I agree with scifi, although I would take 0.003" to 0.004" as being absolute minimum clearances.
Also, be sure that valve stem and guide bore are clean and oil free before checking clearance.
Cast iron is the only material to use for Sloper valve guides.

Dean, You will be pleased to hear that F.W. Thornton have Sloper pistons in stock, but they don't seem to appear on their website.

Although Service Sheet 15 is dated September 1930, I believe it only refers to pre 1930 models, where of course, the ball bearing is against the flywheel, and it's talk of Glut Pins, which were deleted for 1930.
It's interesting to note that Bernal Osborne was also a little confused about the positioning of the bearings, in his article for Motor Cycling Magazine.
He mentions that a previous owner had swapped the position of the bearings, (i.e. from the 1929 arrangement to the 1930 arrangement.)
He goes on to say that the Artist has reproduced the BSA drawing, but fails to mention that the drawing is clearly of the 1929 engine, complete with inner spacing collar and Glut Pins.
It seems that BSA themselves got it wrong, because if you study the OHV engine line drawing on page 13 of the 1930 BSA Motor Cycle Instruction Book, you will see that the arrangement depicted is of the 1929 engine, with the ball bearing against the flywheel, and inner spacing collar. So it seems that the different departments of BSA were also confused.
In practice, I doubt if it would make any difference how you fitted what bearings, as long as you didn't use 3 roller bearings. If fitting a ball bearing against the crankshaft with an outer roller bearing, you would need the inner spacing collar.

Aha! I think I have just had a Eureka moment. More of which later.
Since you're doing the 1930 engine, I believe you are using the incorrect roller bearing, which, of course, gives rise to your question about the possibility of the inner race moving towards the ball bearing, and the consequent need for an inner collar.
I think, if you search on the internet, you will see what N305W and NF305 look like.
Yours has only one flange on the inner race. Mine has 2 flanges. So can you now see that the inner race of the NF305 can't go anywhere, and there is no actual need for the inner spacer?
The Eureka moment I had, was that I discovered that for the 1929 engine, BSA transposed the bearings. i.e the roller bearing goes in first followed by the 2 collars and then the ball bearing. Hence the need for the inner collar on the 1929 engine, but not on the 1930 engine. Ta Da! I suppose you could phone the Factory for advice, but I tried the other day and there was no answer. (Sorry about that.)
So, if it was my engine, I would swap out the N305W for the NF305, and forget about making a collar. It's up to you, and I seem to be in a minority of one.
I couldn't find the Sloper piston on their website either, in fact, I couldn't make much sense of their website at all, but if you email them I'm sure they will put you right.
As I tried to suggest, checking the endfloat is really very simple. Just assemble the crankcases and push and pull the mainshaft in and out with your hand. To be accurate, it really needs to be done with everything dry, as oil will take up clearance. No need to put the cush drive on, or the 1/2 time pinion and nut. Simply push and pull on the drive side mainshaft. That is your endfloat.....if any. There is no thrust face to pull up against (as you say), because the cush drive is on a taper and not up against the bearing (as Mr. Chapmast says,) and I'm fairly sure the 1/2 time pinion butts up against a register on the mainshaft, and does not tighten against the bearing. But it's minus 10 degrees here at the moment, and I don't want to freeze my balls off going outside to check.  So, NO, NO, NO, the cush drive does not lock up against the bearing (again as Mr.C says.)
As you say the Sloper crankshaft can float around, and that is why BSA recommended zero endfloat (less 0.002"), as per Service Sheet 15. Personally, I wouldn't bother about the 0.002" nip.
It would be good to know if you have now got your head round it all.

Regarding pistons, the Hepolite number for the 493cc OHV Sloper is 2687.
I happened to be speaking to Thorntons a few days ago, so asked them if they had this piston in stock and they told me that they had this piston in stock under the Hepolite Part Number, in 3 different sizes.
The fellow even unboxed one to confirm that it had an oil control ring at the top, which it did.
Perhaps they've restocked since Mark bought his?
Mr. Chapmast, your modification looks magnificent. I think you should go into series production.
Not having your engineering skills or equipment, I'm ashamed to say that not having the correct hard felt conical seal, I used 2 felt Corn Pads. Seems to have worked quite well for the last 30 years, without any apparent problems. But as I said before, who knows what will happen tomorrow?

Mr. Oval, Your first 3 sentences are correct. Since you know what year's your engines are, you now know the BSA bearing set up the factory used (for whatever reason.)
Well now, would you believe I've just located the roller bearing I replaced 30 years ago. The outer race has a lip on the outside (when fitted), and since this outer is held solidly in the crankcase and cannot move, and the inner race is double lipped, then the inner race cannot move outwards because rollers will tend to bear against the lip on the outer race preventing the inner race from moving towards the ball bearing. Now it must be that there is not much thrust acting here, because roller bearings are not designed to bear much side thrust.
The bearing I use is an NSK NF 305, an Oriental product I believe. I wonder if you have the correct bearing?
All I can tell you is that I have been using the setup I previously described, without the inner spacing collar (as BSA intended for 1930 to the end of Sloper production) for the last 30,000 hard miles, (after all, these things were built to be thrashed), with not the slightest problem. However, who knows what will happen tomorrow?
So, there you have it, but the choice is entirely yours. You must do what you think best.
I very much take on board what Mr. Chapmast has said about later engines, but as I said before, my concern would be the possibility of the inner collar creating axial thrust and premature wear of the roller bearing, unless you were extremely accurate with the thickness of the collar. But what do I know?
Now, regarding endfloat, I take it you have read Service Sheet No.15? (And also No.15.)
I don't quite understand when you say "nothing is locking the shaft in position."
To check the endfloat, you would simply assemble the crankcases and grasp the mainshaft and try to move it back and forth. You could use a DTI to measure it. (The crankshaft would move in and out of all the inner races, as it did when you fitted the crankshaft, if you see what I mean.) BSA say endfloat should be nil, but the flywheel assy should be perfectly free to rotate. If it's too tight, BSA recommend assembling the crankcases with a sealant (which I think we all do anyhow.) But you may prefer to shave a little off the flywheel cheek?
If there's too much endfloat just fit shim(s) between the flywheel cheek and the roller bearing. But do check the con rod is central.
I remember reading a SKFCO article that suggested all ball bearings should run with a tiny amount of preload, but whether you can be bothered with this is up to you.
I'm going to have a lie down now, but do let us know if this hasn't answered your questions, and I'll have another bash.

It might be worth bearing (no pun intended) in mind that there are differences between the 1929 engines and the 1930/31 engines.
BSA did not fit the inner spacing collar 24-725 to the 30/31 engines, only the '29 and earlier models. Perhaps because of the possibility of it pre-loading the roller bearing. Who knows?
This inner spacer is not mentioned in the 1930 Parts Book.
BSA also deleted the 2 Ballrace Pegs EA 94 in 1930.
I believe the flange on the inner roller bearing race should be fitted towards the ball bearing.
I hope this helps.
It seems odd that you are not using the correct piston. Thorntons still stock many pistons, and the Sloper piston is currently in stock.
However, it's your motorcycle, and of course, you can fit any piston you like. (Same with valves.)

Well now, I got my valves from 'gsvalves.co.uk'.
Rather expensive, but I find everything is these days.
I have a feeling that you might find some in Australia, like you did with the piston.
Cox & Turner can make you some, but, again frightfully expensive.
Unfortunately, neither of these Companies are in Australia.

Aha. That makes a difference. So in theory the barrel is 0.010" over, which is a little on the high side. It might smoke a bit. However, you need to measure your piston carefully at right angles to the gudgeon (wrist?) pin to get the actual clearance, but if you might want to give it a run or two at Bonneville, 0.010" might be OK to prevent it from seizing! LOL.
I get the impression you are in the good 'ole USA with your Wisconsin piston?
There is a company in the UK, F.W Thornton 01952 252892. Email ENQUIRIES@FWTHORNTON.CO.UK
I understand they have the 493cc OHV Sloper piston in stock. Hepolite Part No. 2687. Apparently these are newly made in Australia, and have 2 compression rings and 1 oil control ring. However I don't know if the control ring is at the top or bottom. If it's at the top, you're laughing, because all you'll need is a rebore.
They stock Std, +0.020 and + 0.060. The compression height is 1 1/2" and the gudgeon pin is 3/4" dia.
They also stock liners. The piston will be quite expensive, but what price Fun?
Hope this helps. Let us know how you get on.

 

It seems to me that there is something rather strange here.
The 1929, 1930 and 1931 Parts book show the same Part No. 24-6 for the barrel.
The 4.93 OHV Sloper barrels I'm aware of have 10 fins, so I don't know what your 9 fin barrel is off. Surely, If BSA had altered the number of fins, the Part No. would be different? Who knows?
My view is that the damage to the 1930  barrel will not cause a significant problem, because I don't think the rings will reach the damage. I think you could clean up the damaged edges and put a chamfer on the inside. However, if you fit a piston with an oil control ring at the bottom of the piston, it may well catch. (But see below, re fitting a liner).
I have been using a 2 compression ring piston for the last 30 years, and haven't had any problems. Yes, I sometimes have to adjust the oiling if it smokes too much. I find the adjuster is quite sensitive. Can't really see the damage to the 1931 flange. There seems to be a brass shim covering it?
Now, I failed my 11+ maths exam, but as far as I can see, 80mm is 3.149", so it is 0.008" larger than the figure you give of 3.141". In terms of bore measurement, this is quite a lot.
I wonder if you have been using a pair of callipers to measure the bore, because with a bore of nominal 80mm diameter, plus a clearance of say 0.005", the actual bore size will be larger than the 80mm you have measured. (unless BSA made some undersized barrels?)
In theory, 80mm + 0.020" oversize would mean a rebore to 3.169" plus clearance. Plus 0.040 would give 3.189" and plus 0.060" would give 3.209" + clearance. Are my calculations correct, or have I missed something?? However, a rebore should always be done to the actual piston size.
I think you will need to sleeve either of the 2 larger bores. I used a Hepworth liner, and it didn't break through, but other liners may have larger OD's and break through.
I hope I've got the above correct. If not perhaps some kind gent could put me right.
Your best bet is to take the piston and barrel to an Engineering shop and get their advice, but they won't like the damage.

I think you could answer your own question regarding spitting back by fitting the choke slide, and see if it makes any difference.
You are quite correct in saying that a higher Octane Rating decreases the likelihood of Pinking.
It is a common belief that Pinking is caused by Pre-ignition. It's actually caused by Detonation (otherwise known as Knock). They are two different things, although linked.
The mixture is ignited by the spark plug, and as the Flame Front travels across the combustion chamber, the unburnt mixture in front of it spontaneously combusts, producing a high pressure wave, which, when it hits the cylinder wall, produces a 'Pink' sound. This is called Detonation, and is usually caused by over advanced ignition.
Pre-Ignition, on the other hand, is usually caused by a hot spot, and produces no sound. At it's worst, it will reduce engine power, or even cause the engine to stop.
Pre-ignition can cause Detonation, hence the link.
It was found that raising the Octane number of the fuel reduced the likelihood of detonation (as you say), allowing raised Compression Ratios and more timing advance, thus increasing power output.
Auto-ignition is not a word much used in the UK. (Perhaps in the USA?).
Auto-ignition is when the engine continues to run when the ignition is switched off. It's usually referred to as Running On in the UK. I have never seen a British single cylinder motorcycle engine 'run on'. It seemed to be more common with Motor Car engines in the '50's due to carbon build up and insufficient cooling.
Auto Ignition is also linked to Pre-ignition.
If you are interested in the combustion process, you can do no better than investing in a book by Sir Harry Ricardo "The High Speed Internal Combustion Engine", but it is a weighty tome.

Anyhow, enough of all this technical bo****ks, as long the thing starts, get out there and enjoy it while you can, but try not to let it pink.

At the begining of the '30's BSA changed the bearing arrangement a few times.
For the last 30,000 miles, I have been using 2 roller bearings and 1 ball bearing. The ball bearing is fitted first, followed by the spacer ring and then the roller bearing. The other roller bearing is fitted to the other side. The roller bearing I used was an NSK NF305.
The bearings are 25mm bore, 62mm OD, 17mm wide.
However, the 'Motorcycling' article dated may 19th 1955 states 2 ball bearings and 1 roller bearing. If you search the Forum you should find it.
Then there is an article in 'The Motor Cycle' magazine dated September 1932 quoting a ball and roller on the drive side and a roller on the timing side, and this is the arrangement I have used, so it's up to you.
The crankshaft Main Shaft referred  to will be the drive side engine shaft.
Having 3 ball bearings will probably be OK, but a roller bearing is better able to take the drive thrust.
The bore of the shims will be 25mm to fit the mainshaft and the OD will be the OD of the inner race of the bearing. 

As you've shown me yours, I thought I'd show you mine. As you can see, it took but a few moments to make, and works well. But please bear in mind that I am both a Dullard and a Bodger.
It seems to me that the Peugeot item will have a metric hexagon, necessitating the purchase of a metric socket. But I suppose you could use a pair of Stilsons, like what I do.

You definitely seem to be getting there. Keep at it.
I strongly advise fitting the choke, it may well solve your problem. I wouldn't spend any more time trying to diagnose the spit back until you have done this.
Closing the points will retard the ignition a tad, which is the direction you need to go, although, as far as I can gather, it no longer kicks back?
Yes indeed, the suggestion is a work-around, although it may be necessary even when you have fitted the choke.
Your head is correct in thinking that the highest revs adjusting the mixture screw, gives the correct mixture on tickover. To fine tune, lower the idle screw to get the lowest tickover, and adjust the air screw again.
It's just a question of fiddling about until you're satisfied.
Regarding ambient temperature, I've found this normally affects the older water cooled motor car engines, rather than ancient air cooled motorcycle engines.
In my view, the issue of ignition timing with E5 or E10 is more to do with Octane rating than burn characteristics. But what do I know?
Personally, I have so far never had a problem with E5, or found the need to retard the ignition on many different British motorcycles, but then I use an Octane booster, and can only speak for myself.
If the engine doesn't 'Pink' on E5, then the ignition doesn't need retarding.
I hope this is helpful.

Yes, I would say you have retarded the ignition. You make no mention of using the choke. Does it have one?
It's good to give it a run, but you could easily warm it up in the garage.....depending on the neighbours.
Bear in mind the mixture screw is an air screw, so you might want to screw it in a tad more to richen the mixture if it still spits back.
If you're sure you have no air leaks, you might consider a richer slide.