1958 A7 cylinder barrels

[A7JAY]

Hi all, my first ever post on here although I've been reading and gaining knowledge for quite some time, my question is, how far potentially could the A7 barrel be taken out to? I know they at +60 atm and I'm thinking I could possibly get some standard 69mm tiger 100 pistons in there, I've not stripped the motor yet so don't know what the compression hight of the BSA pistons are or the pin size for that matter, I'm hoping there's enough meat in the spigots to allow another 1.5mm + clearance   

any help and advice would be appreciated thanks

[muskrat]

G'day Jay.
I think you could go out that big BUT with the thin flange A7 barrels it would be a matter of when not if they lift off the cases. The thin flange is a known weakness. DAMHIK 
Cheers

[A7JAY]

Hi Musky do you recon the crank and rods are up to the job? I'm not planning on thrashing the s**t out of it but it defo needs some extra grunt

[rocker21]

yes you can make an A7 produce more power but i would not do it on a set of barrels bored out that far, you can put the 357 cam in, use 8.5 comp pistons, put bigger valves in an alloy head, bore the inlet track out to fit a bigger carb, polish and port the head, and they can go quite quick, lose a bit of bottom end torque , make sure the crank has been properly balanced. done this to one of my engines, also fitted needle roller bearings on the cam and idler gear, crank is also on needle roller bearing, modified oil feed to suit and srm pump fitted.

[A7JAY]

Hi Rocker
so if I do fit a 357 cam would I need to make changes to the valve train? bearing in mind I purchased all new valves, retainers, collets and guides form CheeserBeezer

[rocker21]

quite possible, you may need to modify the head as well, it is possible you may get the springs coil bound,  i had to modify the valves and the base that the springs sit on, had to give it 60 thou more clearance, i broke a pushrod as the springs got got coil bound

[berger]

A7 jay there is a build on here called the berger build i have fitted super rocket inlets in a cylinder head shop gas flowed head suited for 32mm carb . you have to check for spring bind on full lift and i had to get the keepers machined to give clearance on full lift and also the valve collet recess , but mine has a skimmed head and barrel top face. it is fitted with thunder engineering rods and crank balanced by t&l engineering in bedford. erm correction it is called building a berger.

[A7JAY]

berger and rocker did you ever have you're bikes on the dyno?

[berger]

not even run mine in yet but it's hellish throaty , i need some good weather to start opening it up and do plug chops for carb settings , at the moment she has vortexed induced vibes at a certain opening with the needle dancing , she has a sluggish moment after 50mph , work in progress or at the moment no progress.

[A7JAY]

Berger I don't know where abouts you live but my mate has a dyno and he's brilliant with old clunkers, I take all my bikes there including my 300hp gixer 

[rocker21]

not put mine on the dyno, it also has a belt primary drive which has geared it up a bit to roughly a10 gearing,  a bit slow from a standing start but once it gets moving and the revs start to rise it is quick, gone down the motorway at serious speeds and still got lots left,  so far i have 90 + on the speedo confirmed by the gps on the sat nav, so far done about 1700 miles on it,

[A7JAY]

Morning all

so a quick update on my A7

I removed the head and barrels and was surprised to find a few things away from the norm, the pistons are A7SS high comp I'm guessing 8.5 to 1 on +60

the barrels have loads of meat in the spigots 6mm at the thinnest part

the head is definitely A10, Radlan2 is kindly sending me an A7SS ally head

I was pleasantly surprised to find that the cam followers are almost new and also the cam, but don't know what type the cam it is, BTW is there any way to identify the cam in situ?

My idea of maybe fitting tiger T100 or Trident pistons has gone right out the window, the compression hight of the afore mentioned is a mile out, specifically on the trident piston the top ring lines up with the oil scraper ring on the A7 piston and would need longer rods to make that work.

my next option piston wise is standard size A10 pistons, loads of scope to get the barrels bored out to 70mm, I believe the compression hight is very similar to the A7 and the only issue is pin size, I can make some bushes.

Any comments and advise will be greatly appreciated     

 

[muskrat]

G'day Jay.
Sounds your at the spot I was in the 90's with my 57 A7SS racer. Only being able to go up in bore to 67mm to stay in the +5% capacity limit I used std size T160 pistons and played with rod length (A10sj rods shorten the bigend by 2mm). I wanted 14:1 comp to run methanol. Then the "thin flange" barrels let go a few times at 8000rpm  Developed through bolting the head to the cases then the small journal crank snapped a couple of times  .
So it depends how fast do you want to spend? It did win the NSW B grade camps at Eastern Creek in 97-98 but I couldn't keep up with Agostini.
With a bit of work you can fit A10BVSR valves to an A7SS head (machine A7 keepers to take SR collets).
Going to all this trouble throw in a new 357 or 358 cam.
Cheers

Cheers

[A7JAY]

Hi Muskrat

very interesting mate, I did read your post way back regarding what you did with the A7 racer and obviously I've go no intention of racing mine or going that far with the rod situation, I bought a new set of +80 trident pistons as I was going to use one in the C15 and maybe have two left for the A7, but that's not panned out so I've got three new +80 trident/rocket3 pistons if anybody wants um

BTW does anyone have a side by side comparison of an A7 and A10 piston by any chance?