Commando engine in Featherbed

worntorn said:

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

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If you really want to know just read my post about the scratch test tool (12 posts above). That will show you the best balance factor for the RPM you choose. But the only way to make it really run smoother is in the last paragraph.

It currently has just a few thousand miles on a complete rebuild with .080" over pistons.
I would have to chuck all that out and possibly sleeve to standard, unless your pistons come in .080 over?

I bike think the bike is already pretty smooth for a rigid mount. It doesn't destroy light filaments as you & Ashman mentioned.
It would be nice to ride a " silky smooth" Dominator just to see how that feels.
I once rode a Triumph Bonneville that had received dynamic balancing and many other details to improve it. The owner proclaimed it " glass smooth"
I thought it was godawful. The mirrors were a blur and the whole bike was buzzing at 65 mph. On top of that there wasn't a lot of power there.
I was 1500 miles from home at the time and had just gotten off the Vincent.
I imagined riding that Bonny 1500 miles home instead of the Vincent and it really made me appreciate the Vincent!

What constitutes a smooth running engine seems to be quite subjective .

Glen

Glen

Yes there is a lot of talk and subjective opinion but you can't deny the math. I can make any diameter pistons you want on special order - you're talking about a 79mm bore similar to photo below. The bare piston weight would be approx 220 grams for the 6.4" length rods with approx 105 gram small end weight. I can get 2618 alloy anytime but 4032 alloy is more difficult and requires large quantities.

Bit of an intresting Commando / f'Bed here : https://nycnorton.com/racer-2004/

Mussings are , 600 Domi Crank , with Commando Bore , to get the 8.000 rpm of a GOOD Triumph 650 .
Afterall the 500 Domiracer was good for a few R P M s .

Glen , is the 600 Crank comparable to a 750 / 850 Commando crank , strenght wise . ? for a ' budget ' build .

A custom crank , you could go down to the 72./6 500 stroke , or anything else your wallet could stand .

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As for justification for a ' Commando ' engine ( in F'Bed ) a 750 isnt necesarilly a ' Commando ' engine .
the 750 Originated in 61 in the Domi ( Atlas ) so had a similar duration of production , so is equally a ' Domi ' . If not numerically .

As for a open budget , a dedicated cornering nutter , being presumeablyTHE PRIME REASON ONE'D GO FOR SUCH A DEVICE ,
Would be wiser to go for the ' Works ' Domi 750 , factory twin RACE Frame . Thus .



Tho the Triumph ( 650 ) dosnt exactly seem overawed by the dunstall 650 / 750 here ,



Then theres a ' rea' ' Manx ( as in Manx ) Commando , If you have a Spare Manx and a Spare Commando .

Which , If for inspiration , Id say is as good a build as youd get . 750 Combat in 61 Manx Chassis, etc .

Again , if the Budgets no object , with repro everything availabe , no excuses for not doing so .



Been meaning to look up a Lindsey Patent on Canted Engines regarding Vibration .

Seems obviously the way to go .

Not edevouring to be obnoxious , but Head Braces , to resist brakeing forces , perhaps should be a acute angle to horizontal . To vertical and a ' over center ' principal might occur . Heard the head steadyless Manx Vincent at Pukekohe
( the owner was of the opion that this was for vibration only ) was last seen cartwheeling down the paddock , sans front end .
Id go for 45 Deg. Minimum , pref 50 or so to vertical - load path . thru attachments , there . Velly solly .

Pet Gripe is space ship parts on Jurasic Equipment , But whoever pays the piper calls the tune .
However ancint customs deserve some respect in regard to the owners audacity .

In regard to the ROADHOLDING - Probably EQUAL .
As to the HANDLING , The F'Bed is perhaps less willfull on undulateing surfaces at RACING SPEEDS , or over . At 11/10 ths pace .
At least the rider inputs are likely more immediate in their outcome ,thus less likely to go astray.
Or perhaps the Commando Chassis is more highly strung .
Tecnically the longer fork is less ridgid ,
The Factory F 750 Bikes going to twin discs to stop fork twist , despite the increased unsprung weight .
Competitive racing Id prefer the F'Bed , or a reworked custom sturdier Faux Commando frame .

My Impression that the concurrant Leverda , Bennili & Ducati were somewhat more ridgid ,
which was not started to be equaled by the rice burners untill the GSes , tho their 750s forks were likely less
stable under duress than the Nortons . Particularly the ' Short ' Norton forks .

Ran Progessive rate both ends on the Race / road Triton . Most precise ridden with Trigonic tyres on gravel Ive riden .

Matt asked " Is the 600 crank comparable to the Commando crank for strength? "

No, you would have to go to the 650 SS for that.

Re the 650ss vs 650 Triumph. - The Norton won the Thruxton 500 miler against the Triumph and the others three times, the only three years it was entered.

Glen

My friend had a 650 Manxman when I had 650 Triumph. His bike was much better than mine. Nortons were rare in Australia.

Race spec Commando motor in a slimline featherbed frame. 2nd place at Laguna Seca BOTT 750cc 1984 (tight budget & mostly junkyard parts).

To the OP Gian85,

A Commadno engine in a Featherbed frame is an excellent match up. I raced a Featherbed with a Commando engine for a few years and raced against many with same or similar configuration. I started with a race Commando and then moved on to a Featherbed and finally to a Seeley. The engine in the Featherbed is a Combat of unknown pedigree; it shaked badly but I still rode it so I am speculating it had a balance factor of around 53% (suitable for a Commando frame).

The Featherbed frame will give you concise feel and handling when compared to a general Commando frame yet a Commando frame
that has been modified and properly set up will provide excellent performance but still lacks the "concise feel" of a Featherbed. Riders have acclimated to both mounts. I started road racing with a Commando and then had an opportunity to race a Commando built by Herb Becker; it was surreal how smooth it was, even when compared to my street Commando.

The choice between the two configurations is very personal and really gets down to what you want. If it is minimal vibration throughout the rpm and throttle range with very good handling characteristics, then I would suggest a Commando and build from there with blue printing the frame and isolastics and perhaps adding a strategically placed extra isolastic as outlined elsewhere on this forum.

If you are looking for concise very good handling and can tolerate some vibration somewhere in the rpm/throttle position range then I would suggest considering a Featherbed with a Commando engine.

Forget about the Featherlastic.

I hope this helps.

Dances with Shrapnel said:

To the OP Gian85,

A Commadno engine in a Featherbed frame is an excellent match up. I raced a Featherbed with a Commando engine for a few years and raced against many with same or similar configuration. I started with a race Commando and then moved on to a Featherbed and finally to a Seeley. The engine in the Featherbed is a Combat of unknown pedigree; it shaked badly but I still rode it so I am speculating it had a balance factor of around 53% (suitable for a Commando frame).

The Featherbed frame will give you concise feel and handling when compared to a general Commando frame yet a Commando frame
that has been modified and properly set up will provide excellent performance but still lacks the "concise feel" of a Featherbed. Riders have acclimated to both mounts. I started road racing with a Commando and then had an opportunity to race a Commando built by Herb Becker; it was surreal how smooth it was, even when compared to my street Commando.

The choice between the two configurations is very personal and really gets down to what you want. If it is minimal vibration throughout the rpm and throttle range with very good handling characteristics, then I would suggest a Commando and build from there with blue printing the frame and isolastics and perhaps adding a strategically placed extra isolastic as outlined elsewhere on this forum.

If you are looking for concise very good handling and can tolerate some vibration somewhere in the rpm/throttle position range then I would suggest considering a Featherbed with a Commando engine.

Forget about the Featherlastic.

I hope this helps.

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You mentioned 'acclimatising' to the bike. Most of us ride around our handling problems. However a good bike makes a good rider, a bad one simply teaches you how to avoid crashing. These days, I ride and race very well - however it is not me, it is the Seeley. Featherbeds are excellent, if the motor is in the right place and you have the right frame rake and wheel size. I thought I was being smart when I replaced the 19 inch wheels on my Triton with 18 inch to fit better rubber, however I simply turned the bike into a dog. I could still ride it fast, but I used to climb of it at the end of races, exhausted. If you intend to use the bike on public roads, it doesn't matter much what it is. But racing is different - the difference between being excellent and ending up on your bum is virtually nothing.
In Australia, many of our historic guys ride converted road bikes in races. The handling is usually neutral. One of the guys running the sport is anti trick frames - to me that tells me he is a bloody idiot. There is much more to winning races than horsepower.

Back on point:

I wrote "Riders have acclimated to both mounts". There was an instance of two well seasoned and fast Norton road racers who offered up a swap of their rides for "a track test ride". One fellow has a street Commando, started racing a Commando based Featherbed and moved on to a Commando based Seeley Mk2; the other has a highly modified Commando road racer. The swap bikes were the Commando and Seeley.

Neither cared for the other's ride.

So to the OP Gian85 I ask "what are you looking for"

Its like any bike that you hop on you just can't hop on and expect to push it hard straight away, it takes a bit of time to find out how the bike performs, how it handles and how you can get the best out of it, it don't matter what bike whether its a Commando, a Featherbed or a Seely, each bike is different the way they are set up is also important, a bike set up for one person will not work for another person, my Commando/Featherbed is set up for me and the mates who have ridden it the first corners they come to they try to push it hard but they make mistakes or freak out and back off without understanding how the bike reacts, then I tell them to try again without trying to push it and let the bike do the hard work, just point, steer and lean and let the bike do the work and that's one of the best things with my Featherbed the rider is just in control of the speed and power and just lean with the bike the Featherbed does the rest.
I have pretty well set mine up right from the beginning but in the 39 years have made improvements to the front end and suspension, better tyres, cut back a bit more weight, improved ignition system, but the motor is still the same set up as it has proven itself to be very reliable and long life without any problems at all by listening to people in the know all them years ago when I was in my early 20s and long before the internet and doing things differently from my mate who got me into Featherbeds as he made a few big mistakes.
As the OP hasn't got back to tell us what his plans are, whether he wants to build one or what he wants to use it for, mine is set up for raod use and pushing it through the twisties, but I have done a few track day out at Lakeside in my younger days, its a very tight track but the Norton handled it well.

Ashley

" Do you have driven a special motorcycle with Featherbed frame and Commando engine? "

This guy might have .



Hada go Vs one , in a Mk1 2 Door 2 litre V4 Cortina , more torgue than a lotus .
Call it a draw . Anyway , I didnt drive over it, tho it couldve been a temptation .

Matt Spencer said:

" Do you have driven a special motorcycle with Featherbed frame and Commando engine? "

This guy might have .

Hada go Vs one , in a Mk1 2 Door 2 litre V4 Cortina , more torgue than a lotus .
Call it a draw . Anyway , I didnt drive over it, tho it couldve been a temptation .

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It's a very nice bike. In the extreme the centre of gravity is important. The crank in the bike is a bit far back, but at least the top end is forward. You might not think it makes much difference, but in a Triton, if the motor is an inch further back from the front engine mounts touching the frame mounts - there is a distinct difference in feel in fast corners. If the motor is slightly back, the bike can feel airy and vague. A featherbed with a Commando engine is a bit of a beast. And with that drum front brake, you would need to be careful.

In comparison, the motor in my Mk3 Seeley 850 would be a bit further forward. It is a totally different bike to my old Triton - much easier to ride fast. One thing I've noticed is the Seeley feels small, while the Triton felt huge.

All this talk about fitting commando engines in featherbed frames I wonder if anyone has ever fitted a commando engine into a lowboy frame?
Keeping the engine leaning forward on looks alone would be killer I reckon

You still need to be able to get the head off while the motor is in the frame.

wiki sez
https://en.wikipedia.org/wiki/Featherbed_frame#Domiracer_'Lowboy'

In 1962 the race shop closed and was sold to Paul Dunstall, who had already developed his own Norton Dominator-engined race machine campaigned by Fred Neville (deceased 1961) and Dave Downer (deceased 1963). Dunstall successfully developed 500, 650 and 750 versions, later producing a Lowboy frame kits sold to the general public.

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bit more
http://www.jamiewaters.com/forsale.html

Dunstall-Norton Lowboy twin - This is a NOS over the counter Dunstall Lowboy race frame kit. This is the same type kit I used to build my Lowboy 500 in the Motorcycles section, but a 750 twin works too

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https://www.revolvy.com/page/Norton-Dunstall?stype=videos&cmd=list&cr=1

The 1968 catalogue [18] shows race images of Ray Pickrell aboard lowboy race frames for open category, with production classes on Featherbed framed 750 Dunstall Domiracers.[19]

In June 1968 Pickrell won the Isle of Man Production TT race 750 cc class entered on a 'Dunstall Norton Dominator' with a new lap record (average speed) of 99.39 mph (159.95 km/h).[20]

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I have my Featherbed set up so less than a 1/2 hours work can have my motor, GB, primary and engine mounts unbolted and sitting on my work bench to do any major work on it, makes things a lot easier, but so far haven't need to pull it out, its also easy to drop it back in position, its heavy but I have no troubles doing it by myself, its such a good bike to work on.

Ashley

6 pages of the replies, and the OP hasn't replied.

Oh well...

lotsa info out there to chew on