Author Topic: RGS vs. SR head  (Read 7702 times)

Offline Housewiz

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RGS vs. SR head
« on: 18.09. 2012 23:30 »
Would an SR and/or a RGS twin carb head be advised/practical/functional for a RR rebuild?  If the RR bottom end had the recommended upgrades, would the stronger bang in the cylinder cause any issues?  Would the RR frame accommodate the twin carb setup w/o modification?

Thanks,  

Steve

Offline trevinoz

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Re: RGS vs. SR head
« Reply #1 on: 18.09. 2012 23:35 »
Steve,
                I gather you are referring to the early separate manifold head fitted 1954-5 on the RR and later offered in the U.S. as part of the "speed kit"?
You should have no trouble fitting one but the question is, why bother?
Trev.

Offline Housewiz

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Re: RGS vs. SR head
« Reply #2 on: 19.09. 2012 01:05 »
Figured if the factory made the option, why not set up a bike with dual carbs?  Much more work sync'g them?

Offline JulianM

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Re: RGS vs. SR head
« Reply #3 on: 19.09. 2012 08:44 »
Hi Steve, (and Trev)

The "Kit" head was not the same as the early A7 head as many think, it was a completely new casting with quite a few differences. The part numbers were also different.  There was also a twin carb conversion offered for the 500 and this WAS the same as the earlier heads.
Part numbers are 67-1101 for the 500 and 67-1105 for the 650.  Combustion chamber size is larger, valve sizes are larger, and porting is different. "As cast"     My Testing showed a 17% increase in flow between a standard un-ported and "as cast" 67-1105 head against a fully flowed and ported big Valve RR/GS head.  A pretty good place to start I would say! 
Just to make the comparison easy, try riding a T120 Bonneville after a single carb Tiger and tell me which you would prefer.  Both have fantastic manners (so don't tell me twin carbs won't pull in low revs) but the Bonnie is head and shoulders better with a handful of throttle!

Twin carbs when setup correctly and chosen well will outperform a single carb any day when it comes to power,  Very low throttle and trials riding is another matter but can't say an A10 would be ideal for that anyway  ;o)
Twin carbs are easy to setup if they, and your engine are in good condition.

Finding a head is the hardest part!

Good luck,
Julian
55 Ariel HS mk1,
58 BSA Super Rocket Scrambler special,
60 BSA Gold Star, Jim hunter desert racer,
64 Norton N15CS,
65 Triumph TR6 SS,
66 Triumph Bonneville,
71 AJS Stormer,
71 BSA Rocket 3,
71 Laverda 750SF,
71 Laverda/Egli 750SF, Race bike,
73 Norton Commando 850,
74 Moto Morini 3-1/2 Sport,
74 Bultaco Sherpa 350,
76 Beta Cross 50,
77 Moto Guzzi Le Mans Mk1,
80 Ducati 900 MHR,

Offline alanp

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Re: RGS vs. SR head
« Reply #4 on: 19.09. 2012 13:57 »
 My Testing showed a 17% increase in flow between a standard un-ported and "as cast" 67-1105 head against a fully flowed and ported big Valve RGS head.  A pretty good place to start I would say! 
Just to make the comparison easy, try riding a T120 Bonneville after a single carb Tiger and tell me which you would prefer.  Both have fantastic manners (so don't tell me twin carbs won't pull in low revs) but the Bonnie is head and shoulders better with a handful of throttle!

Twin carbs when setup correctly and chosen well will outperform a single carb any day when it comes to power,  Very low throttle and trials riding is another matter but can't say an A10 would be ideal for that anyway  ;o)
Twin carbs are easy to setup if they, and your engine are in good condition.

Finding a head is the hardest part!


Julian
Thanks for that snippit of info. Just as I thought, it has to be better for filling the cylinders if the inlet ports were straighter than the S bends of the single carb. head. I have been shouted down on this point for years based on someone who should have known better years ago saying it makes no difference.
Cheers, now where are the twin carb 67-1105 heads? Virtually impossible to find unfortunately.
Alan 
Member of the 'Last of the Summer Wine Club - Jennycliff'.

Offline The pirate

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Re: RGS vs. SR head
« Reply #5 on: 19.09. 2012 14:34 »
I would love to find a dual carb head for my A10, I think that would be the would be the 'top mod' for any cafe racer. I have never even seen the 'Speed kit' option. I toyed with the idea of turning an old alloy head into dual carb, but have never found a head damaged enough to try. Seems a pity to deystroy a good alloy head on what could be a 'fools errand'.

Anyone like to donate one for me to cut up!!! yeah and pigs will fly as well.

I'm with you Alan, the more curves the more problems with the intake.

Have a great day.
The Pirate

Offline JulianM

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Re: RGS vs. SR head
« Reply #6 on: 19.09. 2012 17:05 »
Nice one here but you can't have it  ;o)

You can occasionally pick them up but are usually mighty expensive!

Keep'em peeled as Shaw Taylor used to say, and Good luck

Julian
55 Ariel HS mk1,
58 BSA Super Rocket Scrambler special,
60 BSA Gold Star, Jim hunter desert racer,
64 Norton N15CS,
65 Triumph TR6 SS,
66 Triumph Bonneville,
71 AJS Stormer,
71 BSA Rocket 3,
71 Laverda 750SF,
71 Laverda/Egli 750SF, Race bike,
73 Norton Commando 850,
74 Moto Morini 3-1/2 Sport,
74 Bultaco Sherpa 350,
76 Beta Cross 50,
77 Moto Guzzi Le Mans Mk1,
80 Ducati 900 MHR,

Offline Housewiz

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Re: RGS vs. SR head
« Reply #7 on: 19.09. 2012 21:57 »
Hey Julian,

Thanks for that excellent reply.  You listed the part numbers which is great - how about what the #'s would be on the correct A10' dual carb head?  One and the same?

Thanks,

Steve

Offline trevinoz

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Re: RGS vs. SR head
« Reply #8 on: 19.09. 2012 22:39 »
Sorry Julian but the kit head has the same casting No. as the 1954/5 RR head but does not have the date code.
The one I have has the ports opened out but I don't know whether this is from the factory or not.
The inlet valves would not be appreciably larger than the RR valves, something like 37mm against 35mm.

Trev.

Offline Housewiz

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Re: RGS vs. SR head
« Reply #9 on: 20.09. 2012 00:12 »
OK guys, what A10 twin carb head has the serial #67-1102 G 54 AM?

Offline duTch

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Re: RGS vs. SR head
« Reply #10 on: 20.09. 2012 06:27 »

 Check out the post that MG Markus did a while back,re; New A10 barrels,- made by Norvin, I think they're doing heads as well but about £1500? Doing ads in 'Classic Racer' ,or similar
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
Australia

Offline JulianM

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Re: RGS vs. SR head
« Reply #11 on: 20.09. 2012 07:49 »
Hey Julian,

Thanks for that excellent reply.  You listed the part numbers which is great - how about what the #'s would be on the correct A10' dual carb head?  One and the same?

Thanks,

Steve

Hi Steve,
Believe me when I say I am no expert in this, all I am going from is personal experience and a small amount of personal research. No second hand info, just checking myself. So I may be wrong on research but I don't think so.  Checking and measuring I have done myself so in the instances quoted these are correct for the parts assessed and measured by me.
Here goes  ;o)
Ally A7 and A10 early RR heads were cast as 67-1102  (part number 67-1101 as you will notice with most BSA parts, casting number is usually 1 digit later than part number)
Some people say that some 67-1105 (casting 67-1106) heads have the "6" stamped in, but I don't believe this. I have seen (been offered) 2 like this and both had modified ports to get to "std" 67-1105 size and you could see that someone had stamped the "6" with different punches so this was either an early factory mod or more probably people passing off the early head as the 1106.  However I think you could modify a 1101 to 1105 and see the same power from both.

Trev,  Do you mean casting number 1102 or 1106?   In the books / papers I have seen the 54/5 RR has part number 67-1101
As I say above though, I think both could be made to do exactly the same job, just one has bigger holes to start with!

My valves are 38.5 Inlet and 35 Exhaust

Interesting comments.
Julian
55 Ariel HS mk1,
58 BSA Super Rocket Scrambler special,
60 BSA Gold Star, Jim hunter desert racer,
64 Norton N15CS,
65 Triumph TR6 SS,
66 Triumph Bonneville,
71 AJS Stormer,
71 BSA Rocket 3,
71 Laverda 750SF,
71 Laverda/Egli 750SF, Race bike,
73 Norton Commando 850,
74 Moto Morini 3-1/2 Sport,
74 Bultaco Sherpa 350,
76 Beta Cross 50,
77 Moto Guzzi Le Mans Mk1,
80 Ducati 900 MHR,

Offline trevinoz

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Re: RGS vs. SR head
« Reply #12 on: 20.09. 2012 23:41 »
Julian,
             Here are some photos of the early alloy heads.
The first 2 show the head which I think is from the "speed kit".
It has 67-1106 and AM cast into it.
On the under side of the LH port is stamped "RR 177".
The next 2 are of a 1954 RR head.
It also has 67-1106 cast but the "AM" also has a date code of "J54".
The under side of the LH port is stamped "RR".
The last pair show a 1955 SS head.
It has cast into it 67-1102 and "AM A55".
The under side of the LH port is stamped "SS".
The first head has 1-5/32" inlet ports which probably matched the separate adapters and carbys.
The 1954 RR head has 1'' ports. This head is in a poor state, having multiple fins broken off. New pieces have been welded on but there is a hell of a lot of work required to get it up to scratch.
The 1955 SS head is beyond repair and is just a source of fins for other heads.

Offline trevinoz

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Re: RGS vs. SR head
« Reply #13 on: 20.09. 2012 23:43 »
Here is the last photo in this series.
Trev.

Offline JulianM

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Re: RGS vs. SR head
« Reply #14 on: 21.09. 2012 08:18 »
Hi Trev,

Very interesting viewing!

A few questions and observations etc. that may help us further in our quest to the final answer.

Do you know for sure of these heads origin?  Not doubting you just a question.
Reading up last night I learnt that the first batch of "Twin Conversion" heads was made for Hap Alzina in "54" for fitment to his special 650 Star Twins to race at Daytona. This was the same year that the first "Kit" was offered in order to get round the rules, this is the kit offered with TT carbs not the later kit with monoblocks from the early 60's  AND I believe the first year certain A7 models were offered with the ally head.
So my thought was that having J54 as the date would surely tally with this?  Could your head be an early first batch "Daytona" head?
Or are all early ally heads cast with 1106 or 1102?  It would be very interesting to know what others have cast in their single/twin ally heads on standard fitment bikes.
If we collect a larger cross section then we can know for sure!   Would clear up an age old question with little doubt.

To be honest it would make more sense if you are correct as making a batch of 200 or so would be a very expensive "Kit" when you already have twin port heads already on the shelf that could be modified to suit.
I think it is Very likely that the "special" heads were used on the standard RR models with bolt on single carb manifolds.
However the factory parts books I have seen referred to 1101 numbers and not 1106, but to be honest I was not looking at any theories here just numbers so could have missed a trick.

The only things I know for sure are these.
1. A totally standard un-modified 1106 head out flows a fully modified RGS single carb head without carbs, by 17% on my SupaFlow flow bench.
2. 650 heads are cast 1106 and the 500 head 1102,
3. The heads that I have seen with casting numbers 110 and that have the "6" stamped in, were without doubt modified 1102 castings. Possibly by private individuals and possibly by the factory before the 1106 casting was available and I have seen reports of the same.
4. Both 1101 and 1105 part numbers were offered as a "Kit" from 1954 onwards sporadically.
5. They worked in period so why won't they work now!
6. They are bloody rare creatures!

Julian
55 Ariel HS mk1,
58 BSA Super Rocket Scrambler special,
60 BSA Gold Star, Jim hunter desert racer,
64 Norton N15CS,
65 Triumph TR6 SS,
66 Triumph Bonneville,
71 AJS Stormer,
71 BSA Rocket 3,
71 Laverda 750SF,
71 Laverda/Egli 750SF, Race bike,
73 Norton Commando 850,
74 Moto Morini 3-1/2 Sport,
74 Bultaco Sherpa 350,
76 Beta Cross 50,
77 Moto Guzzi Le Mans Mk1,
80 Ducati 900 MHR,