Author Topic: Which crank is correct, 52 A10 project  (Read 663 times)

Offline crojack

  • Moving Up
  • **
  • Join Date: Aug 2016
  • Posts: 7
  • Karma: 0
Which crank is correct, 52 A10 project
« on: 06.08. 2016 23:59 »
Hoping I can find some help from all of you knowledgable people.  Just got a complete 52 plunger, but it needs a total rebuild.  Crank/piston/rod went through the case.  I have an extra set of cases and three cranks.  Big question for me now is how to tell which crank is a correct A10 crank.  I've done some searching but can't find anything very definitive.  One has the 6 bolts inside, but has smaller pistons than than A10.  maybe an A7 crank? 
Any help is very much appreciated!

adm edit: changed topic title to reflect content

Online Klaus

  • Valued Contributor
  • ****
  • Join Date: Jun 2015
  • Posts: 372
  • Karma: 10
Re: Which crank is correct, 52 A10 project
« Reply #1 on: 07.08. 2016 06:40 »
Hi  crojack,

wellcome on board *wave*
The A10 crank has 84mm stroke with two kind of journals, big and small. When conrods are fit you can distinguish both by the screwswhere the balancewight is fixt. Small journals has the six bolts inside, big journals three bolts outside.
Crankcases with the stamps DA was allways fitted with  big journals. But Plunger models has all small journals so far as I know.

The 500ccm A7 has a stroke with 72.6mm and a smaller piston around 66mm and they are alll small journals.

cheers Klaus


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

Online KiwiGF

  • Last had an A10 in 1976, in 2011 it was time for my 2nd one. It was the project from HELL (but I learned a lot....)
  • Wise & Enlightened
  • *
  • Join Date: Feb 2011
  • Posts: 1449
  • Karma: 12
Re: Which crank is correct, 52 A10 project
« Reply #2 on: 07.08. 2016 08:49 »
There are various sources of info on journal sizes but this link below is as good a source as any, the original BSA service sheet is probably on this site somewhere....

http://www.bsawiki.com/chaps/9-engine/15-chapter07

I don't think there is any way to tell the a7 and a10 small journal cranks apart without measuring the stroke (tricky) but maybe someone knows another way? Maybe they have casting numbers on them?

New Zealand

1956 A10 Golden Flash (1st finished project)

1949 B31 rigid “400cc hot rod” (2nd finished project, + favourite bike)

1949 C11 rigid, but why!!! (cos it was cheap)

1937 B21, project missing parts, mission impossible?

GL1800 Goldwing, well, the wife likes it

KTM 950 ADV, cos it’s 100% nuts

1952 Armstrong Siddeley Whitley for rainy days (with wife

Offline duTch

  • Ricketty Rocketty Golden Flashback
  • Wise & Enlightened
  • *
  • Join Date: Oct 2011
  • Posts: 4540
  • Karma: 41
Re: Which crank is correct, 52 A10 project
« Reply #3 on: 07.08. 2016 09:10 »
 Hiya crojack, are you related to Kojack?

 As above, I saw this earlier and had a look at the parts lists, and then got sidetracked  *eek* 
 I think there's three different A10 cranks,  but as kiwi says best way is to measure the throw/stroke (Centre of main to Centre of big end)
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 bodger

  • Moving Up
  • **
  • Join Date: Mar 2016
  • Posts: 16
  • Karma: 0
Re: Which crank is correct, 52 A10 project
« Reply #4 on: 07.08. 2016 12:57 »
Haha, hello Crojack, I am betting you are on the west coast and that bike was one of maybe two that fella had for sale, I liked it a lot and hoped someone with the right state of mind would buy it!

I posted about it on Brit bike for sale forum and started an argument about the style of the CL ad...and it had a rod sticking out of the case.  It looks pretty good if that is the one. The cases are hard to find of course, the recent San Jose show had basically none for sale except for a couple of rusty boxes of transmissions and maybe some well encrusted cases...so buy whatever you can wherever you find it, and explore repairing those cases. I hope someone will leap to correct me but I think the A7 and A10 semiunit were only made for 2, maybe 3 seasons....no books handy.

That engine was pretty strong and fast and was a winner on flat tracks in the us for a few early years in the 50s, the A7 version was partially successful and well represented in AM racing. Gene Theissen did I think 123mph on El Mirage was it?..

As I recall there was a spare motor and crank and he was hinting he would sell another one...if this was the Oregon craigs list ad I was on about.

Of course it could be a coincidence....

whichever, congratulations, that is an interesting motor and pretty special in it's way.

The history is that it is I think the first BSA 650 and at that point was still, to my mind, the best design in that the engine and transmission were bolted together, saving about 3" in overall length from the later preunit design.

The transmission and engine share a lot of parts with the later pre-unit design, I have read this was called the semi-unit design. I think the clutch and transmission main shaft are different, some of the later parts can work, and I think that clutch was well regarded....may be wrong..again, heh.

I have the A7 version of it. I think it is a very nice looking design, perhaps the best of the 50s'and 60s for BSA and triumph...well, except for the Gold Star single.

But think what a tidy bike it would have been, a 650 twin as big/small as a B50...in 1954...but instead they made it all bigger.

Anyway...you came to the right place, well done. You will learn much, grasshopper.

The essential engine internals and transmission stayed mostly the same when they seperated the engine and transmission for the swing arm design thru about 1962/63.

I am maybe going to put my engine and trans into a B44/B50 frame..it will almost fit, I have hammers AND tongs.

But you, you have many of the bits for a good useful plunger framed 650, even enough for maybe a full restoration.

Good luck!

Offline crojack

  • Moving Up
  • **
  • Join Date: Aug 2016
  • Posts: 7
  • Karma: 0
Re: Which crank is correct, 52 A10 project
« Reply #5 on: 10.08. 2016 05:24 »
Hello and thanks everyone.  Seems like I need to figure out a way to measure the stroke of each crank.  Is one better than the other? For the three bolt ones, those bolts are placed radially along the outside of the main body?  As opposed to where the six bolts are inside and going through the main part.  Not sure if that makes sense.

Bodger, sounds like the bike you are talking about.   It is complete and the seller has been very helpful with parts and information.  I have an extra set of cases, the ones on there at least the left side one, is pretty bad.  pic attached.
Not planning on a full resto, I really like the way it looks.  I like bikes that look "period correct" what people at the time the bike was new would do to it.  It does need everything gone through, new rims, brakes/bearings/etc. 

Also, who do you guys in the US go to that rebuilds the Lucas stuff?

Thanks!

Offline Clive54bsa

  • A's Best Friend
  • ***
  • Join Date: May 2012
  • Posts: 128
  • Karma: 1
  • Orange SoCal
Re: Which crank is correct, 52 A10 project
« Reply #6 on: 10.08. 2016 06:12 »
where in the US, are you located Crojack?


'54 GF,  '61 SR,  '71 B50MX

Offline Topdad

  • bob hebdon
  • Wise & Enlightened
  • *
  • Join Date: May 2011
  • Posts: 2235
  • Karma: 32
  • l
Re: Which crank is correct, 52 A10 project
« Reply #7 on: 10.08. 2016 11:11 »
What a sad sight ,when these motors let fly they certainly make a good job of it !! Good that it's not put you off and looking forward to seeing it return from the ashes , best of luck.
" rules are made for the guidance of wise men and the blind obediance of fools"
United Kingdom

Offline muskrat

  • Global Moderator
  • Wise & Enlightened
  • **
  • Join Date: Jul 2009
  • Posts: 8237
  • Karma: 106
  • Lake Conjola NSW Oz
    • Shoalhaven Classic Motorcycle Club Inc
Re: Which crank is correct, 52 A10 project
« Reply #8 on: 10.08. 2016 20:47 »
G'day crojack.
 The correct crank for your '52 A10 is the small journal (six bolts inside the flywheel).
The crank with the three radial bolts is a large journal and if salvageable the one to use (it will fit with the appropriate con rods). The std journal sizes are, big end 1.688", timing side main 1.37", drive side main 30mm.
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
Muskys Plunger A7

Offline crojack

  • Moving Up
  • **
  • Join Date: Aug 2016
  • Posts: 7
  • Karma: 0
Re: Which crank is correct, 52 A10 project
« Reply #9 on: 13.08. 2016 00:40 »
Thanks,Muskrat!  I believe I have two of the large journals and will hopefully use one of those.

I'm in Portland, OR. 

The rest of the bike is complete, but will need a complete going through.  I had a 54 a long time ago that was also in poor shape, worse than this one.  I bought it when I was much younger and really had no idea what I was getting it into.  Sold to a friends dad, but still always wanted one.  So, i'm really excited about this one and riding it around eventually. 

I'll keep everyone informed of the progress and will certainly have many many more questions.

Thanks all for the help!

Offline duTch

  • Ricketty Rocketty Golden Flashback
  • Wise & Enlightened
  • *
  • Join Date: Oct 2011
  • Posts: 4540
  • Karma: 41
Re: Which crank is correct, 52 A10 project
« Reply #10 on: 13.08. 2016 03:01 »

 I'm running a LJ in my '52. If you need conrods, I debated using Mapp or I think Carrello, but settled on 'Thunder Rods' from UK. they fitted and work no problems- just a bit heavier @ I think~440 grms , but with some types, some have mentioned a concern with the nuts catching the inside of the cases- guess it's a case (no pun intended) of suck and see
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 muskrat

  • Global Moderator
  • Wise & Enlightened
  • **
  • Join Date: Jul 2009
  • Posts: 8237
  • Karma: 106
  • Lake Conjola NSW Oz
    • Shoalhaven Classic Motorcycle Club Inc
Re: Which crank is correct, 52 A10 project
« Reply #11 on: 13.08. 2016 05:52 »
I need to get rods for the cafe rebuild and am looking at R&R from the US. I would shy away from 2nd hand BSA rods. You just don't know what sort of pounding they've had.
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
Muskys Plunger A7