Author Topic: A7 and A10 crank the same? Surely not ?  (Read 1854 times)

Offline Gasket4450

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A7 and A10 crank the same? Surely not ?
« on: 14.05. 2012 12:58 »
Hello. I am a new member from Kent, UK, and an A10 owner, built from several boxes of bits, over several years, and so I have a reasonable mechanical knowledge of BSA engines. Now that I am retired, I am trying to build an A7 Shoting Star virtually from scratch ( should keep me busy, then.....). I am looking for an A7 crank, having already acquired almost everything else. There is a listing on Ebay for a six-bolt crank, but the seller says in reply to my questions as to which it is: "  Err, I didn't know there was a difference." Not very helpful, really. However, I am aware from this forum, and Roy Bacon's Bible, that the stroke on the A7 is 72.6mm as opposed to 84mm on the A10 - surely if the seller measures the distance between the centre of the crank pins and the centre of the main shaft he should be able to give me an approximate figure one way or the other ? Or is it not as simple as that? I have already asked him about part numbers, 67-384, but he says there are none visible. Any help would be welcome ( although I am now thinking that I shall forget this one, and look for one at the next auto jumble ! )
1960 A10, alive and thriving. 1959 A7 living on borrowed time !

Offline duTch

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Re: A7 and A10 crank the same? Surely not ?
« Reply #1 on: 14.05. 2012 14:26 »
 Hiya Gasket, I don't know much about A7 long stroke, but aren't they about 82mm stroke? From, duTch
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
Australia

Offline Gasket4450

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Re: A7 and A10 crank the same? Surely not ?
« Reply #2 on: 14.05. 2012 14:46 »
Thanks, Dutch. Yes, you're right, the original old long stroke was as you say. These were I believe used on the early A7 models from just after the war up to about 1952/53. I am looking at a 1954-1962 six bolt crankshaft, which I think is 72.6 according to the restoration book I have.
1960 A10, alive and thriving. 1959 A7 living on borrowed time !

Offline kommando

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Re: A7 and A10 crank the same? Surely not ?
« Reply #3 on: 14.05. 2012 15:03 »
Much as you may need the part there are times when the sellers responses tell you to go elsewhere  *eek*

Doubt you could trust them with a ruler.
No BSA twins just unit singles
Scotland

Online bsa-bill

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Re: A7 and A10 crank the same? Surely not ?
« Reply #4 on: 14.05. 2012 15:31 »
Your right on Gasket4450 ,
Quote
I think is 72.6 according to the restoration book I have.
the 650 s kept the longer stroke, the A7s changed to the shorter stroke and maybe accounted for their reputation as a sweeter engine
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Offline Gasket4450

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Re: A7 and A10 crank the same? Surely not ?
« Reply #5 on: 14.05. 2012 19:10 »
Thanks Kommando. I agree with: "......there are times when the sellers responses tell you to go elsewhere 

Doubt you could trust them with a ruler."   

 I didn't like the sound of it, even though the seller said it was standard, and it went for £77, but I gave it a miss. I will try some of the established UK specialists like Cake Street, or Lyford, etc. At least I know I won't get ripped off.
Look forward to being a member of this forum. Best thing invented since the four spring clutch...........( that should prompt some debate !!!)
1960 A10, alive and thriving. 1959 A7 living on borrowed time !

Offline BSA500

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Re: A7 and A10 crank the same? Surely not ?
« Reply #6 on: 14.05. 2012 19:51 »
Where abouts in kent are you out of interest. I am in West Kent Tonbridge.

Offline Gasket4450

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Re: A7 and A10 crank the same? Surely not ?
« Reply #7 on: 17.05. 2012 16:25 »
Ashford, the " Boom Town " of the South East, according to John Ptrescott !!!
1960 A10, alive and thriving. 1959 A7 living on borrowed time !

Offline Gasket4450

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Re: A7 and A10 crank the same? Surely not ?
« Reply #8 on: 21.05. 2012 17:41 »
Quote
the 650 s kept the longer stroke, the A7s changed to the shorter stroke and maybe accounted for their reputation as a sweeter engine
Thanks for the above, Bill. I thought I had it figured out about right. I see there is a crank advertised on Ebay today which is listed as:
".....A7 Gold Flash....." , which again is not helpful. It appears to be a six bolt crank, but I have had to e-mail the seller to ask whether it is A7 or A10. I know they look the same, but is it only members of this most excellent forum who seem to know the difference ???
Regards, Norman
1960 A10, alive and thriving. 1959 A7 living on borrowed time !

Online muskrat

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Re: A7 and A10 crank the same? Surely not ?
« Reply #9 on: 21.05. 2012 20:50 »
 G'day Norm,
                 the easiest way is to support the mains on something ( a pair of bricks will do ). Roll it till the crank pin is uppermost and measure from the ground to the outer edge of the pin ( by eye, with a ruler). Then roll it till the pin is at the bottom and measure up to the inside of the pin. Take the small away from the big and you have the stroke.
 Rough but good enough in the field.
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
Muskys Plunger A7

Offline Gasket4450

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Re: A7 and A10 crank the same? Surely not ?
« Reply #10 on: 23.05. 2012 12:45 »
Thanks, Muskrat.
                                  Simple, but brilliant, of course.*idea* I knew there had to be a 'best guess' scenario, but just couldn't work it out. At least that should prevent some of the half-wits at auto-jumbles trying to pass off A10 cranks as A7's. Now, if only I could think of a way to get a couple of bricks into my pockets......................doh!!!! *smile*
Norman
1960 A10, alive and thriving. 1959 A7 living on borrowed time !