Author Topic: Strange A10 Crankshaft  (Read 1008 times)

Offline Servodyne

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Strange A10 Crankshaft
« on: 18.11. 2018 20:30 »
Hello everybody,
I've recently bought a large journal A10 crankshaft off ebay, but I'm now wondering what I've actually bought as it is totally different to any that I've seen before. The flywheel isn't attached with the usual 3 retaining bolts but appears to be 'shrunk' on with 3 retaining threaded studs that are flush with the outer surface of the flywheel. The question that concerns me is will it be compatible with a 1957 swinging arm A10?
Cheers Jim
1957 BSA A10 Spitfire
1971 BSA A65 Firebird
1971 BSA A70 Lightning
1975 Norton Commando

Offline berger

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Re: Strange A10 Crankshaft
« Reply #1 on: 18.11. 2018 22:44 »
well knock me over with a feather, I aint never ever seen one "O" them there cranks likey that one *conf2* maybe if you measured the flywheel diameter and compared it to one with the three radial bolts you might find its a skimmed down cranky and they've centre popped what's left of the bolts to stop them damn darned suckers flying out and messing up ya engine  :-\ *dunno2* edit could it be a racing crankshaft?

Offline Swarfcut

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Re: Strange A10 Crankshaft
« Reply #2 on: 19.11. 2018 09:47 »
  Jim..... Could be another Unicorn Part, Heard Of But Never Seen.  There are rumours of a One Piece Big Journal Crank, which precedes the more familiar three radial bolt type. I would consider it impossible to manufacture and machine this design of crank from a single forging, so on initial examination it may appear to be in one piece, because of the hidden bolts and hence the myth that is made in one piece.

 As long as the journal sizes are within the accepted dimensions, and the throw is correct, then it should fit fine.  Do not neglect the usual cleaning procedure for the oilways.

  No doubt the respected contributor JulianS will be along soon to offer further enlightenment.

  Good thought there berger, another possible explanation.

  Swarfy.

Online JulianS

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Re: Strange A10 Crankshaft
« Reply #3 on: 19.11. 2018 12:09 »
This is an early Road Rocket crank, changed in 1957 to the version with a removable sludge trap and radial bolts.

Offline Swarfcut

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Re: Strange A10 Crankshaft
« Reply #4 on: 19.11. 2018 12:54 »
  Julian.. Thanks for the possible answer to the mystery. Looks to be a sort of halfway house in the design, larger big end journals but still retaining the small sludge trap plugs and oilway.  Together with a change in design for flywheel attachment. Alas my screen is small and the part numbers were difficult to read so that's how I see it.

   Rumour or a myth, this proves the existence of a relatively short lived and rare part. Another one for the rivet counters in the quest for ultimate originality.

 Swarfy.

Online RichardL

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Re: Strange A10 Crankshaft
« Reply #5 on: 19.11. 2018 13:03 »
Always great to see obscure docs from Julian's treasure trove. One thing that hit me was the "SR" in the engine number for "Scrambles Rocket." I don't think I've seen that before (but that could just be me).

Richard L.
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Online JulianS

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Re: Strange A10 Crankshaft
« Reply #6 on: 19.11. 2018 13:59 »
The "SR" used on Spitfire scramber engines, starting with the CA10SR in 1957 then DA10SR for 1060 season until end of 1961 season when the DA10R engine was used.

Online muskrat

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Re: Strange A10 Crankshaft
« Reply #7 on: 19.11. 2018 18:57 »
G'day Jim.
Quote from Rocket Racer "My understanding is that the 56/57 road rockets originally had what is often called either a transitional or heavy crank: this has a very small sludge trap arrangement and the flywheel is not removeable. the webs are also a different shape and it is solid through the centre. This is also a large journal."
I think the key word is "heavy" so should give good torque.
Cheers
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Offline Servodyne

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Re: Strange A10 Crankshaft
« Reply #8 on: 02.02. 2019 18:23 »
Thanks all for the replies. Some very useful information.
Cheers  *smile*
1957 BSA A10 Spitfire
1971 BSA A65 Firebird
1971 BSA A70 Lightning
1975 Norton Commando

Offline Whipstrut

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Re: Strange A10 Crankshaft
« Reply #9 on: 05.02. 2019 00:35 »
Well folks, there are at least two of these cranks in existence, as I have one too. Always wondered why there wasn't a sludge trap tube, and it weighs 26 lbs.

Offline trevinoz

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Re: Strange A10 Crankshaft
« Reply #10 on: 05.02. 2019 20:08 »
There's more than two in existence.
A friend of mine has at least three.

Offline Servodyne

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Re: Strange A10 Crankshaft
« Reply #11 on: 05.02. 2019 22:28 »
G'day Jim.
Quote from Rocket Racer "this has a very small sludge trap arrangement and the flywheel is not removeable.
I think the key word is "heavy" so should give good torque.
Cheers

Hi
I've just removed the timing side sludge trap plug just to see what the set up is. The crank's on standard size so the plug has never been removed before. Wow, no sludge trap tube, just a 1/4" hole which was virtually clogged with hardened sludge. I certainly wasn't expecting the sludge trap to be such a small diameter hole, but I should be able to clean it out without removing the drive side plug. Next job is to take it for a regrind.
It should make a nice smooth motor with plenty of torque, but I think you would definitely need to run it with a cartridge oil filter.. 
 
 
1957 BSA A10 Spitfire
1971 BSA A65 Firebird
1971 BSA A70 Lightning
1975 Norton Commando

Offline worntorn

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Re: Strange A10 Crankshaft
« Reply #12 on: 06.02. 2019 02:58 »
I don't think you can get extra torque output from a crank whether it's heavy or light, as in measured continuos torque output on a dyno.
The heavy flywheel does give extra momentum, which makes starting off without stalling easier. The downside is they are a little slower to rev up.
I once had an Ossa race bike that came with three external flywheels, two aluminium in different weights and a heavy bronze.
It had the bronze flywheel fitted, so I switched for the lighter al. job. It revved noticeably quicker, which was fun for awhile, but I soon tired of kickstarting it after multiple stallouts when used in stop start off roading. The bronze wheel went back on.

Glen

Online Greybeard

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Re: Strange A10 Crankshaft
« Reply #13 on: 06.02. 2019 09:08 »
Quote

I've just removed the timing side sludge trap plug just to see what the set up is. The crank's on standard size so the plug has never been removed before. Wow, no sludge trap tube, just a 1/4" hole which was virtually clogged with hardened sludge. I certainly wasn't expecting the sludge trap to be such a small diameter hole, but I should be able to clean it out without removing the drive side plug. Next job is to take it for a regrind.
It should make a nice smooth motor with plenty of torque, but I think you would definitely need to run it with a cartridge oil filter.. 
The early flywheels did not have  a tube in the sludge trap. I feel you should remove the other plug and leave it out until you've had the crank ground.

Online morris

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Re: Strange A10 Crankshaft
« Reply #14 on: 06.02. 2019 11:23 »
There's more than two in existence.
A friend of mine has at least three.
Makes me wonder what an enormous quantity of NOS parts will flood the market after we're all dead and gone...  *doubt* *smile*
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