The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: a10sausage on 11.01. 2009 15:44

Title: convert 1960 gold flash to rocket
Post by: a10sausage on 11.01. 2009 15:44
anybody any ideas how to convert a 1960 gold flash to a rocket...can i just add high comp pistons and an  alloy head as it already has thick flange barrels...and i am led to believe the 1960 flash was fitted with a rocket cam as standard....i am sure somebody out there will know...cheers....from the sausage
Title: Re: convert 1960 gold flash to rocket
Post by: stratcat on 11.01. 2009 17:12
The "only" difference between the flash and the super rocket, by the 60's, was the alloy head and lumpy pistons. The cam and barrels were the same.

With the fuel we have now you will just get s loads of pinking if you go for the full 9 to 1 comp ratio. A few years ago (when I had a bit of money) I treated my bike to a full engine rebuild from srm. They highly recomended a lesser compression ratio. I'm glad I took their advice as even with a reduced comp ratio, it pinks if you crack the throttle, two up, up a hill, without touching the ignition lever.

I would ask yourself why do you want to turn it into a SR?
I think the flash has a nicer power delivery and is probably less stressed = longevity. I doubt you would notice the difference in power unless you were caning the wotsits off it!

Oh and welcome to the forum!
Title: Re: convert 1960 gold flash to rocket
Post by: Brian on 12.01. 2009 06:55
I agree with Stratcat re the state of tune.

My plunger has 7.5 - 1 compression and a 356 cam and its perfect, runs beautifully.

By contrast my 61' Flash has a 357 cam and 9.5 - 1 and its nowhere near as nice to ride. Obviously goes harder but even on the highest octane fuel I can get here (98) and the timing at 5/16" advance it will still ping under heavy load. Its a rocket out on the open road but not so nice around town or slower riding.

If you want a motor thats good to ride under most conditions then stick with a milder state of tune.

Brian.
Title: Re: convert 1960 gold flash to rocket
Post by: a10sausage on 12.01. 2009 17:26
thankyou for your help,i really appreciate your information as it seems that the road rocket and rocket gs are not as nice bikes to ride in everyday traffic..although i do have a friend who has a 58 flash that would win the world motorcycle pinking championship contest,if there was one.i am running electronic ignition on my flash and it has never pinked...we both run a fuel tank addative and he is on a mag ignition...i wonder if any other rocket riders out there suffer from pinking as this would put 100% put me off conversion...i am already 90% off the idea already !
Title: Re: convert 1960 gold flash to rocket
Post by: dpaddock on 13.01. 2009 01:34
Hello, A10 Sausage. Quite a monniker you have there.

Pinking is caused by several things, among which are:
     -  combustion chamber deposits/need to decoke
     - low octane/under-spec fuel
     - improper ignition timing (already alluded to)
     - improper fuel/air ratio
     - failure to gear-down when loading the engine below its pinking limit (BSA provides a good four-speed gear box to use for such times; don't be bashful about using it)

The iron GF is arguably one of the best vertical twin motorcycle engines of its time, and it would be a shame to try to alter it. It spawned the SF, RR, SR and RGS variants but never lost its place in the line-up. It should be revered, and those of you who own one can be pleased with its tractability and proud of your choice.
Title: Re: convert 1960 gold flash to rocket
Post by: bsa-bill on 13.01. 2009 15:20
Hi a10sausage and welcome to the forum and to what I imagine is a small band of A10 ers that have have grafted alloy heads on Flash engines.
To be honest I can't argue with those who advise against as my project is a bit of completion as yet, so as I have yet to ride it can't say how it will ride.
I already have a stock Gold Flash that is road going and is great fun to ride, so why am I converting my second one ?

1. because I can
2. because it's fun to do
3. If it's such a bad deal why did BSA make and sell so many Rockets ( would be interesting to know how many)

So far have rebiult both wheels with alloy rims and stainless spokes, powder coated the frame, tank, Painted the petrol tanh,oil tank and toolbox  Wicked Red ( Citrion or Renualt pearlescent colour), new bushes and seals in G/Box, new bushes and bearings in engine plus rebore and new 9.5 pistons.
New carb ( may be asking forum members for advise re jetting ), alloy head with new valves and giudes, 357 camshaft, siamese exhaust, Goldie type headlight and indicators.
Forks rebushed, new stanchion, progressiive rate springs and double damped, hagon rear shocks.
SRM dynamo belt drive and cush drive nut, Lyford alloy clutch pressure plate and swapped six spring to four spring.
Sounds like a lot of work and expense but this is over a five year period, work constraints held me back but now I'm retired it should progress with more speed, I'm hoping to have it on the road this spring.

So I reckon if you want to have your Flash just a tad individualised - go for it you, keep the old parts you can always put it back to Flash status if you don't like it but you will have done it and won't always be wondering what if -----.
If you want to see how far I've got so far have a loook at "Rocket Gold Flash" in "bikes and pictures"

All the besst - Bill
Title: Re: convert 1960 gold flash to rocket
Post by: stratcat on 13.01. 2009 15:52
I would like to clarify my point a little.

I love my rocket and wouldn't have it any other way. It does go like the clappers *smile* *smile* *smile*
and as a sports bike (and living out of town) I wouldn't have it any other way.
I often wonder what the car drivers all think when I overtake them on what, with its black and silver number plate, must appear to be a very old motorbike.

So yes to agree with Dpaddock, drop it a cog and give it some revs, and to agree with bsa-bill, Its your bike do what you want,
you will love it, it's an A10 after all! *smile*
Title: Re: convert 1960 gold flash to rocket
Post by: A10Boy on 13.01. 2009 16:49
Hi a10sausage, welcome.

All hail to the iron A10, its a great engine, and in its standard tune will last for yonks as a pleasant tourer, which is why most of us flash owners bought them.

With regard to conversion and tuning, something to bear in mind. The flash had auto advance ignition timing which works well with lower compression engines, but would probably give way too much advance for higher compression motors, [causing pinking already described] therefore if you go for HC, you might consider changing it for a manual lever so you can retard it a bit when needed. The ally head does give better cooling for the additional heat generated by the HC engine, so has advantages.

Personally, I if I was considering this, I would just swap the heads, and not change the pistons.

best of luck

Title: Re: convert 1960 gold flash to rocket
Post by: LJ. on 13.01. 2009 17:11
... But wouldn't you guys agree that an 'Iron' head sounds far better than an alloy one?
Title: Re: convert 1960 gold flash to rocket
Post by: A10Boy on 13.01. 2009 17:27
Well yeah, and I wouldn't put an ally head on a bike which is obviously a flash unless i was going for the full makeover - which I'm not...
 *smile*
Title: Re: convert 1960 gold flash to rocket
Post by: a10sausage on 13.01. 2009 17:46
Hi Folks!

Thanks for the great answers.  A10 boy is a little concerned about mag issues.  I am running electronic ignition - could there be timing issues with this set-up if I dropped HC pistons in and an alloy head?  My 1960 Flash is also running the incorrect carb.  It's an amal 376 - I will also change it to a 389 to get the correct performance.  Would a big valve alloy head give better performance than a small valve?  In my 1960 Flash I think it should be a big valve iron head.  If I just swap the head for an alloy one I take it there will be no performance gain, it would be purely cosmetic.
Title: Re: convert 1960 gold flash to rocket
Post by: bsa-bill on 13.01. 2009 18:24
Others will correct me if I'm wrong on this (does happen these days) but as I recall the difference between a big valve head and a standard alloy head is very small ( am I right in thinking we are talking a few thou ).
Somewhere in the bottom shed I have a bigvalve head spare, has one broken fin and needs guides and valve gear, must dig it out and put it in order.

All the best - Bill
Title: Re: convert 1960 gold flash to rocket
Post by: stratcat on 13.01. 2009 19:31
LJ - yet another very pertinent observation.

Even with the tappet clearances spot on the ally head can sound like you are dragging a cooker down a cobbled street!
(it was a joke, honest, my engine is in good condition *smile* *smile*)

I don't know about the big valve thing, I always thought it was an advertising gimmick aimed at the yank market.

I would be interested to know if there is a difference.
Title: Re: convert 1960 gold flash to rocket
Post by: A10Boy on 14.01. 2009 15:02
Others might give more detail, but I seem to remember reading that the exhaust valves were the same.
Title: Re: convert 1960 gold flash to rocket
Post by: Richard on 14.01. 2009 17:29
the exhaust valves were slightly larger dia. on the "big valve" head but only just larger and I may be wrong but I beleive the inlet manifold had a slightly larger bore.
Richard
Title: Re: convert 1960 gold flash to rocket
Post by: stratcat on 15.01. 2009 19:43
So which bikes were the big valve head fitted to? I don't recall any mention of it in literature, apart from the american ad's of the day.

Was it an export only thing? or an extra cost option?

Just wondering.
Title: Re: convert 1960 gold flash to rocket
Post by: a10sausage on 15.01. 2009 20:28
i think the big valve heads where on the 1960s flashes and rockets..take a look at this   [url][http://atlanticgreen.com/a10alloyhead.htm/url]
Title: Re: convert 1960 gold flash to rocket
Post by: bsa-bill on 15.01. 2009 20:37
did a google and found this
-------------------------------------------------------
67-1549
This head is for the 1960/63 Super Rocket & 1962/63  Rocket Gold Star.  No visual difference from the 67-1126 head was detected.
The valves for 1960 and up Super Rocket were intake #67-1551 1.455" (37mm?), exhaust #67-967 1.38"(35mm?)
The inlet valve for the Big Valve Super Rocket and Rocket Gold Star was #67-961 @ 1.5"(oh wow).
-------------------------------------------------------
can be found at ---   www.atlanticgreen.com/a10alloyhead.htm

Anyway it's 45 thou - might make a diiference.

All the best - Bill
Title: Re: convert 1960 gold flash to rocket
Post by: trevinoz on 15.01. 2009 20:41
I am pretty sure that the big valve head was introduced for the 1960 season therefore was fitted to all Rockets. I am also sure that the inlet valve only was slightly enlarged and the exhaust valve stayed the same dimensions as previously.
As far as I know, the Flash valves never altered in size.
   Trev.
P.S.  The heads can be identified by the number cast into the bottom of the inlet manifold.
        67-1126 = Road Rocket / Super Rocket  1956 - 59
        67-1549 = Super Rocket, Big Valve head from 1960
        67-1571 = Late Super Rocket and RGS. the "49" was ground out and "71" stamped in it's place.
Not sure of the difference between the last two, the valves are the same, but I have seen reference somewhere to the inlet ports being modified, probably for 1962.
Title: Re: convert 1960 gold flash to rocket
Post by: trevinoz on 15.01. 2009 20:45
Bill, I think you will find that the 1.5" inlet valve was listed as an oversize valve and was not fitted during production.
Also, it is 45 thou larger.
             Trev.
Title: Re: convert 1960 gold flash to rocket
Post by: stratcat on 15.01. 2009 21:58
That's interesting.

I wouldn't have thought that 45 thou was a big difference either,

But then I am not an engine designer. So what do I know?

I am tempted to go out and check the serial no on my cylinder head.

Am I sad? Actually it's far too cold for that. I might just pour myself another scotch instead *smile*
Title: Re: convert 1960 gold flash to rocket
Post by: bsa-bill on 16.01. 2009 12:53
Now Sratcat I've just been down to my bottom shed to check the head number and it is  67-1549, might just join you with that dram   *beer*

All the best - Bill
Title: Re: convert 1960 gold flash to rocket
Post by: dpaddock on 16.01. 2009 20:31
Gullible, perhaps, but never "gullable", Richard L.
     David

Title: Re: convert 1960 gold flash to rocket
Post by: RichardL on 16.01. 2009 20:57
Help, I need a spell checker. Nevertheless, allow me to foist this specious definition to justify my college education:

gullable adj. One so gullible that he can be gulled by a gull.

I said it was specious.

Anyway, thanks for the correction Dave.

Richard L.

Title: Re: convert 1960 gold flash to rocket
Post by: stratcat on 17.01. 2009 10:32
...or, perhaps, pooped upon by one.

Isn't that supposed to be good luck!
Title: Re: convert 1960 gold flash to rocket
Post by: groily on 17.01. 2009 19:02
Last time I was pooped upon by one of these pests was in Castletown IoM - dropped a CB900F Honda (this is years ago) and 2 stone of kippers from Peel on the road back to Douglas later in the day. Memsahib moaned about all the broken ribs too - but she took most of the impact and the kippers were saved and stayed in their boxes. She said it was because I'd mouthed vulgarities in the general direction of Fairy Bridge. I suppose one makes one's own luck!
Title: Re: convert 1960 gold flash to rocket
Post by: stratcat on 17.01. 2009 19:42
she took most of the impact
That was kind of her *smile*

I bet that has cost you dearly.it would be horrible for something
Seriously though, it is my biggest worry when out with the mrs on the back. Pillions always come of worse and whilst I accept the risk for myself.....well it doesn't bear thinking about.