Morgan, I have NOS A70 BSA/Hepolite pistons. At this time,I can offer,one pair, of one of, the following- STD. - 71-2710 stamped 71/2666 +.020- 71-2884 stamped 71.2667 +.040- 71-2885 stamped 71.2668 Yes, slashes and dots. These pistons include rings,gudgeon pins,and circlips. For less than 1/2 the ED V piston price.+ shipping.
At factory timing specs, my 9.5:1 engine is not happy with R+M/2 93 octane -97ron fuel. It is happy with R+M/2 96 octane -100ron fuel. Others here seem to have better luck,with lower grade fuels. Send me a pm,if interested.
1969 BSA A65T w/A70 engine 1970 Royal Enfield Interceptor S ll
I read once that people at BSA were quite excited about the development potential of the A70. And it's possibly because of what was found out about the A65s in 1970 when Umbeslade Hall technicians built an engine for the photo shoot '71 model Firebird. They ported the twin carb head's inlet ports to the design drawing, not something the factory had ever done. The result was a much more responsive, better accelerating motorcycle, with around 8HP gain on their dyno over production line engines. The std production twin carb head flows around 109cfm @ 28"W giving around 50hp at the crank, to get 58hp would require 123cfm, equivalent to the best stock Commando head. On the 650 it would mean the engine would make power to 8,000 or so. On an A70 power to 7,100rpm, and there would be a lot of it right through the range. Probably faster than a 3 because it's lighter. Plus there is development potential on top of that especially with the strengthened crankshaft. 142cfm through a properly machined head could give power to 8,000 and around 65-67hp with a relatively small port, which would give a very healthy midrange. And this would be a mildly tuned engine; 9-1 comp and stock Spitfire cam.
I think what they built with the A70 was simply what they needed to homologate the flat track 750, had BSA not run out of money I think the A70 in following years would have realized much more of it's potential.
Had a good long test ride today and it runs different to my A65 for sure with that long stroke. I'll be back to discuss A70 parts soon. Allan on above photo its not tidy at all we rode a long test ride on twisty rainy roads so its pretty dirty. I will spend time cleaning it tomorrow and take photos for the insurance and maybe some to post here and there..