Commando motor in solid frame

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After retiring my Commando based racer I acquired a slimeline with a Combat motor. It came with a Dunstall dual disk but I fit it out with a Triumph dual disk front end. The motor was still balanced for a Commando so it was a handful to use in anger and was not kind to the frame or rider. This was my first experience with a solid set up on a road course and it had a stock four-speed gearbox that would occasionally go to a false neutral upon downshift. Lots of things to sort out. During a race at Mid Ohio Race Course while coming down the paddock front straight I would snick it down to third and drop it into a left hander of moderate to high speed. This instance I got a false neutral and as any novice would do I snicked it down again while leaned over free wheeling......and dropped it into second!

Needless to say, I was really impressed with how that bike hobby horsed through a good portion of that turn while leaned over! I thought to myself, "my old Commando would have wound up the frame and spat me off in a heart beat". I was really impressed and had a new appreciation for the inherent stability of a motorcycle.

I am now thinking of rebuilding that slimeline and fitting it out for the street. A Commando is a great handling bike and has it's own characteristics but a Featherbed is really special to me. The Featherbed was, in part, what started me down the slippery slope of Seeley Mk2 racers. In reality, I am too big for a Seeley Mk2; a Featherbed or Commando are better fits for me.

I encourage all hard core Commando riders to try a Featherbed if you get a chance.

jseng1 said:
Commando motor in solid frame
Click to expand...
 
jseng1 said:
Commando motor in solid frame
Click to expand...

In observing Featherbed Specials of late, one thing stands out with this one: The forward weight bias afforded by the tilt of a Commando engine as opposed to an upright Atlas, Triumph Twin or even a recently featured 600cc Yamaha Inline-4. The Yamaha-motored special and the last 500 Triton I looked at appeared to have room to shift the powerplant forward quite a bit, but the opportunity wasn't taken advantage of. I know older racetrack refugees tended toward a rearward weight bias, but is there a reason for doing so when the mounting plates are custom-made and the engine location is fluid before they are carved?
 
Danno said:
I know older racetrack refugees tended toward a rearward weight bias, but is there a reason for doing so when the mounting plates are custom-made and the engine location is fluid before they are carved?
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Interesting observation. My Featherbed I was referring to above used the Converta Engine/Trans Plates which allowed a forward slant ala Commando in a Featherbed frame. I have heard from others over the years that they strived to move weight forward on vintage road racer builds (Herb Becker and others). My first hand experience on the track was to instinctively want to crawl up on front of (bias rider weight forward on) the Commando in a big way and a little less so on the Featherbed (with Converta Plates) and not too much on the Seeley Mk2. Sorry but this is as quantitative as I can get. Herb Becker moved engine mounts even further forward on the 500 USS Norton Seeley by gusseting and through bolts through the front down tubes on the Seeley Mk2 frame and that bike handled like a dream. He moved that engine about as far forward as one could possibly move it.

I vaguely remember weighing the bias on my 750 USS Norton Seeley with values around 53/47 front/rear and maybe around 50/50 with the rider in a neutral position. This build had a 16 lbs crank and Steve Maney Barrels and Cases and a TTI magnesium gear box. I recall total weight (w/o fuel) of around 285lbs but please do not hold me to any of these numbers as I have been drinking with my new Croation neighbors tonight.

For fast track work, all I have ever heard for vintage British is get mass/weight bias forward. I suppose this probably also applies to Vintage 750 Ducatis and many other vintage class bikes.
 
Danno said:
jseng1 said:
Commando motor in solid frame
Click to expand...

In observing Featherbed Specials of late, one thing stands out with this one: The forward weight bias afforded by the tilt of a Commando engine as opposed to an upright Atlas, Triumph Twin or even a recently featured 600cc Yamaha Inline-4. The Yamaha-motored special and the last 500 Triton I looked at appeared to have room to shift the powerplant forward quite a bit, but the opportunity wasn't taken advantage of. I know older racetrack refugees tended toward a rearward weight bias, but is there a reason for doing so when the mounting plates are custom-made and the engine location is fluid before they are carved?
Click to expand...

The featherbed has a long frame cradle and a short swinging arm. This means that putting the engine 'up front' (especially a compact 'unit construction' engine) creates a poor situation for the chain, as it is a very long run with a varying tension caused by the short swinging arm. Best case is that the chain will simply flap around and grind things away and wear out quickly. Worst case is a broken chain. Its also easy to get the relationship between wheel-swinging arm- gearbox sprocket spindles wrong. Doing this can mess up the handling. I know this cos I did it once and suffered bad rear end 'patter' (basically, the engine power pulses were working against the shock spring resulting in a high frequency 'patter' and this took a lot of time to find out)!

On the track, short circuit scratchers oft favour the forward engine option whereas endurance racers tended to put more emphasis on good chain run as a broken chain, or even increased pit stop time for frequent adjustment / replacement could cost you a place.

For road use I would suggest that a good chain run is far more important to usability, but a forward engine is important to looks.

So, whether you're a track racer or cafe racer, putting a relatively short engine into the relatively long featherbed frame loop is always a compromise, and that is probably why we see some where this is clearly space to put the engine more forwards.

Whatever... a well built 'classic' featherbed special still takes some beating, they just look 'right'. And anyone who's seen them on the track in modern day historic racing will confirm that they still handle brilliantly.
 
Good point on the relationship of the rear axle, swingarm spindle and counter sprocket centerlines. I can see this as being problematic with a unit construction engine as you say but in the case of a Commando with non-unit construction you have the ability to park the gear box (counter shaft) where it needs to be and park the engine (balance of weight) where it needs to be. Crank to main shaft center distances then becomes a function of clutch basket and engine sheave size and belt sizes available. I do not recall what the centers are with the Converta engine/trans plates but they worked well. The relationship between the countershaft, swingarm spindle and rear axle looked and behaved well with the Converta Plates.

As a side note, Herb Becker configured a frame (perhaps Doug McRae's Commando) where one was able to adjust the vertical position of the swingarm spindle.
 
Dances with Shrapnel said:
As a side note, Herb Becker configured a frame (perhaps Doug McRae's Commando) where one was able to adjust the vertical position of the swingarm spindle.
Click to expand...

I thought about doing that! Its really easy to do on a featherbed with those big, flat, vertical gusset plates too.

Anyway John, you surely have the honour of having the biggest Commando engine in the lightest (rigid mounted) frame award don't you?

Can you share your riding experience regarding vibes, etc?
 
Dances with Shrapnel said:
https://en.wikipedia.org/wiki/Drag_(physics)
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For motorcycle applications, there is something notably lacking in that wiki discussion.
At speeds below ~40 mph, air resistance is fairly minimal for motorcycles.

This means common motorcycle data points don't really fit those equations.
For the average motorcycles (whatever they are),
it is commonly quoted that ~10 hp is needed to do 60 mph,and ~32 hp to do 100 mph.

Compare those numbers to their car example there,
wiki said:
A car cruising on a highway at 50 mph (80 km/h) may require only 10 horsepower (7.5 kW) to overcome air drag, but that same car at 100 mph (160 km/h) requires 80 hp (60 kW)
Click to expand...
 
Here's my version of Commando in a featherbed. Actually the engine is part Commando part Atlas.

Vibration is almost non existent under 3500, but over 4000 it's noticeable. On the road I don't thrash it too much so its quite comfortable.


Commando motor in solid frame
 
Fast Eddie said:
Dances with Shrapnel said:
As a side note, Herb Becker configured a frame (perhaps Doug McRae's Commando) where one was able to adjust the vertical position of the swingarm spindle.
Click to expand...

I thought about doing that! Its really easy to do on a featherbed with those big, flat, vertical gusset plates too.
Click to expand...

Wouldn't that also make it easy to move the pivot forward and use a longer swingarm? I don't think a longer chain run is such a drawback when the pivot is kept close to the countershaft.

I just think when going to the trouble of building a special like a Triton or a Commando-engined Featherbed, forward engine placement and a longer swingarm would be fairly minor details that would produce a much better motorcycle than just tossing a motor in a frame is wasn't designed for and hoping for the best.
 
I know this is not very popular among many here, but I built a chopper of my -70 Commando once (mid 70:s). I cut the commando frame off and welded a rear end from an old BSA of some sort to it, mounted the engine in solid mounts and rode that bike a lot for 7 or 8 years. Never had any problems with vibrations, it was my back that finally gave up :( . I had the original 750 engine a few years, then it more or less blew up, so I put a 850 in it instead, worked just as great concerning vibrations.
Tommy
 
There is a frame which is usually relatively cheap when you find one. The BSA A10 frame (Gold Flash) is very much under-rated. The problem is that as standard the fork-yokes have too much offset, so if you fit a hot motor, the bike becomes scary. The sixties unit construction Triumph fork yokes fit straight in and transform the handling. I don't know how you would go for height if you fitted a commando motor. You might have to remove the motor from the frame when you wanted to take the head off. I was offered one of those frames for $200 a few years ago and I'm sorry I didn't buy it - they are not all bad. I've had a couple of Tribsas in my time and they handled better than my Triton ever did.
About the long swing arm in the featherbed frame - improving the handling by doing that is supposition - try it. The way the bike handles when accelerating out of corners is affected by the length of the bike and the way the rear suspension is set up - they change the rake.
 
Rohan said:
Dances with Shrapnel said:
https://en.wikipedia.org/wiki/Drag_(physics)
Click to expand...

For motorcycle applications, there is something notably lacking in that wiki discussion.
At speeds below ~40 mph, air resistance is fairly minimal for motorcycles.

This means common motorcycle data points don't really fit those equations.
For the average motorcycles (whatever they are),
it is commonly quoted that ~10 hp is needed to do 60 mph,and ~32 hp to do 100 mph.

Compare those numbers to their car example there,
wiki said:
A car cruising on a highway at 50 mph (80 km/h) may require only 10 horsepower (7.5 kW) to overcome air drag, but that same car at 100 mph (160 km/h) requires 80 hp (60 kW)
Click to expand...
Click to expand...

What is notably lacking regarding motorcycle applications is not in that wiki discussion (eh, know what I mean, know what I mean, nudge, nudge, know what I mean, say no more......). Unless someone is going to dispute the laws of physics or fluid dynamics, the analysis is consistent with common knowledge and practice. As an example, the material presented in the wiki link is consistent with the material presented in Tuning for Speed by Phil Irving, Sixth Edition, pg. 245.

I suggest that one or more of the numbers you claim as being commonly quoted are off. As an example, in my youth we had a two-speed mini bike with a 5 HP engine which was easily capable of +50 mph with a governor; and that is 5 HP before mechanical and rolling resistance losses (with small wide wonky tires), probably sub-optimal top gearing and aerodynamics of a medium sized refrigerator.
 
Danno said:
I just think when going to the trouble of building a special like a Triton or a Commando-engined Featherbed, forward engine placement and a longer swingarm would be fairly minor details that would produce a much better motorcycle than just tossing a motor in a frame is wasn't designed for and hoping for the best.
Click to expand...

Fair enough. With a Unit Triumph engine/gearbox you are somewhat locked into fish or cut bait so there is a compromise but with a non-unit Commando you have options for the location of the gearbox as well as the engine. As far as a Featherbed swingarm length, I am not sure it has been established definitively that it is too short.
 
I am not sure about the size of the Featherbed swing arm, I run the stock swing arm and my 850 sit forward and my motor to frame is well balanced, if you put a longer swing arm on then you be changing the whole design of the Featherbed as well as the handling, I get very long life out of my rear chains so have never had any problems with broken or over streched chains, my last chain lasted well over 40k and I am still running my second rear sprocket, not bad for my Featherbed as I have done well over 140k in the 35 years of it being built.
When I built it up in my younger days I didn't use sicence or gave any throught about how to mount it all I knew I wanted the motor tiliting forward the same as when in the Commando, wanted it sitting as low as I could get it and built the engine mounts to match, what ever I did I got it right the first time and its been set up that way ever since, I am running the Commando front end, with Commando wheels front and rear 19" and have not notice any conserns with the handling it turns into corners quickly and when I put the power down when in a corner it pushes it out of the corners with ease, sometimes I got to look back to see if I did go through that last corner, it so hard to desribe the way it handles and the lightness of the whole bike and having a hot motor that was built for the Featherbed frame its such a perfect match and one thing for sure you have to have a strong head stay and where I have my engine mounts to frame mounts I put cube steel spacers in between so you can't over tighten the bolts, I also run a large mounting bolt and spacers from the middle part of the frame where the the big mounts are throught the engine plates with spacers and it seems to tighten every thing up perfect.

Ashley
 
The beauty of the commando engine in the featherbed frame is the weight distribution would be better than with other motors. If there is a lot of weight on the front, the featherbed bike always feels less vague in corners. So you are more confident about what it is going to do when you push it harder.
 
Dances with Shrapnel said:
https://en.wikipedia.org/wiki/Drag_(physics)
Click to expand...

Dances with Shrapnel said:
What is notably lacking regarding motorcycle applications is not in that wiki discussion (eh, know what I mean, know what I mean, nudge, nudge, know what I mean, say no more......). Unless someone is going to dispute the laws of physics or fluid dynamics, the analysis is consistent with common knowledge and practice. As an example, the material presented in the wiki link is consistent with the material presented in Tuning for Speed by Phil Irving, Sixth Edition, pg. 245.

I suggest that one or more of the numbers you claim as being commonly quoted are off. As an example, in my youth we had a two-speed mini bike with a 5 HP engine which was easily capable of +50 mph with a governor; and that is 5 HP before mechanical and rolling resistance losses (with small wide wonky tires), probably sub-optimal top gearing and aerodynamics of a medium sized refrigerator.
Click to expand...

Nope, no cigar.
And it certainly doesn't take 80 hp for a motorcycle to do the ton.
I have a baby Villiers with a claimed 3hp, and it will (supposedly) do 45 mph.

If you read that wiki link you gave, then double the speed requires 8 times the horsepower.
As I quoted previously, in shorthand, thats horsepower cubed. :!: :!:
My apologies if that was too shorthand for you...

The common examples oft quoted are rather based on solid examples.
Both the Norton 16H and BSA M20 had approx 10 hp, or slightly more, and were good for 64 and 62 mph respectively. Since the WW2 Brit Army required those numbers carved in stone, they are well tried and tested.
And BSA Goldstars of immortal fame each came with its own dyno certificate (which the owner received), and anything north of early 30's hp was good for 100 mph. At Brooklands even, before the war, so again well tested. Cammy Nortons claimed 32 hp for the Inter, although you have to remove the muffler and adjust the cam overlap to get your ton.

BTW, low 30s hp out of a hotrod prewar 350 goldie (ancestor) was a stronger stage of tune than a Combat Commando - if a Combat even gave its claimed 65 hp. Per litre of course....
 
OK, time to break out the chalk on the sidewalk. If a vehicle requires 10 Hp at X mph to overcome wind resistance, then it must overcome (8 X 10) Hp of wind-related power at 2X; quite simple math.
It really looks like you are confusing a motorcycle with a car or perhaps you overlooked the drag coefficient (Cd) or perhaps you overlooked the cross-sectional area but for certain, you are confusing a simple concept for others.

The Coefficient of drag (Cd) and cross-sectional Area are quite different between a motorcycle and car, don't you think; or are you also disputing that????????

Do the math and you will see; Phil Irving and others have, and have done quite well at explaining things - back to the books laddie!

The bottom line is that power to overcome wind resistance is proportional to the cube of the speed, and not the square of the speed as some poor soul had mistakenly stated early on in this thread.
 
Rohan said:
And it certainly doesn't take 80 hp for a motorcycle to do the ton.
Click to expand...
Nobody is stating that. Your reading skills are atrocious. The example cites a car, not a motorcycle, you know, four wheels instead of two. :lol:
Rohan said:
Lets not beat around the bush, air resistance rises with the cube of the speed.
Click to expand...
Then you state:
Rohan said:
If you read that wiki link you gave, then double the speed requires 8 times the horsepower.
As I quoted previously, in shorthand, thats horsepower cubed. :!: :!:
Click to expand...
So which quote of yours is it????? Is it, force (resistance) is proportional to the cube of the speed or power is proportional to the cube of the speed?
Force is proportional to the square of the speed.
Power is proportional to the cube of the speed.
I feel like I am pounding sand into someones ear and sadly watching it dribble out the other.
 
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