Author Topic: Difference between 67-1549 & 67-1571 Cyl Hd's  (Read 2705 times)

Offline sprint

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Difference between 67-1549 & 67-1571 Cyl Hd's
« on: 20.05. 2014 14:17 »
What is the difference between 67-1549 & 67-1571 Cyl Hd's?

It is my understanding that there was never a specific RGS head but just the large valve version of the SR engine, 67-1549 with 1.5" inlet valves instead of 1.455" fitted?

So what is a 67-1571 head, which is often referred to as a RGS head?

Offline Topdad

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Re: Difference between 67-1549 & 67-1571 Cyl Hd's
« Reply #1 on: 20.05. 2014 16:28 »
My book notes 'em has 67-1122 a7ss,67-1126 road rocket, 67-1549 super rocket and 67-1571 rocket gold star .
The tech details have been lost to me ages ago but always assumed ( and we know what happens to assumptions )  that there was a difference in the RGS head and the super rocket  but given BSA's management they could just have differentiated to add a few pounds/dollars to the price. I have heard 'em called big valve but just thought it was for the american market and hep etc, be interesting to get the full SP from more knowledgeable members , regards Bob.
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Online bsa-bill

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Re: Difference between 67-1549 & 67-1571 Cyl Hd's
« Reply #2 on: 20.05. 2014 17:17 »
Bob I'm sure his has come up before (I had a big valve head) the difference in valve size is very small, someone will correct this but was it 3 or 4 thou, sounds not a lot but maybe did give room for a bit more gas flow.
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Offline sprint

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Re: Difference between 67-1549 & 67-1571 Cyl Hd's
« Reply #3 on: 20.05. 2014 20:48 »
Bob I'm sure his has come up before (I had a big valve head) the difference in valve size is very small, someone will correct this but was it 3 or 4 thou, sounds not a lot but maybe did give room for a bit more gas flow.

Inlet valve on the 'big' valve head will be 1.5" instead of the std 1.455". But it seems that both 67-1549 and 67-1571 can be 'big' valve heads?

Online trevinoz

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Re: Difference between 67-1549 & 67-1571 Cyl Hd's
« Reply #4 on: 20.05. 2014 22:08 »
The "big valve" is 37mm as against the "small valve" 36mm.
The 1-1/2" valve is an over size valve and to my best knowledge was never fitted as standard in any head.
The 1571 head was not exclusively fitted to the RGS, the RGS engine being a standard engine.
I have pondered this question for some time now and comparing the heads, there seems to be no noticable difference.
The best that I can come up with is that the 1571 head was used when a 1-3/16" carburettor was fitted.
My RGS has a 1549 head and my BVSR has a 1571.

Trev.

Offline sprint

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Re: Difference between 67-1549 & 67-1571 Cyl Hd's
« Reply #5 on: 21.05. 2014 08:12 »
Is the info here not correct then about the 'big' valve inlet and exh valve sizes? http://atlanticgreen.com/a10alloyhead.htm

Offline Topdad

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Re: Difference between 67-1549 & 67-1571 Cyl Hd's
« Reply #6 on: 21.05. 2014 15:19 »
Thanks Trev and Bill for info will store away. Anyone have an ideaof the biggest valve poss on an iron head. I got SRM to do this to mine along with a spitfire cam plus follwers but can't remember how big they were. They are a standard size as I obtained a replacement easily when it was needed due to my idoticy . Have an idea that it wasn't much smaller than these mentioned, any ideas welcome regards BobH
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Online trevinoz

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Re: Difference between 67-1549 & 67-1571 Cyl Hd's
« Reply #7 on: 21.05. 2014 22:34 »
Sprint,
                 I don't know where the bloke on that site got his information but I can only go on what I have and that is 37mm inlet valves on both heads.

Trev.

Offline dynodave

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Re: Difference between 67-1549 & 67-1571 Cyl Hd's
« Reply #8 on: 12.06. 2014 19:41 »
Hi Guys
Sorry. I know I don't post here much at all.
On my BSA web page for heads (http://atlanticgreen.com/a10alloyhead.htm) I simply documented what I had in the heads I own. I have at least a dozen and probably more than that, counting 3 different dual port heads.
I am in agreement with the position that RGS engines are the same as big valve super rocket engines. The only thing I do believe, is that the advertised dyno run in and testing proved it met or exceeded the minimum performance for the RGS. Therefore this added testing could account for the different engine part #42-0202, though the build components could have been 100% identical as the BVSR.
I have NOT seen or examined a 1571 head or it's markings. So you all have one up on me.
dynodave
61 Gold Flash* 63 Super Rocket* 63 RGS

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Re: Difference between 67-1549 & 67-1571 Cyl Hd's
« Reply #9 on: 12.06. 2014 20:12 »
Hi Dave,
What numbers are on the heads of your SR and RGS ?

Regards
John
1961 Super Rocket
1963 RGS (ongoing)

Offline sprint

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Re: Difference between 67-1549 & 67-1571 Cyl Hd's
« Reply #10 on: 12.06. 2014 21:46 »
Hi Guys
Sorry. I know I don't post here much at all.
On my BSA web page for heads (http://atlanticgreen.com/a10alloyhead.htm) I simply documented what I had in the heads I own. I have at least a dozen and probably more than that, counting 3 different dual port heads.
I am in agreement with the position that RGS engines are the same as big valve super rocket engines. The only thing I do believe, is that the advertised dyno run in and testing proved it met or exceeded the minimum performance for the RGS. Therefore this added testing could account for the different engine part #42-0202, though the build components could have been 100% identical as the BVSR.
I have NOT seen or examined a 1571 head or it's markings. So you all have one up on me.

I now have both a 67-1571 and 67-1549 (cylinder head cast No's). The only difference I can see is that the 67-1549 uses the long shouldered nut to hold the rear of the rocker box and the corresponding studs will be shorter?

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Re: Difference between 67-1549 & 67-1571 Cyl Hd's
« Reply #11 on: 12.06. 2014 22:21 »
Sprint,
              All alloy heads use the sleeve nuts on the rocker boxes.
If you have one without, it must have been changed by someone in the past.

Trev.

Offline sprint

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Re: Difference between 67-1549 & 67-1571 Cyl Hd's
« Reply #12 on: 13.06. 2014 09:41 »
Sprint,
              All alloy heads use the sleeve nuts on the rocker boxes.
If you have one without, it must have been changed by someone in the past.

Trev.

Thanks Trev

That leaves me a bit confused?

The 67-1549 that I have just obtained has the rear cly hd holes counterbored to take a sleeved nut, which I assume requires shorter studs in the inlet end of the rocker box, see photo.

My 67-1571, on bike at moment, simply has the same holes just parallel bored 5/16" clearance and uses std nuts and washers. and as a result the rockerbox inlet end studs are long, which is a pain as you have to remove them before you can remove or fit the rockerbox with the engine in the frame.

A friend has a 57 RR and  60 SR and they also have long studs at the inlet end and std nuts and washers, though I don't know what heads he has or if the rear holes are counterbored?

Offline dynodave

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Re: Difference between 67-1549 & 67-1571 Cyl Hd's
« Reply #13 on: 14.06. 2014 00:32 »
Hi Dave,
What numbers are on the heads of your SR and RGS ?

Regards
John

The SR is head is 1549  (just went and checked at the warehouse) , and the RGS (GA10-15xx) was a basket case and I have several 1549 heads to choose from (no 1571's)  but one head came with the bigger valves. However...I may go for one of my late 650 twin carb heads and 389/689 monoblocs.
dynodave
61 Gold Flash* 63 Super Rocket* 63 RGS

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Re: Difference between 67-1549 & 67-1571 Cyl Hd's
« Reply #14 on: 14.06. 2014 00:48 »
Sprint,
                      I can't explain why your head is not counter bored.
I have all four Rocket heads and they are all bored.
Even the 1954 SS derelict head is bored.
Has someone put sleeves in the holes?

Trev.