Crank end float?

[KiwiGF]

I've no experience of the a7 but yes with the a10 when the Cush drive drive nut is done up correctly the inner race of the roller bearing is clamped hard against the crank, and any shims between the the inner race and crank are of course also clamped up.

As per the previous post there should be no real need for  loctite.

I have noticed that it is possible for incorrect Cush drive parts eg the splined sleeve to be fitted but which look ok at first look, so it is best to double check this clamping will occur in practice (no need to fit the spring while checking this) and that you do not parts from a different bike!

If you have an old bearing you can perform trial fits more easily and hence get the shim thickness worked out by using emery cloth to grind out the old inner a small amount so it is a easy fit over the crank and use that for trial figments, when you have the shim thickness right you can then use your new bearing inner, hopefully then only having to fit it once.

[RichardL]

I have been of the belief that the inner race needs to be a good secure (not monster, necessarily) friction fit on the crank and that just tightening the cush nut is not enough to prevent a loose inner race from spinning.  In fact, it wasn't enough the last time my loose inner race spun and ate my shims despite a cush nut torqued to 65 lb. If uncertain about the security of your inner race, I see no reason not to add the Loctite. Knock on wood (because I haven't recently dropped the sump plate) but my shims seem to be still in tact.

Richard L.   

[beezermacc]

When dealing with endfloat forget about the sprocket and cush spring etc. However, it is essential to make sure the crankshaft nut is very tight as this is what stops the main bearing inner race rotating on the crankshaft and wearing the axle out. The end float is caused by the crankshaft floating between the shoulder of the main bearing outer race and the shoulder of the timing side bush; these are the two edges which stop the crankshaft making a sideways bid for freedom. The usual way of limiting endfloat is by fitting shims between the main bearing inner race and the crankshaft flywheel; in effect this makes the crankshaft longer because it puts the inner race closer to the shoulder of the outer race. It is worth getting this right as the conrods are supposed to be at right angles to the crankshaft. Excessive endfloat gives the conrods an opportunity to tilt sideways. Obviously there will be enough clearance at the small and big ends to allow the conrods to travel sideways before they actually tilt but all this waggling about is undesirable and makes for a noisier engine which will wear out sooner.

[duTch]

 Col, I'm not clued up on A7's, but my take on service sheet 208 is that I've led myself to believe (disclaimer) the early A 7's used a ball bearing in the Drive side main, and as a result doesn't have lateral play.

[bsa-bill]

despite a cush nut torqued to 65 lb.

was about to comment  but beezermac did and put it more succinctly than I would, yes 65 or whatever on the outside of the crankcase pulling everything across the crank together - not good for  any mating surfaces in there and negates the point of working towards any clearance at all. one of those things where you need (well ok I need) to see it all before you to understand how it goes.

[East_Coast_BSA]

It is worth getting this right as the conrods are supposed to be at right angles to the crankshaft. Excessive endfloat gives the conrods an opportunity to tilt sideways. Obviously there will be enough clearance at the small and big ends to allow the conrods to travel sideways before they actually tilt but all this waggling about is undesirable and makes for a noisier engine which will wear out sooner.

I was told that the reason has nothing to do with connecting rod side travel or movement.  The reason that you need a minimal amount of side movement is for oiling.  The thrust washer on the timing side needs to be as close to the crank as possible.  Any excess gap or "lateral play" will allow for oil to escape past the thrust washer and into the crankcase, instead of being forced into the crankshaft and up through the connecting rods.  The smaller the gap, the more oil gets pushed through the crankshaft.  It's nothing more than a "regulated leak path", so naturally tighter is better.

[trevinoz]

Col,
                Have a look at the assembly and you will see that when the crank nut is tightened against the splined sleeve, force is transmitted throught the sleeve, spacer and inner race to the crankshaft shoulder thus keeping everything in place. The end float is between the rollers and the outer race lip  and the timing side bush flange and the crank on the timing side.
The long stroke A7 had a ball main bearing which locked the crank in place, as long as the bearing didn't move in the case.

[beezermacc]

I was told that the reason has nothing to do with connecting rod side travel or movement.  The reason that you need a minimal amount of side movement is for oiling.  The thrust washer on the timing side needs to be as close to the crank as possible.  Any excess gap or "lateral play" will allow for oil to escape past the thrust washer and into the crankcase, instead of being forced into the crankshaft and up through the connecting rods.  The smaller the gap, the more oil gets pushed through the crankshaft.  It's nothing more than a "regulated leak path", so naturally tighter is better.

The A10 doesn't have a thrust washer. What East Coast says is true to an extent but is coincidental and not a design feature. If the timing side bush is sufficiently worn to allow oil along its length in quantity the crankcase web may prevent a little bit of oil escaping into the crankcase, but, don't forget that there is nothing on the other end of the timing side bush preventing oil pouring into the timing chest  / crankcase, therefore the 'oiling' argument becomes redundant. A minimal amount of endfloat is required to prevent scuffing of the timing side bush shoulder and main bearing shoulder. Scuffing would cause heat and damage. Excessive endfloat will cause 'barreling' of the big end shells and little end bush and cause the pistons to twist in the bores which will also make the rings barrel.

[RichardL]

Col,
 The end float is between the rollers and the outer race lip  and the timing side bush flange and the crank on the timing side.

First of all, I'm on thin ice when I question either Trev or Andrew (Beezermacc), both of whom I have huge respect for in the BSA-knowledge world. That said, here is the point I am trying to make. It might be wrong, but I'm trying to make it.

Based on what Trev said (above) the endfloat between the outer race lip and the timing side bush means that the pressure against the rollers, and hence against the inner race, and hence against the shims is released to the extent of the endfloat. If you have a loose inner race (like mine in the link) it can then spin. Another way I want to look at this (even if I'm looking blind) is as follows: If you could hold a loose inner race in place with enough pressure from the lip of the outer race pushing against the fractional ends of the rollers, which, in turn, push on the inner race with a fraction of their diameter, it seems to me those rollers wouldn't roll or would be destroyed.

After you kick my ass you have to buy me a beer.

https://www.youtube.com/watch?v=OqDcQTP9xmg

Richard L.

[duTch]

...it seems to me those rollers wouldn't roll or would be destroyed.

So what you're effectively saying, is this tightness in turn could cause the whole bearing to lock up and the shaft will spin around it and destroy the shims. ..?
 Sounds reasonable

[kiwipom]

hi guys, surely the crank is pulled up tight against the inner race with the end float play at the timing side bush,cheers

[KiwiGF]

Dutch, there does seem to be confusion on this and I have pity for the original question asker!

In regards shims being destroyed in my opinion on the a10 this could only happen if the cush drive nut was too loose to clamp the inner race and any shims up tight.

Doing the nut up tight does not (or at least should not) cause the roller bearing to seize. If it seizes there is something seriously wrong.

The end float occurs at both ends of the crank and is measured after doing the nut up tight.

003" end float is quite noticeable and on my bike the 003 movement was quite easily seen and felt and accompanied by a definite clunk as the crank moved, I did not believe it was only 003 until I measured it with a dial gauge.

If the inner race of the roller bearing is not clamped tight by the nut then incorrect parts are causing the problem eg an incorrect splined sleeve. A trial fitting should be made to ensure the splined sleeve can can slide along the crank enough to clamp the inner race, and that the nut can tighten onto the sleeve.

I have come across people who thought the Cush nut should only be done up just enough to allow a split pin to be installed in the end of the crank shaft, however my understanding is that the nut has to be done up tight enough to contact the splined sleeve which in turn pushes the inner race onto the crank eg clamps the inner race up tight so it would then take a lot of force to make it spin and wreck the shims behind it....

[beezermacc]

Let's start from the beginning on this! When you build the bottom end you fit the timing side bush and main bearing outer to the crankcase halves. You fit the inner race to the crankshaft - make sure it is tight up against the flywheel. The inner race must be tight on the crankshaft so there is no danger of it sliding out of position when measuring the endfloat. You fit the crankshaft in the crankcase and tighten everything up. You feel for endfloat and take a reading with a dial gauge. The optimum is 1 thou but the dial gauge will indicate more than 1 thou at this stage. You dismantle it all and fit as many shims as necessary behind the main bearing inner race to reduce the endfloat to 1 thou. You build it all up again (with the conrods this time) and check for 1 thou endfloat with the dial gauge. The endfloat is simply the amount of sideways travel allowed between the main bearing outer and timing side bush. As far as endfloat is concerned that's it - job done. 

All the cush and sprocket stuff is a red herring as it is merely a mechanism fitted onto the end of the crankshaft axle outside the main bearing so it cannot have any effect on endfloat. However, the cush system and sprocket float on a splined sleeve and it is this sleeve (and spacer) which must be securely fixed the crankshaft to prevent backlash and wear on the splines of the sleeve and crank. So the nut on the end of the crankshaft has to be really tight and serves to lock in place the inner cush mechanism and main bearing inner to the flywheel. It is sensible to build the cush and sprocket onto the crank, on the bench, before installing the bottom end into the bike as final tightening of the crankshaft nut may disturb the main bearing inner and, therefore, the endfloat...........

[beezermacc]

First of all, I'm on thin ice when I question either Trev or Andrew (Beezermacc), both of whom I have huge respect for in the BSA-knowledge world. That said, here is the point I am trying to make. It might be wrong, but I'm trying to make it.

Based on what Trev said (above) the endfloat between the outer race lip and the timing side bush means that the pressure against the rollers, and hence against the inner race, and hence against the shims is released to the extent of the endfloat. If you have a loose inner race (like mine in the link) it can then spin. Another way I want to look at this (even if I'm looking blind) is as follows: If you could hold a loose inner race in place with enough pressure from the lip of the outer race pushing against the fractional ends of the rollers, which, in turn, push on the inner race with a fraction of their diameter, it seems to me those rollers wouldn't roll or would be destroyed.

After you kick my ass you have to buy me a beer.

https://www.youtube.com/watch?v=OqDcQTP9xmg

Richard L.

I'm not quite sure what you mean but the problem seems to focus on the inner race of the main bearing. In normal circumstances this is locked in place by the crankshaft nut so it is not free to travel an, therefore, will not release the pressure on the shims. Does that help?

[bsa-bill]

[quote ] the inner race of the main bearing.In normal circumstances this is locked in place by the crankshaft nut so it is not free to travel an, therefore, will not release the pressure on the shims. Does that help?[/quote]

with respect beezermacc - no, it can't be clamped if there is 0.003 thou clearance, and Kiwipom the 0.003 will be at whichever end it decides to be, and Richard the shims are not behind the outer race but behind the inner race.

and I think if I have time I'll dig out a schematic if I can find one  because I'm sure like others I've missed or misunderstood several of the post's on this (including beezermacc's ) as it's going arouns in circles a bit (see what I did there),