Surprising engine modification.

M

Murray B

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Nov 29, 2011
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Posted on the site http://www.thefang.co.uk/parallel.htm

“Mick Hand's 'Little David'. Based on the 1960's Honda CB72 and 20 years in development, this bike still holds the 250cc world record at 9.8secs! Crankshaft was modified to 360° configuration and primary drive converted to gear rather than chain...Compression ratio was 6.5:1 and boost from the Marshal cabin blower over 30 p.s.i...”

Any Honda twin I have ever seen had a 180° configuration. What advantage would there be to changing it to 360° like a British twin?
 
The domestic versions of the Hawk and Scrambler, sold in japan, could be had with 360° cranks just like the single carb Dream series. They used a single of points and a double-ended coil along with the 360° crank but were otherwise quite similar to the ones sold in the US. The smaller Hondas (CA 92/95, CB/CL 160, CB/CL 175) all had 360³ cranks.
 
mikeinidaho said:
The domestic versions of the Hawk and Scrambler, sold in japan, could be had with 360° cranks just like the single carb Dream series. They used a single of points and a double-ended coil along with the 360° crank but were otherwise quite similar to the ones sold in the US. The smaller Hondas (CA 92/95, CB/CL 160, CB/CL 175) all had 360³ cranks.
Click to expand...

Thanks for the information, mikeinidaho, but I was interested in why Mick Hand chose to modify the crank to 360°. It is clear that the fellow is some kind of mechanical genius and it would be great to know what advantages the modification gave.
 
Most of the export bikes were 180°, the CB77, 125s, 175s 250s and 450 included - you can pick it in the offbeat exhaust note. Its in the spec sheets for them too, google. With the head off, one piston is down a hole....

Supercharging a 180 twin is notoriously difficult, the longer dwell on one cylinder plays havoc with the mixture strength, so its very likely to be so it evenly feeds both cylinders.
Must be making serious horsepower with those times and that boost....
 
Asked on mc-engine list to be told as Rohan says = equal time of blower feed to each jug, other wise takes a huge air plenum not to starve some jugs or over feed others.
 
Thanks for the information guys but he could have used two smaller superchargers or one with a split chamber rather than making his own crankshaft. Building parts like that from scratch can't be easy.

What I am wondering is if the sideways vibration from the rocking moment of a 180° crankshaft would make the vehicle unstable at high speeds? My uncle had a Honda 450 Hellcat that went like a bat but wiggled like a fish at high speed. That sort of wobble is the last thing the rider would need on a drag bike going around 100 mph.

Anyway, the answer is probably not obvious so I will try to contact Mike Hand and ask him.
 
Supercharging a single is reportedly even more difficult than a twin, of any variety, so twin superchargers is not the way to go. The plenum has to be HUGE, and a backfire is not good....

Article on race CB450 Honda - they can be made to go.
Engine design has nothing much to do with handling, it seems, nothing a new frame won't cure....

http://www.motorsportretro.com/2011/11/drixton-honda/
 
I see this is quite an old subject but I have only just come across it whilst just chilling. I have been a friend of Micks for nearly 40 years and were part of the same dragrace team during the early, mid seventies. As you say Little David was based on the Honda CB72 Dream bike from the mid 60's. The crank was 180 degree but was bolt together. To use one blower only Mick unbolted the crank, made bigger stronger bolts and reassembled it at 360 formation. This involved him in making new cams too. Subsequently the power of the motor decreed the primary chain and clutch to be not up to the job so Mick made a new bigger clutch and made it gear drive. This in turn meant the motor had to run in the opposite direction to drive the bike forward, so he had to make another set of cams to get the valve timing right. The list of mods Mick made to the bike is endless but running as a 250 it went high nines, as a 330 it went 9.3/9.4 and at its biggest 360cc 9.08/157. Mick is now 65 yrs old but is heavily involved in the design, build and development of the words first compound turbo drag bike "Storm". Its quite a challenge but I'm sure the team will get the results they want. Keith Parnell
 
Good to hear from you on this Keith, interesting info.
Running the engine backwards for gear drive, and new cams, now that shows determination !
Cheers.
 
Forgot to mention Mick used 68 degrees fixed ignition advance with 85% nitro/meth mix. I rode 250cc Little David at a meeting at Greenham Common, went 10.1. Mick hadn't done a nine at that time, made him rush to the timing hut to get the result!
 
Rohan said:
Supercharging a single is reportedly even more difficult than a twin, of any variety, so twin superchargers is not the way to go. The plenum has to be HUGE, and a backfire is not good....

Here’s one man who could do it, Brian Chapman on his Vincent Comet powered Mighty Mouse, he got it into the eights, 8.96; producing an estimated 125bhp at 9000rpm and returning a fuel consumption of .....only .......four miles per gallon :!:

http://www.youtube.com/watch?v=nexai2NkM9s

http://www.trakbytes.co.uk/mouse.html
Click to expand...
 
Interesting. He certainly nailed it, then. Disappointing there are no large photos, to see how the supercharging is rigged. Or any discussion of the cams used.

4 mpg. Lets see, @ 1/4 mile, thats ~16 runs per gallon.
Half a pint of methanol/nitro per run.
Some model aircraft use more than that...

Somewhere the other day was mentioned that the big top fuelers require 1500 bhp just to turn their (massive) superchargers. Power to burn, literally...

P.S. Chuckled at "tilt the motor forwards by 15 degrees. The motor itself was used as a stressed member". Anyone looked how a Comet is, standard ?
 
Rohan said:
Interesting. He certainly nailed it, then. Disappointing there are no large photos, to see how the supercharging is rigged. Or any discussion of the cams used.

4 mpg. Lets see, @ 1/4 mile, thats ~16 runs per gallon.
Half a pint of methanol/nitro per run.
Some model aircraft use more than that...

Somewhere the other day was mentioned that the big top fuelers require 1500 bhp just to turn their (massive) superchargers. Power to burn, literally...

P.S. Chuckled at "tilt the motor forwards by 15 degrees. The motor itself was used as a stressed member". Anyone looked how a Comet is, standard ?
Click to expand...

From what I remember reading about the Mighty Mouse years ago, Brian made the cams in his workshop; it took him 2 or 3 attempts to get it right for this engine.
 

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