Britbike forum Forums British motorcycles in general The competition forum A65 Thunderbolt head on a racer

I might have need of a Thunderbolt Head for a A65 motocrosser. I've heard that the side car guys in Australia use them. I was wondering if they have a flow better single carb manifold instead of the short stubby BSA manifold?

Pretty sure Nick uses the dual throat webber which acts much like a dual carb set up. Dad(Mark Parker) uses twin carbs on his Firebird with the thunderbolt head. Not heard of any other options, not that means there arent any 😉

If they are restricting you to a single carb then there is no manifold that is available.
You'll have to make one. We cut the back off the head and weld stubbs on. My old
outfit had a manifold made up but it's easier to just weld stubbs on. You'd have
trouble getting a weber to fit on a solo and i assume you wouldn't want one anyway.
The weber conforms to the regs as it was available from 1958 onwards in various
guises. A DCOE40 works very well and is easily setup. The pluses are a light throttle
balanced carburation and a proper racing carb with great flow etc. The minuses are
the fact that it is quite bulky. Many sidecar racers with triumphs, nortons, weslakes
etc used webers not just us. (This was back in the uk in the 60's 70's)
Mark's set up using 2 flat slide carbs is ok if the regs allow it.

Thanks Ben and Nick.

Looking at a possible Rickman A65 project where the frame (I think) won't allow me to use the Lightning head. So I may start off with a thunderbolt head and then look at upgrading to two carbs as you say by welding something on. There a lot of room but I don't think there is that much room for the weber...

Thanks while I sound out whats possible.

My manifolds are bolt on. Nick's Weber manifold lines up exactly to them from memory. I doubt it's possible to get the same flow unless it goes into the head oval and in line.

This shows where the bolts are. As both std locations are no good. There is weld for the high one. Also weld to the sides of the port which is around 37X30 approximately squashing a piece of 34id alloy pipe in a vice is pretty easy. Welding stubs eliminates screws.





These would fit an Bandit/Fury I expect.

Twin carb heads with straight short manifolds are about 270mm between carbs without filters so more suited to an OIF. With longer curved manifolds we use on RGVs it's around 225mm.



I imagine a 650 would be pretty wheel spinny on full noise.

Mark - Lovely pics. I may have found a head to my specs. Thunderbolt with two mounts for AMAL MK1 welded on the back. If this deal goes through Ill post up some pics. You are not going to believe what I found for the bottom end... It's not in my hands yet so I can't say.

GSXR1000 Mikuni throttle bodies are 36.7mm bore bolted together in pairs of two with 71mm spacing. Maybe that would work?

Bill, The message box is full. You have my email if you need it. Cheers, PRT

Curious if your FIND did happen….? Hope so, Please kill the suspense !

Sorry been away doing stuff. Bought an A70 motor and a 1965 A50B dual carb motor. Have no clue what I'm going to do with them yet.

Took the dual carb Thunderbolt head because it was so weird I figured Id come up with a crazed use and it wasn't very much. 30mm intake ports on a 69ish head.

The Rickman frame idea got expensive for an old frame. Perhaps the A70 goes in the Thunderwing...

Best thing you could do is drop the A 70 motor in a BSA Fury / Tri Bandit frame , With a few bulletproofing fixings .

https://www.pressreader.com/uk/real-classic/20180505/281517931733375

Were a few hill climb versions round 1980 . Rob Northish Chassis . & it fits good .

Theres a outfit in england ended up with truckloads of them . Dont think the prices are spastic .
Compact with a bit of balls , if you keep it light .

Tripped over pictures in C W or Cycle of Dave Aldana with the timing side cover off . Must have anotrher look .
He'd been up to something . I think it had the timing side bearing . ( BSA works rider ) .
The end feed oiling , iron bodied pump & decent oil capacity & it should stay together .

A bit of hysteria from 18 year olds trying 8000 rpm on ' used machines ' and before you know it theyll have
you thinking itll never get you round the block .

A A 70 is a RARE TREASURE . So DONT go drilling HOLES IN IT . A Commando crank in it and youll have a few cubes !
better to ' see its right ' than ' fix it up ' . Check youre Tappet settings before anything else . Then if it has a cam , youll know
the ballpark clearances straight off . Rather than them BEING LOST .
Are there any aluminum 750 big bore Barrels around ? . youd loose the chaffing from the iron on alloy , weight & leaks .

Was a pile of A70 stuff came up a while ago , Inc 5 motors . was there only 200 made ?

A Kiwi lapped all the mating faces & used Steam Pipe Gasket Paper for gaskets . Not a iota of a leak . Bar a AMAL Tickler.
The Dust made that evident , in the backwoods .

Maybe 200 bikes but a lot more motors and bits.
BUT those cranks are all 50 years old now and most were
used in chairs etc.
Also they are easily forged.

And Modify the Pressure Release set up , if you do . NOT a hole in the frame . No wonder E got rid of it .

Hardly insurmountable !

750 motor in a 350 frame! I like it. About 10 years ago a Fury popped up in New Jersey on craigslist for 500 US. I missed it by 1 hour.

Curious. No idea where the frames you are talking about ended up. Nothing shows online.

True. But this one came with crank bits and case machining i've not seen in and any other A65. Also the stamps are all in the right places. And I've yet to see somebody forge the pad stamp under the numbers on on the LH engine case. Not impossible but quite difficult.

Youtube provides...




Really tight fit but I do have the Dual Carb Thunderbolt Head

What he doesn't mention is that bike has a devimead/SRM 750 on it which
makes the engine about 10mm or so shorter.
You would be in for a few more mods with either an a65 or a70. Unless, of
course you fit one of John's 750 kits on a standard stroke lump.

https://www.oldbikemag.com.au/triumphs-last-gasp-abandoned-bandit/

Artical above .
Was one ' at the time ' in Aus, magazine articals saying 35.000 Miles ?? no trouble .

WHICH MAKES YOU WONDER .
Some say Indian lec start was no use , so production abandoned ?
ALTHOUGH IT HAD A KICK START . parently a blanking plate was beyond them .

A CLASSIC BIKE ( U ,K, Magazine , or similar ) had a write up on one , along with the supply source ,
who had puloined ALL available components . Maybe 200 of most . Inc. Frames .
Dunno if the forks etc were common to others ? Meridan snookered disc brake 500s & T 120 V's in their ' take over ' .

ANYWAY , a pommy classic bike nutter or perhaps a enquirey to them or BSA O C uk ,
should eventually hold fruit .Was a photo of the old barn type building . Dragonfly M C maybe perhaps , or not .

WORTH A TRY anyway .

In New Zealand was a Green Triumph in the 70s , at Bill Whites . At the platform halfway up the stairs to the spares dept .

MOTAT had one the same , or the same one , Also . Maybe still there ? a lotta stuff disapeared there , were told .

R R Merlins , piece by piece etc etc . Tank Enines etc . Beckingham gave them a brand new in case Submarine periscope / telescope . They chucked it in the roof of a fishing trawler cabinoutdoors . That was the end of that , eventually . So half of the stuff theres not there . A Mosquito had arrived in full .

SO , chase it up , if youre inclined to try one , would go like stink . Around 1980 classic bike had photo of a Devimead 750 Hill Climb Comp, one ,

https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.alamy.com%2Fstock-photo-triumph-bandit-750-ridden-by-tony-hayward-37289552.html&psig=AOvVaw3hojoasP2Np07n2Yta0Ero&ust=1648970043051000&source=images&cd=vfe&ved=0CAgQjRxqFwoTCLC--6Dq9PYCFQAAAAAdAAAAABAD

https://www.flickr.com/photos/[email protected]/45175723482

750 bandit Triumph , in search .

ALSO the Vetter Tri Twin ' prototype ' pioneered that and the T160 Tank Shape , so tryn get one of em too . Tell em to donate it to a worthy cause ![img]https://www.flickr.com/photos/[email protected]/45175723482[/img]