers stay on the crank, outer case simply pulls off. These days the bearing type NJ offers an easier but slightly more expensive solution. Here the outer race, cage and rollers remain in the crankcase, the bare inner race stays on the crank.

 The same problem of moving the inner race on and off remains, but access is easier with less chance of damage to a new bearing. I've had success starting it with a Stanley blade carefully hammered between race and crank, gentle heat and a succession of thicker wedges....old knives, chisels, ground wedge on a flat bar.

   RD is on the money here. There is no sound reason why the race has to be a super tight fit on the crank.  Assembled correctly the cush nut is holding everything tight against the crank. If you are an inner race sitting under some 65/75 ft/Lbs of torqued down cush nut, you ain't goin' nowhere.

 In practice, and in unenlightened times many earlier owners would be unlikely to achieve this torque, with a drift and backyard coal hammer. Maybe this was a belt and braces design to ensure that at least there was some physical interference fit even with the cush nut looser than it should be. The split pin in the crank end serves more as a safety to prevent damage to the cases if the cush nut loosens, rather than a marker to say the correct torque has been achieved. Guilty as charged, m'lud. Thought it was tight when the hole appeared. I know better now.

 Service sheet 208 recommends the nut is tightened "as securely as possible" tightening with a C spanner and Crank Float is allowed up to 0.005" Good enough, back then.

 There is debate as to whether a simple deep groove ball race would do a better job on low stressed engines, as on the early Longstroke and early A50/65. No end float at all. Works OK on other contemporary designs. Bearing Type NUP offers a more expensive best of all worlds, outer race and rollers stay in the case but with no end float other than that present in manufacture, as the cush nut and drive sleeve tighten down.

 Swarfy.

Online RDfella

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Re: main bearing shimming
« Reply #5 on: 12.07. 2020 10:04 »
Best 'chisel' I've found over the years is a mechanical hacksaw blade (approx 1 1/4" wide) broken off square and sharpened at the end. Very useful as a scraper too. Have several kicking around my workshop. Often used for scraping off paint, old gaskets etc but also a wizard for getting behind bearings such as we're discussing to get that first start before moving up to thicker chisels.
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Online Greybeard

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Re: main bearing shimming
« Reply #6 on: 12.07. 2020 10:56 »
It was also assembled without the cork on the top hat breather and apparently was running away happily until it was hit by a Transit van *doh* :( :( *cry*
Yup, that will happen if you leave the cork out!   *sad2*

Online Greybeard

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Re: main bearing shimming
« Reply #7 on: 12.07. 2020 10:59 »
I used an old wood chisel to remove that bearing from the crank.

Online sean

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Re: main bearing shimming
« Reply #8 on: 12.07. 2020 17:32 »
There is a 10 thou shoulder on the crank ...add a 10thou shim that was on the old original set up and ten thou between the inner race and the metal roller cage that 30 thou space between the cage and the crank face

Online Colsbeeza

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Re: main bearing shimming
« Reply #9 on: 12.07. 2020 22:54 »
Hi Sean,
I just did mine last week. I eventually purchased three NJ206 bearings (one sacrificial and one spare), which leaves the Outer bearing with rollers in the Driveside crankcase. Much easier to remove from the crankshaft. Many think it important to buy a C3 Clearance bearing too. so I did. It has a plastic cage, so it also avoids overheating to remove it if it was on the crank.
Shims were a problem. I used shims from 3 different sources to get the combination I needed. All the shims were a little thicker than the stated thickness, and some sets have 10,5,3 thou shims, others 10, 6, 2 thou.
More likely 10.4, 5.3, 3.3  and 10.2, 5.5, and 1.7.  Muskrat advised not to use more than 3 shims, but I could not achieve the thickness I needed with less than 4. A damned PITA. However, I don't race it or rev it to 8000rpm like Muskrat did (once just before it blew). But then he did have a lovely Colleen looking on!! *lol*
My NJ206 inner was also tight on the shaft, and I did grind the inner on the sacrificial bearing for shim adjustment. I did not want to ease the crankshaft diameter by emery. John Chaterlea scared the bejeezus out of me *pull hair out* with tales of shim shredding. His analysis of crankshaft forces is very frightening enlightening.
I did have to get the final inner off again due to small differences in the new inner dimensions ( they all had axial differences of about 0.3-0.4 thou). I used boiling water and a thin chisel to start, then used a puller to get it off. All up, I assembled the crankcases about 10 times before I was happy to apply some gasket goo - (Hylomar). Had to settle for 0.0018".
Col
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Australia

Online sean

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Re: main bearing shimming
« Reply #10 on: 13.07. 2020 14:24 »
Thanks for the reply think I will order another bearing and hone the I’d of the one I have for fitting purposes .
Need to find some better shim. Packs the ones they sent are too sloppy on the I’d and all but 1 shim measure .004 the other shim is .005 4shims in total in the package .
The crankcase on this motor has never been split it only has 3000 miles still the factory punch marks on the flywheel end plugs...and I know the 2previous owners
Any way origionally it was fitted with a Hoffman bearing and a 10thou shim there is .001 difference in width between the Hoffman bearing and the NSK         
I am assuming the factory because they were using the Hoffman bearing on all the motors just threw in a .010 shim on all the motors can’t see them checking end play on every motor on a production line .
Before I split the cases there was .005 end play with the .010 shim .
Where did you order shim packs from and was one set a better fit than the others ?
Would like to have 1 shim made but no access to a surface grinder out here in the boonies

Online mugwump

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Re: main bearing shimming
« Reply #11 on: 13.07. 2020 15:03 »
If the i/d of the shims is too close to the crank journal o/d isn't there a chance of the the shim fouling on the crank journal radius? or am I talking out of my hat again

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Online sean

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Re: main bearing shimming
« Reply #12 on: 13.07. 2020 15:35 »
not really much of a  radius The original shim was fine but the ones I received from Baxter cycle were almost 3/16 too big on the I’d and flop all over

Online berger

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Re: main bearing shimming
« Reply #13 on: 13.07. 2020 18:03 »
no mugwump your not talking out of your hat, I found my shims had been pressed into the inner race a bit when I took it apart a couple of years ago, hence when measuring end float on the rebuild I made sure I had loads of pressure on them so as not to end up with a false reading

Online muskrat

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Re: main bearing shimming
« Reply #14 on: 13.07. 2020 20:47 »
G'day Fellas.
I make my own shims. Easy with very sharp scissors, or curved tin snips.
Cheers.
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