Author Topic: Cush Drive Question  (Read 430 times)

Online DJinCA

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Cush Drive Question
« on: 17.02. 2019 16:47 »
As I mentioned in my intro, I am working on a pile of parts that are '51 and '52 plunger A10.  My intent is not restoration, at least for now, but to get the bike on the road as a rider, even if a bit ratty.  I am working on disassembly and trying to inventory what I have vs. what I need.  There was no clutch (I have since acquired one from a club member) but the engine sprocket is for a triplex chain.  I understand that the triplex was used on the Super Flash and was optional for some A7/A10s. 

My question is if the bearing a sliding sleeve parts I have are correct for a duplex sprocket, or if there are differences between these parts for the duplex and triplex.  I would think that they are the same, but don't want to assume when it comes to Brit bike parts because I have laughed at that joke before.

Thanks,
Dave

Offline a10gf

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Re: Cush Drive Question
« Reply #1 on: 17.02. 2019 18:39 »
Hello, looks like some correct parts, but the twin sprocket seems to be different to what my plunger uses, see https://www.a7a10.net/BSA/techpics/cush.jpg
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Online DJinCA

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Re: Cush Drive Question
« Reply #2 on: 17.02. 2019 20:14 »
Hello a10gf,

It's sort of hard to tell because I haven't cleaned any of the parts in the picture, but it is a triplex sprocket, and the camming sufaces sit down inside the sprocket.

Offline a10gf

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Re: Cush Drive Question
« Reply #3 on: 17.02. 2019 20:56 »
Yes, meant that triple sprocket. Am thinking the plunger used exclusively twin chain, and that your clutch is (should be) a 6 spring (with the dome cover) + twin chain, so the '3' sprocket may be of the wrong type, someone on the forum may indentify it and shed more light.
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Online trevinoz

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Re: Cush Drive Question
« Reply #4 on: 17.02. 2019 21:59 »
Apparently triplex was an option for the U.S. market.
I have found a sprocket on a standard A10 bottom end which I bought at a swap meet.
A friend picked up a triplex basket at another time.

Online trevinoz

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Re: Cush Drive Question
« Reply #5 on: 17.02. 2019 22:48 »
Dave, pictured are cush parts from a 1951 A10.
Note the spring is a square section but round section springs will do just fine.
Note also the large nut, it has a spigot on it unlike the later type.
As to whether the triplex sprocket will work, fit it up and check chain alignment.

Online Swarfcut

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Re: Cush Drive Question
« Reply #6 on: 17.02. 2019 23:03 »
 Hi Dave.  Standard set up for Home Market  plunger or rigid A7 or A10 is an 80 link Duplex Chain, and a 27 tooth engine sprocket, 54 tooth clutch chainwheel.  Unless you are lucky, finding a triplex clutch to match will be difficult.  I assume you have sourced a Duplex Clutch, so could use this with the triplex engine sprocket and duplex chain as the chain pitches are the same. 

   The triplex chain was only used for the Super Flash (USA) as standard, or for special home market orders. So, you may have a Super Flash Engine, or the triple sprocket which is from a Super Flash.  The later unit models also use a triplex chain, so it could be  a spurious part, say from an A65, which has 28 teeth. The Genuine Super Flash Frame has a Swan Neck bend in the vertical frame tube  under the saddle.

 The drive sleeve varies. Early models do not have a crank seal, just an oil slinger and a spiral groove on the sleeve, which is a very close fit with the crankase hole. It acts as an Archimedes' Screw, to prevent engine oil entering the primary chaincase.  Later engines have an oil seal and a smooth area on the drive sleeve to run on the seal, as pictured above. The sleeve will be the same length for triplex and duplex sprockets.

 Do a trial  assemble of the cush drive without the spring. The nut should screw onto the crank and bottom against the end of the sleeve, so that when finally tightened it clamps the main bearing inner race against the crank web. There should be smooth movement of the cush drive ramps, and the cush outer part should slide easily along the spline on the drive sleeve.  The nut should have a raised section to match the end of the drive sleeve, described earlier as a spigot, by Trev....The later S/A nut is flat, and is the wrong part, often mis described as plunger, and also often found as a spurious part with basket case purchases. The nut should go on far enough to pass the cross hole in the end of the crank, which is for a split pin to stop a loose nut machining a hole in the chaincase.  Properly assembled, with the spring, the nut is done up tightly to around 65 ft/LBS. Plenty of information elsewhere on this forum about this nut, main bearings, crank endfloat and the all important crankshaft sludge trap clear out.

  Good Luck.

 Swarfy.

Online trevinoz

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Re: Cush Drive Question
« Reply #7 on: 18.02. 2019 00:41 »
Swarfy, the scroll on the sleeve was only used on fairly early engines.
I have only seen one which I fitted to my 1950 Star Twin engine.
I have stripped quite a few 1951 engines and they didn't have the scroll.

Online DJinCA

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Re: Cush Drive Question
« Reply #8 on: 18.02. 2019 01:31 »
Thank you Gentlemen,

I knew that I came to the right place to ask about this.  It looks like i have a usable sliding sleeve and bearing, but an incorrect nut.  Trev suggests that my round wire spring will work satisfactorily.  My clutch is for duplex chain as was suggested by Swarfy.  I will look at the crankcase options to see about fitting an oil seal.  The bike (using the term loosely for a true basket case) came with a bare set of cases that needed (and have received) a minor repair and the a set that were assembled with a crank and cam but need more major repairs (posts forthcoming in the engine section) both with late 1951 dates (52 model year)

The triplex sprocket is from A7/A10 or something else of that era, and not something cobbed together from an A65 part.  I guess I will either test fit the triplex to see if will align, or look for someone that actually needs the part and look to trade it for the duplex.  My sprocket appears to be in pretty good shape, but i clean it up to get a better view.

Thanks for the help and advice.

Dave

Online BSA_54A10

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Re: Cush Drive Question
« Reply #9 on: 18.02. 2019 06:18 »
Swarfy, the scroll on the sleeve was only used on fairly early engines.
I have only seen one which I fitted to my 1950 Star Twin engine.
I have stripped quite a few 1951 engines and they didn't have the scroll.

However one of the nice things about BSA's can also be a nightmare
Nearly all BSA's have the same size crankshaft so a lot of wrong parts will almost fit.
Same for the clutch hub ( splined bit ).
So there is a better than average chance you have a box full of wrong parts.
AFAIK M20/21 engines never got an oil seal so their cush drive centres had a scroll .
For the A & B series BSA cut off the scroll and supplied a smooth machined spaces to run on the oil seal
Bike Beesa
Trevor

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Re: Cush Drive Question
« Reply #10 on: 18.02. 2019 08:00 »
     Trev is right about the scrolled sleeve, only found on early engines. and this demonstrates BSA's development by incremental changes rather than radical redesign. The scrolled sleeve is only used with early crankcases that do not have the oilseal, but have the oil slinger, 67-347, described as a" bearing shim" in the parts book The scroll works reasonably well, only failing when the spiral groove becomes clogged with carbonised oil and debris.  The later spacer design is only used on S/A engines, which also have a different, shorter drive sleeve, never  fitted as standard on rigid and plunger engines.

  A smooth sleeve will fit into the non seal crankcase, but will be ineffective at keeping back the oil. To fit a seal to an early crankcase will require the case to be opened up to some 55mm.  This is slightly larger than the inner diameter of the main bearing outer race, which serves to locate the seal laterally.

 Crankcase halves were date stamped on an irregular basis, presumably based on how much time was allowed to complete the operation and on how conscientious the guys were.

   In manufacture, the crankcase halves were bolted together, with their bushes fitted, and the camshaft and main bearing locations line bored. The cases were stamped with a matching number, on each case, at the front of the engine. A factory matched pair will have the same number, in the same style of stamp.  As a quick test, a camshaft should rotate freely with the cases lightly drawn together. Miss-matched halves that bolt together well can be matched by retaining the two cam bushes in the timing side case, just replacing and line boring the drive side cam bush and replacing the timing bush and line boring it to the main drive side bearing location. This involves more work and expense but makes redundant parts useable. A camshaft that binds in an otherwise matched pair of cases will probably be bowed... spin it in a lathe to check run out.
 
   If the triplex sprocket is the right part it could be used in the short term with an endless duplex chain....A split link may foul against the unused outer teeth. Obviously sourcing the correct matching duplex sprocket is the best way forward. Mix and match, similar but incorrect parts from other contemporary models, plus heavy handed abuse etc are all lurking in the background.

 Like I said, Good Luck.

 Swarfy

 

 

Online trevinoz

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Re: Cush Drive Question
« Reply #11 on: 18.02. 2019 20:30 »
As I stated, I have stripped 1951 engines which didn't have a scrolled sleeve but they also didn't have a seal, only the slinger.
Perhaps BSA found the scroll no more effective than the smooth sleeve.
I am pretty sure that the scrolled sleeve I had came from a YA7 engine. It now live in a ZA7S engine.
As Swarfy said, have your cases bored to accept the later seal.

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Re: Cush Drive Question
« Reply #12 on: 18.02. 2019 21:40 »

 Dave I was wondering why your nut is wrong,  and the I realized I was looking at Trevs picture... *bash*

 As stated,  I'll say that sprocket should be ok to use if everything is aligned properly, although maybe a SF owner needs one and you could do a trade...

 Interesting stuff about the scroll - my engine came with a a scrolled sleeve *and*
a slinger, and it's stamped 23.12.52, but not to say that's how it left the factory- maybe retro-fitted.
 I think it's well known that ( according to the spares list) the seal wasn't standard until '54....I had the scroll ground off anyway and put a seal in,  and that was long before I knew of the change.
   I also have another sleeve I found at a swappie   that  has slightly wider seal flange, so presume it was for post '53...
 

Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
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Re: Cush Drive Question
« Reply #13 on: 19.02. 2019 11:37 »
As I stated, I have stripped 1951 engines which didn't have a scrolled sleeve but they also didn't have a seal, only the slinger.
Perhaps BSA found the scroll no more effective than the smooth sleeve.
I am pretty sure that the scrolled sleeve I had came from a YA7 engine. It now live in a ZA7S engine.
As Swarfy said, have your cases bored to accept the later seal.

Yes Trev,
But did you strip it in 1951 ?
My first A 10 was a horrid mis match of long & short stroke part plus parts from every model BSA had ever produced.
But it ran so I rode it
And when things went bang I went to the wreckers, broken part in hand and bought the cheapest bit that looked almost the same.
Even the 2 original one owners A 10's in the club had wrong parts fitted  to them, because the owners actually rode them every day for decades.
People always remember things like what was replaced after a prang or blow up but no one remembers the routine maintenance  items replaced because it was routine.
I could not tell you the number of times some one has come with a bike that has better than 100,000 on the clock, swears on a pile of bibles the engine has never been opened then you get inside & find bolts with stripped heads, Star washers where flat ones should be & evidence of multiple overtightenings.
Bike Beesa
Trevor

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Re: Cush Drive Question
« Reply #14 on: 19.02. 2019 14:26 »
 After all these years, a completely original and unmolested machine would be very rare. Back in the day a "near" part rather than the "proper"part was often used, simply because the bike was needed  for daily transport, and just had to be just good enough for that. Same day parts delivery was unheard of.

  That poor crank nut......thousands must have been butchered over the years with the hammer and drift style of maintenance. These days an angle grinder and some steel tube makes a nice peg spanner in a matter of minutes.

 Swarfy.