Commando engine in Featherbed

gtiller said:

Wow - this has gone wildly off topic!

I was watching this with interest until the Triumph and Harley engines paid a visit to the post.

I am stalled on my commando engine/featherbed project due to lack of funds.

@baz a good question regarding the headstock.

Here's what we have done on my project:

View attachment 11803

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Your headstay looks pretty strong as they must be, when I first built mine the biggest advice I got from people I talked to was the headstay has to be strong, I made mine out of the same size plate as my engine mounts 5mm plate 2 bolt at the top of the headstock and 1 bolt on the top cross member on the frame and the 3 allen head bolts on top of the head and is very rigid. a flimsy headstay will over time crack the frame down tubes near the headstock.

Gian the OP has not commented since he has started this thread and his reason whether he is thinking about building a Commando/Featherbed or just toying with the idea, or he's been put off by all the other motors been tossed around etc.

Another thing as well a Featherbed frame and swing arm is shorter than a Commando frame and swing arm so shorter wheel base, my Wideline runs stock Commando hubs laced to 19" Akront alloy rims and my Slimeline has 18" alloy rims and with stock Roadholder front end.

Ashley

Well, if money is no object, why not re-phase the crank?

I wonder if anyone has simply tried "clocking" a Commando crank using existing bolt holes in a different alignment?

I don't even know if the holes are evenly spaced (why WOULDN'T they be?)

Who knows, maybe there's a combination that is close enough to work with minor flywheel balancing and a crank-triggered ignition...

@baz yes, it’s rigidly mounted.

A few people were trying to talk me into doing a featherlastic, but I couldn’t see the point. To me, it kinda defeated the object of using a featherbed frame in the first place.

It’s a Combat engine which we’ve tweaked (PW3 cam, Maney barrel and pistons, polished internals etc)
I have a Fullauto head, which will go on eventually, but I want to get Jim to play with it when funds allow from my side.
I have the balance factor at 75% - time will tell if that was a good choice or not!

@ashman I went for 19 inch wheel on the front, 18 inch on the back - the tyre circumferences are nigh on the same, I did it purely for tyre choice.
Commando hubs front and rear (MK3)
I have Manx stanchions, Molnar external progressive springs and one of JRB’s Manx Lansdowne kits for the front end.

gtiller said:

@baz yes, it’s rigidly mounted.

A few people were trying to talk me into doing a featherlastic, but I couldn’t see the point. To me, it kinda defeated the object of using a featherbed frame in the first place.

It’s a Combat engine which we’ve tweaked (PW3 cam, Maney barrel and pistons, polished internals etc)
I have a Fullauto head, which will go on eventually, but I want to get Jim to play with it when funds allow from my side.
I have the balance factor at 75% - time will tell if that was a good choice or not!

@ashman I went for 19 inch wheel on the front, 18 inch on the back - the tyre circumferences are nigh on the same, I did it purely for tyre choice.
Commando hubs front and rear (MK3)
I have Manx stanchions, Molnar external progressive springs and one of JRB’s Manx Lansdowne kits for the front end.

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Very nice set up with your motor, my 850 has been built close to Combat specs as my workshop manual that I brought way back in 77 had at the end a high performance section on the Commandos stage one was for road and stage two was for full race set up, it told what cams to run on both stages as well what to do with the piston tops for valve cut a ways as well what work was needed for the head of both stages, from porting and valve angles to what jets for the carbies, even to the point of cutting slots in the side covers for more air to get around the oil tank to running a Lochart oil cooler, to even putting a supercharge on them, at the time was a lot of good information that helped me out, at that time there was not many cam profiles around and Ivan Tighe in Brisbane made cams etc and had the 2S cam profile and built up my stock cam to Combat specs, he was also the man that put me onto the crank balancer who was just down the road from his workshop, both these old gentlemen be both long gone now as they were in their late 60s back in 81 when I started on my build.
At the time it cost me $47 for the cam build up and grind and $45 to get the crank balanced for the Featherbed frame, at the time my only transport was a 125 Suzie dirt bike and carried my crank and all that had to go with it in a backpack hanging off my shoulders and had to travel over the other side of Brisbane, bit of a back breaker lol.

Ashley

Not sure about your 75% balance factor
I can remember back in the day they used to recommend 72% in a shimmed tight commando proddy racer

@baz agreed - that was the risky bit.

There were so many different opinions ranging from Mick Hemmings 84 (his tweaked 750 in a Slimline) through to Maney's 75 (his spec 750 mounted rigidly)

I guess i'll find out one day!

If I recall correctly, in later years, Maney bumped his recommendation up to 78%. More significant is that the recommendation was for a race engine in a Seeley Mk2 frame.

@Dances with Shrapnel yes - 78% is his recommendation for 750 short stroke as well as 920 race engines in Seeley frames and similar.

His recommendation to me was to stick to 75% for a "warm" 750 in a featherbed.

...it's done now, so we'll see if it shakes itself to bits in due course.

Can't be any worse than an Atlas

The way to determine the best balance factor is to use a scratch tool - sharpen a wire or thin shaft to a needle point and mount it to a heavy weight on a stand (if you want to get fancy you can have the wire slide in and out of a heavy tube in a precise manner). Securely tape a piece of polished sheet metal to the middle of the timing cover. Rev your bike to 4000 or 6000 RPM or wherever you want to check it. LIGHTLY AND MOMENTARILY touch the needle point to the polished sheet metal (this takes practice - use a helper to tap the sliding needle point or try tilting the running bike MOMENTARILY into the scratch tool). Repeat in several different places to get a data base. Look at the scratch marks under a microscope. It will probably be an oval shape.

If the oval is stretched front to rear then the balance factor is too high. If its stretched top to bottom then the balance factor is to low. Everything else is just guesswork. If you error then error as little as possible on the high side. Always calculate in "wet" specs (oil in crank). Tell us what you find.

There is no perfect balance to keep an Atlas from buzzing your brains out because the Norton twin is inherently out of balance somewhere throughout its crank rotation. The only solution is to solve the problem at its source and reduce the reciprocating weight (pistons, pins, small end of rod).

gtiller said:

@baz yes, it’s rigidly mounted.

A few people were trying to talk me into doing a featherlastic, but I couldn’t see the point. To me, it kinda defeated the object of using a featherbed frame in the first place.

It’s a Combat engine which we’ve tweaked (PW3 cam, Maney barrel and pistons, polished internals etc)
I have a Fullauto head, which will go on eventually, but I want to get Jim to play with it when funds allow from my side.
I have the balance factor at 75% - time will tell if that was a good choice or not!

@ashman I went for 19 inch wheel on the front, 18 inch on the back - the tyre circumferences are nigh on the same, I did it purely for tyre choice.
Commando hubs front and rear (MK3)
I have Manx stanchions, Molnar external progressive springs and one of JRB’s Manx Lansdowne kits for the front end.

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If I had the frame, gearbox and the motor, I would build the bike. If I was starting from scratch, I would not. There are better ways to go. A BSA A10 frame with unit Triumph fork yokes is a good starting point, if you can get a decent Jawa speedway motor. For a road bike, you would be better buying a BMW. It would be cheaper and better. 'Because I can' is never a good reason for doing anything.

When I built my Seeley 850, I did it because it was a good thing to build and there was a bit of authenticity about it. Gus Kuhn had built Seeley Commandos and raced them successfully in the UK. Building the bike and getting it to perform extremely well in races has made the exercise worthwhile. But if you are building a road bike, you really do not have a similar sense of purpose. You might end up with a bike that is interesting to spectators, but not actually do much. Developing a bike to perform gives a sense of achievement, and functionality determines what the bike will be. With a road bike, the bike can be anything with two wheels and still be OK.

acotrel said:

'Because I can' is never a good reason for doing anything.

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Oh yes it is!

ESPECIALLY if you can for FREE (or almost free).

...and MOST especially if it involves scratch-building a BIKE!!!

I like building things and what's better than building a bike from scratch and this was my first ever build, I got my Wideline frame cheap and I always had a love of Featherbed Norton's, more so than the Commando, when I got my Featherbed frame in 79 I took 2 years before diving into it before the conversion, so I just didn't jump straight into it, I had a plan in what way to go by talking to people who have done it with race bikes, my mate and the way he did his, balance factor was the big issue and getting the right person to do it and the gentleman who did mine knew what he was doing, I put my trust in his ability the same as my cam builder, but putting my trust in my head man at the time was a mistake, he did a complete stuff up and was only on the Norton for two weeks before his stuff up started to show its ugly head, lucky I found some one who really knew his stuff and saved my head from a costly mistake.
But the day it fired up for the first time and on the first kick as well, then the first ride another mate Grame brother of my mate who got me into Norton's was on his Commando and was egging me on to push it through the corners but I wanted to get to know my build before pushing it, it took me about a month of riding it before I started to push it hard after the motor was run in and clocking up more miles and the more mile on it the better it got, so what I done was done right from the very first time and so far has proved itself to be quick, great handling and very reliable it has never let me down except for a broken rear chain in the 38 years of riding it, nothing shook off it and in that time I have only change a few things on it and upgrading to better things like front brakes and ignition system and better carbs, but now thinking of going back to new set of Amals in the future.
It survived a major fire in the first few months being on the road and I was on it when it went up but only damaged the top side of the bike and was back on the road a week later, well next day really but had to wait for the seat to get remade, lesson learned don't run volicity stacks without air filters or have a leaking petrol tap.
I have seen a few Commando/Featherbeds in my time not many but none come close to my build and having a one off bike it gets a lot of attention where ever it goes and with the JH Maggie it fires up with little effort first time every time.

Ashley

baz said:

Not sure about your 75% balance factor
I can remember back in the day they used to recommend 72% in a shimmed tight commando proddy racer

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There is not much difference. Some guys go as high as 79%. Anything above 70% is smooth at around 6000 to 7000 RPM.

I have ridden my mate's 650 Triton, my own short stroke 500cc Triton and a genuine 500cc 1961 Manx. My mate's Triton was a Manx frame with 18 inch wheels. It was very stable in corners and the motor is an inch further back than it is in my 500cc Triton. I could ride my Triton faster in corners, but not as fast as the 500cc Manx. The 650cc Triton is still an excellent bike.

I would like to know how to get smooth running in the 3500- 4500 rpm range.
That's where these bikes run much of the time if you are using them for long distance travel and adventure.
Some people can tolerate a lot more vibration than others, but it's also down to the type of riding you like to do.
If you just go for a short local putt or even hooligan run now and then, this is quite different from sitting on the Interstate at 75- 80 mph (80 mph speed limit in much of Montana) for 3 hours. I dislike the Interstate and try to avoid it, but sometimes it is necessary to run on it for awhile in order to get to the good roads. You need a reasonably smooth runner for this.

Glen

With the Commando crank, changing the balance to 72% simply involves filling the hole in the bob-weight with a steel plug. If you tap the hole and bought some threaded steel plugs of different lengths, you could adjust the balance factor and get it lower them 70 % But you would need to start with short plugs and progressively add more, loctiting each one with blue Loctite. Then when you've got what you want, punch the end of the threads on the final plug.
Getting the balance factor right is mainly 'arse beats class'. You never know the right balance factor until you ride the bike. Personally, I would adjust the factor to 72% and tolerate the shake at low revs. With my Seeley, it only rocks backwards and forwards when idling. At 4000 RPM, it is probably OK. I've never noticed it vibrating much at any revs.
When they made the first Commando, if it had rocked when idling they never could have sold it. In stop-start traffic, it might have been really bad. Their competition was the CB750 Honda. In the 1950s, they would not have had a problem. Have a look at a Royal Enfield Interceptor or Meteor.

Glen mine is silky smooth around town and right up to 65mph even with the cam then it gets a few vibs but once over the 70 it smooths out again and from 70 to 90mph is very smooth, but after the ton it gets the vibs again but it smooths out again after about 105 and again way up in the high RPMs it will get the vibs, I no longer ride at very high speeds now and I am happy doing the ton every so often, as I say I can ride mine all day long whether around town or some back roads and on the highway it loves cruising between 70 and 90mph.
When the vibrations come in at certin RPMs its only in the handle bars ends I get it and no where else, my foot pegs don't suffer or my body, just the ends of my handle bars when it happens.

Ashley

Actually, with my Seeley 850 the throb at low revs as you accelerate from a stand-still is a really good feeling. It feels like a good bike should. It wouldn't be good in traffic, because it would give you the urge. And that is the whole thing about the bike. My friends have suggested I should register it and ride it on the road. I would end up in jail - it is impossible to ride it slow enough. Nobody could ever have that much restraint.

I can ride my Norton in top gear at 40 mph and its really smooth, under that speed I have to drop down to 3rd, but the cam really kicks in just on 4500 RPMs and you know when it kicks in, the cam runs very freely right up till it goes bang so got to watch how far you rev it to, it will spin up past red line if you let it, my stock motor would valve bounce at 6500 RPMs but this motor will keep going.
My whole Featherbed is so well balance and if I pull it up in first it will stand nearly straight up and stay there while pushing down the gear lever for second and third while going through the rev range, but this was all done in my younger days as now I only occasionly lift it, doing it all the time just wears out chains a sprockets as well tyres, well the back one anyway lol.
My wife knew all my favirote places where I pulled wheelies and she always knew when to hang on, but the first time I did it with her on I nearly lost her off the back, with the innerstate seat she was very comfortable on the Featherbed, more so than my other bikes.
But now the Featherbed is only solo rego as the third party insurance is to high for duel rego.

Ashley