Author Topic: A10 Big Valves - Rare?  (Read 4268 times)

Offline trevinoz

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Re: A10 Big Valves - Rare?
« Reply #15 on: 04.08. 2011 23:21 »
My two-bob's worth.

              There is a lot of confusion as to what was originally fitted to the "big valve" heads.
I have both, 67-1549 & 67-1571.
The inlets are the same size, 1.455".
I asume that the difference in the heads is the inlet tract as some export machines were fitted with an 1-3/16" carby.
I have attached a page from the factory tuning notes which states that the inlet valves are increased in diameter [1.455"] by fitting valve 67-961 which is listed in some publications as a Super Rocket, '58-'59, 1/16" os, making it 1.5".
I am again assuming that the author means to increase the inlet valve from 1.455" to 1.5".
I think that the Atlantic Green site is wrong in stating that the RGS & Big Valve were fitted with the over size valves as I have never seen a parts book which would back it. Nor the heads in my possession.
Logic tells us that BSA would give a head, with different size valves to standard, a new part number.
My parts book only lists the 67-1551 valve and the book includes all markets machines.       


Offline Rocket Racer

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Re: A10 Big Valves - Rare?
« Reply #16 on: 05.08. 2011 06:47 »
If the valve seats have enough meat on them to cope with the std 1.455 inlet big valve I'd be using that.
I fitted large valves to my earlier '55 head, supplied by draganfly and am now having to fit smaller valve seats on the exhaust so I can go back down on the zorst valve diameter. I didnt have valve to head issues with 8:1 pistons but was getting valve clipping.
My racing oracles opine that the big A10 zorst valves are too big in relation to the larger inlets.
I'm running with a 357 cam and looking forward to better reliability with a smaller exhaust valve.
That triple port head is just sad.
A good rider periodically checks all nuts and bolts with a spanner to see that they are tight - Instruction Manual for BSA B series, p46, para 2.
New Zealand

Online chaterlea25

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Re: A10 Big Valves - Rare?
« Reply #17 on: 05.08. 2011 21:54 »
Hi Trevor,
You maybe correct surmising that different size inlets were used for different "export" markets ???? ????
I compared two 67-1549 heads and one has a 1 3/16 inlet port 30mm) and the other 1 1/8 (28mm) or so
Both did not look as if they had been worked on by "home tuners *eek*
The 67-1571 on my SR has a 1 3/16 port and had 1.5in valves fitted when I first got it??

All this tells us is that more or less "anything goes" when waffling on about these heads *conf* *conf*

John O R
1961 Super Rocket
1963 RGS (ongoing)

Offline jfligg

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Re: A10 Big Valves - Rare?
« Reply #18 on: 22.08. 2011 17:51 »
Hi Guys
  My 1959 Brocher advertises a big valve head.  I'll let you guys know when I get it apart.  Jeff