4-spring clutch hub adaptor 42-3170A - large or small taper?

[mikeb]

I'm still trying to fit a 4-spring clutch to my plunger b33. The clutch hub adaptor 42-3170A I've received is not as I expected. It has a smaller diameter in the taper (compared to the standard 42-3170) so sits further out on the mainshaft, ie further away from the gearbox and so more out of line with the crankshaft sprocket. In the supplier's defence (burtons), they did state this as 'small taper' but for various reasons I thought I'd take the risk. I was expecting 42-3170A to have a larger diameter on the taper and so fit closer in to the gearbox, as it states on the feked page:
https://www.feked.com/bsa-4-spring-clutch-hub-adaptor-large-taper-a-and-b-group-models-circa-1954-63.html
and implied on the draganfly page: https://draganfly.co.uk/shop/137246/clutch-adapter-not-alternator-m/

So - does this one modified 'A' part number have two variants? Can anyone make sense of this?

What to do? I'm tempted to try and turn the taper diameter out a bit but aren't sure i have the machining skills for the accuracy required. anyone care to estimate how hard the job is? its a taper but on a key.

Thanks

[BagONails]

G'day Mike, a couple of years ago I went through a whole world of problems in my primary drive including being sent the wrong clutch adapter. (Triumph 4 spring clutch fitted) It's all here in this thread which may be of some help to you:
https://www.a7a10.net/forum/index.php?topic=16364.0

I ended up machining the part to get the clutch running where I wanted it and had to find the correct cush drive sleeve bearing as well (PO had the wrong part in there).

It is possible to bore the adaptor in a lathe with carbide tools but the material is extremely tough / hard. It took quite a while and there was a lot of trial and error with marking blue before I was happy but I can report that everything has been functioning perfectly so far since the rebuild.  I could say more but its all there in that thread if you haven't seen it as yet. Best of luck with it all.
Cheers Baga'

[mikeb]

thanks for your comments Bagga', I hadn't seen that thread. I think I'll have a go at widening the taper, like you did, as not much to lose. mailing stuff back to blighty is time-wasting and often random in what gets sent back.
interesting that your adapters didn't mate well with the mainshaft taper - neither my original a10 or replacement adapter mate well with the b33's mainshaft, even tho i keep reading all bsa mainshafts are 4* taper. I might blue mine up and get a better sense of what is happening here. Also interesting John's comments about using a die grinder vs a cutting tool. Maybe I'll start with a carbide tool and see if i can cut it without the keyway destroying the tool, then if that fails consider a die grinder if i can mount it on the tool post somehow. I have a dremel but imagine that's a bit gutless for the task.

[mikeb]

the plot thickens on this. to fit the B, the a10 hub adapter would need to move inboard about 7mm to line up the chainwheel. but there is only about 3mm of inward travel possible before the inner end of the adapter would hit the small shoulder on the B33's mainshaft - see pics.
So i'd need to bore out the last 4mm of the taper so it clears the shoulder - ie bore it out to extend the inner section of the rear scroll bit of the adatper.
But that means the shortened taper would make only 14mm of contact (not 18mm) and the key would protrude out the front of the adapter and strike the retaining nut.

This is all surprising as many folk mention making this mod. So:
1. either the correct adapter is of completely different design (ie, not just the same item bored out a bit)
2. or i'm not understanding this.
3. or..???

any thoughts?

Thanks

PS the constraint is I can't fit the clutch further outboard (and space out the crank sprocket to align) as the clutch basket would then foul the tin primary cover.

[BagONails]

Your latest post dropped in just as I was about to post a reply!


I can't think of a way out of this without machining an extended taper into the mainshaft but that is a much bigger job. Maybe worth another try at phoning around the suppliers and see if there is a correct or at least more suitable adapter on the shelf somewhere?

Alternatively you might get away with the shorter taper engagement but make sure that there is at least 0.25mm clearance between the shoulders with the nut torqued up to ensure it fully locks on the taper.  Sorry I can't help much more than that.

[mikeb]

I’ve finally got the new 4-spring cush centred clutch on the B33 and can note a few fun facts.

The 42-3170A is usually specified as a large taper, that is, a larger diameter taper to fit further inboard on the mainshaft. This is the one to fit the 4-spring clutch on to the plunger/rigid B.

I phoned LF Harris (super helpful) who state the spec on the 42-3170A is 0.753” – 0.754” (ie 19.10mm) on the inboard (wider) side of the taper. This compared with the standard 42-3170 which is 0.739” – 0.730” (ie 18.53mm). It can be hard to measure that inboard diameter – the outboard (smaller) diameter of my standard 42-3170 measured 16.56mm.

There is also a 42-3170A (same part number!) sold as a narrow taper and said to fit the alternator B31/b33 models and possibly some ‘later singles’. I got sent one of those. The outboard (smaller) end of the taper measured 15.96mm. This is NOT what you want for this job. It sits about 3.4mm further outboard on the mainshaft (compared to standard 42-3170).

As I ended up with 2 incorrect clutch hub adaptors, sent one at a time from 12,000 miles away, I took inspiration from Ian’s post above and the other thread referenced and widened the taper to fit. Setting the taper angle was difficult and trial and error (I don’t have a suitable dial gauge). I couldn’t usefully cut the hard steel with a carbide tool (especially with the keyway smashing the tool) so made a mount for a pencil die grinder on the tool post (inspired by Chatterly John’s post elsewhere – my pic below). After many tiny grinds, checking with blue and finally lapping with fine paste (I know some people think that’s a bad idea) it fits the m/s taper at least as well as the standard clutch adaptor fits on my a10. The clutch adaptor now sits 3.76mm further inboard than the standard 42-3170 and the chainwheel aligns with the crankshaft sprocket. The 3.76mm is less than I first thought needed and there was no problem with the adaptor hitting the shoulder on the mainshaft (tho I did take 1mm off the inboard end of the taper to be sure).

Very importantly the 4-spring clutch fits inside the tin chaincase. I added an extra spacer under 42-3237 and had to make a new key as the old one was loose. 42-3267 is blue loctited on at about 70 ft/lbs. As the hub has a cush centre I removed the standard cush spring and made a spacer (long story as why, for another thread if it ever happens) – still tighten to usual specs. And the pushrod needed to be 3/4" longer – currently in 3 sections with a 1/4" ball assisting.

The clutch is so much lighter! I stupidly put an a10 amount of primary case oil in the tincase B, which I have been doing for years on the 6-spring . But it oiled the new plates together and graunched into first. Now cleaned and the right amount of ATF (which is not even leaking – yet).

So… the new 4-spring on the plunger is a great improvement. And make sure you get the right version of 42-3170A.

[muskrat]

G'day Mike 
Well done.
You must have a good quality 3 jaw chuck. My Chinese one has more run out than the City to Surf
Surprising how little it takes to move on the taper.
Thanks for posting.
Cheers

[berger]

i have seen how difficult it is to turn metal off these original hardened BSA parts when my brother did the gear for the rrt2 lower first gear conversion and worty's cush sleeve , that made a mess of the carbide tip although it was a tip made somewhere in the far east.

[KiwiGF]

I’m rather envious of the “pencil die grinder”, also the holder, never heard of them before. Where did you source them? (Asking for a friend)

[mikeb]

musky thanks for the encouragement. not sure if my chinese 3-jaw is better than yours, maybe my attention to detail is worse.
kiwi - i got the pencil die grinder from 'machinery house' - there's one in chch and akl (its an aussie chain). not sure if i'd recommend it as gutless and the tiny tools with 3mm shafts are not that rigid. next time I'd buy a larger item with 1/4" collets. I made the tool holder - easy as the die grinder body being 5/8" dia. only fiddly bit being to get it centred with the chuck centre. as per Chatterlea John's post elsewhere, I faced the stone.

EDIT: I’m noting this idea to get a response and in case someone else gets stuck. If the 4-spring had not fitted the tin chaincase even with the correct 42-3170A, I now think the easiest thing to do may be just make a spacer (eg 3mm) between the crankcase and the chaincase, and then space similarly behind the cush sleeve (or get one with a wider shoulder and reduce it) and spacers behind the footpeg and the brake lever (or bend it). The point being there is nothing holding the chaincase at the gearbox end and only 3 bolts at the crankcase end. So just move it out to accommodate a wider clutch basket. Just a thought… ???

[KiwiGF]

musky thanks for the encouragement. not sure if my chinese 3-jaw is better than yours, maybe my attention to detail is worse.
kiwi - i got the pencil die grinder from 'machinery house' - there's one in chch and akl (its an aussie chain). not sure if i'd recommend it as gutless and the tiny tools with 3mm shafts are not that rigid. next time I'd buy a larger item with 1/4" collets. I made the tool holder - easy as the die grinder body being 5/8" dia. only fiddly bit being to get it centred with the chuck centre. as per Chatterlea John's post elsewhere, I faced the stone.

EDIT: I’m noting this idea to get a response and in case someone else gets stuck. If the 4-spring had not fitted the tin chaincase even with the correct 42-3170A, I now think the easiest thing to do may be just make a spacer (eg 3mm) between the crankcase and the chaincase, and then space similarly behind the cush sleeve (or get one with a wider shoulder and reduce it) and spacers behind the footpeg and the brake lever (or bend it). The point being there is nothing holding the chaincase at the gearbox end and only 3 bolts at the crankcase end. So just move it out to accommodate a wider clutch basket. Just a thought… ???

Thanks Mike, only $107 not bad eh, I have a dremel and made a holder for that a while back but it was not solid enough, the pencil grinder looks a better option.