Author Topic: A7 Plunger Star Twin '52 cylinder\head\crank  (Read 563 times)

Offline Richard A

  • A's Best Friend
  • ***
  • Join Date: Jul 2016
  • Posts: 40
  • Karma: 0
A7 Plunger Star Twin '52 cylinder\head\crank
« on: 12.09. 2016 15:31 »
Hi, can anyone help I am looking for a standard A7 cylinder block (part no 67-378) and cylinder head (part no 67-524) as I'm trying to get my Star twin back to standard spec and when purchased I did not realise that some helpful person had put A10 parts on!

Guess I will find more disasters when I pull it apart, but at the moment running ok.

Thanks

Richard

Online Klaus

  • Valued Contributor
  • ****
  • Join Date: Jun 2015
  • Posts: 376
  • Karma: 10
Re: A7 Plunger Star Twin '52 cylinder\head\crank
« Reply #1 on: 12.09. 2016 19:21 »
Hi Richard,

if an A10 barrel was fit on A7 crankcases you can be sure, there was also an A10 crank inside.
A7 crank has another strocke, so the A7 barrel is shorter with 7 fins, the A10 was 8 fins.
It makes no sens to get an A7 barrel without the right crank.

cheers Klaus


If you think, everything is under control, you are not fast enought.

Offline Rocket Racer

  • Wise & Enlightened
  • *
  • Join Date: Jun 2009
  • Posts: 1430
  • Karma: 16
  • A kiwi with a racing A10 rig and too many projects
    • NZ Classic Sidecar Racing
Re: A7 Plunger Star Twin '52 cylinder\head\crank
« Reply #2 on: 13.09. 2016 02:28 »
Like Klaus, not wishing to rain on your parade, your intention to return it to a 500 very noble... but if it happens to have a LJ crank in it why would you want to take that out. Quite a nice option that would make it look like a 500 would be to fit A65 rods which allows the barrel to be milled shorter by 1/2" so has the same number of fins as a 500, but still a 650  *yeah*
Just a thought.
Tim
A good rider periodically checks all nuts and bolts with a spanner to see that they are tight - Instruction Manual for BSA B series, p46, para 2.
New Zealand

Offline Richard A

  • A's Best Friend
  • ***
  • Join Date: Jul 2016
  • Posts: 40
  • Karma: 0
Re: A7 Plunger Star Twin '52 cylinder\head\crank
« Reply #3 on: 13.09. 2016 09:50 »
Gents,

Many thanks for your helpful comments and yes I've now managed to measure the stroke and it matches an A10 at 84mm so seems I have the head, barrel and crank of a swing arm A10.
The idea of the A65 conrods does appeal so I will look into that over the winter.

Richard

Offline Rocket Racer

  • Wise & Enlightened
  • *
  • Join Date: Jun 2009
  • Posts: 1430
  • Karma: 16
  • A kiwi with a racing A10 rig and too many projects
    • NZ Classic Sidecar Racing
Re: A7 Plunger Star Twin '52 cylinder\head\crank
« Reply #4 on: 13.09. 2016 22:16 »
A nice thing about a65 rods is the later ones (also used on the A70) were alloy with steel caps, so hold oil pressure better!
There is a bit of work required in shortening the barrels, I think I posted a copy of an article "what makes that beezer go" on how to do it on my racing sidecar thread as my A10 "looks" like an A7 as its shorter!
http://www.a7a10.net/forum/index.php?topic=1998.75
A good rider periodically checks all nuts and bolts with a spanner to see that they are tight - Instruction Manual for BSA B series, p46, para 2.
New Zealand

Online muskrat

  • Global Moderator
  • Wise & Enlightened
  • **
  • Join Date: Jul 2009
  • Posts: 8269
  • Karma: 106
  • Lake Conjola NSW Oz
    • Shoalhaven Classic Motorcycle Club Inc
Re: A7 Plunger Star Twin '52 cylinder\head\crank
« Reply #5 on: 14.09. 2016 10:19 »
Started a new topic Con rod length. http://www.a7a10.net/forum/index.php?topic=11056.0
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
Muskys Plunger A7