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Originally Posted by Magnetoman
Originally Posted by Shane in Oz
I've started machining the 8" dia x 1" steel for the MM press jig,
That jig might not help with your current problem. The jig makes it a lot faster to get the two halves aligned and gently pressed together.
It's looking more and more likely that the crankshaft is going to have to come apart, in which case it will have to be put together again.

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Originally Posted by Stuart Kirk
Originally Posted by Shane in Oz
.......We opened up the gap in the press using..... a wedge ......Before starting, it was 3.002" at the crankpin, and 2.978" opposite. we got it to 2.992", and 0.05mm (0.002") runout.......
The press and wedge idea works fine as well.
As mentioned before, at this stage I would be working with the nuts nearly fully tight and aiming to get the flywheel width within a thou or two all the way around. It looks like you got it down from .024" pinched to .010" pinched.
For whatever reason, the runout on the shafts came down to 0.05mm at that particular amount of pinch. The flywheels seems to want to come back to that point even after being splayed out rather than pinched.

The press wasn't even reading on the pressure gauge with the crankpin nuts rather loose, but tightening the nuts brought the runout back to where it was before.

Applying enough pressure while the nuts are close to final torque might fix things, or it might "fix" them good and proper.

This is the first built-up crankshaft I've done battle with, so it's hard to gauge how much force can safely be applied.

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Originally Posted by Shane in Oz
.......Applying enough pressure while the nuts are close to final torque might fix things, or it might "fix" them good and proper.

This is the first built-up crankshaft I've done battle with, so it's hard to gauge how much force can safely be applied.
You're correct. It is a judgement call and none of us want to damage any rare old parts, but keep in mind these cranks are surprisingly stout, and can be very resistant to moving when one is chasing that last one or two thousandths.

That's why the jack screw idea can be useful. You can get a better feel of how much force is being applied to move the crank.

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Originally Posted by Stuart Kirk
That's why the jack screw idea can be useful. You can get a better feel of how much force is being applied to move the crank.
They are certainly on the to-do list once the press plates have been faced.

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Actually the gauge was reading to the first & second division which I think are 250 kg a piece


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Preparations for the recently completed BSA National rally (it all went very well in the end, in a soggy sort of way) limited the available ZB32A time, but the remaining gearbox parts arrived in the interim.

This, of course, led to reviewing Magnetoman's Alloy Clipper thread for tips on reassembling the rigid/plunger gearbox.

While not as concise as BSA Service Sheet 608, it was rather more entertaining.

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It appears the gearbox is missing the 24-4237 mainshaft spacer between the bearing and 1st gear, so that's another learning exercise on the lathe.

Fortunately, Neale Gentner provided the dimensions and much more useful information on BSA M type gearboxes
The spacer should be 0.755" i.d, 1.225" o.d and 0.125" thick.


While plucking up the courage for the machining, I installed the sleeve on the engine drive-side roller bearing outer race. I was a bit skeptical, but the combination of freezing the race and mini-Mjolner applied to the supplied installation tool managed to get it in place. The o.d. with the sleeve installed is 2.4643", measured at 3 spots. To save referring back, the race is 62mm o.d, or 2.4409", so the sleeve added around 0.024".
That should allow cleaning up the ovality and belling in the housing without removing too much metal. Building up the magneto platform will have to come first, though.

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We proceed apace. A snail's pace, but it's progress of sorts.

The 24-4237 spacer is now machined to size, so if it's not too wet tomorrow I can start on the trial assembly of the gearbox to check end float and selector positions.

I've also pressed the new bearing in to the new QD rear drum, so that's almost ready to assemble.

And just for luck, I also have the crankshaft apart, which was on the "avoid if at all possible" list. There are pronounced lips at the outer ends of the tapers of both flywheels, which could well explain the 0.006" runout.

Time to ask for advice again. The "traditional" way to handle the lips would be to dress them with a file,, but is this something better done with a boring head on the mill? It really does just need a smidgeon taken off, but the boring head should allow much more control.
While the crankshaft is apart, the centres should be tidied up as well to allow runout to be checked between centres as well as on the trueing jig.


...and this was all going to be so straightforward

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Originally Posted by Shane in Oz
........I also have the crankshaft apart.........There are pronounced lips at the outer ends of the tapers of both flywheels, which could well explain the 0.006" runout............The "traditional" way to handle the lips would be to dress them with a file,.....
To go even more traditional, I would consider a deburring scraper to clean up those tapers you have. Does it look like pressure from the nut has deformed the taper caused the burring or has the crankpin been moving in the flywheel? Those crankpins are designed to fully seat the taper AND have the step in the pin pulled up tightly to the inner face of the flywheel. Look to see if there are contact marks there. IIRC, this one was seriously loctited together and may not have been tightened properly.

Originally Posted by Shane in Oz
.............While the crankshaft is apart, the centres should be tidied up as well to allow runout to be checked between centres as well as on the trueing jig.......
That is an excellent plan. Exactly what I would do.

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Originally Posted by Stuart Kirk
To go even more traditional, I would consider a deburring scraper to clean up those tapers you have.
That's a good idea - thanks
Originally Posted by Stuart Kirk
Does it look like pressure from the nut has deformed the taper caused the burring or has the crankpin been moving in the flywheel? Those crankpins are designed to fully seat the taper AND have the step in the pin pulled up tightly to the inner face of the flywheel. Look to see if there are contact marks there. IIRC, this one was seriously loctited together and may not have been tightened properly.
It certainly appears to be from the nut.
That raises another question - would it be worthwhile to chamfer the nut or flywheel slightly?

It was only pinched opposite the crankpin, and pretty well spot-on as far as twist is concerned. It probably hadn't been run after the crankshaft was assembled.
Oh, I almost forgot the grease in the main bearings. It certainly hadn't been run for long like that.

Originally Posted by Stuart Kirk
Originally Posted by Shane in Oz
.............While the crankshaft is apart, the centres should be tidied up as well to allow runout to be checked between centres as well as on the trueing jig.......
That is an excellent plan. Exactly what I would do.
I think it came from one of your posts.

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Originally Posted by Shane in Oz
..
Originally Posted by Stuart Kirk
Does it look like pressure from the nut has deformed the taper......
It certainly appears to be from the nut.
That raises another question - would it be worthwhile to chamfer the nut or flywheel slightly?........
I wouldn't think chamfering the nut or flywheel is a good idea. I would want flat contact faces for those relatively thin crankpin nuts to better resist flexing.

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Originally Posted by Stuart Kirk
I wouldn't think chamfering the nut or flywheel is a good idea. I would want flat contact faces for those relatively thin crankpin nuts to better resist flexing.
Thanks.
That brings me to the next challenge. Somewhere along the way, the nut has chewed the flywheel face - goodness only knows what torque had been used.
Anyway, would it be worth a light pass with a face mill or fly cutter to ensure the surface is flat and parallel to the outer faces of the rim?


btw, did I mention that the thrust washers were missing? It was definitely worth dismantling the crankshaft.
At least the oil ways were clean, and the crankpin doesn't look too bad. The con rod is back on and I pumped a stack of oil in.
Maybe it would have been better to have checked the tapers with bearing blue while it was apart, so it should probably come apart again.


and, of course, there is some bruising to the inner rims of the flywheels allowing them to rock slightly on the mill table, so they will need to be skimmed. The silver lining is that it's an opportunity to experiment with the 5C collets in the lathe.

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Originally Posted by Shane in Oz
Anyway, would it be worth a light pass with a face mill or fly cutter to ensure the surface is flat and parallel to the outer faces of the rim?
The surface doesn't need to be parallel to the rim, it needs to be accurately perpendicular to the taper. Use the shaft to fixture the flywheel taper parallel to the mill's spindle and then face the surface (nb. this sentence was easier to write than it will be to do...).

Originally Posted by Shane in Oz
it's an opportunity to experiment with the 5C collets in the lathe.
I don't know what the spec is on a 5C collet, but asking it to hold a BSA flywheel seems like it could be pushing it.

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Originally Posted by Magnetoman
Originally Posted by Shane in Oz
it's an opportunity to experiment with the 5C collets in the lathe.
I don't know what the spec is on a 5C collet, but asking it to hold a BSA flywheel seems like it could be pushing it.
The cunning plan is to hold the mainshaft in the collet, then skim the inner rim of the flywheel, which in theory should then wind up with the face perpendicular to the mainshaft and crankpin hole.

The drive side mainshaft is 25mm diameter, so the 1" collet should hold that. The timing side mainshaft is 7/8", so that's covered.
This is the first time I've used the 5C collets, and it turns out that the draw tube needs a spacer, which didn't come with the lathe adapter.

Sigh. Making the tools to make the tools to work on the bike.

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Originally Posted by Shane in Oz
Making the tools to make the tools to work on the bike.
The next circle is re-making the tools that you forgot you already had made to make the tools to work on the bike.

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How about some somewhat simple micrometer measurements first? Measure thickness of the web around the crankpin, assuming it isn't too torn up from years of use (abuse?). If it is fatter at the flywheel rim, that could be part of the truing problem and could be from simple wear and tear, OR BSA lack of quality control.
Do you have a source for those missing thrust washers?

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The 1" collet doesn't have the range to clamp the drive side mainshaft fully, so I've ordered a 25mm collet, which should arrive by the end of the week.
On the other hand, the 7/8" collet seems to clamp the timing side mainshaft quite well, but it's not fully dialled in on al faces yet.

Originally Posted by Stuart Kirk
How about some somewhat simple micrometer measurements first? Measure thickness of the web around the crankpin, assuming it isn't too torn up from years of use (abuse?). If it is fatter at the flywheel rim, that could be part of the truing problem and could be from simple wear and tear
The plan was to skim the inner face of the flywheel rim, then clamp the flywheel on the million table on 1-2-3 blocks, dial the shaft in vertically and then check the mounting face before skimming it.
Magnetoman, cyborg and you will all go crook on me if I don't tram the spindle, so I'll do that first.

Originally Posted by Stuart Kirk
Do you have a source for those missing thrust washers?
They're now on order from Mike Reilly.

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“No plan of operations extends with certainty beyond the first encounter with the enemy's main strength.”
Field Marshall Helmuth von Moltke

If experience is any guide, how you actually end up doing it will be slightly (or significantly) different than how you initially plan to do it, so remain vigilant against the buildup of tolerances. Skimming a face such that it ends up slightly tilted with respect to the taper for the shaft will result in the nut trying to tilt the shaft off-axis.

A 1"-dia. surface that has a TIR of a seemingly-negligible 0.0001" would, if there were no other constraints (which there are) tilt a 4" shaft to give it almost a 0.001" TIR. A slightly exaggerated drawing showing the effect of facing the bottom surface not quite perpendicular to the axis of the taper:

[Linked Image]

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Originally Posted by Magnetoman
Skimming a face such that it ends up [i]slightly tilted with respect to the taper for the shaft will result in the nut trying to tilt the shaft off-axis.

A 1"-dia. surface that has a TIR of a seemingly-negligible 0.0001" would, if there were no other constraints (which there are) tilt a 4" shaft to give it almost a 0.001" TIR. A slightly exaggerated drawing showing the effect of facing the bottom surface not quite perpendicular to the axis of the taper:
That is most certainly a concern, which is one of the reasons for asking for advice from those who have been there and done that.

I'll try to get some pics and measurements posted today. The runout on the drive side can be explained by the collet allowing the shaft to rock, so I'll wait for the 25mm collet to arrive before removing any metal. The timing side flywheel has runout as well, despite the collet holding the shaft snugly.

Fortunately, the flywheels are 8" dia, so the TIR of each shaft should be less than the TIR of the flywheel surfaces.


Hmmm, the mainshafts are riveted to the flywheels, so they might not be dead perpendicular.or dead centre. That calls for another revision to the plan. and probably more tools to make tools to make tools to work on bikes.

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Originally Posted by Shane in Oz
That calls for another revision to the plan. and probably more tools to make tools to make tools to work on bikes.
I'm reminded of advice a family friend gave my wife when I was about to get my degree and we would be moving to Chicago. When my wife expressed concern about what she would do after the move, the friend told her to just have a kid and that would take care of her time. Based on that, if anyone has concerns about finding something to fill their free time after they retire, my advice is to just buy a BSA and rebuild it. Hell, forget buying a bike, just buy a BSA crankshaft and rebuild it. That should take care of at least a year...

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Originally Posted by Magnetoman
Hell, forget buying a bike, just buy a BSA crankshaft and rebuild it. That should take care of at least a year...
At least it's slightly cheaper than painting a Vincent smile

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Originally Posted by Shane in Oz
Originally Posted by Stuart Kirk
....... Measure thickness of the web around the crankpin,.... If it is fatter at the flywheel rim, that could be part of the truing problem.......
The plan was to skim the inner face of the flywheel rim..........

Originally Posted by Magnetoman
.......Skimming a face such that it ends up slightly tilted with respect to the taper for the shaft will result in the nut trying to tilt the shaft off-axis......
[Linked Image]

MM's eloquent artwork exactly illustrates the reason to first measure for variation the width of the boss (web) around the crankpin.

Any attention to inner or outer faces on the flywheel rim or counterweight is for now a distraction from the real problem.

If the BSA crankpin didn't have those steps in it and had a constant diameter bearing surface like a Harley, you could install the pin in one half, put it on (previously checked and trued) centers in the lathe, and then with the pin at TDC do a lengthwise sweep of its top surface to see if it's in agreement with the axle shaft. If it slopes, you could have a problem with the taper.

Since the BSA pin isn't straight, you might need to make a dummy pin for a checking tool.

Alternatively, do a thorough clean, inspection and deburr, and then reassemble and see if it trues up any better. That's the "toaster effect". Basically, you take it apart, shake the crumbs out, and lo and behold it starts working again, but you don't really know why. It works for me every now and then but it also pisses me off. I like to know what I did.

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Originally Posted by Shane in Oz
Originally Posted by Magnetoman
Hell, forget buying a bike, just buy a BSA crankshaft and rebuild it. That should take care of at least a year...
At least it's slightly cheaper than painting a Vincent smile
Low blow that.

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Originally Posted by Stuart Kirk
Originally Posted by Shane in Oz
At least it's slightly cheaper than painting a Vincent smile
Low blow that.
You have to excuse Australians for their behavior, no doubt due to having been confined to an island covered with deadly species in the middle of nowhere after having been shipped there from debtors prison.

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Originally Posted by Magnetoman
Originally Posted by Stuart Kirk
Originally Posted by Shane in Oz
At least it's slightly cheaper than painting a Vincent smile
Low blow that.
You have to excuse Australians for their behavior, no doubt due to having been confined to an island covered with deadly species in the middle of nowhere after having been shipped there from debtors prison.

Irish political prisoners if you don't mind sir
+ free settlers who committed some social crime making them unacceptable in a civilised society
Then of course there were the dregs left over from the Californian gold rush.
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