Author Topic: Wad'll it do mister?  (Read 1132 times)

Offline trickytree

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Wad'll it do mister?
« on: 13.06. 2010 13:47 »
Im collecting parts for my second bike build at the momment, not realy sure what its going to be just yet but will be based around some A10 plunger cases and gearbox that I have. Found a A7 rigid frame that has "had a few lugs chopped off" but i have yet to go and see it. It will be an oily rag, I'm going to spend the money on the engine, not pretty shiny things.

I am however pretty sure what I would like it to do performance wise. I want a big, lightly stressed motor, not a screamer. I want it to be relativly low reving and able to cruise at a steady 70-80 mph with a little in reserve when needed and with decent mid range punch for overtaking. And I would prefer all my fillings to still be in my teeth when I climb off at the end of my journey.

I realise these bikes are now 40 plus years old but is it unreasonable to expect a A10 based engine to do the above? I have a few plans and ideas in my head but before I reveal I would like to here from you guys that own and ride these bikes just to get an idea of what there capable of in standard(ish) trim in the real world.

Cheers, Paul.
1965 A65 Bobber
A10 Bitza project

Offline bonny

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Re: Wad'll it do mister?
« Reply #1 on: 13.06. 2010 14:36 »
i'm doing pretty much the same thing as you paul , building a lightly stressed engine so its understressed and reliable . i tuned my 500 triumph when rebuilding it and i am sorry now that i did. i think a standard golden flash engine should give you what you are looking for and thats the way i have gone , lowish compression and the mildest camshaft that bsa used. anything i have read on the flash suggests this will give you what you want, unless some of the more experienced on here can tell us different.   

Online muskrat

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Re: Wad'll it do mister?
« Reply #2 on: 13.06. 2010 15:35 »
G'day Paul.
                   to keep the revs low you'll need to lower the primary ratio or go up a few teeth on the g/box sprocket. Big job for the primary as you would have to convert to s/a  type with a s/a main shaft in the plunger g/box.
356 cam, 8:1 pistons, smallish (26-28mm) carb, lengthen the inlet tract as much as you can with a spacer between head and carb (all for torque rather than H/P), and a heavy large journal crank.
 I have gone the other way for H/P. 357, 10.5:1, 2 x 30mm, short inlets, but I'm a rev head !!
 Build it how you want it and have fun.
Cheers
'51 A7 plunger, '57 A7SS now A10CR, '76 XT500, '77 AG175 '83 CB1100F, '81 CB900F project.
Australia
Muskys Plunger A7

Offline mikethebrush

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Re: Wad'll it do mister?
« Reply #3 on: 13.06. 2010 16:55 »
I would have thought the a10 engine , rebuilt and in properly set up will answer most of your  needs, bsa built under stressed reliable engines but im not sure you will have much power in reserve and not reallly sure why you want it

my A7ss cruised happily at 70- 80 with a little bit left if I had to open up for some reason and was always a good starter and reliable runner

if i had tried cruising at 90 I would probably wrecked the engine as the revs would have been over 6000 rpm and 90 is the top end of its performance any way

my mates goldie 500 is a lovely bike to ride, but doesnt tick over and runs lumpy till it comes on cam , once there it will happily cruise at 90 and have plenty of reserve

basicly what im saying is that its either understressed and low revving with a lower top end and cruising speed or its tuned and and its powerband is higher
1959 BSA A7 SHOOTING STAR

Offline LJ.

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Re: Wad'll it do mister?
« Reply #4 on: 13.06. 2010 19:38 »
I'll bet that over the years just about everything and anything has been done to the A10, I think you should experiment as you go along according to what you find and buy. When you start having ideas then you need to start paying bigger money.
Ride Safely Lads! LJ.
**********************
1940 BSA M20 500cc Girder/Rigid- (SOLD)
1947 BSA M21 600cc Girder/Rigid-Green
1949 BSA A7   500cc Girder/Plunger Star Twin-(SOLD)
1953 BSA B33  500cc Teles/Plunger-Maroon
1961 BSA A10  650cc Golden Flash-Blue
1961 BSA A10  650cc Golden Flash-Red

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Re: Wad'll it do mister?
« Reply #5 on: 14.06. 2010 02:35 »
I agree LJ, I have tried a few things over the years. It's a shame I didn't have this forum to save me time, money and broken bits at the time. Just trying to save Paul the same. The old saying, How Fast Do You Want To Spend, springs to mind.
 Mike, my '51 A7 has the original top end off my '57 SS and a 357 cam. It will sit on 60 all day with the odd burst of 70-80 but wouldn't like to do it all day. Constant high revs kill the small journal cranks.
 The gearing on the cafe gives me 60 at 3250rpm which I think Paul is after. To keep the stress level down more torque is needed. HP = top speed, torque is how fast it gets there.
 Paul, look for thick flange barrels and large journal crank.
Cheers
'51 A7 plunger, '57 A7SS now A10CR, '76 XT500, '77 AG175 '83 CB1100F, '81 CB900F project.
Australia
Muskys Plunger A7

Online Brian

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Re: Wad'll it do mister?
« Reply #6 on: 14.06. 2010 07:45 »
80mph cruising with some in reserve, low stressed and smooth. Couldnt be easier, go down to your local bike shop and buy a 1000cc japanese bike.

Unfortunately what you want is outside the design parameters of our old bikes. The performance you want is possible but not in a low stressed state. You can go down the road of modifications and tuning that will get you what you want but it takes a lot of time and development and most of all, truck loads of money.

If you do choose to go that way then I would look for a s/arm model, not a rigid. A late swing/arm model will give you a set of thick flange barrels, big journal crank and then you could get a alloy head. Also a lot safer sitting on a s/arm frame at 80mph than on a rigid.

Hope I havent burst any bubbles but you need to be realistic or you will end up spending heaps of money on something that will not live up to your expectations. A rigid or plunger A10 will cruise all day everyday at 65mph and go forever, start asking more and you may find out what the "big bang theory" is all about.

Offline mikethebrush

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Re: Wad'll it do mister?
« Reply #7 on: 14.06. 2010 11:50 »




Brian you explained things much clearer than I did and I agree 100%, maybe in my youth I pushed the bike harder than I should have, I was used to riding yamaha rd's and lc's, its a testament to the strength of the parralell twin that it didnt give out
Its also a testament to the superior handling of the design that it outlasted the japanese bikes which had a habit of literally taking to the air when you least expect it, quite spectacular but more than a little scary
Im going to be stripping my engine shortly and will be able to assess if I damaged it, im going to have to remove the kickstart as im finding my right boot gravitating towards it and I dont want to kick it in case something has siezed in the engine
1959 BSA A7 SHOOTING STAR