The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Gearbox, Clutch, Primary => Topic started by: jhg1958 on 22.11. 2019 17:26
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Can you get oversized bushes for the layshaft? The bushes are badly scored as is the layshaft. The layshaft is loose in the bearing but it hard to say of that is normal or important.
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As far as I'm aware nos layshafts don't exist. I ground down mine until it was clean and then turned up an undersize bronze bush to suit. Easy to do on a lathe but you'll need a proper cylindrical grinder for the shaft.
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The layshaft small bush and journal are often scored.
NOS swinging arm type layshaft on ebay at the moment;
https://www.ebay.co.uk/itm/BSA-A7-A10-B31-B33-Gearbox-Layshaft-f-Swing-Arm-Mod-42-3019/163941607486?hash=item262bae683e:g:84AAAOSw29ZdyteN
Plunger layshaft is different.
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Thanks for this it is a good spot. At £130 plus £40 for the bushes I think I will see about getting my layshaft reground. This BSA is proving expensive but I suppose I should not be surprised.
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The Layshafts are certainly different, but identical as regards length, the shaft diameters and splines. The essential difference is in the position of the circlip locating groove for the pressed on pinion. The pinions of plunger and S/A boxes are different, having the circlip location machined to match the appropriate layshaft. As long as the layshaft matches the pinion type, they should interchange, but then the rest of the gear pairs may have to be selected to match, as over the years the gear engagement dogs vary in shape slightly...."pointed versus flat" Worth a try, you might be lucky with what you have.
Worth asking your local crank grinder to put a shine on the damaged layshaft.
Swarfy.
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Can you get oversized bushes for the layshaft? The bushes are badly scored as is the layshaft. The layshaft is loose in the bearing but it hard to say of that is normal or important.
Short answer yes, there are suppliers who sell them, this relevant ? https://www.a7a10.net/forum/index.php?topic=6053.0
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Hi All,
The shafts are not that hard and can be turned readily with carbide insert tooling
The most important thing is to dial in the unworn part of the shaft to absolute zero runout
Forget doing this on a lightweight mini lathe *eek*
John
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As far as I'm aware nos layshafts don't exist. I ground down mine until it was clean and then turned up an undersize bronze bush to suit. Easy to do on a lathe but you'll need a proper cylindrical grinder for the shaft.
every layshaft I've ever seen is worn, so I get my engineer to clean up the shaft and make bespoke bushes.
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has anybody tried (successfully) to have the layshaft bearing surface spray welded and reground to size ilo oversize bush?
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I have had them hard chromed and ground to size.
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that's a much better approach Trev, good prompt, I'll see whats available locally, cheers
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I just had a closer look at my layshaft and am a bit confused by the wear pattern. Take a look at the photos please, the end (single) gear is very loose on the end of the shaft because the shaft appears well worn, yet its so specific in the wear pattern that it looks like the shaft is "stepped". Questions it raises for help please:
1. does the end gear ever run on the stepped up part of the shaft and if it does then why is the end sooooo worn? the diameters are 0.747 and 0.738, substantially different and so precisely stepped, why??
2. if the gear needs to run along the whole distance then I'll need to either machine it down to same diameter, maybe 0.73, then make a new bush for the gear, this would seem to be the most cost effective solution vs hard chroming and machining back to standard with a standard bush, is there any reason not to do this eg case hardening of the shaft etc??
appreciate thoughts, thanks
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Jules. No mystery, its a classic example of layshaft wear. With the layshaft 3rd and 2nd gears assembled onto the layshaft, a hardened steel washer goes on, (internal champher facing clutch side) next to the splined shoulder, followed by the big bushed first gear. You should find the wear shoulder is now level with the front face of this gear. This gear does not move along the shaft. It runs between the hardened washer and the top hat face of the layshaft bush. The thickness of the washer controls layshaft endfloat. The wear has taken place where the layshaft bush in the inner cover supports the shaft.
Swarfy.
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thanks Swarfy, so I think what you are saying then, in reality, is that the rest of the shaft is actually "unused", so its effectively still at the original size unworn?? is that right....if that's the case, then I could just replace the bush in the big (1st?) gear to match the worn end of the shaft and leave the shaft as is (assuming the wear is reasonably even all round), is that a real possibility?? cheers
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Jules, the shaft in new, unworn condition is a close as a gnat's knacker to 3/4". BSA Service sheet 702 gives the finished reamed ID of the layshaft bush as 0.7495/0.7505" This dimension is the same for the bush in your first gear. By chance I have a used layshaft to hand, and the plain part of this measures 0.748", slightly less worn than your largest dimension.
The clincher is the other end of the layshaft, which gets most of the abuse. Very bad means replacement or custom grinding as outlined above and a custom bush to fit. If this end is OK, replacing the bush on the first gear, plus a custom undersize layshaft bush, size finished to produce a good running clearance with the most worn part of your shaft should fix things. Really depends on the wear pattern and how close to perfection you want to be. You have at least 10 thou of wear.
New standard bushes are always slightly undersize when fitted, so you may get away with just fitting one and not having to ream to size.
Anyone know how much smaller than nominal size these bushes usually are?
The reason for a softer material "wearing" a harder one is cited as abrasive particles becoming embedded in the soft bush and then proceeding to machine away the shaft.
Swarfy.
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Hi Swarfy, thanks for the explanation, I've just had a closer look and assembled it into the housings...
First point is really end float, is there a max and min? obviously its worn but it seems a lot, yet to measure it..how/where do you shim it out to reduce the end float, because I'm sure that wherever you bias the shaft could affect the gearshift performance, I'm not replacing the blind bush, so maybe put a shim in there?? The hardened washer doesn't have a chamfered side either, does that mean its worn down? whats the best way to fix the end float please? cheers
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there is only one hardened washer that fits on the layshaft and should have a slight relief in it that sits against the shaft and the full flat side against the first gear cog. you don't have to be fussy with shims at the blind bush end, once the sandwich plate and gasket is on it normally is anything between 10 and 20 thou
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Jules, bergs has given you the answer, here's the how and why.
The layshaft has a circlip, in a groove at the blind bush end. This circlip acts as a stop to position the layshaft pinion on the layshaft such that the pinion flat base is level with, or more usually, slightly proud of the layshaft end. This is the datum that positions the layshaft in relation to everything else. This pinion face runs against the top hat face of the blind bush. You can see now that layshaft and loose first gear need a spacer to keep everything within bounds. The spacer is the washer that goes between the layshaft shoulder and first gear cog. No shim or washer is fitted at the blind bush end. Adjusting the thickness of this washer (Part no. 67-3251) controls the layshaft endfloat when the inner cover is replaced. With new bushes, etc a new standard washer should be good enough. Depending on what you have, it may be easier to make one.
The layshaft has a very slight radius where the diameter changes. The correct washer has the inner edge relieved to clear this radius. Maybe your washer is not original. It should be hardened.
Endfloat on the layshaft will depend on the position of the fixed pinion on the layshaft, the amount of wear on the top hat faces of the layshaft bushes, face wear on the first gear cog, the thickness of the washer and also the thickness of the gasket between the inner cover and the gearbox casing. We assume the basic castings are standard.
With old machines that have been through mis -guided hands there is plenty of scope for things to be not quite right.
Plunger and swing arm layshafts are different. Plunger layshaft has a plain blind bush end. S/A has a scroll. Circlip groove is nearer the end of the shaft on plunger, the pinion gears have the corresponding location step deep in the pinion (plunger) or at the dog tips (S/A)
Both shafts are dimensionally the same, so sometimes get mixed up. Check you have the right parts.
Check the pinion is on up to the circlip on the layshaft. If all in order, leave the pinion in place, but if it has to come off, removing the pinion requires a lot of force. Knocking the pinion off the shaft with a steel tube is how the drive dogs get broken off, so use a proper press. One root of the pinion gear teeth has an oil hole, this corresponds with an oilway to the centre of the layshaft.
Swarfy.
Additional. Looking at the second picture I reckon I can see the circlip, at the tip of the pinion dogs, so that should be a S/A layshaft. Even the oil holes line up! Pinion looks to have the later type of round profile drive dogs.
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all clear now, and I found the bevel/chamfer on the washer too, its not much! thanks Swarfy….
I've been going through bits and pieces I bought years back in prep. for this restore and found these new bearings, 2 are for the gearbox and the other is x4 for the wheels ('56 A10 s/a, which has Ariel type full width hubs, I believe), they are all "sealed" type bearings...I'm pretty sure they are the right sizes, but what about the fact they are sealed, is that an issue for the gearbox? I believe they will be fine for the wheels, but do I need to change anything when I fit them, assuming they are correct/ok to use??
see pic..cheers
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you can pop the seals out if you want, on the out put big gearbox ball race I take one side of the seal out to help keep the oil in the box, on the wheels you can leave them sealed, the smaller ball race on the main shaft take them both out if you wish
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thanks Berger, I did consider that, then thought "well if they are sealed for life, why not leave them alone", is there any reason to remove them in this enclosed environment, do you know? if they don't need the splash lubrication, is it actually detrimental to leave them sealed? cheers
PS I measured the layshaft endfloat the other day without sealer/gasket fitted, and its about 15 thou, so figure with the gasket/sealer, it'll end up around 20 thou, which seems a lot of float actually (physically). I've found an old shim that fits the shaft and am thinking it would work well between the floating (1st?) gear and the bush, and will help locate the gear and reduce its potential to "wobble" - what do you think? any reason not to?? cheers
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I remove one side of the big bearing just for it to get oil, they are sealed so muck doesn't get in so there's no harm in letting the gearbox oil fully lubricate the small bearing, as for the float you could try that if you wish but my box ran perfectly with 20thou. to make the bush less wobble it needs bushing to the worn shaft as near as one can be made unless you have the shaft ground true and a perfect bush fitted. the shim might get chewed up. my experience is these boxes run with loads of bush play as mine did for years
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Jules. A single thicker washer is the best way. Moving the fixed layshaft pinion towards the blind bush is another option but would be difficult without a press. If you go down the extra washer route put it between the original washer and the loose first gear. Putting it outboard between gear and bush will alter the gear teeth axial relationship between the first gear and the mainshaft pinion gear.
The large gearbox bearing is effectively in its own poorly lubricated compartment, so could be left sealed. Probably a dab of grease needed to lubricate the oilseal, which will still need to be retained to locate against the bearing and the big circlip. Halfway house is to remove inner bearing shield, as bergs does but leave outer in place as an extra oilseal.
Swarfy.