anyone got experience with commando engine in wideline frame with isolastics? if so any photos

baz

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Don't forget the headstock on a featherbed frame is supported by the head steady
Some of the new replica featherbed frames have an extra tube at that point to support the headstock
 

texasSlick

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Featherlastic has been done, but IMO doing so is an exercise in futility.

The beauty of the Featherbed frame lies in its excellent rigidity, despite its light weight. It gains this rigidity by utilizing the engine and gearbox to stabilize the inherent weak points in the frame, those being at the sweeping radii of the twin loops. Putting isoelastics at those points loses that rigidity.

More on this concept is found in Reply #137 ... https://www.accessnorton.com/Norton...-against-all-engineering-princip.17675/page-7

Slick
 

ashman

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Featherlastic has been done, but IMO doing so is an exercise in futility.

The beauty of the Featherbed frame lies in its excellent rigidity, despite its light weight. It gains this rigidity by utilizing the engine and gearbox to stabilize the inherent weak points in the frame, those being at the sweeping radii of the twin loops. Putting isoelastics at those points loses that rigidity.

More on this concept is found in Reply #137 ... https://www.accessnorton.com/Norton...-against-all-engineering-princip.17675/page-7

Slick
Solid mounts are all part of the handling in a Featherbed frame, put rubber mounts and it won't be the same and really the only thing you hear about the Featherlastic builds are from the builders who was selling them, you can get a smooth Commando/Featherbed by balance factor or light weight engine parts but I went with the balance factor of my crank at 72% I built mine in the early 80s and I still ride it today and after 39 years have only lost the top gear box nut and one muffler mount bolt.
If you do go down the Featherlastic road then please don't use a original Featherbed frame there are plenty of replica frames around but then they aren't a true Featherbed frame in my opinion.

Ashley
 

ashman

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This is mine
 

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Plenty of Featherbeds around stuffed with Triumph, Vincent, Harley and other motors. Why not a Norton powerplant?
 

robs ss

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Plenty of Featherbeds around stuffed with Triumph, Vincent, Harley and other motors. Why not a Norton powerplant?
I think the point being made, which I agree with, is that if you want to put a commando engine in a featherbed then do it without isolastics - ie: rigidly mounted as all featherbed twins were.
Cheers
 
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All featherlastics are not the same. I have ridden the root beer colored one shown in previous. Handling is excellent. Bike rides smooth like a commando. Note that swing arm does not float with engine like commando. Bike that norton should have built.
 

texasSlick

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IMO, the better approach to a smoother Featherbed, is to do the JS Eng approach, i.e., rigid mount the engine, use the lightest reciprocating mass on the planet, longer rods (Carrillo), and the appropriate balance factor (consult with the foremost expert on that factor, Jim Schmidt of JS Eng).

Slick
 
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I think the point being made, which I agree with, is that if you want to put a commando engine in a featherbed then do it without isolastics - ie: rigidly mounted as all featherbed twins were.
Cheers
A rigid mounted Commando engine will have the wrong engine balance factor, so, crank will need rebalancing.
 

Fast Eddie

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If you do NOT mount the swing arm to float with the engine you‘ll get chain issues. Mounting thus will also cause the rear chain to act on the isos in an unusual manner as the chain tries to pull the power train backwards (same forces that mean the rear chain always pulls the primary chain tight).

If you DO mount the swing arm to float with the engine, you’ll lose more of the inherent featherbed solid handling and add weight cos you’ll need a full Commando cradle.

Both methods are doable and have been done, you just need to know the pros / cons before deciding.

Personally, I decided that the best way to rubber mount a Commando engine is in a Commando frame. I’m still contemplating building a Commando featherbed one day, but if I do it’ll be solid mounted and balanced accordingly.
 
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Fully with you Slick re: the Jim Schmidt approach.
In my context (750 engine / Medium CR pistons / stage 0 camshaft), no need for re-balancing the crankshaft as mentioned by Jim on his web site.
Vibrations-wise, the result is up to my highest expectations. No loose nut, no burned bulb, still a clear view in the mirror after more than 50 000 km of use (touring speed and rpm).
 

grandpaul

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I like both ideas - re-balancing and rigid mounting the Commando engine, AND/OR iso mounting the engine, but retaining the featherbed swingarm system.

I'll bet some crafty person like the one who built the brown one, figured it out where the chain doesn't upset anything, as it doesn't on all stock featherbed bikes. I'd recommend one of my spindle kits as part of the fix, but I'm not making them any more.
 

Fast Eddie

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I'll bet some crafty person like the one who built the brown one, figured it out where the chain doesn't upset anything, as it doesn't on all stock featherbed bikes.
Quite right, stock featherbed bikes don’t have too many chain issues.
Then again, the engine is solidly mounted. Mounting the engine on isos and the swing arm to the frame is when the issues arise and the chain gets a really hard time.
Which was all known by Norton of course, hence why they did what they did with the isos.
If they Cudda mounted the swinging arm to the frame, I’m pretty sure they wudda !
 

grandpaul

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I wonder if a pattern for a Commando power unit could be tweaked to move the transmission a bit closer to the power unit, and the swingarm spindle as close as possible to the relocated transmission? Probably been done already...
 

baz

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Quite right, stock featherbed bikes don’t have too many chain issues.
Then again, the engine is solidly mounted. Mounting the engine on isos and the swing arm to the frame is when the issues arise and the chain gets a really hard time.
Which was all known by Norton of course, hence why they did what they did with the isos.
If they Cudda mounted the swinging arm to the frame, I’m pretty sure they wudda !
I like the way the yam fj12 motor is rubber mounted in the frame
The engine has a small adjustable rubber buffer on the drive side that runs in a cup to keep the motor from moving back
The xjr13 has a linkage to keep alignment
Admittedly these engines don't jump up an down like a commando motor but there's a fair bit of movement and quite a lot of horse's to control
 

ashman

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What about the top head stay, on a Featherbed frame the top head stay has to be strong and solid if they aren't then the top frame tubes will crack how does the Featherisoslastic stop that if there it any movement from the motor.
As Jim has said who needs isoslastics on a Commando/Featherbed, when I built my C/F back in the 80s and no internet I went the cheapest way with my motor by balanced by a gentleman who knew all about the balance factor for what I wanted and at the time only costed me $45 to balanced, but these days there are a lot more inturnal parts you can build your motor with which will also make the C/F run smoother, but of course the parts aren't cheap and adds to a lot of money which is ok if you have it.
After 39 years of riding my C/F you think I would have kept it if wasn't smooth to ride and it was a everyday rider till 7 years ago when I brought my new Thruxton and now my C/F is semi retired just like me, but I still love taking it out.
Who needs friggin isoslastics, if done right don't need them.

Ashley
 
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