1930 Sturmey Archer Type LS240 Gearbox

Well, I put an 'ad' for a couple of parts in the Wanted Section and there was some interest in the box I'm renovating for another member.

It came from a 1931 P&M Panther model 50 - but its a pre-'31 box as it has the single spring clutch, doesn't have a shock absorber in the clutch centre and has a loose ball race on the output shaft drive side instead of the later caged ball race.

So here are a few pictures of it as I took it apart and discovered things I didn't like .

This is the complete box with the kickstart lever removed:











The clutch pressure plate has a single spring and the boss just unscrewsd:





All the clutch components laid out (except the hub).





There is a rather crude roller bearing at the back of the clutch drum. The rivets holding it together are separating and I bet these bearings are impossible to replace. Time will tell.





The three-speed selector mechanism is rod operated from a lever on the side of the fuel tank.





Extracting the clutch centre:





The output sprocket is held on by a nut that is locked with a plate:








The clutch is operated by a 'quickthread' plunger operated by a lever.





The box is lubricated with Mobil 'Gargoyle' grease that is a thick gloopy oil. It flows so you don't get spinning bits drying-out inside. It doesn't want to come out though .








The second gear pinion on the output shaft engages internally and on the end. There is some wear in the dogs and one tooth is missing (its a 20-tooth pinion, Nortons used a 19-tooth close ration version ).














This is the main bit I'm looking for if anyone can help source one .


Underneath, a mounting stud was missing and the hole had been plugged with wood .








This is the three-speed cluster in 1st gear position:





Second gear position:





And third gear position:





The cluster with the kickstart shaft and gear lever added:








The kickstart shaft runs in a sleeve that is screwed into the end cover. This sleeve is (was - I've now bust it ) severely cracked. To date I haven't been able to remove the threaded base but I'll have to be a bit firmer with it. I'll turn up a replacement out of alloy.











More of the clutch operating 'quickthread'.





No mistaking the origin .





So, I hope you 'Classic Bike' people out there find this interesting. I'll add more as I re-assemble it (but don't hold your breath).

Bob.

That 2nd gear could probably be welded, machined and heat-treated I know a guy in Lichfield who does special machine shop jobs. He might know a suitable welder. It probably a better option than a new part as its run in with its partner gear.

The casing could be clamped up to a bearing race as support and TIG welded but oil in the cracks wont help it to knit together very well.
maybe the cracks can be slotted out with a small die grinder or high speed burr.

Another option is Lumiweld low temperature soldering style system for aluminium, but the cracks would have to be filed out and a support made to hold all the parts in place.

Done properly, its tough stuff I've seen a VW van gearbox lug repaired with Lumiweld. The snag is it runs out of wide joints unless a mould is made around the part.

Bendy toy said:

That 2nd gear could probably be welded, machined and heat-treated.

The casing could be clamped up to a bearing race as support and TIG welded.

Another option is Lumiweld low temperature soldering style system for aluminium.

Click to expand...

Yes, I'll consider having the gear repaired (or copied) if I can't find a replacement.

The kickstart sleeve has a separate Part No. and is supposed to unscrew. I've now bought 500mm of 2.5" alloy round bar and, when I've got the broken bit off, I'll turn-up a replacement. Those five holes in the flange must be for a Service Tool that unscrews the sleeve.

Fun and games.

Bob.

Your making better progress than me Bob
Everything I touch either costs a fortune or has to be made.
Have the front girders completed now after having all new bushings made for them.
I contacted a guy last week who said that he had a cylinder for my 500 engine 1929 but he never returned my call.
i am unfortunately finding there's an awful lot of guys in to classic bikes that seem to be full of piss and wind.
I'll soldier on as you say looks like we may well be trawling the bike jumbles next year.

robmack said:

I am unfortunately finding there's an awful lot of guys in to classic bikes that seem to be full of piss and wind.

Click to expand...

That's for sure

And they all want "Restored Bike" value for their heaps of incomplete junk.

I have been contacting bike clubs and dealers in the UK and on the continent for parts - no joy yet.

When I was in Sweden in 2007 I met three guys who had 'barns full' of classic British bike stuff, they bring lorries over to the major Autojumbles and buy-up loads of stuff. I'll see if my Swedish friend can exert some influence.

It turns out that the kickstart sleeve isn't threaded, so I've had to machine it off and thread the end cover. I'll post pictures when its looking presentable.

I'm glad to hear that you are not waiting for the box to be returned .

Bob.

I've really enjoyed reading this Bob and am in awe of your engineering skills, ta for going to all the trouble of posting up the pictures

Looking forward to seeing how it progresses, good luck with sourcing the parts

Andres

Outtomunch said:

Looking forward to seeing how it progresses, good luck with sourcing the parts

Andres

Click to expand...

Hi Andres,

I've been making progress and I'll post another interim report shortly.

The box isn't finished yet, but it looks as though I've found a replacement 2nd gear pinion and kickstart spring in Austria. I'm waiting for the post to arrive in the New Year.

Bob.

Very interesting thread Bob. Are you aware of HPC gears for stock gears.

Brian

Excellent stuff. Good luck with that gear. If the original is to be repaired, get it up to cherry red before welding to take out the case hardening. Weld it and heat again to relive internal stress, then machine the tooth/teeth. Case harden again when done.

Let's hope the one from Austria fits.

When these were made the 'box was geared down on the primary drive to run slower than the engine, because the gearbox could not handle the engine revs.

Almost all manufacturers have continued with this tradition of high torque low speed boxes. Who knows why, - higher revs = less torque so parts can be smaller.

Next instalment:

Well, following on from my previous post – I have been busy over the holiday period.

Firstly, I tried to unscrew the kickstart sleeve. As the sleeve was badly cracked on both sides I found a socket that was a good fit down inside and used a strap wrench around the outside. The result . . Three pieces of sleeve on the bench and a sorry-looking end cover .

Next I sawed & filed a flat on each side to allow me to use a large open-ended spanner on what was left.





This didn’t work either and closer investigation showed that there was no join underneath the flange. I guess the exchangeable sleeve was introduced in 1931 – the year for which I have the parts diagrams.





So those five holes that I thought were for a factory unscrewing tool?? They are to allow the kickstart spring to be tensioned.





So nothing else for it but to machine-off the broken flange, bore it out and thread it. First I carefully measured all the dimensions on the outside and inside (here).





Next problem . . How to centre an odd-shaped object like the end cover with the axis of the lathe??

I looked at the lathe’s faceplate and measured the thread on the headstock mandrel – 1.5 inch BSF, which has an 8 TPI thread. Fortunately that is one of the 48 threads covered by the lathe’s threadcutting gearbox. I then turned-up a piece of alloy round bar to 1.5” and cut an 8 TPI thread on the outside.





This was a larger diameter than the kickstart shaft hole in the end cover. I turned half of the threaded billet down to a tight sliding fit in the end cover, screwed it into the centre of the faceplate and slid the end cover onto it.





It was then just a matter of rotating the end cover to get the best fit between the screw holes and the slots in the faceplate, bolting it down tight and finally unscrewing the threaded alloy billet from the back.





The next step was to remove the lathe chuck and screw on the faceplate. The lathe motor is a 1.5hp single-phase with a five-step pulley driving a countershaft. This was put on the slowest setting and the lathe’s back-gear was set to slow speed. Essential with a nasty unbalanced object like this!





I then turned the broken sleeve flange off, leaving as much alloy underneath as possible.





The next decision was what size of thread to cut in the end cover. I could have made the whole thing a ‘one-off’ but decided to use a standard thread.
Measuring the cover showed that a 1.75 inch thread would be appropriate so I consulted my thread tables:

1.75” BSW (British Standard Whitworth) = 5 TPI (sounds too coarse to me).
1.75” UNC (Unified, Coarse) = 5 TPI (still too coarse).
1.75” BSF (British Standard Fine) = 7 TPI (sounds promising).
1.75” BSP (British Standard Pipe Thread) = 11 TPI (Hmmmm I like the thought of that).

All of those threads are available on my lathe.

In the event I settled on 1.75” BSF, So I worked out the thread depth (normally, thread depth = 0.64 X the pitch, so, 1/7 inch = 0.143”, x 0.64 = 0.091”, x 2 = 0.182”) so subtracting twice the depth from the diameter of the thread crest gives the starting hole size of 1.57 inch (still with me ?? ).

I then bored the kickstart shaft hole to the thread trough diameter.





Then, setting the lathe to 7 TPI, I very carefully cut the female thread in the cover. It took ages as the ‘spring’ in the tool means that I could only cut 3 thou increments and to maintain the relationship of the feed screw with the back-gear meant that I had to back-off the cutter, reverse the apron out by reversing the motor, then re-set the cross-slide and take another cut. I do have a thread positioning indicator on the lathe but I won’t bore you with the problems of re-positioning a 7 TPI thread using an 8 TPI lead screw (there is a chapter devoted to it in my "Screwcutting on the lathe" techniques book).





With the thread cut in the end cover I turned my attention to the replacement sleeve. I cut a lump off a 500mm length of 2.5” alloy round bar and roughed-out the overall shape. I then cut a 7 TPI male thread on the end – which was not easy as my lathe doesn’t have a clutch!





Eventually the embryonic sleeve fitted the end cover.





However, I had intentionally cut the thread longer than necessary so the excess was measured.





And the thread was machined to its initial size (it will need more clearance later). The tailstock, with the dead-centre, was moved out of the way for the final parting cut.





Looking promising.





Now it was a matter of turning the sleeve and flange to pre-finishing size. Because the sleeve is between the flange and the alloy billet that is held in the chuck I had to cut right-of-centre to left and left-of-centre to right with different turning tools.








I didn’t cut right up to the flange and then used a 6mm profile cutter to turn a radiused curve between the sleeve and flange. This is stronger than a 90 degree junction.





I also radiused the edge of the flange – just like the original.





Next the sleeve was bored out to 13mm (my largest HSS twist drill) to give room for the boring tool.





Then the sleeve was bored to less than finished size before being parted-off the alloy billet.





I am going to need a method of holding the sleeve for finishing, so I bored and threaded the left-over piece of alloy in the lathe.





Another long, slow job, but finally the sleeve fitted (after I had turned the face square to the thread).





I then put masking tape on the sleeve and held the mounting square in the lathe. The outer surface and rear faces were then turned true to the front face.





So far so good.








And this is where I am now. I have been cleaning-up the kickstart shaft with metal polish and if it looks OK I’ll bore the sleeve to fit. If the shaft is too rough I’ll set it up in the lathe and skim it true. The sleeve will then need less metal taking off before fitting.





I’ll put up more as I proceed – unless you prefer to watch paint dry !!

A wise man once said, “Owning a lathe doesn’t make you a Machinist” . . . I’m learning, but no doubt experienced Machinists would have done it differently. I’ll wait for the incoming flack .

Bob.

Bendy toy said:

Excellent stuff. Good luck with that gear. If the original is to be repaired, get it up to cherry red before welding to take out the case hardening. Weld it and heat again to relive internal stress, then machine the tooth/teeth. Case harden again when done.

Let's hope the one from Austria fits.

When these were made the 'box was geared down on the primary drive to run slower than the engine, because the gearbox could not handle the engine revs.

Almost all manufacturers have continued with this tradition of high torque low speed boxes. Who knows why, - higher revs = less torque so parts can be smaller.

Click to expand...

I'd like to repair the broken gear - but I'll look for someone who is experienced in that sort of thing. There is a member of the Ariel Owners' Club who has a couple of these boxes on bikes and all second gear pinions are broken. He welds and re-profiles them as you suggest.

Running the boxes faster will mean that they have less torque to contend with, but I suspect the problems are with the change mechanism rather than with the gears and bearings.

They would either need synchromesh . . or they'd sound like BMW boxes .



Thanks for the input.

Bob.

and a happy Xmas Bob.

Bob,
If the K/S shaft is to far gone, then get a later splined style shaft, part off the splined end and bore the end. Take the end off your existing shaft and turn the end down to match your new inner part. Braze or Silver Solder the 2 parts together.

We did the above on my dads 1923 Raleigh and its done approx 10,000 miles without problems since.

HTH
Neil

NeilDD said:

If the K/S shaft is to far gone, then get a later splined style shaft, part off the splined end and bore the end. Take the end off your existing shaft and turn the end down to match your new inner part. Braze or Silver Solder the 2 parts together.

Neil

Click to expand...

The kickstart shaft isn't bad, just some light scoring on the shaft. There is some wear where the cotter pin pulls-up but that could be fixed with weld and a milling machine (I don't have a proper one ).

It does seem overly long, though, but as I don't have the bike (its in Isle of Skye) I can't check the lever clearance. The layshaft sockets into the end of the kickstart shaft but apart from that the alloy sleeve appears to be the only bearing surface (perhaps I should have turned it out of steel ).

A large bloke leaping on ther lever is going to give the sleeve a hard time, no wonder it was cracked .

I might need to re-bush the shaft to get more support from the layshaft.

I think the splined shafts/levers came-in around 1931 as my diagram shows a different shaft to the one I've got.

Bob.

scotboxer said:

and a happy Xmas Bob.

Click to expand...

And a Merry Christmas and Happy New Year to you and the family, Peter.

I've still got those Autocom parts for you .

(I hope that SatNav mount is holding-up ).

Bob.

Well what can I say?
I am very impressed with your turning skills Bob.
I would'nt have known where to start with that.
I really hope that the gear is the correct one.
Did I tell you that I have managed to source another 600cc barrel?
Unfortunately no luck with the 500cc one but I have been told that they are externally physically the same.
I also have the 500 and 600cc pistons and picked up a push rod tube last week.
So I have pretty much everything for the engine just a bit of head scratching to do now but I'll get there.
If I can I will may'be pay you a visit sometime soon, or if you fancy another trip to Skye your always welcome.
Cheers Rab

robmack said:

So I have pretty much everything for the engine just a bit of head scratching to do now but I'll get there.
If I can I will may'be pay you a visit sometime soon, or if you fancy another trip to Skye your always welcome.

Click to expand...

So, is that the motor heading my way (Gulp ) .

My turning skills aren't that great, but I'm learning. I'm going to make another couple of sleeves as I'm not too happy with the first one. Next time I'll try a different thread cutting technique.

Considering what you started with . . . . . . .






You appear to be making good progress with the restoration .










It would be better to keep it as a 500cc motor so that everything is as near original as possible.


We'll have it running in 2013

Bob.

Haha 2023 maybe, that last pic was taken before I decided that there was too much play in the girders and stripped them back off to have them re bushed.
I have since re painted the fork blades again and am still not happy with them.
I am hoping that we should be able to sleeve down one of the two 600 barrels and retain the 500 capacity. Funny to see that pic of all the parts on the bench half of which have nothing to do with the motor.It is even more surprising that there wasn't 1 single seized bolt on the whole bike, not bad considering I spent a day last year taking the headers off of my 1150.

Bob, I have received an email from a none member who has stumbled across this thread. He says he might have some of the parts you are looking for.

I have forwarded his email on to you

Paul G (BHT) said:

Bob, I have forwarded his email on to you

Click to expand...

Got it, thanks Paul.

I have replied. I don't need much at the moment but its useful to know that parts are available in case I find a problem during assembly.

It'll be interesting to see what he's got.

Bob.