Author Topic: Twin carb head.  (Read 1433 times)

bulltaco

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Twin carb head.
« on: 27.05. 2010 10:56 »
Hi,
I've been given an early A7ss head with the detachable single carb manifold, along with a pair of billet single carb stubs.
Can anyone recommend somewhere in UK which could alter the combustion chamber to A10 size and perhaps enlarge the inlet tracts?.
I'm aware that performance gain is minimal but it's to go on my Wideline Dominator framed A10 Rocket which is for cafe racer "show" as much as for "go"!.

Offline A10Boy

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Re: Twin carb head.
« Reply #1 on: 27.05. 2010 11:20 »
Hi and welcome to the forum.

You might try The Cylinder Head Shop in surry on 01428 685883

www.cylinderheadshop.co.uk


Regards

Andy

1958 Super Rocket
Plus
1974 Kawasaki Z1a
Yam XJR 1300

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Re: Twin carb head.
« Reply #2 on: 27.05. 2010 13:57 »
G'day Bulltaco,
                         Welcome to the forum.
 That mix sounds interesting, although the BSA s/a frame performs as well as a wideline.
 GIVEN a '54 A7SS head !!! He must be feeling guilty about sleeping with your wife ! *smile*
 I have done that mod. Matching the A10 bore is not that hard with a dremel. Don't be too greedy with the porting, I have seen them break through to the stud holes. Fit new seats to take later A10 valves 1.41" inlet and 1.38" ex.
 Have fun tweaking
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
Muskys Plunger A7

bulltaco

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Re: Twin carb head.
« Reply #3 on: 27.05. 2010 17:11 »
Thanks for that guys, all very helpful.
Cylinder head shop looks like the real deal but maybe my sporran is too deep or my arms are too short to be able to take much advantage of their expertise!.

Never thought about a dremel but after offering up an A10 copper gasket, you're right,it doesn't look too difficult to blend in the diameter of the combustion chamber.
 The ports are 26mm and they look like they have plenty of scope to blend out to 30mm but maybe 28mm would be more sensible.

I also got an unusual front wheel, I'll get a photo up later on as I have a query about that too.

There is a story to all this. The Dommie was the very first bike I had on the road, in 1961, then sold it and had the usual succession of 60s big bikes. I got the 1958 Road rocket in 1968 and wrote it off fairly spectacularily in early 1970, all cycle parts badly bent but the engine/ gearbox virtually undamaged. Regular road riding came to a halt then and the BSA engine/box went under the bench. Years of trials riding followed, then in 1978, driving up the A9, I saw a guy pushing a british bike and recognised the number as my old Dommie, now a Triton with a very blown motor.
I bought it on the spot and loaded it on the trailer I was towing, and the cycle parts joined the BSA bits under the bench.
Fast forward to 2007, recuperating from heart surgery, and this cafe racer project was born. I had it running last summer, it's in bits again for some tarting up. My intention is to develop it as a conversation piece cafe racer as much as anything, including (don't laugh) a pair of Wal Phillips injectors which are also "under the bench". And yes, I know they can be dodgy, I once saw an Ariel with one on go up in flames after petrol pee'd everywhere.

Offline Big Nick

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Re: Twin carb head.
« Reply #4 on: 30.05. 2010 21:17 »
I would try srm if i was you. Have you found the A10 twin carb web sites ? The web site say that enlarging the A7 head to A10 size is what they did. I also have one of the A7 twin carb heads and i bolted on to my A10, it looked cool but did not really change the performance. Have you read the eddy dow tuneing sheet ?
1932 500cc rudge
1936 500cc cotton pyton
1952 M20 with B31 motor
1952 Plunger A10
1954 New Hudson Autocycle
1962 A10
1982 BMW R100

bulltaco

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Re: Twin carb head.
« Reply #5 on: 31.05. 2010 19:49 »
Hi Big Nick,
Given my age (65 a fornight ago) and the probability that the bike will be ridden only on sunny dry Sundays round the local by-ways I'm reluctant to throw loads of cash at it , the professionals are not cheap!.
As muskrat suggested I've borrowed a Dremel to blend the A7 combustion chamber to the A10 size.

I got the head and a pile of other bits from the widow of an old friend who died recently. I know he fitted the head on his Super Rocket a long time ago but found that with the smaller A7 combustion chambers the C.R. was too high for comfort with the 9-1 pistons he had in at the time.

I haven't read the Dow tuning notes, seen them on ebay from time to time though.
Thanks
bulltaco.

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Re: Twin carb head.
« Reply #6 on: 31.05. 2010 20:13 »
Hi Bulltaco.  If you blend the combustion chamber to suit the larger bore of the A10 you will still suffer the same problem as the previous owner due to the smaller cc of the combustion chamber, meaning a hike in compression pressures. Are the valve sizes smaller than the A10 alloy head? this could reduce flow through the ports reducing performance.  It would be a real pity to mess around with what is quite a rare head these days if you're not certain it will work. I would love to buy the head from you if you would consider selling it (it is the correct head for my 1954 A7SS project) and you coulld perhaps put the funds towards buying a A10 head. Please drop me a personal message if you could be interested. Regards, Peter
Peter C    Cambridgeshire. UK   1935 Blue Star. 1937 B24 Empire-Star, 1950 A7 Rigid.  1952 A7ST.  1953 A7ST.  1953 A10 Super Flash.  1954 A7ST.  1955 A7SS.  1955 A10.  1956 A10RR.  1962 RGS.  1962 DBD34

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Re: Twin carb head.
« Reply #7 on: 31.05. 2010 21:58 »
Hi Andy

The cylinder head site has a great link to a site called heritage remembered. Not sure if you have checked it out but there is some great stuff on there.

Jim
1959 A10 SR
1938 Wolseley 14/60
1955 Ferguson TEF20 tractor
1965 Ferguson 135 tractor
1952 Matchless G80 rigid
1960 BMW R60
1954 Matchless G80S
1955 Ariel 500 VH
1951 Sunbeam S7DL
1960 Matchless G12 with Watsonian Monza
......and loads of lawnmowers

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Offline Big Nick

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Re: Twin carb head.
« Reply #8 on: 01.06. 2010 07:10 »
those twin carb heads are really sort after. i have the eddie dow sheets , i will post it on this site , no need to buy
1932 500cc rudge
1936 500cc cotton pyton
1952 M20 with B31 motor
1952 Plunger A10
1954 New Hudson Autocycle
1962 A10
1982 BMW R100

bulltaco

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Re: Twin carb head.
« Reply #9 on: 01.06. 2010 09:03 »
Hello spanersc,
No joy on this sale I'm afraid!.
BTW I've looked through some of your posts and can't help thinking you've chosen a lengthy and expensive way to get a bike, by buying frames, swinging arm etc all separately.