Commando engine in Featherbed

Hello guys,
one semply question.
Do you have driven a special motorcycle with Featherbed frame and Commando engine?
I attend your impressions.
Thanks.
Gian

You would get more responses quicker if the title of your thread was "Commando engine in Featherbed?"

I believe you can edit the title yourself...

Folklore is that if you fit the best motor into the best frame, you get the best bike. If you fit anything other than a Manx motor into a featherbed frame, you do not get the best bike.

Yes I used to have one
A big valve 750 powermax 10.25 -1 pistons / lightened balanced crank 3s cam lightened rockers
Ported head etc etc in a wideline it was horrible!!
The reason being it vibrated so badly
I had the crank balanced to atlas spec but because I had the engine leaning forward the balance factor was wrong!
Also I had made the engine plates out of stainless steel that I mirror polished
Looking back now it was a bit of a recipe for disaster
The crank was so light with such high compression the bike would never idle
The stainless was so slippery it couldn't hold the engine tight ,it used to shake the float bowls off the carbs
Blew all the bulbs , split the battery tray, split the petrol tank it was the only Norton I'd owned that used to shake out the rocker spindle plate bolts!!
It was quick though with superb handling, it had a tickle TLS on the front with racing greens
I was around 22 years old at the time if I did it again I'd try and get the crank balance right
Or just use a commando frame
Cheers

Don't listen to acotrel as fitting a Commando motor into a Featherbed frame if done right will give you a great handling, very light and a very torque motorcycle, I built mine way back in the early 80s and still own and ride it to this day, but the most important thing is which way you go, I did mine on a low budget but worked well for me using the right people at the time, my crank was balanced for the Featherbed frame by a old gentleman at 72% this got rid of most of the vibrations and it was a pretty smooth bike to ride, then there is the Cam you want to use, my stock cam was built up to Combat specs SS or 2S profile, then there was the head work as well involved and jetting of the carbies.
But today there are so many other thing you can do that I didn't have when building my hotrod Commando/Featherbed there are Jim's lighter pistons, conrods and valve train that makes the job worth while but you have to open your wallet up.
My Commando/Featherbed was a everyday rider for most of its life, it is always rode hard and has never let me down, except for a broken chain, in the last 7 years I spent the money improving it that I didn't have in my younger days upgraded the internals to the Commando front end, different carbies, a Joe Hunt Maggie, alloy round oil tank, better front brakes, but its still the same bike with a few improvement to make it handle even better and stop quicker, I still running the same cam, crank and still have the orginal valves in the motor, so what I have done to it has worked very well for me and I still take it out for the day, still give it heaps and I just love riding it, its still my hotrod Norton, but I also have 2 modren Triumph Thruxtons in my collection one 900 and my new 1200, but the Norton Featherbed is my favoiurite to ride and it still give the modern bikes a good run in the twisties.
I some time got to look back to the corners I just pushed it through to see if I did go come off them it feels so stable.
My Norton is semi retired now just like its owner but its still going strong but is showing its age, has paint scratches, dents in the tank and paint pealing off, but its the way I like it as its been well ridden all it like and it shows it very proudly.
Hope this helps.

Ashley

baz said:

Yes I used to have one
A big valve 750 powermax 10.25 -1 pistons / lightened balanced crank 3s cam lightened rockers
Ported head etc etc in a wideline it was horrible!!
The reason being it vibrated so badly
I had the crank balanced to atlas spec but because I had the engine leaning forward the balance factor was wrong!
Also I had made the engine plates out of stainless steel that I mirror polished
Looking back now it was a bit of a recipe for disaster
The crank was so light with such high compression the bike would never idle
The stainless was so slippery it couldn't hold the engine tight ,it used to shake the float bowls off the carbs
Blew all the bulbs , split the battery tray, split the petrol tank it was the only Norton I'd owned that used to shake out the rocker spindle plate bolts!!
It was quick though with superb handling, it had a tickle TLS on the front with racing greens
I was around 22 years old at the time if I did it again I'd try and get the crank balance right
Or just use a commando frame
Cheers

Click to expand...

Balancing the crank to Atlas specs, 750 Atlas motors were prone to bad vibrations, I have my 850 motor tilted in the Featherbed , frame, I use 5mm steel engine plates, my crank was only balance and not lighten or polished, the head was only ported and opened up for better fuel flow and breathing, I still run my orginal light bulb in the head light and the orginal 57 Wideline tank, so if done right they will run very smoothly, I was in my early 20s when I built it and I am now 60 there was no internet back then and relied on people who knew what they were talking about.
I was lucky a mate who got me into Nortons when I was 17 had a hot 750 Commando in a Wideline frame but his was set up wrong and his crank was over lighten and his motor wasn't tilted, so I learned off his mistakes, I also brought my Featherbed frame off him in 1979.

Ashley

Baz
My Cafe Atlas (ex-racebike). Used to vibrate so badly that the mirrors would fall off. The foot peg rubbers would disappear. And if you revved it up to redline at night the lightbulb filaments would break and you were riding home in the dark. It didn't matter what balance factor was used - I tried them all. Its simply because its a side by side single and the reciprocating weight shakes everything to pieces. The short rods just make everything worse. That's why I came up with the lightweight pistons and longer rods (with ultralight components for solid frames like the Atlas). We're talking about 1/3 reduction in reciprocating weight plus the smoothing effect of longer rods (think about it). Nothing falls off anymore and its comfortable to ride. It went from torture to pleasure and that's why I'm still in business.

I didn't do this just or kicks - it was a matter of survival.

Not featherbed, but for over 30 years, I have an 850 Commando engine in my N15 (Matchless frame ).
For 2 years now with lighter JS pistons and longer rods.
Balance factor around 68– 70 % dry.
Footrests are rubber mounted, connected below the engine and are completely vibration free.
Vibration dampers inside the handlebars ( among countless other mods ..)
It still vibrates some, but overall it is very comfortable and my favorite traveling bike.

By changing the balance factor, you can usually put the vibration at the revs where you want it to be. At 72% BF and rigidly mounted motor, a Commando engine is very smooth at 7000 RPM, but at 3000 RPM, the bike will physically rock backwards and forwards. My friend has a 650cc featherbed Triton and is building a 750cc motor for it. Even with the changed balance factor, the motor will not rev over 4000 RPM, probably because of the way the vibration causes the rubber mounted carbs to flood. Below 4000RPM, it has massive torque, but above that - nothing. It is not jetting or timing, because he has been racing his 650 for several decades.

gearing makes a big diff. I'm on and off the freeway and live in the country so I can use 4 to 1 overall gearing.

Ludwig, do you run a standard AMC 4 speed gearbox or is that modified as well?
Nice looking bike

Well I must have a freak of a bike because mine is very smooth riding around town and its best cruising speed on the highway is between 65 to 90 MPH, yes it does have its moment with vibrations at some RPMs but most of the time its smooth as, I have only lost 2 nuts off it in 37 years of riding it and its wasn't my nuts lol, one exhaust muffler mount nut and the top gear box mount nut as for my foot pegs they are smooth all the time, my steel handle bars use to get some vibrations in the ends from certain RPMs but changing to 6mm wall alloy Rental bars fixed that problem, I have blown a few tail light bulbs but I fixed that by putting some elec tape around the edge of the bulb and metal part of the bulb and haven't replace the bulb since

Ashley

I don't understand how you get away with it Ashley. There are plenty of others who don't. One thing that helps that I know of is a heavy crank. The thing I hated the most was blowing the head lamp at night then having to drive home in the dark. This was an ex-race Atlas with stock rods and pistons and I used to revv it out without mercy. Somewhere I switched to a Halogen head lamp and an LED tail light - that and the lighter pistons solved the problem.

acotrel said:

By changing the balance factor, you can usually put the vibration at the revs where you want it to be. At 72% BF and rigidly mounted motor, a Commando engine is very smooth at 7000 RPM, but at 3000 RPM, the bike will physically rock backwards and forwards. My friend has a 650cc featherbed Triton and is building a 750cc motor for it. Even with the changed balance factor, the motor will not rev over 4000 RPM, probably because of the way the vibration causes the rubber mounted carbs to flood. Below 4000RPM, it has massive torque, but above that - nothing. It is not jetting or timing, because he has been racing his 650 for several decades.

Click to expand...

I think you're quite wrong there Alan.
Balance factor merely trades off vertical imbalance for horizontal imbalance - this rpm link is just a furphy.
The thing that will shift the resonant vibration with rpm is the stiffness of chassis and fixings. The lighter/stiffer the fixings (including engine/gearbox mounting plates) the higher the resonant frequency will be. the looser/heavier they are, the lower the resonant frequency will be. One caveat though - if your resonant frequency is low, say 2000rpm, there will be a second harmonic at 4000rpm and so on. So... stiffer and lighter is better.
You cannot, however, shift the resonant frequency by altering the balance factor - it's just an old wives tale.

Hi Ludwig,
Before you went with JS pistons and rods, was it a comfortable ride or did you suffer for 28 years?

Ed

ludwig said:

Not featherbed, but for over 30 years, I have an 850 Commando engine in my N15 (Matchless frame ).
For 2 years now with lighter JS pistons and longer rods.
Balance factor around 68– 70 % dry.

Click to expand...

jseng1 said:

I don't understand how you get away with it Ashley. There are plenty of others who don't. One thing that helps that I know of is a heavy crank. The thing I hated the most was blowing the head lamp at night then having to drive home in the dark. This was an ex-race Atlas with stock rods and pistons and I used to revv it out without mercy. Somewhere I switched to a Halogen head lamp and an LED tail light - that and the lighter pistons solved the problem.

Click to expand...

Like I say Jim my Norton must be a freak as it has always worked well, I built I in the early 80s and on the road in 82 and its been on the road all that time mostly a everyday ride except for the usual pull down times and added mods and its major rebuild just over 7 years ago, but other than that its always been on the road, its never let me down and its always ridden hard and I push it to its limits quite a bit, but the last 5 years its semi retired and only ridden when I feel like it now as most of my ride time now is on the 1200 Thruxton S as well my long distant riding, but when out on the 850 Featherbed I have a lot of fun with it.

Ashley

Mine is part Commando part Atlas in a slimline. I have the engine tilted forward ( I thought I had bought a Commando engine!!!).

I think ( it's a long time ago) I had the crank balanced to 72%. It is very smooth up to about 3500 then vibrates quite a lot from 3500 to about 4500 and smooths out a bit up to 7000.

Unfortunately the highway speed limit is about 3800 with my current gearing so I plan to raise the gearing to fix that.

I never noticed vibration when I was racing it, but sitting for long periods on a highway ( OK, more than about 5 minutes) it get uncomfortable.

ludwig said:

The lighter pistons are an improvement, but it was pretty comfortable before.
I don't know if it is feasible on a featherbed frame, but insulating the footrests from vibration makes a world of difference.

Click to expand...

A good idea. My 650ss has very little vibration coming thru the bars, mirrors are clear at 70 but the footrest do buzz annoyingly at this speed.
Going to have a look at doing a mini isolastic there.

Glen

Ludwig,
That is a lovely looking bike, but one thing intrigues me; how did you get the Norton script on the timing cover level with the Commando engine upright?

Martyn.