The BSA A7-A10 Forum

Technical => Clutch, Primary, Gearbox => Topic started by: Davie L on 29.08. 2012 19:05

Title: Layshaft bush external diameter
Post by: Davie L on 29.08. 2012 19:05
I have bought a new bush to replace the Layshaft end bush, however found that it was too small and spun around in the casting. I had had to heat the casting to remove the old one.
I sent the new bush back to the supplier with the bush that I had removed assuming that it had perhaps been made too small. It was checked and to my surprise *eek* I was told that it was the correct size and that the one removed was oversize, meaning, I was told, that the casing had been opened out to accept a larger bush.
Now what I find difficult to comrehend is the reason anyone would do this. Surely any wear would be in the bush and not the casing. Has anyone come across this before or are there slightly differen diameter bushes for gearboxes of different ages?
Title: Re: Layshaft bush external diameter
Post by: muskrat on 29.08. 2012 20:46
 G'day Dave,
                 could it have been bored out to take a torrington bearing like in a RRT2 box by a po. Size difference is thou's or mm's?.
Title: Re: Layshaft bush external diameter
Post by: KiwiGF on 30.08. 2012 02:58
Hi Davie,

I reckon this sort of thing will happen, I'm thinking of all the oversizes bushes in my engine/gearbox!

As per Muscrats question it makes a difference how much oversize it is, a few thou oversize would indicate that the bush had spun in the casing and worn it that way (due to no oil maybe), or less likely it had been replaced a few times without heating it up, and the casing got worn oversize that way.

I've got oversize (on the O.D.) cam, idler and main bearing bushes, and probably a few others I don't know about yet. One day this may come as a surprise to a new owner!

I'm in the process of my refurbing my 56 s/a gearbox, and part of that was to replace the layshft bushes.
The drive side bush is not so easy as its "blind", for me a std bush was not usable as the layshaft was worn undersize (which is common and undersize bushes are available for that reason), so the layshaft was ground to make it round, and then a special undersize "blind" bush made by my machinest, this bush actually has a threaded "cap" to make it blind so it could be easily line bored after being fitted in the case, and the cap was fitted after the boring. My machinest reckoned this method was easier than buying an undersize blind bush and using a reamer to make it suit the shaft.

The kickstart side layshaft bush was easier to replace. I bought a new (std) bush from Draganfly, this is made with a slightly undersize I.D. I guess this is to allow for it to be bored to suit the shaft after fitting. The new bush was made in sintered material (unlike the OEM) and without an internal scroll (again unlike the OEM) but that is OK for a sintered bearing according to my machinest (who really knows his old brit bikes).

I've noticed that new engine bushes I've bought are slightly bigger on the O.D. than the old bushes I've removed, in the region of a thou, this MIGHT be due to suppliers realising that most of our cases are a bit worn by now? For me that meant I could get away with replacing an old bush that was too loose in the casing with a new one bush, but only in some, not all instances..........

I hope that helps.
Title: Re: Layshaft bush external diameter
Post by: Flatboy 1950 on 30.08. 2012 06:17
My brother restored a couple of s/a A10's some years ago & at the time worked for the Atomic Energy Board where he had access to some of the best workshop equipment on earth.
He had 3 A10 gearboxes in pieces & all 3 had the layshaft scored on the inboard end.
He ground the best shaft to clean up the score marks , then re-bushed the case & cover.
The shaft spun perfectly in each one , BUT when he bolted the parts together , the shaft locked up.
He found that the hole in the main case was not bored square to the gasket face!
He bored the case to correct this , made a new bush with an o/s  O.D. to suit the enlarged hole & everything was perfect.
The fact that all 3 layshafts were scored suggests that the same problem was present for a number of years !!!
Could easily cause the bush to spin in the case if the layshaft clearance was a little less than usual.

Regards , Flatboy.
Title: Re: Layshaft bush external diameter
Post by: Davie L on 30.08. 2012 07:40
Thanks for your responses guys. The point that I am confused about is the fact that the old bush fitted the hole correctly, was tight and did not spin around. It was however worn internally and needed to be replaced. The new bush, which I would perhaps expect to be the same size or slightly oversized, was too narrow, albeit by only a couple of thou.
The supplier told me that he had tried the 'new' bush in other gearboxes he had and they were a tight fit.

I think I will just have to get a new one made.

Anyone know of anyone in the Glasgow area who could make one for me ?


Title: Re: Layshaft bush external diameter
Post by: bsa-bill on 30.08. 2012 12:10
Hi Davie
I would think any good machine shop would make a new bush for you.
Border Engines in Berwick made one for my first box to suit the tidied up end of the layshaft
Title: Re: Layshaft bush external diameter
Post by: KiwiGF on 30.08. 2012 22:32
Hi Davie, I guess the old bush was a "one off" just like the new one you are about to get made. If only the bikes came with a list of "special fixes" from the PO ;) life would be easier!

Out of interest is the drive side or kickstart side giving you problems?

If it is the kickstart side it might be easier/cheaper to get a new cover, but the chances are it will on sale because it has got an oversized housing..... *eek*

Have you decided what I.D. you want a one off bush made too? e.g. to allow for reaming or boring to size after it is fitted or not? (the bush I.D. will shrink slightly due to being compressed by the housing) , or are you aiming to get it to have the right clearance without reaming or boring after being fitted in the case?

A prior post mentioned that the housings are not necessarily lined up and this can cause shafts to seize up etc, this is a problem that does not occur if the bushes are made undersized so thay can be line bored or reamed after installation in the housings.

Of course getting this sort of "one off" machining work done can get expensive......and keep the bike off the road for a while.

Title: Re: Layshaft bush external diameter
Post by: duTch on 14.03. 2015 17:24

 I came across this while looking for sizes for the RRT2 layshaft needle rollers, does any one have sizes or part numbers for these...???

 Kiwi, hows that bush mod going ? I was thinking while playing earlier that that would be a good idea, as I have a similar concept with a long story box, and then I found this thread

 I had in mind if it's worth sleeving a well worn layshaft, and adapting needle rollers in a STD box....?....thoughts....?
Title: Re: Layshaft bush external diameter
Post by: kiwipom on 14.03. 2015 20:32
hi guys/ Dutch, hope this helps, cheers
Title: Re: Layshaft bush external diameter
Post by: chaterlea25 on 14.03. 2015 23:24
HI Dutch and All,
I'm Just going to paste in the notes that I have saved on the needle roller vs bush equipped gearboxes
I have borrowed these texts from the Britbike forum, (BSA Gold Star section) With acknowledgements to Magnetoman ;)
On the bush outer diamater question, I very often find the sizes are different and just make bushes to suit

The layshaft of the needle roller bearing gearboxes are different from the Std boxes, there should be NO oil groove in the needle roller shafts, if a std layshaft is fitted, the needle roller bearings will be ruined in no time.

The needle roller bearings should not protrude inside the box, but the correct washers should be used on both ends .
P/N; 43-3078 on the drive side(0.108 thick) and P/N:42-3079 on the timing side (0.113 thick)

Also note that the "B" gear of the std box is slightly narrower than the "B" gear of the RRT box, so some extra shimming may be necessary to obtain the required endfloat of the layshaft.

Te endfloat should be 0.25 to 0.5 mm, check this with the cover fully tightened. (approx. 0.01-0.02 inch)

Concerning the oil hole in your bearings; the original manufacturer of the bearings (Torrington) has gone out of business years ago, and all the replacement bearings I have seen do not have this oil hole. I do not think that this will be much of a concern, since the bearings are below the normal max. oil level in the gearbox.

Registered: 08/02/01 Posts: 1875 Loc: California    The Gold Star parts book (red cover) shows all 3 items by part number. But that book does not give you dimensions... so I just measured 2 of the 3 parts as follows...42-3078 Layshaft thrust washer (clutch end), O.D. = 1.164" and 0.100" thick42-3079 Layshaft washer, (cover end)67-3203 Layshaft thrust washer -goes between 1st and 2nd gears, the bevel inner edge goes towards 2nd gear, 1.090" O.D. and 0,085" thick.

For those who are not familiar with BSA's letter ident for the gears, here's the way it's done. It's easy to become familiar with the system and it will eliminate any confusion.
A - 'sleeve' gear, the reduction gear on the mainshaft
B - pressed on layshaft, the reduction gear
C - mainshaft 2nd gear that engages the A gear in 4th
D - layshaft 2nd gear that engages the B gear for 2nd
E - mainshaft 3rd gear that engages mainshaft G for 3rd
F - layshaft 3rd gear that engages H for 1st
G - pressed on mainshaft 1st gear

shim washers:
43-3078 between shell and layshaft 'B' gear.
1 5/32" - 1.156" OD, 11/16" - 0.687" ID, 0.108" thick

67-3203 between the 'F' and 'H' gears
1 3/32" - 1.094" OD, 3/4" ID, 0.093" thick

42-3079 between the 'H' gear and middle cover
1 1/4" OD, 3/4" ID, 0.113" thick

67-3161 behind the kicker ratchet pinion bush
1.1625" OD, 3/4" ID, 0.075" thick

Note: the 67-3203 shim between the F and H gears on the layshaft should be fitted with the chamfer against the spline to allow for the slight radius in the shaft.

I would guess if you run into shimming problems it's because there may be some non standard pieces installed. An issue easily overlooked, is the 'bushing' box pressed on 'B' layshaft reduction gear is narrower then the 'T' box gear. If this gear is fitted in a T box there will be excessive layshaft end. I've had BI suppliers send the wrong gear. Be careful.
Or perhaps the tranny was converted at one time from a 'bushing' box to 'T' configuation by fitting Torrington layshaft bearings. This will change the shimming requirements.

I should have mentioned the Torrington part numbers in an earlier post. The reason I ordered the bearings from a motorcycle parts supplier in the first place is I hadn't taken the gearbox apart yet at that time so I didn't know what bearing was required for the SCT2/RRT2 sleeve gear. Now I do. Anyway, the required Torrington bearings (with dimensions, in case you need to locate an alternative manufacturer) are:

Sleeve gear (only used on the SCT2 and RRT2)
13/16" ID, 1-1/16" OD, 7/8" wide

Inner cover (used on both 'T' and 'T2' gearboxes)
3/4" ID, 1" OD, 3/4" wide

The bearing needed for the main gearbox housing depends on whether or not a separate, slightly convex, 'cap' is pressed in at the outer end of the hole in the housing to seal the oil in. If the housing has such a cap, then an open ended bearing is used. If not, than one with a closed end is required.

Main gearbox housing (used on both 'T' and 'T2' gearboxes)
B-1112-OH (open ended)
M-11121-OH (closed end; note, the extra '1' at the end of the no. isn't a typo)
both are 11/16" ID, 7/8" OD, 3/4" wide

Title: Re: Layshaft bush external diameter
Post by: duTch on 15.03. 2015 00:21

 John, you posted while I was chasing up the thread at the bottom, and I lost the page *smile*.....Thanks for that, I also have seen that a few times(last night), but just noticed the bearing numbers# at the bottom- thanks *wink2*

...and now back to the start

 Thanks KP, keep forgetting about that- but not what I need. I'm after the physical dimensions of the Torrington needle rollers....and/or a part number....?
  It might be a total waste of grey-matter, but thought if the roller outer was the same size or not much different, with a hardened sleeve on the shaft changing a Needle roller cage would save a lot of messing around instead of reaming bushes, and the shaft would last longer

 Reason KiwiGF mod got my attention, is because I already grafted a Layshaft and CR gears into my Plunger box, but with different NR bearings, and I originally had a simple welsh plug to seal it. Decided that was ineffective, so cut the end ~5mm off the old bush from same hole and used that with sealer.
 The other day I mentioned in another thread about drilling a different oil feed to the NR bearing because the original bush feed hole was covered by the bearing, and I just found a picture of it so have added that (the nut in the NR is in the background-means nothing)
 ..whoops was thinking this was a different thread that I was also looking at last night: (

 eyes'r goin' funny.... *eek*
Title: Re: Layshaft bush external diameter
Post by: Briz on 15.03. 2015 19:24
I recently did this bush on my mate Jims box.
Yes, the shaft was scored, so I ground it down to 17mm (.669" from the stock .687") and bored the old bush to take a 17mm DU bush which has a 19mm OD.
Title: Re: Layshaft bush external diameter
Post by: duTch on 20.03. 2015 08:54
 So Briz, you did a sleeve within a sleeve , so to speak...??

John, I'm a bit baffled by those measurements-
both are 11/16" ID, 7/8" OD, 3/4" wide

..All the shaft I have are ~11/16" on the drive side, and ~3/4" on the timing side even the shaft that I'm real certain came from my original RRT2 Box, which has a bigger 6T speedo drive gear(~0.540), and a matching 10T worm gear-(but which was worn ?, and I had ground to 18mm to fit a bodgy bearing)

 What I am proposing is to bore out the bush casing OD's to 1.0" on both sides, to accommodate a 1.0" x 0.750" x 0.875" (1 x 3/4 x 7/8) needle roller, and make a inner race/sleeve with an OD to suit and an ID to suit the worn shaft, after being machined/cleaned up (~0.680~?)

 There's a stock inner race that is 3/4 x 1/2", but my mate reckons that to machine that out to ~<0.680, would be un-viable, and easier/cheaper to make an inner from scratch
 The reasoning I use, is that the parts are available (except the inner sleeve/race), but by the time I buy a bush, and then fork around line reaming it, it's gonna work out just about the same in price, and if there's a next time- much easier......??

 My question is ;- how much can the shaft be machined to not compromise it's integrity- doesn't need to go more/less than 11/16', given the measurements you've posted above??  that would give a sleeve/inner race of ~1/16" thick..??

 I feel This should continue over in another thread...?

...Maybe here?

Title: Re: Layshaft bush external diameter
Post by: chaterlea25 on 20.03. 2015 14:50
Hi Dutch,
My understanding of "both bearings" is either the open or closed ended type depending on which one is required
I would be reluctant to reduce the shaft diamater by more than 1mm, I'd try and find another shaft !!

The problem with machining/grinding a shaft for needle rollers is to obtain the correct surface finish *work*
I woud think if the shaft end cleaned at 17mm and the correct surface finish achieved you could run it directly in a metric needle roller, below this size my opinion is that the shaft size would be below the hardening ????

The shafts are not that hard and can be machined in a lathe using inserted tool tips