Behind the clutch

[muskrat]

G'day Denis.
That chain groove would be because a po had fitted a Xheavy duty or O ring chain at some stage the rear wheel would have been out of alignment throwing the chain to the outside of the sprocket. Standard chains are to be used, well able to handle the mammoth horse power of our bikes 
The original "seal" was to do both, retain oil and keep dirt out. My 51 A7 still has the original and still works (somewhat) but will be replaced next tear down, possibly with duTch's set up.
Cheers

[morris]

Ouch...! that don’t look good. The proper oil seal is 7mm wide. Could try make a ring/washer with a groove turned out to locate the seal?
In addition to Musky’s comment above, could also be that at some point the sprocket nut worked itself loose and the sprocket started wandering around.

[Swarfcut]

Denis, Looks from the pictures that whoever messed with it first time round wasn't too good. The groove looks to be the result of neglect, a worn, loose flappy oversize chain, plus probably a loose sprocket, and from the helicoil in the gearbox mount, not too cute on Whitworth threads or  assembly detail.  Before you commit to more time and effort, check the rest of the motor for impending doom. This costs nothing, and better to have a nasty surprise now, rather than fixing this problem and finding a crack or worse in the other crankcase half. Any pulled threads can be all fixed at the same time rather than piecemeal.

 As a start, check the crankcase halves are a matched pair. There should be matching numbers stamped on the front of each, just below the dynamo mounting position.

  For  the seal, I would get a new one, BSA Service sheets give the original dimensions, so any modern seal to that size will do. Or measure the hole, the shaft diameter and decide the width of seal you need, and select from a modern oilseal chart. Fits with the open lips towards the clutch, to keep the oil in.  Then you need to source or make/commission a retaining cup for the seal, as suggested by Morris. Because the case has been thinned, the cup can be made thick enough to hold the seal and have three good deep threads for three small bolts which will hold the dished oil slinger pressing, behind the clutch. A bit like Morris' original washer, but deeper and internally relieved to hold the seal

 The crankcase here is under no great strain, and with the primary cover on will cope OK, despite the deep groove.  Alloy welding is an alternative to build up the thickness to hold the seal but will add to the cost.

 Swarfy.

 Additional.  The gearbox drive sleeve, the one that carries the gearbox sprocket, should have no in/out movement, as the main ball bearing outer race is located by a circlip, which also retains the sprocket oilseal. A missing circlip and a worn bearing location will allow the sprocket  to move out from the gearbox, on the drive sleeve so take off the sprocket to check the seal and circlip are in place. There should be no play in the ball race, but the mainshaft bushes in the drive sleeve will always have a bit of radial play on a well used machine. The other end of the mainshaft is supported by another ball race and there should be no in/out play.

[RoyC]

You could always use HTS 2000 Aluminum Repair.

https://www.youtube.com/watch?v=RCrixbXz4rc

[Swarfcut]

Roy, that looks like a modern version of our old friend Lumiweld. With practice and skill, a following wind and fair weather, some folks get good results, not me, so I would  be a bit reluctant to practice on a vital engine part, and leave that to the professionals. Rectifying a poor repair done with this sort of semi soldering/brazing is difficult as it contaminates the parent metal, so only use if you are sure you can do it right first time.

Swarfy.

[BSA_54A10]

Roy, that looks like a modern version of our old friend Lumiweld. With practice and skill, a following wind and fair weather, some folks get good results, not me, so I would  be a bit reluctant to practice on a vital engine part, and leave that to the professionals. Rectifying a poor repair done with this sort of semi soldering/brazing is difficult as it contaminates the parent metal, so only use if you are sure you can do it right first time.

Swarfy.

Dead right Swarfy,
 Lumiweld's patient expired quite some time ago
Every now & then it reappears under a new name claiming all of the same magical properties as Lumiweld used to.
never ever to be used on any engine part as it will soften & run.
Basically a Zinc based solder & filler rod.
Welding with real aluminium or even boging with  Devcon are both substantially better options.

[denis]

Hi all a10 Wizards,
Sorry for the late reply, and thanks all for your input.
I’ll turn a washer with a groove as suggested by Morris, and as Swarfcut suggested I did check, it’s a matched pair, but there is another worrying thing that will need welding, I will have to find someone to do it for me as I don’t TIG.. bummer. Can it be done without taking the whole thing apart?
Thanks all, Denis

[denis]

Also, the gearboxes were both attached to the engines with 4 bolts and not 2 bolts and 2 studs as mentioned in the part lists, would that make any difference?  Aaaaand yes the gearbox foot set screw holes are already too big for 5/16, and seem just ok for 3/8, which won’t leave any play with the frame..
Swarfcut, on both my gearboxes the thing on which the sprocket go (called drive sleeve?) do have roughly 2,5 mm in and out play (pic with red pencil) is that normal as the seal and circlip you mentioned is the one shown on the other pic? 
Thanks for all, D

[chaterlea25]

Hi Denis,
The sleeve gear can move in /out until the sprocket and nut are fitted
I can see from your photos that the circlip holding the seal is not seated properly (the ends are too close together)
These can be problematic to fit due to the seal inner face having too thick a rubber facing (but it needs to be compressed to seal)

John

[Swarfcut]

Denis The cracked case can be left for now unless there was a sign of an oil leak, showing the crack goes through to the inside of the crankcase. To be welded with any success, the cases need to be stripped and cleaned and the extent of the crack examined. Four bolts to the back of the engine make assembly of the box to the engine a little easier, less risk of damaging the new seal, just make sure the bolts do not bottom in the blind holes. Threads are Whitworth.

 Gearbox lower mountings are best helicoiled, if possible. Custom made shouldered  stud is an alternative. Don't go drilling out the frame lug. Another gearbox casing if you can get one.

 Gearbox bearing....Should be free of play in any direction, and be firmly gripped by the gearbox case. With the seal removed, look for a distance from the outer race to the circlip groove, this should be slightly less than the thickness of the outer edge of the seal, as outlined by Chaterlea John.  If the distance is too small, see if the bearing can be knocked further into the case, to make sue it is fully seated. No luck here.....could be the wrong bearing. Heat the case first with a hot air gun or small gas torch, to expand the housing. If the bearing has failed, again heat the case and the bearing will knock out easily.

 The sleeve gear is usually a nice snug fit into the centre race, sometimes tight, but any previous wear may allow the movement you have. With the nut and sprocket in place, this movement will disappear as the nut is tightened.

Swarfy.

[denis]

Hi everyone,
Crikey, it’s been a while!  Now my Ural is running again, back to BSA! I just realised I forgot to tell I made a washer as mentioned by Morris, see pic attached if I managed to load them. If not, I will try again.
Next problem is; I made two little dowels to go in the frame, and of course the holes don’t line up anymore.. could anyone tell me the measurements between the holes with the dowels and the front engine mounts on the frame? And how much of a tweak should I allow me to grunt it in? 
Also, is it normal that the frame is much wider than the engine where I put the dowels?  (Roughly 6mm) I can’t see any washers or the like in any part lists?.
As for the crack in the engine cases on the pics in a previous post, a friend told me to drill it oversize and turn another dowel to fit in as the hole is already way oversize, is it a good idea or over the top?
Thanks all in advance,
Denis

[denis]

Here goes the other side of the washer as I sent twice the same..

[morris]

Hi Denis, maybe picture below may help?
The distance between bottom (dowel) and front engine mount is roughly 10 1/4 in (measured in situ so may be a little out)
Regarding the crack, I would leave it as is. Drilling the hole out will only weaken it further.

[denis]

Thanks Morris,
I printed the drawing and a mechanic friend let me use is garage floor, chains and jacks, hopefully it will all fit and come together nicely, just like on a Honda   
The cracked hole is already so much oversized that I don’t think the whole mm that I ‘m gonna have to take out will weaken anything further.  My axle can be put through the engine without touching anything   
I wonder what happened to that bike! 
Anyway if I have time today I’ll see how thin a dowel my lathe and I can manage before anything.
Good day all,
Denis

[Greybeard]

If a bike with a sidecar is involved in a collision the frame is very likely to get twisted. My own bike used to have a sidecar; it tends to steer left; I think the frame must be a bit off.