Author Topic: Crankshaft side play/shims etc  (Read 3960 times)

Online bsa-bill

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Re: Crankshaft side play/shims etc
« Reply #45 on: 24.11. 2015 11:48 »
Quote
Allowing the inner race to turn against the shims and wreck them.

Some fettle this by peening the crank, not something that I'd be happy with but maybe there are members here with a more professional view
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Offline BSA500

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Re: Crankshaft side play/shims etc
« Reply #46 on: 24.11. 2015 12:09 »
The bearing inner race is not 'sloppy' in its fit, no play, just doesn't require a puller to get it off like other people have reported.I will be trying the loctite 461 or other type of bearing 'glue'.

Online chaterlea25

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Re: Crankshaft side play/shims etc
« Reply #47 on: 24.11. 2015 18:12 »
Hi BSA500,
If the cush drive nut is properly tightened how the bearing can move relative to the crank and chew up the shims, is the question  *????*
If there is miniscule space between the shaft and bearing (sliding fit) I can see engine vibration and driving foces overcoming the clamping force of the cush drive nut leading to wear on the softest item (the shims) 
I do not think "loctite" is a permanent  repair *sad2* Remember heat softens loctite type products

So solution's ??

1) have the shaft built up and remachine to press fit ?
This would be the "perfect fix"

2) instead of placing the shims between the crank and bearing, fit shim between the bearing outer race and crankcase,
At least this would not result in more chewed up shims ?

3) Attempt the loctite repair and have to repeat it again in a couple of thousand miles if you are lucky *problem*

My 2 cents worth
John
1961 Super Rocket
1963 RGS (ongoing)

Offline BSA500

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Re: Crankshaft side play/shims etc
« Reply #48 on: 24.11. 2015 20:37 »
Over the years the time between shim chewing has varied quite alot with no obvious reasoning. I have been riding this bike for 25+ years and the cush nut has never been loose so hopefully we can ignore that.
I think that some bearing inner races may have been a little tighter by a few thou depending on supplier and that may have saved some shims. I only noticed the shims were chewed this last time when I took it down for a rebore no other indication like vibration just a lack of power.(not a lack of smoke  :! ).
I shall try the loctite 641 (not 461 duh) as the crank work is a little out of my budget(none) and finding someone local is a chore-there is one company but the prices are eye watering  *eek*.
Just to add I have had many thousands of miles before the shims went over the years its just working out why some fail early-this time it wasn't really a fail as it appears that a)I'm a tonka and mis measured or b) the bearing shifted which is still my fault-probably

Online cyclobutch

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Re: Crankshaft side play/shims etc
« Reply #49 on: 25.11. 2015 08:19 »
The ID of the inner race should not vary anything like as much as a few thou, it must surely only be tenths. But it’s an interesting point – if you could either find a bearing factor who would take the time to find you one on the tight side of whatever tolerance is provided, or if you have a local tame one who would allow you a happy Saturday morning in their storeroom pulling them one by one from their packaging until you found one with a better fit. Like they're going to hold a big stock of these.
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Offline BSA500

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Re: Crankshaft side play/shims etc
« Reply #50 on: 25.11. 2015 08:59 »
The ID of the inner race should not vary anything like as much as a few thou, it must surely only be tenths. But it’s an interesting point – if you could either find a bearing factor who would take the time to find you one on the tight side of whatever tolerance is provided, or if you have a local tame one who would allow you a happy Saturday morning in their storeroom pulling them one by one from their packaging until you found one with a better fit. Like they're going to hold a big stock of these.
Local bearing factors rarer than hens teeth. Brammer is my nearest one and they want your first born as a down payment.

Online cyclobutch

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Re: Crankshaft side play/shims etc
« Reply #51 on: 25.11. 2015 12:06 »
Kind of figured I was probably dreaming.

I was apprenticed at Hoffmans in Chelmsford. Whenever I was helping myself to ball races off the line there I used to pick the quietest ones off the noise test rig just before they went into packaging.
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Online RichardL

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Re: Crankshaft side play/shims etc
« Reply #52 on: 25.11. 2015 12:47 »
Hi BSA500,
If the cush drive nut is properly tightened how the bearing can move relative to the crank and chew up the shims, is the question  *????*
If there is miniscule space between the shaft and bearing (sliding fit) I can see engine vibration and driving foces overcoming the clamping force of the cush drive nut leading to wear on the softest item (the shims) 
I do not think "loctite" is a permanent  repair *sad2* Remember heat softens loctite type products

So solution's ??

1) have the shaft built up and remachine to press fit ?
This would be the "perfect fix"

2) instead of placing the shims between the crank and bearing, fit shim between the bearing outer race and crankcase,
At least this would not result in more chewed up shims ?

3) Attempt the loctite repair and have to repeat it again in a couple of thousand miles if you are lucky *problem*

John,

I am sticking my neck way out when I counterpoint with someone like yourself with sooo much more bike building experience than myself. Nevertheless, here goes.

If the cush drive nut is properly tightened how the bearing can move relative to the crank and chew up the shims, is the question  *????*

I believe that, if this were true, there would be no space for oil film between the ends of the rollers and the shoulders of the races.

I do not think "loctite" is a permanent  repair *sad2* Remember heat softens loctite type products

So far, it seems to be at least a 1000-mile fix, but I admit that I'm not pulling my sump plate to certify my sump is shim-free. Regarding "softening" of the Loctite, the disassembly temperature (while hot) of 641 is about 100 deg. C. greater than the operating temperature of motor oil and about 50 deg. C. more than the flashpoint of Castrol GTX 20/50. (I had to go looking up this data.)

Attempt the loctite repair and have to repeat it again in a couple of thousand miles if you are lucky *problem*

I'll report back in another 1000 miles (or sooner?) if this happens.

Richard L.
Plan on signing up for the world-wide 2017 DISTINGUISHED GENTLEMAN'S RIDE on September 30, 2018. Watch website at https://www.gentlemansride.com for details.

Offline trevinoz

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Re: Crankshaft side play/shims etc
« Reply #53 on: 25.11. 2015 20:06 »
Richard, have a good look at the drive side arrangement. Tightening the cush nut against the splined sleeve will hold the inner race tight against the crankshaft. This has no relation to bearing clearance, i.e. end float, which is set by shims, thus giving end of roller clearance for the oil film which concerns you.

Offline East_Coast_BSA

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Re: Crankshaft side play/shims etc
« Reply #54 on: 25.11. 2015 20:12 »
I chewed up the shims in my motor after about 2000 miles.  The Cush-nut was loose.  I removed the engine (complete) and lifted the cylinders up just enough to get the cases apart.  I was able to get some more shims from the fellow who rebuilt the motor.  I got the end play down to .003".  I also used a Loctite Stud and Bearing mount that's good to 500 F on the inner race.  I always use Loctite 518 for case halves.  You smear it on with your finger, just enough to turn the aluminum red.  There was no measurable change in the end play after application.  Nothing squeezes out either, so the film is down in the "tenths" range.  I use the same stuff of the base gasket for the cylinders.  It works very well.  After 1500 miles, my end play is still good and nothing in the screen.  The best way to ensure proper torque on the cush-nut is to "Rope" the cylinder.  Back the crank off about 90 degrees from TDC on the compression stroke and slide a good amount of thin rope into the cylinder.  Turn the motor until it locks and torque the nut.  This is the recommended method from Rotax and it works well on any application.  As far as locking the inner race, it only needs more force than is applied by the spinning bearing.  Most two-strokes have crank bearings that you heat to 300 degrees F and drop them on the crank.  The interference is only a few thousandths.  They wll spin at better than 10,000 RPM and hold without any problem.  You would be amazed how easy they are to press off.  A proper torqued cush-nut at 60 ft/lbs is more than adequate for holding the inner race in position.  I used a touch of Loctite as a "Belt and Suspenders" type of thing.  I'm sure there would be no problem if I didn't use it, but since it was apart I applied it.

Online RichardL

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Re: Crankshaft side play/shims etc
« Reply #55 on: 25.11. 2015 21:36 »
Trev,

I am both glad and sorry to say that you are right, but, of course. I had to run to the garage to partially put my disassembled A7 back together to see it properly. So, is this then saying that no matter how loose the inner race is it will not spin with a well-tightened cush nut?

This leads to my next question. With a loose inner race, are we depending on friction between the compressed shims to be sure the inner race keeps turning at exact shaft speed?

Finally, should I just give up and admit that shim destruction only occrs with a loose cush nut? *????* *conf* *smile*

Richard L.
Plan on signing up for the world-wide 2017 DISTINGUISHED GENTLEMAN'S RIDE on September 30, 2018. Watch website at https://www.gentlemansride.com for details.

Online chaterlea25

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Re: Crankshaft side play/shims etc
« Reply #56 on: 25.11. 2015 23:14 »
Hi Richard,
Trevor beat me to respond to your last Q

Quote
So, is this then saying that no matter how loose the inner race is it will not spin with a well-tightened cush nut?

This leads to my next question. With a loose inner race, are we depending on friction between the compressed shims to be sure the inner race keeps turning at exact shaft speed?

Finally, should I just give up and admit that shim destruction only occrs with a loose cush nut? *????* *conf* *smile*

Try and imagine this scenario *????*

The cush nut will clamp the bearing race and shims  endwise,
Suppose there is even a 1- 2 thou radial gap between the bearing inner and crank mainshaft
The pressure holding the bearing inner depends on the friction between the end faces of the bearing race
and crank oneside and spacer  on the other

I can see engine power pulling the crank towards the gearbox?
the power stroke pushing the crank downwards against the bearing?
engine vibration acting in a couple of different directions? (vectors)

I can see all these forces overcoming the clamping friction and the crank moving realtive to the beairng inner
by our supposed 1 - 2 thou
This tiny amount of movement over thousands of engine revolutions would eat away at the shims  *ex*
Of course as the shims wear and clamping pressure from the nut is lessened  so the shims wear more until they break up  *sad2
Then you go to clean the sump filter and find the remains there *problem*
You then embark on a strip down only to find the cush drive nut loose and blame yourself for not doing it up properly *????*
When in fact it is loose because of the loss of the shims and the resultant wear on adjacent parts *ex*

Aside from the temperature considerations of using loctite,
Does it have the mechanical strength of steel to withstand the mechanical stresses mentioned above ?
I very much doubt it *sad2*

I have heard of bearing races being electro plated to increase their interference fit ?
But I have no experience of this !!

John's 2 cents worth *????*









1961 Super Rocket
1963 RGS (ongoing)

Offline East_Coast_BSA

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Re: Crankshaft side play/shims etc
« Reply #57 on: 25.11. 2015 23:27 »
Trev,

I am both glad and sorry to say that you are right, but, of course. I had to run to the garage to partially put my disassembled A7 back together to see it properly. So, is this then saying that no matter how loose the inner race is it will not spin with a well-tightened cush nut?

This leads to my next question. With a loose inner race, are we depending on friction between the compressed shims to be sure the inner race keeps turning at exact shaft speed?

Finally, should I just give up and admit that shim destruction only occrs with a loose cush nut? *????* *conf* *smile*

Richard L.


I would say that pretty much covers it.  Since the inner race spins freely on the crank, the amount of diametral clearance doesn't matter.  It's not a source of "resistance" when it comes to spinning.  Loose is loose.  Most shim stock is in the upper 40's to low 50's in hardness (Rockwell C scale), which means it's not much softer than the bearing race and definitely harder than the crank.  There isn't any compressability issues going on there.  It's certainly not going to distort in any way when it's torqued into place.  60 ft/lbs of torque on such a small area is a lot of force, and you only need enough to overcome the force generated by the spinning bearing.  The few stories I've heard of shim destruction involved loose Cush-nuts.  When I spun mine, the first thing my motor guy asked was "Did you torque the Cush Nut?".

Offline East_Coast_BSA

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Re: Crankshaft side play/shims etc
« Reply #58 on: 25.11. 2015 23:33 »
Hi Richard,
Trevor beat me to respond to your last Q

Quote
So, is this then saying that no matter how loose the inner race is it will not spin with a well-tightened cush nut?

This leads to my next question. With a loose inner race, are we depending on friction between the compressed shims to be sure the inner race keeps turning at exact shaft speed?

Finally, should I just give up and admit that shim destruction only occrs with a loose cush nut? *????* *conf* *smile*

Try and imagine this scenario *????*

The cush nut will clamp the bearing race and shims  endwise,
Suppose there is even a 1- 2 thou radial gap between the bearing inner and crank mainshaft
The pressure holding the bearing inner depends on the friction between the end faces of the bearing race
and crank oneside and spacer  on the other

I can see engine power pulling the crank towards the gearbox?
the power stroke pushing the crank downwards against the bearing?
engine vibration acting in a couple of different directions? (vectors)

I can see all these forces overcoming the clamping friction and the crank moving realtive to the beairng inner
by our supposed 1 - 2 thou
This tiny amount of movement over thousands of engine revolutions would eat away at the shims  *ex*
Of course as the shims wear and clamping pressure from the nut is lessened  so the shims wear more until they break up  *sad2
Then you go to clean the sump filter and find the remains there *problem*
You then embark on a strip down only to find the cush drive nut loose and blame yourself for not doing it up properly *????*
When in fact it is loose because of the loss of the shims and the resultant wear on adjacent parts *ex*

Aside from the temperature considerations of using loctite,
Does it have the mechanical strength of steel to withstand the mechanical stresses mentioned above ?
I very much doubt it *sad2*

I have heard of bearing races being electro plated to increase their interference fit ?
But I have no experience of this !!

John's 2 cents worth *????*



Just because the crank is pulled or deflected does not mean that the torque disappears.  It means that it will increase the pressure on one side of the race as opposed to the other side.  It doesn't eliminate it.  Once again, the force that is required only has to be greater the force of the spinning bearing. 

Online RichardL

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Re: Crankshaft side play/shims etc
« Reply #59 on: 26.11. 2015 02:03 »
  There isn't any compressability issues going on there. 

East Coast,

A lot of interesting stuff in this. Just for clarification, regarding compression of the shims, I wasn't referring to squishing but to the affect on static friction.

John,

It seems you are saying that shim destruction is inevitable, with the inner race working its way loose regardless of an initially tight cush nut. Yes, that would be sad. Incidentally, the last time my shims got shredded I thought the cush nut was tight, but it wasn't. I don't want this to be some definitive explanation, but it does seem oddly coincidental.

Richard L.

 

Plan on signing up for the world-wide 2017 DISTINGUISHED GENTLEMAN'S RIDE on September 30, 2018. Watch website at https://www.gentlemansride.com for details.