http://corpsesfromhell.blogspot.com/2012/02/twin-engined-bsa-m20-vampire.html

Looks like a bit of fun, but almost no gain considering power to weight, ive got a bike mag somewhere with a similar bike, 2 m21 motors both bored to take Jaguar pistons (from a 4.2L 6cyldr engine) capacity was 1500cc & he had both pots firing at the same time.
In the same article another chap had engineered a tasty 1000cc V Twin from B50 parts.

I remember that article Fred..The guy worked at Bovington Tank Museum (appropriately!) and bizarrely timed both engines to fire together making effectively a 1500cc single!
A lot of thought has gone into the layout of this bike but with a total weight that must be around 550-575lbs it does seem a bit pointless. No more so than me trying to build a 'fast' M20 though I suppose...Sometimes you just have to do these things and I guess we shouldn't get too focused on logic, value and all that stuff..
I dithered for years over whether it was 'sensible' to pour a few thousand pounds into the M20 sprinter to create a bike that ultimately nobody will really want and I don't have a use for other than having a tilt at a rather 'odd' speed record...
Finally I decided that just wanting to do it was a good enough reason..and the results of that line of thinking do make the world more interesting..Ian

email (option): ian@wright52.plus.com

Just out of interest, what is the top speed or 0-60mph of your 'fast' M20 Ian?

I'll let you know when it's finished Bill.. ...The fastest recorded M20 built to date (normally aspirated) did 112mph over a flying quarter (Pat Jeal)...The UK record for a single cylinder sidevalve over the same distance is held by a Norton 16H at 116mph (Nigel Fox)...I'd like to get to the other side of those two...Ian

email (option): ian@wright52.plus.com

It most certainly is all about the Challenge.

Hell! That's some going for an old M20. You'll have to keep us up to speed with the build (no pun intended!).

You might need a full dustbin type fairing to reach these speeds, also the sprint clubs don't run flying 1/4 or kilo anymore (too much health & safety risk with the modern bikes) so it will be difficult to get a venue.
But these records Pat Jeal and I set were only one way anyway - get some sort of proper timing , maybe a run at Pendine Sands in Wales the locals will love it - so best of luck to you !

email (option): nigel.fox9@btinternet.com

A friend of mine used one of the runways at Speke airport, I think he did it on a weekday when it was quiet and he paid to use it, I don't think it was expensive, but possibly you could use a surviving runway of a WW2 airfield if there is any left that are long enough.

email (option): davmax@ntlworld.com

THE Nigel Fox ?

Hi Nigel,see Ian's post "Im putting my M20 in the dustbin" he is doing just that
Cheers Rick

email (option): richardholt@rocketmail.com

Hi Nigel...Sorry to hear H&S paranoia may prevent an attempt on these records in the same way that they were done originally....The problem is there are a limited number of suitable venues...I may try the NSA when they are running an event at Elvington....Ian

email (option): ian@wright52.plus.com

almost no gain considering power to weight?

Before: 12 hp ÷ (M20 complete bike + rider)
After: 24 hp ÷ (M20 complete bike + rider + 2nd engine)

Huge advantage. Power is more than doubled because parasitic driveline drag is less than double.

To balance out (more advantage), the 2nd engine would have to weight as much as the entire original bike and rider.

The usual coupling of 2 singles is both at TDC with one firing and one on overlap.

email (option): sales@victorylibrary.com

Well a BSA G14 1000 Vtwin, which is a bit like 2 M20's inline albeit with a shared crank has fairly dull performance & consistently overheating rear cylinder.
So i suppose it depends what constitutes "gain" to you, to me I'm looking for good acceleration, good handling & reasonable economy so my hack bike has one efficient engine ( an M24) rather than two (fairly inefficient) M20 engines.
Adding an entire extra engine just for 12hp extra is a terrible pay off.
Brakes will suffer & so will suspension & if left as they are count as a loss.
Your calculation left alot out, like the extra weight of the longer engine cradle tubes & extra plates, but most important the extra weight of the fact they all need to be more substantial than before.

All of those things are quickly discovered by those companies who build stretched limousines, ie a horrible amount of extra strengthening is needed just to maintain original structural integrity of the chassis when you stretch out & add weight & they need to ad extra power simply to cope with that extra weight.

The chap that did the double engined M21 in 1984 had problems mounting the front Carb & had clutch problems as well, mainly because he realised the project was only really viable if he upped the capacity of each cylinder to 772cc.
If as in your example you just use standard output M20 engines then lots of little things keep chipping away at the expected power & weight figures to result it a machine with .... well, almost no gain : D

My "guesstimate" is that you would get the equivalent "feel" of a 19hp bike when you actually rode it, with underperforming brakes, suspension & handling.

It's not a brilliant plan I wouldn't have thought as the M20 engine isn't the best candidate by far for such a project..Better to have simply fitted a B33 engine which is 23 BHP....
It's all rather like the army reconditioned M20 engine I bought off a chap a few years back who had originally purchased it to put into a home built hovercraft...I think the project was doomed at the design stage... ...Ian

email (option): ian@wright52.plus.com

It 'IS' just about doing something, because you can! However pointless. Some people do jigsaw puzzles?? others climb Mount Everest????? It's more about the challenge than the end result to my mind. Ron

email (option): ronpier@talk21.com

Getting an M20 powered hovercraft to leave the ground would certainly meet the 'challenge' part... ..Ian

email (option): ian@wright52.plus.com

Bang on!

I was tempted to correct your remarks, but you've revealed enough of your engineering competence to render such effort pointless.

Still curious - what is your regular line of employment?

My usual work: http://victorylibrary.com/brit/brit-tech.htm

email (option): sales@victorylibrary.com

"I was tempted to correct your remarks, but you've revealed enough of your engineering competence to render such effort pointless".

I'm also curious Panic! Which one of us was your above remark aimed at?
Ron

email (option): ronpier@talk21.com

I think it was aimed at me : /

My employment until very recently was running the ill fated "Twin M20 engined hovercraft company" :D

I will take on board you veiws on my engineering competence but can assure you if i fell into difficulty in the water (not a good swimmer) i would rather someone who's done alot of swimming jump in to help than someone who simply published a swimming article.
: )

Hi,
Trying to follow the theme !
Power to weight ratio doesn't matter at all when you have a long run !
Power gives you the speed !
If 24hp gives 95mph,48hp will give 119mph !(unfaired)
Bhp needed is cube of speed !
All the best
To all !

email (option): nigel.fox8@btinternet.com

The above is all nonsense.

Fastest speed of an M20 is obtaind by chucking it out the back of a Horsa without a parachute.


Welbikes went nearly as fast.

get those slide rules out, what would be the terminal speed of an M20 from a set exit altitude? say 1320 feet.

It gives a whole new aspect to 'a flying 1/4 mile'.

email (option): deadsheds@yahoo.com

here is the Wikipadia article on Terminal Velocity:

http://en.wikipedia.org/wiki/Terminal_velocity

Cheers,

Lex

email (option): welbike(at)welbike.net

who gives a monkeys about power to weight and all that b....cks I think its a great machine.

Yes .. why not strap an anvil on it as well. :D

I'd like to know what happened to the "Heemskerk" ....
http://i556.photobucket.com/albums/ss3/Bungitonhere/IMAG1082.jpg

I've thought about this some more and changed my mind...It won't corner very well as the frame has been extended by at least a foot to get the second engine in...It must weigh in the region of 600lbs...The additional engine/magdyno alone weighs in at approx. 1cwt...
If everything is set up well and the strange porting arrangements work as well as the original it will be making approx. 26BHP...Slightly more than a 23BHP rigid B33 that weighs around 250lbs less...

It's a good example of what can be produced if your not really thinking straight or aren't concerned about the usefulness of the end product...
A bit like a custom bike with 1" ground clearance or any of the other dumb things they do to make motorcycles impractical/unusable....

The build standard and finish is also poor and not a good example of well thought out and executed engineering....

Personally I can find little to recommend it after looking in more detail and thinking about it....It reflects an unfortunate current trend for lashing things together without too much consideration for the quality of the end result and then elevating them to the status of Art, Genius and Motorcycle all rolled into one....Ian

email (option): ian@wright52.plus.com

Hi,now come on Ian,at least he thought a little about it,a bit like this guy
who thought a lot about it,enjoy
http://youtu.be/Nzx8Y--UNto

cheers Rick

email (option): richardholt@rocketmail.com

And then,along comes a showoff,smoking the bloody place out
http://youtu.be/6ratfuML9QA
cheers Rick

email (option): richardholt@rocketmail.com