Cush drive questions

[Drew Back]

Have not figured out how to get thumbs on here so here is direct

http://i691.photobucket.com/albums/vv276/monadrew/BSA%20PLUNGER/DSC_1079800x376.jpg

[a10 gf]

67-2055 seems to belong to a longstroke engine, is that whay you've got ? (please post engine nr).

It's a big mystery  , from the last picture, everything looks correct.

About the picture, just post the simple link (edited it), and added the picture as attachment.

And added a pic of my cush which has been working perfect, all look the same to me as on your picture.
So why can't the spring be compressed properly...?? 

[Drew Back]

Ok this is what I have

 http://i691.photobucket.com/albums/vv276/monadrew/BSA%20PLUNGER/DSC_1077800x373.jpg

[Drew Back]

Im trying to fit all this up on a 1956 A10 plunger I pulled this cush drive off a 1950 A7 ZA78918 my A10 is BA1014573..

[a10 gf]

^^^ To my (meager) knowledge, these numbers should give interchangeable cush parts. Someone please correct this if wrong!

My spring does not really compress and it is 1.5 inches long.

If that is correct (38mm), compare that to the numbers I posted. Looks like it's as simple as a shot spring.

To continue todays great cush saga: see picture, approx 10mm clearance below nut, actually did test it by standing (85kg) on the assembled unit as on pic, still the spring kept 'springy' and not bottoming out on the inner bearing. That spring is strong, to say it mildly.

[morris]

Hi Drew Back,

a10gf is right in assuming a shot (or wrong?)spring I think.
I just measured my 52 plunger's spring (2 lobe type) which happens to be apart for the moment.
It's 48 mm long (which is a tad more than 1 7/8 in)

[wilko]

The outer part doesn't even look like a two  lobe either. Somebody has had a grinder on it in the past!

[a10 gf]

Somebody has had a grinder on it

Can't recognize any signs of that, looks very much like the original part, see scan here > http://www.a7a10.net/forum/index.php?topic=8452.msg59913#msg59913, and everything (except the spring thickness) similar to my cush system which has always behaved perfect.

[BSA_54A10]

BSA made all their own cranks so not supprising they are all interchangeable and easily mixed up.
The early cush drives used a 4 lobe cush and a shorter spring.
The C series used a shorter weaker spring.
All of these plus your can be mixed & matched.
So unless your lobes are drastically worn down you need a new spring.
Now before you you order the spring , check carefully the alignment of the sprockets as the boss behing the different sprockets are all diferent lengths.

[Drew Back]

I really appreciate every ones knowledge and advice I suspect the parts including spring are just plain trashed/worn out..I will be going to my nearest dealer next Saturday (I know a long time to solve mystery)to figure all this out..Plunger stuff in my area is all most non existent..
One more question though will the single chain clutch hub work with all the other parts of the duplex clutch hub?

[Brian]

I've just re read this whole topic and I'm starting to think maybe there is nothing wrong at all.

Firstly the nut that holds the spring on must be done up tight. Now when you say you can move the sprocket do you mean in and out or can you rotate the sprocket on the shaft ? If the sprocket rotates on the shaft thats meant to happen, but you should not be able to turn the sprocket a full turn. Usually with the spring on and the nut done up fully it is very hard to turn the sprocket by hand. With the cush drives with two lobes you can move them further by hand than the four lobe type.

As the lobes ride up each other that gives you your drive but the lobes should not be able to ride over the top of each other. When the spring is fully compressed there should not be enough room for the lobes to go right over.

This action of the lobes riding up each other is what gives you your "cush" effect, it takes the harshness out of the drive as you accelerate. 

I would definitely stick with the twin chain and plunger clutch as this type of clutch is far better than the six spring type as fitted to the swing arm models.

[duTch]

 Drew,
 I read on from where I finished off and agree with Brian, doesn't sound like you had it done up at all, let alone TIGHT- 65 ft.lb.
  Even with no spring fitted, the sprocket lobes and sleeve lobes would still engage, in fact the spring broke and it still rode ok- just made funny noises...

  Fairly sure I have a spare inner sleeve from a swing arm model, and they are obviously not interchangeable.
 They're same length, but the external splines splines/dia. are different, which makes the S/A sliding sleeve different to match, and are obviously shorter when compared in pictures (parts lists). There's also 3 different types of spring nuts, but only the stepped one one fits the plungers(as I discovered).

   I reckon you need a new spring as Morris suggests, and just tighten the nut and see how it goes.

[chaterlea25]

Hi All,
Does the spigot on the nut for the plunger crank fit into the end of the cush drive sleeve
In Drew's photos the engine end of the sleeve cannot be seen, the  drawing posted shows a different shape at the engine end from the swing arm type sleeve
The nut spigot seems to butt against the end of the sleeve at a much smaller diamater which wouldn't give much clamping area
I'm wondering if the sleeve is the correct one?

John

[duTch]

 John as far as I can tell it's the correct one. Plunger ones are stepped and butt up tight to the inner sleeve, as the S/A ones do, so the sliding sleeve can slide over the minor diameter of the stepped bit. The S/A outer (sliding) sleeve is shorter and has a different nut, sliding sleeve and I think a shorter spring(citation needed).
  I only (think I)know this 'cos I recently had to deal with it, so dug out the specs. of the replacement spring that I'm not happy with.
  Length      43.5mm.... should be ~ 47.5 (1,7/8 as Morris suggetsed)
  Inner dia. 44.5 (Outer add 8mm x2= 60.5)-  I measured inner, as I feel it's more critical, and the replacement is too big by ~ 2mm, and doesn't seat on the nut landing very well, and will affect the loaded tension to a degree, and combined with short spring, I think makes a big difference.
   I've been meaning to make comment since I did mine, as I reckon the spring being too short, not enough pre-load, it allows too much movement and sometimes makes funny noises(but not like before).
   The compressed length is fairly irrelevant, as they will all end up much the same length with the nut tightened properly.
 Drew, your spring may be from a S/A...?
 That's my couple of pebbles worth....for now

 Minor editing done by me..
 18.10 AEST (GMT+9?)
   

[trevinoz]

My springs are all square section, I don't know whether they were changed to round section in later years.

Trev.