Author Topic: '57 A7SS Clutch- 6 spring or 4 spring conversion?  (Read 743 times)

Offline Whatnow

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So,  *roll* jumping ahead to the .

The 6 spring is obviously toast, I'd question the 1980s replacement friction plates.
The only parts that haven't suffered from the wet garage are a bearing and packet of springs.

Straight question, full 6 spring clutch or 4 spring conversion?



And the rear wheel sprocket r/h/s pic 1? 47t solid, would  that be part of the 1970s Rocket conversion?

Northamptonshire 1957 A7SS

Offline Swarfcut

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Re: '57 A7SS Clutch- 6 spring or 4 spring conversion?
« Reply #1 on: 06.09. 2023 08:41 »
 OK, the llned  driving plates may be a bit rusty around the edges, but look to still have the maker's name visible and appear unused. The lining are thin, a new Surflex plate to hand is  only 3.8mm thick. The clutch centre looks to be the later type with the reinforced driven fingers, I think I can see the tips of a couple, but I think the clutch pressure plate is earlier, without the cut outs to clear those tips.
 I reckon it is well worth cleaning up those clutch bits just to get a runner, with a potential saving of some £200 or more if buying new clutch parts. Certainly good enough in the short term. No good having the finest clutch powered by the most dog rough motor.

 Put the money towards the correct cylinder barrel and possibly a set of pistons to match. Probably cheaper to put the alloy head in a safe place for now and find a cylinder head from an early A7 plunger engine to match existing barrel.

 If a full blown concours restoration is on the cards, arrange long term finance now......

 Swarfy.

Offline Whatnow

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Re: '57 A7SS Clutch- 6 spring or 4 spring conversion?
« Reply #2 on: 06.09. 2023 09:47 »
thanks Swarfy
the friction plates were new and unused, wasn't sure if they would still be good.
You are correct the 1980s replacement plates don't fit the pressure plate.

Concours? I think runner is the first target but without needing to do anything twice.


Northamptonshire 1957 A7SS

Offline Whatnow

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Re: '57 A7SS Clutch- 6 spring or 4 spring conversion?
« Reply #3 on: 06.09. 2023 22:22 »

 Put the money towards the correct cylinder barrel and possibly a set of pistons to match. Probably cheaper to put the alloy head in a safe place for now and find a cylinder head from an early A7 plunger engine to match existing barrel.
 Swarfy.

Off section topic  but correct cylinder barrel?
 I take it you mean this and the head are not OE..not just the +40 pistons

Northamptonshire 1957 A7SS

Offline Swarfcut

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Re: '57 A7SS Clutch- 6 spring or 4 spring conversion?
« Reply #4 on: 07.09. 2023 08:35 »
 BSA were very good at making incremental changes over the years, the result being that incorrect parts from different models will fit. The cylinder barrel is a case in point. Pre '53 engines have narrow fins, the fin size was increased when the Swing Arm framed models were introduced. The cylinder head you have there is the later wide fin alloy type. But the barrel appears to be the early type. Have a look at online images etc and the difference will jump out.

 Internally the head bolt spacings, bore and combustion chambers are the same dimensions, so it all fits. But.....A7 and A10 barrels also differ in height and bore, likewise the cast iron and alloy heads A7 and A10 while externally similar in configuration, differ internally with respect to combustion chamber size, inlet tract and valves.

 Luckily there is plenty of published data to identify what you have, most BSA castings are numbered, and parts books are available as reprints or conveniently in the Forum Literature Section. Draganfly also have an excellent comprehensive website. There is also Haynes, which is a good basic primer, but in retrospect, not without fault.

 The oil pumps on these bikes are prone to stiffen up on long term storage, the body is alloy and prone to creep, and although the first instinct is to jump on the kicker, this can cause damage, so be warned.

 Sourcing the correct barrel to match existing pistons is the ideal, but Sod's Law means heavy money to start with if you have to get new pistons, the Forum has lots of information as to the pitfalls of the various aftermarket  brands.

 Looking again at the picture at the start, the bodgers' art is epitomised by the long sticky out bolts on the front mudguard bridge, so be prepared for a few surprises along the way.

 A note on nut and bolt threads.... Threads into alloy are generally Whitworth (BSW), most aftermarket fasteners are UNC which for most applications is fine, primary case screws for example. The rest of the nuts and bolts are CEI, also known as Cycle Thread or BSCy, but there are exceptions, Head Bolts being BSF. So, stripped and damaged threads are to be expected where some fool has forced an M6 bolt down a 1/4 Whit hole..... For replacements, Specialist suppliers, eg Nooky's Nuts in Essex are your best source, (as is Grandad's nut and bolt tin). Forum also has a Nut and Bolt Chart ( cross reference to part number) in the Literature Section. Not perfect, a few missing and unknowns,  but overall pretty good.

 Swarfy.

 


 

Offline Whatnow

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Re: '57 A7SS Clutch- 6 spring or 4 spring conversion?
« Reply #5 on: 07.09. 2023 10:23 »
Thanks Swarfy
 something to discuss with my build buddy, trying to plan a strp down and in depth inspection to see where the land lies.

Northamptonshire 1957 A7SS