The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: sean on 11.07. 2020 20:57

Title: main bearing shimming
Post by: sean 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
Title: Re: main bearing shimming
Post by: RDfella 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.
Title: Re: main bearing shimming
Post by: chaterlea25 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
Title: Re: main bearing shimming
Post by: sean 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 .
Title: Re: main bearing shimming
Post by: Swarfcut 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.
Title: Re: main bearing shimming
Post by: RDfella 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.
Title: Re: main bearing shimming
Post by: Greybeard 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*
Title: Re: main bearing shimming
Post by: Greybeard on 12.07. 2020 10:59
I used an old wood chisel to remove that bearing from the crank.
Title: Re: main bearing shimming
Post by: sean 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
Title: Re: main bearing shimming
Post by: Colsbeeza 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
Title: Re: main bearing shimming
Post by: sean 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
Title: Re: main bearing shimming
Post by: mugwump 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
Title: Re: main bearing shimming
Post by: sean on 13.07. 2020 15:35
(http://)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
Title: Re: main bearing shimming
Post by: berger 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
Title: Re: main bearing shimming
Post by: muskrat on 13.07. 2020 20:47
G'day Fellas.
I make my own shims. Easy with very sharp scissors, or curved tin snips.
Cheers.
Title: Re: main bearing shimming
Post by: Colsbeeza on 13.07. 2020 22:12
Hi Sean,
I purchased two sets from two local suppliers in Australia. One was an MCA-304 set for the large journal A10 crank - 10,6, & 2 thou. The other was an MCA-H304 set for the early A65 - 10,5, & 3 thou. The third set was an A10 set from OneStopBikeBits on evilbay. They were unmarked, but were advertised as 10, 6, & 2 thou. I also had the same problem as Berger, where I got a false measurement but for a different reason. Some of the shims had been pressed out of sheet and had some overflow. I dremelled that off carefully. All shims were the same diameter. The shims were also about 1-1.5 mm over the shaft diameter. I presumed necessary because of the radius. I mounted the crankshaft vertical but lightly in the vice ( using heaps of rag & cardboard so as not to damage the Timing side journal), placed the shims as centrally as possible, and dropped the inner race over and clamped it down with the cush sleeve, spacer & nut. When the inner cooled, it clamped itself very well. I didn't use Loctite, but a tiny drop of Loctite 641 may have held them in place with more surety. Anyway it seemed to work OK.
I remember doing this with my old A7 in 1969 - don't remember knowing or doing any of this.! That bike was as reliable as you could want. Makes you wonder why we are so pedantic. We know too much these days.!
Col
Title: Re: main bearing shimming
Post by: Greybeard on 14.07. 2020 10:09
I rebuilt the back axle of my brother-in-laws Austin 7. I had to fabricate new top hat shaped  holders for felt oil seals. The only suitable material I had was shim stock. The method I evolved was to clamp the shim stock between 2 sheets of plywood. My press drill then was a Black & Decker mounted in a B&D press device. I used a fly cutter to cut large washers. This process was fraught with finger slicing risk. I soldered the bits together and as far as I know they are still in the axle.
Title: Re: main bearing shimming
Post by: RDfella on 14.07. 2020 12:08
Ref GB's flycutter - don't attempt this without sandwiching the metal between plywood as he did, or you will cut your fingers off! Works well for drills or holesaws as well, giving a neat cut.
Title: Re: main bearing shimming
Post by: sean on 14.07. 2020 12:59
just happen to have one of them in my tool box and found a few rolls of shim stock I had sitting on a shelf the last 20 years .
I have some eletrical knock out dies for punching holes in electric boxes I may try if I can find the right size.
Title: Re: main bearing shimming
Post by: Greybeard on 14.07. 2020 13:17
I ground the cutting edge down to give a narrower cut.

It was a really hair raising exercise until I discovered clamping the metal between the plywood.
Even with leather work gloves on I was terrified of the metal picking up and flying into my fingers.

When I used plywood, I think I may have put screws right through the wood and metal to lock it together.
Title: Re: main bearing shimming
Post by: BSA_54A10 on 16.07. 2020 09:34
FWIW I use a nibbler for cutting shims ( and head gaskets. ) and some of them are even useable .
Title: Re: main bearing shimming
Post by: sean on 16.07. 2020 13:51
Used a hole saw and snips on the thicker .020 shim stock
Title: Re: main bearing shimming
Post by: UKlittleguns on 18.07. 2020 13:23
Hi Everybody,

I also make my own shim washers.  I make a flat ended punch with the OD and ID sized to the washer.  The ID hole only has to be about 2 mm deep.  Keep the edges sharp.  I put the shim on a block of hard rubber, the punch on top and wack it with a big hammer.  You can also use a fly press or a simple vice (depends on the shim thickness for the best choice).  I think this technique is known as 'Rubber Blanking'.   Works a treat.  It gives washers that are burr free and perfectly flat.

Simple mild steel works well for a few washers but will then need sharpening.  Hardened silver steel is better for multiple washers.

Regards to all. 
Title: Re: main bearing shimming
Post by: Greybeard on 18.07. 2020 23:21
Sounds good UKLG but would require equipment that I do not have, a lathe for instance!  *smile*
Title: Re: main bearing shimming
Post by: UKlittleguns on 19.07. 2020 12:16
Hi Neil,

This method doesn't always need access to a lathe.  In the past I've used an old bearing inner race ground flat on one side with an angle grinder.  As long as the edges are kept sharp it doesn't have to be perfectly flat.  Nice thing about this is the steel is good quality, holds its edge and the OD/ID dimensions have to be correct.  To tell the full story, perhaps the hardest thing is finding the correct grade and thickness of rubber.  I tend to use a 1/2 inch thick block made up from 4 inch square layers of old inner tubes held together with glue *smile*

Best regards

Len.     
Title: Re: main bearing shimming
Post by: KeithJ on 22.07. 2020 19:53
When I rebuilt my last engine, I measured the end float, after removing the bearing, I measured the shims which were on the crank.  I then made up a "dummy" bearing to the same dimensions as the replacement from ally which just slid on the crank and in the case.  Assembled it to see what I needed to add or take off to get the end float.  Worked for me.
Title: Re: main bearing shimming
Post by: bikerboy on 26.09. 2020 15:08
I find that two small and thin wood chisels do the job, one either side of the bearing, provided you put equal pressure on both chisels my bearings normally pop off not problem
Title: Re: main bearing shimming
Post by: sean on 26.09. 2020 16:54
Spaenaur carries shims ready made in .005 .010 .015 (ordered a shim set from Baxter cycle all were .005 ) I honed the I D of a new bearing so it slips on the crank easily for shim measurement then ordered the same bearing for final use .
I used 2 Bowie hunting knives on their side and twist them to remove the brg
Title: Re: main bearing shimming
Post by: BSAmoto on 27.09. 2020 20:19
Had to shim my crank and did it "my way":
I prefer a tight bearing on the output shaft so I had the shaft laserwelded and ground to the correct diameter. The inner bearing got heated to about 100degr and slipped over the shaft and will stay tight. The outer race was fitted to the cases and cases assembled to measure the play. As play was only 0,25mm I made a shim washer of 0,5mm to go behind the outer bearing. To correct for the needed play the outer race was then removed from the primary case and ground down 0,27mm on the outside - thus giving me 0,02mm sideplay cold. The crankfacing side was ground another 0,5mm to give more space for oilmist entering. The reason for a thicker shim washer is that it is easier to make for me and I can adjust always the play by grinding. The bigger shim behind the bearings outer race is a much larger surface so it will never be beaten to pieces that fly around inside the cases.
cheers, Harty
Title: Re: main bearing shimming
Post by: RDfella on 27.09. 2020 20:25
Good heavens.
Title: Re: main bearing shimming
Post by: sean on 28.09. 2020 13:46
Had to shim my crank and did it "my way":
I prefer a tight bearing on the output shaft so I had the shaft laserwelded and ground to the correct diameter. The inner bearing got heated to about
100degr and slipped over the shaft and will stay tight. The outer race was fitted to the cases
and cases assembled to measure the play. As play was only
0,25mm I made a shim washer
of 0,5mm to go behind the outer
 bearing. To correct for the
needed play the outer race was
then removed from the primary
case and ground down 0,27mm
on the outside - thus giving me
0,02mm sideplay cold. The  crankfacing side was ground
another 0,5mm to give more
space for oilmist entering. The
reason for a thicker shim washer
is that it is easier to make for me
and I can adjust always the play
by grinding. The bigger shim
behind the bearings outer race is
a much larger surface so it will
never be beaten to pieces that fly
 around inside the cases.
 
I have read somewhere but my old foggy brain can’t remember where , not to shim the outer race this is the method Harley uses to set the end play on the older models using the Timken tapered bearings on the crank .....the only  difference I could see between the 2 methods of end play shimming would be possibly off setting the crank shaft .025 or what ever shim was used and putting pressure on something on the timing side of the motoR
cheers, Harty
Title: Re: main bearing shimming
Post by: BSAmoto on 29.09. 2020 20:29
I will never put a thin shim behind a bearing race on the crankshaft. Have seen too many engines with a lot of internal damage due to thin shim pieces floating around, of course never had a problem when putting the shim behind the outer race in the case. And grinding it to the desired size and sideplay is no big deal for me as I have all the neccessary machinery.
cheers, Harty
Title: Re: main bearing shimming
Post by: RDfella on 29.09. 2020 21:15
"I will never put a thin shim behind a bearing race on the crankshaft". Whyever not? The bearing is not rotating on the shaft and the shim is compressed between bearing and flywheel. It can't go anywhere. Only possible failure from an engineering perspective is perhaps if the bearing is a press fit on the mainshaft. In such circumstances, there's no guarantee that the cush drive nut is actually moving the bearing hard up against the shim. Another reason to ensure the bearing is a push, not a press, fit.
Title: Re: main bearing shimming
Post by: BSAmoto on 29.09. 2020 22:39
Easy one: shim on shaft is always thin and has small surface. Take a look at a thin shim after it spent a time between the inner bearingrace and the crank web - it will be dished. By tightening the mainshaft nut it WILL sooner or later slim down and creep out between the relatively small flanges of crank and inner bearing race, thus it becomes dished, only way to avoid this would be a trapped shim but I digress.... Having a sliding fit for a main bearing and relying on the clamping force of the mainshafts nut is not the best engineering practice. You will get away with it up to a point but once the powers that are working on the shaft/bearing are too high - it will just hammer itself lose or to pieces - whatever comes first. This RR crank was worn undersize - of course because the stupids that "restored" this engine did everything wrong and did not have a single clue. So while I had it on the machine to grind the laserweld to size I measured up the available play in the mainbearing (which got oversized by plating/grinding its outer race by 1,5/100mm to restore proper grip in the cases) and decided that I want it to grip the shaft on its own. Again - not suggesting that anyone has to follow my practice but I have the means and machinery to make it right and so I do.
cheers, Harty
Title: Re: main bearing shimming
Post by: RichardL on 29.09. 2020 22:55
Harty,

I, personally, try not to have so little play to correct that only a thin shim will correct it. If I have to make a stack, thicker shims at the ends of the stack. Not having your resources, the shims are behind the inner race. Hasn't failed for about 5K miles since clamping inner race against the web while bearing-retaining  Loctite set up.

Now, to my question. If you pre-shim behind the outer race such that excess height must be ground off that race, how do you measure the amount to grind off?

Richard L.
Title: Re: main bearing shimming
Post by: BSAmoto on 30.09. 2020 10:13
Hello Richard
I assemble the crank into the cases and measure endfloat with the outer bearing race bottomned in the primary case half, all screws, nuts, bolts clamping the cases together - minus sealer.  Then with a dial gauge set up at the cranks end the endfloat is measured. Lets say it is 0,25mm and we want only 0,05mm it would mean I insert a 0,2mm washer behind the inner race or the outer race of the primary side bearing. If I had the correct washer made of suitable material I would be finished here - but I have no suitable washers as I mainly do Norton and Vincent engines. So I made a washer. The reason I use a thicker washer and grind the bearing down a bit is due to my grinding machines not holding a thin shim on the magnetos - it will just fly away or if it stayed on the magneto it will become a bellville spring due to internal stress. So in our example the washer is 0,3mm too thick - this is the amount that I grind off the bearing.  As the radius on the outer race of the bearing is a lot larger than the radius of the recess in the crankcase there is no reason to fear the bearing and washer behind will not go fully home. As I said before - even lose races on the crank with some glue and some clamping force of the primary nut will hold but the amount of transferable output will be reduced and once the shim behind the race is collapsing the wear starts as there is no clamping force at all. You will first notice that something is amiss when you hear the knock when the lose bearing hammered the crank undersize or when the splines on the crank are worn away a good bit - both needing costly repairs.
cheers, Harty
Title: Re: main bearing shimming
Post by: RichardL on 30.09. 2020 15:55
That explains it. Earlier this year (before the fall of Rome) I tried to grind a thin shim using the surface grinder I had access to at the time. With extremely little experience with  surface grinders, I soon learned of the lack of magnet strength to hold the piece and the potato-chipping of the now-waste-of-time part.

Richard L
Title: Re: main bearing shimming
Post by: muskrat on 30.09. 2020 21:47
G'day Harty.
I beg to differ.
In the original set up a C3 clearance bearing is used meaning both inner and outer race is an interference fit (pressed onto crank, shrink fit in case) to give the correct running clearance in the bearing. When the inner is pressed onto the shaft sandwiching the shim and the cush nut is done up to 65-70 ft/lb the shim can't escape. The shim is under two forms of clamping, interference fit of the inner means it won't move and the clamping of the cush nut makes sure of it.
With the shim behind the outer race it is only relying on the shrink of the case around the race (the alloy case expands more than the steel race). Then add any hammering of the crank/outer race due to the end float (which will be larger when the motor heats up). Then add to that any crank flex working through the rollers onto the outer race we have a lot of forces trying to "rock, rattle & roll" the outer race in the case. Notrun used "superblend" bearings to combat this.
In conclusion. If it's done the way it was originally designed there will be no failure of the shim. Most if not all shim failures are due to the inner bearing being loose on the shaft and/or the cush nut not tensioned correctly.
Just the way I see it.
Cheers
Title: Re: main bearing shimming
Post by: BSAmoto on 30.09. 2020 23:48
Hello Muskrat - I see where you come from. That´s why I had added 1,5/100 mm for proper grip on the outer race to make sure the bearing stays in place. (Yes, I ground the outer race internally to get my desired running clearance as it was closing up due to the shrink fit internally and externally) Still the relatively small surface of a shim behind the inner race is not good practice - only if it is trapped which would mean to machine the inner bearing race and cranks flange as well. As I said before - this will easily work up to 40hp or maybe a little more but once you turn 7200 revs on the german autobahn to find out what the thing will do (238km/h) , especially with a 905 Norton (with third mainbearing added in my new crankcase half that was cast for this motor to help the crank coping with the power) those little shims are not up to the job. Lesson learned. Not that I would give the BSA that punishment - it will fly to pieces long before....If the dimensions of crank and case were done correctly, no shim at all would be needed. For Nortons there was only ever a shim to go behind the outer race available - never one to go on the crank. Seems they knew why. I know now too. Yes, the shim was on the timing side - in case you would ask.
I am not giving advice. I just tell what I do and why. Today I added 3 long lost fins to the cylinderhead (two in the middle of the stack), milled and welded up all 5 posts on the head to get proper metal back for new threads, replacing the bronce inserts with inserted helicoils.... did I tell this engine was "restored" by a superduper shop in Nizza / France ;-) Tomorrow I will make proper valve guides and fit them to the head and voila - no more rattle or smoke.
cheers, Harty
PS: superblends were added when the cases got stiffening ribs - before those ribs we got away with very high power output of the 750 Norton - Mr Axtell knew his stuff and prefered the early cases for his hot engines as they were flexing with the crank... just as the thin BSA primary side does.
Title: Re: main bearing shimming
Post by: metalflake11 on 01.10. 2020 02:04
Harty, have you not considered the ultimate solution to this problem, the needle roller bearing conversion?


Title: Re: main bearing shimming
Post by: BSAmoto on 01.10. 2020 08:55
Hello Metalflake: no need for the needle roller bearing in this bike - the last "mechanic" fitted a big oilpump to compensate the knock on the timing side. Now that I made a proper bearing and ground the TS end to cylindrical and round dimensions again I doubt that I will ever wear out that bearing as this bike is to be used around our back roads and will not be thrashed because of 0,060" pistons and last undersize journals of the crank.
cheers, Harty
Title: Re: main bearing shimming
Post by: Truckedup on 03.10. 2020 16:53
 Most of my experience is on Triumphs having ball and roller bearings on both mains. The bearings are supposed to be a light press fit and there's also the CN ,C3 etc internal bearing clearance to consider.. 
 So on the A10, use a  C3 bearing with hopefully a light press fit and shim for a few thousands inch clearance ?