The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: sprint on 28.06. 2013 18:43
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What is the acceptable limits for the crank end float on a Super Rocket?
Thanks
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Hi.
The maximum permissible crankshaft end float is 0.003". This is all to do with the main bearing type used, and end float controlled by shim,s.
Correct measurement procedure is important, suggested methods are by using dial Indicator or feeler gauges.
Upon engine reassembly target would be 0.001" end float, but never easy to obtain accurate measurement.
Search topic,s regarding end float to learn inspection methods
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Thanks for the reply.
What are the implications of having more than 0.003"?
Since the crank is effectively sprung loaded on the drive side via the shock absorber spring is the drive side bearing of the split roller or a ball type? Either way the crank is free to move slightly under the tension of the spring?
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Hi, try these searches (from the forum welcome page, or in A7 & A10 Engine or from http://www.a7a10.net/forum/index.php?action=search):
crank end float
end play
crank shim
see http://www.a7a10.net/forum/index.php?topic=1352.0 for search tips.
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What are the implications of having more than 0.003"?
Since the crank is effectively sprung loaded on the drive side via the shock absorber spring is the drive side bearing of the split roller or a ball type? Either way the crank is free to move slightly under the tension of the spring?
Well, nothing really terrible is going to happen with -say- .010" end float. PITA to do as you have to drag the bearing off the crank to correct it.
The spring loading of the shock-absorber is only applied to the sprocket. Its self-contained to the sprocket shaft assembly. Has no effect on the crank as a whole.
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What are the implications of having more than 0.003"?
Since the crank is effectively sprung loaded on the drive side via the shock absorber spring is the drive side bearing of the split roller or a ball type? Either way the crank is free to move slightly under the tension of the spring?
Well, nothing really terrible is going to happen with -say- .010" end float. PITA to do as you have to drag the bearing off the crank to correct it.
The spring loading of the shock-absorber is only applied to the sprocket. Its self-contained to the sprocket shaft assembly. Has no effect on the crank as a whole.
Thanks for the reply.
That is a bit more confidence for me as 0.010" is what it currently measures with a dial gauge. It looks like the guy who re-built it put the shim between the bearing and the oil seal distance piece and not between the crank and the bearing? I m loathed to have to do a complete engine strip unless it is absolutely critical/necessary?
Is it a ball or two part roller bearing that is fitted to the drive side?
However, it is my understanding that there is a sliding bush on the M/S that the E/S, cam, and spring are attached to with only the crank nut being directly connected to the shaft so the crank will be free to move on this sliding bush the extent of what ever free play there is under the S/A spring tension alone? Or have I got it wrong?
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Yeah, I see what you're saying. Its been about 30 years since I worked on a A10 cush-drive! I cant remember if the nut tightens up on something solid or just tensions the spring.
But for this to allow crank movement, the inner bearing would have to be a sliding fit on the crank. Which it isn't.
The main bearing is a roller, so this allows end float.
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Hi Andy,
The crank nut MUST tighten against the sleeve solidly this forces the sleeve against the seal spacer, then the bearing +any shims aginst the crank, when its all tighened up theres no spring effect on the crank.
The main bearing is a single lipped roller
HTH
John
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I have just joined the Forum today, and ask you sainted members for an opinion on the crank end float. I have re-commenced the final stages of getting my 1960 A10 Golden Flash up and running, having purchased this bike from England in 1985. Most work was done from 1987-1989 (Yes it has been a while). I was starting to panic, as my knees are starting to weaken ( I am 64)and I want to get to kick-start and ride this machine.
I had assembled the motor in 1989, but thought I should now dismantle and re-assemble due to the time interval. This time, I am getting the help of a more experienced British bike restorer, but this is his first A-model. I fitted an NF206 drive side bearing. This seems to be the most-often specified bearing, and it allows the outer race to remain in the housing whilst the inner race can slide out of the housing still attached to the crank. The bloke helping me (Phil) is puzzled by the timing side bush, which is a typical steel outer with bronze insert. The steel face bears against the end of the T/S crank is also steel. I had set the end float to 0.0015" using shims behind the D/S bearing as per the BSA Service Sheets. There is nothing to prevent the crankshaft from wearing up against the T/S bush. He was expecting to see the steel outer of the bush to have a bearing metal such as white-metal or bronze, and I must say that it has always seemed odd to me. I know there should be no shims on the T/S end, so is it correct to use the NF206 bearing and the usual T/S bush.?
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Col,
Welcome to the forum. That's a pretty good intro. Looking forward to some photos.
The simple answer is, yes the steel face of the bush is designed to ride up against the crankshaft web in a world of oil. I think the forces there are not great, being only the result of the cush spring force and incidental side-to-side bumpimg, which you have gone a long way to avoid by getting the play to 0.0015". One thing to be careful of is any looseness in the inner drive-side race on the crank. If you have doubt, some Loctite 641 bearing-hold juice might be the answer. If the race spins, conventional shims get shredded. Some folks here have gone with a one-piece shim which has been ground to fit.
Richard L.
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Hi, Col & Welcome
If your T/S bush is two piece make sure the two pieces are pinned/pegged together
There are several posts here on the merits/ and arguments of different bush types
What is certain is that after this many years a lot of bushes are not a good fit in the crankcase causing loss of oil pressure to the bearings
It would seem that a trued up case and custom one piece bush is the way to go (other than needle roller conversion)
Make sure the crank sludge traps are cleaned
Check oil pump and pressure release valve or fit new ones
The main bearing you have is the correct type
I think the forces there are not great, being only the result of the cush spring force and incidental side-to-side bumpimg,
Richard,
Cush drive spring and assembly are captive on the drive side and do not affect crank bearings or shimming
HTH
John
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Thanks for the reminder. John. Definitely not pulled (or pushed) toward the timing side bush, so, no forces on that face due to the spring. I knew that at one time but you made me refresh my memory (and accuracy).
Richard L.
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Thanks Richard & John,
Can I then assume that the only way to prevent the inner D/S bearing from spinning and shredding shims is to ensure it is a fairly tight fit, using Locktite if needed.? There seems to be no other means of ensuring that the shims remain firmly trapped behind the bearing.
Cheers
Colin
Here is a recent shot as I lowered it from my mezzanine.
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Thanks Richard & John,
Can I then assume that the only way to prevent the inner D/S bearing from spinning and shredding shims is to ensure it is a fairly tight fit, using Locktite if needed.? There seems to be no other means of ensuring that the shims remain firmly trapped behind the bearing.
Cheers
Colin
Here is a recent shot as I lowered it from my mezzanine.
I used loctite on mine because it spun and ate the shims, but I believe that the root cause was the cush-nut being loose. That nut tightens up the entire stack of components (outer spring retainer/nut, splined sleeve, shim and inner bearing race). This is what prevents the inner race from spinning on the crank. I think the spec. is around 65 ft/lbs. That will hold it in place, I just used the loctite because I happen to have some in the garage.
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Hi East Coast BSA,
I thought that only applied to early A7 models. ie. tightening up the cush drive pulls the crank up tight. BSA Service Sheet 208 says that this does not apply to the A10. (See Attachment) However, there appears to be no mechanism to pull up on the bearing other than tapping up the bearing against the shims using Loctite to tighten everything up before assembly in the crankcase.
So for the later A10's, is this all that prevents the shims coming loose.?
Cheers
Colin
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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...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 *smile*
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hi guys, surely the crank is pulled up tight against the inner race with the end float play at the timing side bush,cheers
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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....
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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...........
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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?
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[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),
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The .003 'clearance', if we use the correct terminology is 'endfloat', in which case the inner race is clamped to the crankshaft but is free to float with the crankshaft until the rollers hit the shoulder of the main bearing. The inner race must be clamped to the crank or it will spin and wear the axle out, and the shims will wear and drop out.
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Well Chaps,
Sorry I have opened up yet again a can of worms which seems to have been aired several times on the forum in the past, but I think I now understand.
There is a wide range of views on the assembly of the crank. So here is my summary--
I did assemble it correctly all those years ago to 1.5 thou end float, using shims totalling 14 thou, but do not remember whether I fully understood it then.
I did not use any Loctite.
Now that I have it apart, I will remove the inner bearing, recheck the shims and refit the inner bearing using a smear of Loctite 641, which seems to the most suitable Loctite composition. To be safe, if I find that I have used a number of very thin shims, it may be good insurance to replace them with fewer but thicker shims. I see they can be purchased in 2,6 and 10 thou packs on eBay or get some made.
I will duck down to the workshop and check out the drive side cush assembly in next few days, and if you are correct I should see that there is a sleeve over the D/S crank which passes through the outer D/S bearing and locks up against the D/S Inner bearing to clamp the shims tightly between the D/S Inner bearing and the crank web. This will allow the whole crank and cush assembly to move back and forth to the amount of end float, hopefully only about 1 - 1.5 thou.
Given the relatively warm Australian climate, I don't think I need any more end float.
Is my thinking correct.?
I'll get back to you later.
Cheers
Colin
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Yeah Col, sounds good..except which passes through the outer D/S bearing
..but I know what you mean, so all good *wink2*
NB re my earlier acknowledgement of Richards idea- was done on the phone in some down time on a job...tricky to stay on track, I knew what he meant at the time(maybe I put the wrong sugar in my coffee *eek*)
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All,
First, apologies for causing some trouble here with my misread of Trev's post. Now very obvious, in retrospect, that pressure on the rollers is not what's pushing on the inner race. (Bill, I don't think I said that the shims were behind the outer race, but amongst my other errors, so what.) Now, reading Trev's post (and then Beezermacc's) more clearly, end-float existing between the lip of the outer race and the face of the TS bush is also obvious in retrospect. My lingering question, and I am not even going to try to answer it myself, is this: could the inner race creep around the crankshaft regardless of the tightness of the cush nut?
Finally, back to the simple advice that I thought was good way back in this thread. What's wrong with throwing in some Loctite to provide a touch of insurance against a loosening cush nut?
I hope this makes up for my most recent stupidity.
Richard L.
P.S. Forum title demotion forthcoming.
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loose = yes, tight = no
If the nut (no not you) loosens it will move eventually regardless of loctite.
Yes Richard. Lost & Bewildered will be your new title.
Cheers
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it will move eventually regardless of loctite.
My Dear Ozzie Mentor,
Are we talking about the same Loctite? This stuff ( http://www.loctite.com.au/3319_AUE_HTML.htm?nodeid=8797924360193 ) is not supposed to let go until you put 250ºC directly on it.
Richard L.
Mystified and Flummoxed
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right then, apologies for misinterpreting various aspects of this thread if needed.
beezermacc, I assumed by clamping you meant laterally in which case no float, but I'm going to be in there shortly so better get it sorted in me mind.
Richard - no you most certainly did not say the shims were behind the outer race, I sort of read that in with the clearance between the outer bit.
could the inner race creep around the crankshaft regardless of the tightness of the cush nut?
this morning I was sure that would be a yes - now *smile*
btw way I'm still pondering your forum binge posting *conf*
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Richard - no you most certainly did not say the shims were behind the outer race, I sort of read that in with the clearance between the outer bit.
No issue, at all. Who could blame you while it was nested amongst my actual misunderstandings.
Richard L.
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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...........
This is also my understanding of how everything works. When I put loctite on my inner bearing, I bolted up everything on the bench (including the cush-drive) before I measured end float. It was tedious because I had to do it a few times, but I'm pretty confident that it was correct when I installed the engine back into the bike.