BSA A65 'single'?

YukoNorton

YukoNorton

Joined
Sep 4, 2017
Messages
131
Country flag
Years ago I had a tired non-original '69 A65 Lightning in need of a rebuild. I had an idea to get the cam reground the same for both cylinders, so the cylinders would both fire at the same time, essentially, act as a single. Although I sold it without rebuilding it, I still think about it. Have I just been living in the bush too long or is this something that could work? I was going to do it just to be different - I remember reading about some of the early twin-piston singles, so it seemed like an interesting idea at the time, plus my buddy had a big single cylinder enduro which was a blast to ride. What are some thoughts on this? Terry.
 
This can be done on a Triumph twin, by welding each timing side rocker to its drive side partner and removing the pushrods from one cylinder.

Then one lobe, follower and pushrod opens both inlet valves and the same happens on the exhaust side.

There appears to be an alloy pillar between timing and drive side rockers on an A65, so I suppose it would need more engineering, like a special camshaft.
 
Didn't NSU, Puch or maybe DKW make a split single - the two bores shared a common combustion chamber?
I can find a few references to 2t's, but I just have this memory of a 4t.
Maybe delusional.
 
Thanks TT,the reason I felt the BSA A would be a good candidate was the single cam - it would just be a replacement with no other mods.

PG, interesting to see this was done on a HD KR750 and it won! "At the Terre Haute Half-Mile Bart Markel experimented by changing the timing on his KR so that both cylinder fired at the same time. It proved to be advantageous on the slick, hard-clay track and the “Twingle” carried Markel to victory."

NG, there were a few models with the twingle, under the Allstate banner: http://allstateguy.tripod.com/id8.html
http://www.bike-urious.com/allstate-puch-quadfecta/

Another thing that was interesting and kinda similar, was the Honda race bikes, the NR 500 and NR750,(New Racer or, Never Ready) which had oval pistons (shaped more like a skating rink) and two conrods per piston - like a single-twin, but they were v-4s. They revved to like 20,000 RPM: http://www.motorcyclenews.com/sport/motogp/2015/november/mcn-plus---nr500-honda-failure/
 
I don't think you can make the cylinders in a 45-degree v-twin fire at the same time. Twingling a 360-degree twin was tried on a 450 Honda but the vibrations proved to be insurmountable. Imagine the crank flex the Superblends would have to absorb.
 
I believe it has been done in the pre 65 scrambles world. The hypothesis being that it helps with traction and drive in the mud etc.

I wouldn’t like it, I’d be constantly thinking ‘this things only firing on one’ !!
 
Good one Fast. Thanks to the Prince of Darkness, it has been many times the brit twins have run as singles!
 
There was the Yankee Z a 500 enduro bike which had a twingle engine made by Ossa using two Ossa 250 barrels.
 
Thanks Danno, it looks like the 450 Black Bomber had the 360 crank only in their first year, 1965. An interesting read:

The 1965 444cc twin Black Bomber had double-overhead camshafts at a time when the only motorcycles so equipped were purpose-built racers. Four caged roller bearings supported the crankshaft, primary drive was spur gears, valves were seated by torsion bar valve springs, a pair of 36mm constant velocity carburetors, and the electric starter always worked. testers noted several faults, including poor rear shocks, vibration, oddly spaced gear ratios, and a dry weight of 412 pounds. http://www.motorcycleclassics.com/c...onda-cb450-black-bomber?pageid=3#PageContent3

Thanks batrider, that Ossa Yankee Z is an interesting machine: http://www.motorcyclespecs.co.za/model/Classic/ossa_yankee_500_scrambler.htm
 
Back in the late 60's and early 70's, flattrack-mad Americans were slapping any hot engine they could find into Trackmaster, Redline and other purpose-built chassis. All the British engines, twins and triples, as well as 2-stroke 3-cylinder Kawasakis and Suzukis competed on the dirt ovals Honda's 180-lb. 750 4 was tried but deemed too heavy. Tridents and Rocket 3s had some success on the Miles, but they were heavy also. Their riders usually went back to the twins on half-miles and TTs. The failed twingle experiments demonstrated that no avenue would be left unexplored. It was thought the 450 engine, with it's closely-spaced rod throws and light center crank wheel (thanks to outboard flywheels on each side) would be able to handle the excess pressure put on by both cylinders firing at once. Obviously it didn't work as well as planned.

Lots of examples here:
https://www.pinterest.com/jaygosvenor/flattrackers/
 
Last edited:
I'm sure I read somewhere about somebody firing a z1000 Kawasaki as a twin to try and gain traction on a grass tracker, would be easy to do cut and weld the cams and away you go
 
Thanks Danno, I guess being up here in the bush ridin' dirtbikes kept me from exploring the flat track scene - no wonder they called the experimental twingles as 'big bang engines'.

Thanks Biz, would a twin four be 'four-in'? The grasstrack info is also interesting: https://grassrootsmotorsports.com/forum/grm/big-bang-engine/71028/page1/

The “big bang” concept – has recently been applied by both Yamaha and Kawasaki on their inline-four MotoGP engines. Recently we have seen reports that Virgin Yamaha is using a “big bang” firing order on its Yamaha R1 race bikes in the British Superbike Championship. http://www.motorcycledaily.com/2005/04/08april05_bigbang/

This is interesting, although not motorcycle specific, there's lots of learning for me here:
EPI Inc. is a small corporation, started in 1994, which specializes in the design and development of piston engines and power transmission systems and subsystems for a wide variety of applications.
EPI has developed successful high performance engines and power transmission systems, subsystems and performance improvements for diverse applications including aircraft, helicopters, auto racing, boat racing, oil exploration, trucks and locomotives.
http://www.epi-eng.com/piston_engine_technology/engine_technology_contents.htm
 
I thought the advantage in having a twin motor is the impulses are separated so the bottom end does not get thumped so hard. Flex in the crank is still a major weakness of most twin motors. The only advantage I can see a big single having, is the way the power is put on the ground by the rear tyre. On dirt, smooth power delivery can be a disadvantage. On speedway bikes, it is common to promote slip by using trials tyres, you would never use a knobby tyre, but in motocross the power delivery is often better if it comes in strong pulses and gives more drive.
 
The advantage is intermittent traction, a seamless 'slip-and-grip' where rhe tire has time to recover repeatedly from any loss of traction compared to a smoother power pulse.
 
I've heard that tyre recovery theory applied to road racing. I don't know whether I believe it. Seems to me that racing on slick tyres is about achieving traction due to the heating caused by slip.
 
Thanks acotrel. I'm not sure about it either, but In the article noted above from 2005 by motorcycledaily.com, they refer to this interesting theory of wheelspin and rear-wheel traction control on high HP superbikes:

A standard inline-four fires its cylinders at regular intervals – one cylinder every 180 degrees of crank rotation. This creates a constant delivery of power to the rear wheel, which can make it difficult to maintain rear-tire traction, or to regain said traction once it has been lost via wheelspin. Since this effect becomes more pronounced as power output increases, it is especially noticeable in current Superbikes (many putting out 200+ horsepower) and MotoGP bikes (220-250 horsepower).


Years ago, Superbike racers discovered that it was easier to modulate the power to prevent wheelspin on the Ducati V-twins than it was to do the same on the Japanese inline-fours. This is because there is a longer interval (in terms of both time and crankshaft rotation) between cylinders firing, which gives the rear tire a “break” – time to recover traction and match its speed to that of the motorcycle.


The “big bang” engine attempts to transfer this characteristic to the inline-four by changing the firing intervals of the cylinders. By firing two cylinders close together, followed by a long break, then the other two cylinders in close succession, then another long break before the cycle begins, a “big bang” motor gives the tire some recovery time. This gives enormous benefits to rideability and tire wear.


I have not researched anything more recent to further support this theory or if the predictions in the article have been realized.
 
Electronic rider aids such as traction control, wheelie and wheelspin control may have eclipsed altered firing orders in the search for traction and tire life. A couple of years ago, Honda MotoGP teammates Dani Pedrosa and Marc Marquez were battling as they came out of the infield and onto the front straight at indy. Marquez' footpeg caught Pedrosa's wheelspin sensor wire and as Dani wisted the wick, he was immediately spit off from the unmitigated full-power drive off the corner.
 
Re;” The “big bang” engine attempts to transfer this characteristic to the inline-four by changing the firing intervals of the cylinders. By firing two cylinders close together, followed by a long break, then the other two cylinders in close succession, then another long break before the cycle begins, a “big bang” motor gives the tire some recovery time. This gives enormous benefits to rideability and tire wear.”

Also prior to the two strokes being abolished, the 500 2T were converted to “big bang” to get more tyre traction, the downside was the primary drive gear had to be replaced after every GP otherwise it would explode due to the stress.
 
You must log in or register to reply here.
Back
Top