a10r "big valves"

[63a10r]

  ok. after much research (most of it to verify PREVIOUS research) i have only become more confused. am i to understand that the difference between "regular" a10r valves and so-called "big valves"  is only .005"? this is what i have seen written, repeatedly, i might add. and without opening up the intake ports only that much, as well as takin .005" out of the id of the valve seats, the extra valve area would not even count. what gives?

[trevinoz]

I measured some valves and I get :- R.R. and S.R. - 1.435",  Big Valve :- 1.455".   Thats .020".  Wow! I have seen listed o/s valves at 1.5".  Marketing ploy from B.S.A. ?

[63a10r]

oops. i erred in my interpretation. i get it now. it was the oversize thing that confused me. thanx for the straight answer. i still cant suss out how bigger valves  would do any good without corresponding seats. do you have to use  "big valve" seats also? this super rocket better be all its cracked up to be, or im goin back to my triumphs!

[trevinoz]

Mate, if you you build your engine carefully and use 357 cam with stock carby you will be more than satisfied. As to your head, surely if it is a big valve head the seats and ports are correct. I think there 3 different types of rocket heads with integral manifold. They can be identified by numbers on bottom of manifold.

[63a10r]

can you tell me what that # should be for a 1962 super rocket big valve hhc? this project is really getting me worked up. i have high hopes. i may have to eat the crow offered up by my bsa riding friends!

[trevinoz]

Which # is that? Engine , frame or part?

[63a10r]

the frame/motor numbers are compatible. i was referring to the #on the head.

[trevinoz]

Here we go. Road Rocket head cast-in number - 67-1136, usually with RR stamped adjacent.                                     
                 Big valve head cast-in number - 67-1549.                                                                                     
                 Some heads have the '49' ground out and the number '71' stamped in their place. I may be corrected but I think these may be the heads with modified inlet tract which is mentioned in late sales brochures.  I hope this helps.

[bsa- bill]

I have a bigvalve head, unfortunatley it does require guides, valves , springs and has a broken fin.
I was going to repair it ( bought a batam alloy head for replaceing fin ) but a complete rocket head came my way with all the work done so I went bought it.
Intend to put the bigvalve head on Ebay at some stage ( kind of busy at this time )
anyway as has been stated , i'm not sure there's much advantage

all the best - Bill