Author Topic: Are thick (1/2") flange barrels only available for 650 A10  (Read 518 times)

Offline dodmo

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Having read through the other posts on barrel identification last night  am I right in thinking that an engine fitted with thick flange barrels must be 650cc?

cheers
Dod

Online Klaus

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Hy Dot,
yes thick flange barrels are only for A10. Except Daytona Barrels they are 6 fined but realy hard to find.

chees Klaus


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Offline dodmo

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Thanks Klaus,

As you may have seen  I am (was?) selling my bike on eBay.
There were some people questioning the discrepancy between it being listed as an A10 but having an A7SS crankcase number.
but the barrels definitely have a 1/2" flange and the bike is registered as a 650 with that engine number. So I think I am right

All the best
Dod

Online Klaus

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Hello Dot,

I ve seen the advert, its an A10 650 and the cases are A7 Shootingstar. The cases from Swiningarm are all  the same for 500 and 650.
 cheers Klaus


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Offline dodmo

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Thanks Klaus *grins*

Offline Swarfcut

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dodmo. Anyone with a basic knowledge of the engine can tell what's inside at a glance. You are right.

    A10 barrel thick flange (late) or thin flange  (early) all have the same nominal bore and have 8 fins. The A7 has a smaller bore and only 7 fins on the barrel.
   Barrels also come in thin fin..pre 54/55 or thereabouts or the later wide fin type.. The basic fin area profile is the same for both engines, later wide fin type barrels introduced to improve cooling.
   All thick flange barrels are the later type and have wide fins, and are only found on the A10. As power outputs rose, the barrel mounting flange had a tendency to fracture, so the casting was changed to give more strength to this area.  Hence the term "thick flange"

 As Klaus says the crankcases are the same basic casting. The common parts mean on a bike like yours you would expect to find a mix'n match approach to its construction. Looks OK to me.

 Swarfy.

Online JulianS

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The A7 thick flange barrels, 67 1310, get a mention in this US bulletin.

Online RichardL

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...and the hole in the left con rod gets due mention.

Richard L
Plan on signing up for the world-wide 2017 DISTINGUISHED GENTLEMAN'S RIDE on September 30, 2018. Watch website at https://www.gentlemansride.com for details.

Offline Swarfcut

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Julian, I stand corrected on that one, never having seen or heard of a thick flange A7 barrel. At least it was a competition or export rather than home market product. Or do such things appear regularly and my assumption is incorrect?

 The parts list you posted is interesting. On the basis that those are the only parts used, it does not make sense to me unless I am missing the point. As far as I know, the A7 crank only came as a small journal. The A65 rods 68-53 are big journal so can only be used with the 650 later big journal crank, which has an 84mm stroke.  So retaining the original stroke and boring the A7 barrel to 70mm takes you back to where you started, and the barrel is too short. If I am wrong and the A7 crank  was available with big journals, then it makes more sense...70mm bore, 72.6 mm stroke, A65 rods.  The parts list indicates the original pistons and crank are used, so there is something amiss or I have missed a basic glaringly obvious fact. The length of the rods need to be long enough to allow the piston skirt to clear the flywheel at BDC.

 No doubt the trick engine folks will put me right. Meanwhile I will check the parachute, anticipating  the expected crossfire.

 Regards

 Swarfy.

Online Klaus

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Hi Swarfy,
The common A7 have all small journals and thin flange barrels with 7 fins.
I think there was only a small batch for the Daytonas, having a 6 fin thick flange barrel, and a big journalcrank as the later A10 but the shorter stroke . Only buid for racing.
I started a projekt using A7 SS case and a modified A65 crank with a shortend A10 thickflange barrel. Top end is a twin carb Shootingstar head. Its still in progress, looks like an A7 but it is 600 ccm.
Have a look at the date,it was in 1964 I guess the sell old stock parts.

cheers Klaus


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Online JulianS

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The conversion was based on the A10 bottom end rather than the A7.

I agree with Klaus that it was BSA Incorporated getting ride of stagnant stock.

Around the same time they were selling off early Road Rocket heads, the ones with detachable manifold, as part of a twin carb conversion.

Only seen the thick flange A7 barrel mentioned twice - once as above then in a March 1957 parts price list from Hap Alzina in California. They seem to have preceded the A10 thick flange which was covered in a parts bulletin in May 1957.

There was an article on doing a short rod A10 conversion in "Motorcyclist" February 1958 issue (American magazine) this used an A10 barrel which was machined down to the appropriate height. You had to be careful with piston skirt to flywheel clearance.

Offline dodmo

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This is all great stuff guys.
Thanks to everyone.
Dod

Offline trevinoz

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Julian, I don't think that the speed kit alloy heads were old stock.
I have one which I think is from the speed kit as it has no date embossed.

Offline Rocket Racer

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I've certainly seen first hand an A7 thick flange daytona barrel and seen the references to large journal daytona A7 rods for use in short rod A10's for drag racing
The 54 A7ss and road rockets had twin port heads (the basis of the twin carb option). For the USA race scene BSA made all sorts of special bits not commonly seen like the BB32R framed shooting stars.
I have an A10 thick flange barrel modified to the smaller A7 fin number so variations are out there.
Then there's always the transitional heavy LJ cranks that I've found in very early american imports and never quite figured out when they started.
I suspect they went into selective motors from '54 as my unmolested 54 twin port road rocket with the original 10TT9 carb has one fitted and was on std bores, bearings etc and has one. I had previously thought these cranks came out around 1956 when the americans were snapping cranks.
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.
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Online Black Sheep

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Years ago I picked up a thick flange A7 barrel and pistons boxed as a factory replacement service unit. Bought them as it was cheaper then a pair of new pistons. Didn't realise what I had bought at the time...
2 twins, 2 singles, lots of sheep