Author Topic: 7 fin A10 barrel  (Read 617 times)

Offline Beeza

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7 fin A10 barrel
« on: 05.05. 2018 03:37 »
Does anyone Know what this barrel was used for, 'the one in the middle'.
Measures up at 70.6 mm, so first over size.

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Re: 7 fin A10 barrel
« Reply #1 on: 05.05. 2018 05:35 »

  Maybe an A7, if they can be bored that far *conf2*, or someone has done a 'short-stroke ' A10 conversion...*dunno*
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
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Offline Beeza

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Re: 7 fin A10 barrel
« Reply #2 on: 05.05. 2018 06:08 »

  Maybe an A7, if they can be bored that far *conf2*, or someone has done a 'short-stroke ' A10 conversion...*dunno*
Definitely A10, same height as the A10 barrels either side, left is thick flange A10, right is small fin A10.
This one has a 5/8" flange and 7 fins, the bottom fin was removed prior to casting, a bit similar to my Daytona A7 6 fin barrel

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Re: 7 fin A10 barrel
« Reply #3 on: 05.05. 2018 06:52 »
I think it strange that they take a fin off the std barrels for a competition motor. *dunno*
Might be that they thought the extra air speed would cool it better and save a few oz to put into the flange.
Cheers
'51 A7 plunger, '57 A7SS now A10CR, '76 XT500, '77 AG175 '83 CB1100F, '81 CB900F project.
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Muskys Plunger A7

Offline Beeza

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Re: 7 fin A10 barrel
« Reply #4 on: 05.05. 2018 07:16 »
I think it strange that they take a fin off the std barrels for a competition motor. *dunno*
Might be that they thought the extra air speed would cool it better and save a few oz to put into the flange.
Cheers
I think they take the fin off so as to be able to fit the nuts, the nuts are slightly taller than the usual nuts.
Your thoughts are quite feasible also Musky.

Cheers

Online bsa-bill

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Re: 7 fin A10 barrel
« Reply #5 on: 05.05. 2018 10:59 »
Quote
I think it strange that they take a fin off the std barrels

and leave a casting mark intact ???
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 BSA_54A10

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Re: 7 fin A10 barrel
« Reply #6 on: 05.05. 2018 12:20 »
With the extra thick flange it is a competition barrel for sure.
The extra height of the barrel flange makes it impossible the get the nuts on the crankcase studs so they gat cast without the bottom fin as per the Daytonas
So that my friend is a very rare pair of pots you have.
Will have to go and reread some of the history books to see what they were & where they were used.
First guess would be for a chair where the unlimited class was very common.
Bike Beesa
Trevor

Online bsa-bill

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Re: 7 fin A10 barrel
« Reply #7 on: 05.05. 2018 14:21 »
Quote
so they get cast without the bottom fin

Aha -
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

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Re: 7 fin A10 barrel
« Reply #8 on: 06.05. 2018 07:44 »
The rivet counters and anally retentive bolt polishers will have a conniption fit and the hazing, & ridicule will be merciless. To spare you the shame, degradation and embarrassment, Box it up and get me a ship quote to the USA. 
Ill use it on my replica racer A10 rigid thingy and take the slings and arrows with aplomb.
While puttering in the shop this weekend I was looking to see what others might have done for Compy cylinders other than $1500 bits at ABSAF.  Anyone ever machine and sleeve a cyl to take a 750 cc liner?

(Links to such discussions welcomed, I have read a lot on using Norton cranks and building Hybrid BSA 800-900cc motors)
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Re: 7 fin A10 barrel
« Reply #9 on: 06.05. 2018 09:55 »
Quote
Anyone ever machine and sleeve a cyl to take a 750 cc liner?

Often some discussion as whether it's safe to go +80 so to get 750 cc might be a stretch
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

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Re: 7 fin A10 barrel
« Reply #10 on: 06.05. 2018 10:20 »
Quote
Anyone ever machine and sleeve a cyl to take a 750 cc liner?

Often some discussion as whether it's safe to go +80 so to get 750 cc might be a stretch

I have successfully ran 80 over Triumph 650 without calamity But assume boring to that size in a BSA would leave it a bit thin.  Overbores on Norton cyl twins is always a Vegas odds crap shoot. About half the time (or more) you either run into casting voids, dross or defects OR discover the cyls are hair cracked right above the flanges on the 750s.

However what I am talking about is machining a stock BSA cyl to take sleeves to a 750cc bore + or - and opens up some options on what pistons to take.
Some decry sleeves as asking for trouble, But if properly sized and machined they are fine for something like a Preunit BSA Twin (Street use of course and a sedentary pace in general)

I am sure others have done this. Just looking for links or accounts of others who have tried?   

I dont have much to measure with. Currently have multiple A10 motors but only 2 thin flange cyls. 
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Re: 7 fin A10 barrel
« Reply #11 on: 06.05. 2018 11:02 »
Quote
Some decry sleeves as asking for trouble
not me, Flash was +60 when I bought it, for the reasons you state I got liners to take it back to stock, been fine.
Back in the day I suppose barrels where readily available so it would just be a case of comparative cost.
Still not sure there would be enough meat in A10 barrels to take a liner that allows 750cc, interesting tho
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

Online KiwiGF

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Re: 7 fin A10 barrel
« Reply #12 on: 06.05. 2018 12:23 »
Quote
Anyone ever machine and sleeve a cyl to take a 750 cc liner?

Often some discussion as whether it's safe to go +80 so to get 750 cc might be a stretch

I have successfully ran 80 over Triumph 650 without calamity But assume boring to that size in a BSA would leave it a bit thin.  Overbores on Norton cyl twins is always a Vegas odds crap shoot. About half the time (or more) you either run into casting voids, dross or defects OR discover the cyls are hair cracked right above the flanges on the 750s.

However what I am talking about is machining a stock BSA cyl to take sleeves to a 750cc bore + or - and opens up some options on what pistons to take.
Some decry sleeves as asking for trouble, But if properly sized and machined they are fine for something like a Preunit BSA Twin (Street use of course and a sedentary pace in general)

I am sure others have done this. Just looking for links or accounts of others who have tried?   

I dont have much to measure with. Currently have multiple A10 motors but only 2 thin flange cyls.

No way one can make a big bore (750cc) a10 using stock barrels, you would end up with a set of fins nothing else. It’s only just possible to bore the barrels enough to sleeve them back to std.

My a10 is sleeved back to std as many are, works fine, I might even be able to reborn the sleeves to next over size, should I live that long.
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Offline Beeza

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Re: 7 fin A10 barrel
« Reply #13 on: 07.05. 2018 08:50 »
Seem to be running of topic, max boring has been discussed elsewhere.
I have also found a place for this barrel, as Trev said definitely competition.