Engine sprocket distance piece question

[RogerSB]

I know the distance piece no. 67-1138 must be fitted 'chamfer in' towards the engine and must be tight against the drive side mainshaft bearing. But does anybody know why it has an internal chamfer? See pic.

[Greybeard]

Is it just to clear the machined radius between the web and the shaft?

[bsa-bill]

just a thought
is it to allow for any flex of the crankshaft, if there was no chamfer then any flex however small would possible result in a crack developing

[RogerSB]

Thanks GB
Yes, it must be - it's somebody elses pic, I added the text.

[chaterlea25]

Hi All,
The chamfer is there to clear the radius and to ensure the spacer clamps the bearing (and shims) against the crank web

John

[orabanda]

I also install a 1/16"cross section o-ring (viton is preferred) on the crankshaft before fitting the spacer. I can't remember the o-ring ID (don't have my notes on hand), but it will be in the range of BS022 (1"shaft) - BS024 (1 1/8" shaft). If someone measures the shaft, I can confirm the part no for the o-ring.

The o-ring compresses into the chamfer when the spacer is installed. As long as the o-ring does not exceed 1/16"cross section it will compress into the chamfer without preventing the spacer from making metal to metal contact with the flange on the crankcase flange

This ensures that the primary case is sealed from the crank case (eliminates the leakage path along the crankshaft). Without positive sealing of the ID of this spacer the lip seal in the LH crankcase is compromised (oil will leak into the primary drive, mainly when wet sumping causes the crankcase to fill up to the spacer).

[Greybeard]

Clever!

[RogerSB]

Thank you all for your response.
Orabanda, what a good idea.
My A10 is 1961 but unfortunately I can't say (with 100% conviction) what the mainshaft diameter is. However, the modern equivalent drive side bearing BSA 67-0670 for A7 / A10 1949 - 1963 is NF206E with a specified inside diameter of 30mm (1 3/16").

[Colsbeeza]

Gents, I have fitted the 4-Spring clutch, after a nightmare of problems which I will post separately.
I have a question about the Distance Piece and would like the benefit of your vastly superior knowledge and experience.
I am now checking the sprocket alignment, and have attached a couple of shots for reference.
However, the clutch sprocket is a little further inwards than the engine sprocket by about 2mm.
I could remove the clutch again and look for a different clutch centre adaptor, but that could take months. Getting the right adaptor could also be a hit-and-miss affair, not to mention costly.! Shimming the taper crossed my mind, but only for a second.!! 
The logical solution would seem to be to use a thinner Distance Spacer to move the engine sprocket inwards also.
The existing one is 10mm thick, which seems to be a standard Part No. 67-1138.
Are there thinner ones available, or should I machine down the existing to 8mm.?? I know the outer surface is also the sealing surface, so I may have to hold it from the inside to machine it.
Alternatively, I could machine 2mm of the face of the sprocket holder (Bearing Part No. 42-0069) to move the sprocket inwards.
As I don't have a lathe, I'll have to get someone to do that.
To answer some questions which may arise:
    The bike is a 1961 S/A GF.
    The clutch appears to be an early type.
    There appears to be enough chain clearance from the inner chaincase.
    The adaptor clears the back of the chaincase OK, and the scroll seems to be correctly placed.
    Before pulling it apart, I rode it a few miles and no noises or obvious problems.
    I polished the mainshaft taper using very fine grit, and managed to get a good fit.
    I loctited the Clutch Nut, but also fitted the lock washer, as the face of the inner basket had been ground by a PO,
    presumably because he might have used the wrong rollers (1/4 x 1/4 "??). I am hoping the washer distortion may take up
    some of the slack. Otherwise the basket looks in good condition.
Just want to get it well-aligned.
Thanks in anticipation
Colin

[Billybream]

Hi.
Cannot see clearly but have you fitted the large disc and gaskets that fit between engine case and primary back cover, they should amount to distance you are out.

[RogerSB]

It seems that after 60+ years even the same models have ended up slightly different .

If you have fitted the two gaskets 42-7509 and spacer disc 42-7518 have a close look at the sprocket bearing 42-0069 as there seems to be ones with different measurements. Have a read of reply no 25 by Chaterlea25 here:-

https://www.a7a10.net/forum/index.php?topic=7290.15

Also there was another post where someone measured different bearings and they were different in overall length and the shoulder widths were different thicknesses. It seems that plunger ones are longer overall than s/a ones but the shoulders are thinner than the s/a ones (see reply no 32 by trevinoz) who gives the sizes. Maybe someone has fitted the wrong bearing in the past .

Edit: I fitted a complete SRM 4-spring clutch kit and in my case the clutch sprocket was further out than the engine one so I had to add a fistfull of shims 67-2057 (0.060" worth) between the distance piece and the engine sprocket to move it out. My sprocket bearing was the correct one for s/a. Luckily the cush drive nut (SRM hex mod) does not touch the chaincase cover .

[morris]

Not entirely shure but from memory I'd say the distance piece on your picture seems rather thick 

[RogerSB]

Here's a couple of photos of a distance piece.

Make sure the inside chamfer faces in towards the crankshaft. I had to strip mine down again when I had some doubt whether I put it on the right way?' I even had the chaincase fitted, added oil and went for a test ride. Everything was fine. However, that night doubt suddenly jumped into my head and then it niggled me and I just had to strip it down to check. And it was on the right way after all.

I even take photos of work I'm doing, for just that reason, but in this case my photo just confirmed my doubt because the machining/wear/lighting angle/etc on the flat outside of the distance piece looked just like the chamfer was on the outside (see the photo) .

[Greybeard]

I'm glad I'm not the only one that does things like that

[muskrat]

Billy, the inner cover and disc have no bearing on the sprocket alignment.
Col, as long as there's enough clearance for the chain I'd machine off the spacer.
Cheers