can i use a A7 cylinder on a A10 engine?

[motoauthentica]

i bought a cylinder bore measures 70.20mm i thought it was a standard A10 cylinder but i count the fins now and looks like theres only 7 fins, and ive read 8 fins is A10. i think i can use this cylinder, bout thought id ask in case im wrong??? thanks

[Klaus]

Sorry to tell you no
The A7 barrel is shorter than the A10 one.

regrda Klaus

[Swarfcut]

 A10 Standard bore is 70mm, with rebore oversizes of 0.5mm, 1mm, 1.5mm, or in old money plus 20,40,60 thou. Plus 10 thou oversize may have been available way back when......

 That bore size not what you expect.... It may not be an A10 barrel either so a picture will help identify this false start.
  A7 barrel has no cut outs at the bottom skirt...bore is 66mm.
 A10 requires cut outs to clear the rods with its bigger crank throw, and is another visual guide to the differing castings.
Swarfy.

[Radlan2]

Just to add to previous comments, unless you sleeve it back to 66mm it will not now fit an A7 either. The pin height is different between A7 and A10 pistons so you cannot easily, IE, without custom rods, build a 'Big Bore' A7.
     Some suppliers now advertise +0.080" pistons for A10 which could help you?
    HTH

[motoauthentica]

Sorry to tell you no
The A7 barrel is shorter than the A10 one.

regrda Klaus

OK thank you sooo much to everyone that has responded that helps alot. ill try and post a few pics of this cylinder because someone said it may not even be a A7 cylinder.

[JulianS]

There were short rod A10s out there. Using either a shortened A10 barrel or an A7 barrel.

Motorcyclist magazine February 1958 ran an article on how to do it - involving shortening the A10 barrel. Copy attached not the best quality.

BSA Incorporated, the US East Coast importers, issued a service bulletin in 1964 which gave the parts needed to convert an A10 to short rod which included using an A7 Daytona barrel.

[Swarfcut]

Reading through Julian's article it is apparent that a big journal A7 crank and matching rods were available, never thought they were used on home market models.

 The later 1964 bulletin lists rods ( 68 prefix) from the later unit A's which in A50 and A65 guise use the same big end dimensions as  big journal A10 crank.

 Swarfy

[Radlan2]

   Regarding the Daytona A7 connecting rods, anyone got one? And I would love to know if there really were LJ A7 crankshafts available to accept them? Plus what pistons did they use? the nearest I can find are BB32 Goldstar but they are are hensteeth now, plus you need a pair.
   I fitted an A65 crank to my Daytona rep, LJ A65 crank stroke is 74mm compared to 72.6 for the A7. it is not straight forward though, A7 drive side bearing is metric and A65 is imperial along with other differences  Thunder engineering made me special length rods with .750 small end eye so that i could use A10 pistons giving a swept volume of 600cc.
         Chris
     

[motoauthentica]

There were short rod A10s out there. Using either a shortened A10 barrel or an A7 barrel.

Motorcyclist magazine February 1958 ran an article on how to do it - involving shortening the A10 barrel. Copy attached not the best quality.

BSA Incorporated, the US East Coast importers, issued a service bulletin in 1964 which gave the parts needed to convert an A10 to short rod which included using an A7 Daytona barrel.

absolutley LOVE that magazine article WOW what a treasure thanks so much for posting and sharing that stuff that is what keeps me up at night!!!!

[Radlan2]

absolutley LOVE that magazine article WOW what a treasure thanks so much for posting and sharing that stuff that is what keeps me up at night!!!!
   I agree, that's what makes this forum so good. I have done this conversion to my Spitfire scrambler daily rider. it does use different dimensions to the BSA speed equipment version ie barrel height is taller than A7, also requires more piston scallop and special push rods but does use STD A65 con rods. but a great guide.

[motoauthentica]

A10 Standard bore is 70mm, with rebore oversizes of 0.5mm, 1mm, 1.5mm, or in old money plus 20,40,60 thou. Plus 10 thou oversize may have been available way back when......

 That bore size not what you expect.... It may not be an A10 barrel either so a picture will help identify this false start.
  A7 barrel has no cut outs at the bottom skirt...bore is 66mm.
 A10 requires cut outs to clear the rods with its bigger crank throw, and is another visual guide to the differing castings.
Swarfy.

heres a few pics of the barrel i have

[berger]

well erm i don't know if it's the photo but those fins seem to be spaced too wide for A7 barrels maybe you have something special

[JulianS]

Looks like an A7 barrel to me. The casting number showing -67 1070 - is the right number for A7. A thin flange A10 barrel casting number is 67 1074 and thick flange 67 1210.

[Swarfcut]

     Moto  Yes, it's A7, reckon it is the start of someon's failed project and a waste of time if your intention is to build a running bike from a basket case.

 We call it Sod's Law.... Common in the world of used parts. Anyway you know now   how to identify wide fin barrels, first introduced for 1954 models. Looks to be well greased up so time for a serious measure. Less wear at the bottom of the skirt, this will be closest to the parent bore. Top edge above top ring also acceptable, but wear ridge can be removed to re-ring with plain compression rings.....and also conceal wear from the unwary. Accurate measurement is required.

 Shame, otherwise it looks good and could be reclaimed with care by fitting liners. back to 66mm, A7 Standard bore. Major castings as here carry an identifying number which is not always the same as the part number. More to explore about part numbers in previous forum posts.

Meanwhile pictures of the engine parts you already have along with any identifying numbers will help us tell what you actually have.

 Swarfy.

[berger]

it just seems odd to me going by thickness of the barrel itself ,it seems to have a lot of meat to say it's 70mm