270 degree crank

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john robert bould said:
...and as yet no one as stepped forward the give the facts, and more importantly the MATHS behind them, Maths was Phil Ervings starting point and the most important,
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There are quite a few sources to get the "maths" explained including several threads on this forum, no need to do this again and again - and the very interesting fact about all these sources I've seen so far (although that includes anything from Irving directly I have to say) is that they completely fail to quantify the rocking couple a parallel twin crankshaft with offset crankpins produces whilst going in detail about the mass forces. Hardly surprising as it depends on actual engine outer dimensions and it's far more difficult to quantify the engine mount loads - which you need in order to quantify the vibration load the rider is exposed to. If the rocking couple effect is mentioned at all it is just treated as neglectable - and that is simply wrong and wishful thinking as the overall vehicle design needs to take exactly this into account. In a Commando it is a stupid mistake ta accept a rocking couple because of the specific situation of the Isos.


Tim
 
Not math nor same low scale of imbalance as a 270' firing on both jugs but its easy to feel the slightly annoying horizontal imbalance on a 360' iso Cdo if one of the plugs wires is left off when you take off. I had to get to hwy speed and steady throttle before I released it didn't feel right and look down to see plug lead dangling...

As for the advantage of 90' offset for one piston reversing while the other is fastest, works a treat on inline fours but Norton and others 'solved' that with a heavy flywheel. A forum thread on crankshaft prono, revealed the majority of racers trying various mass cranks found the heavier cranks gave best tract times. Are there any successful offset cranks run with advantage in racers?

Offset cranks and Cdo's always seem to revolve around solving isolastic handling limits by solid mounts then trying to solve the pilot and structure fatigue. I'm here to tell ya there is flying carpet handling magic lurking in a Cdo 360' rubber baby buggy. Only thing annoying to me is tempts to speeds and tossing that gets air borne on perfectly flat pavement and over very rough pasture that vibe like murder until the tires touch again and smoothness returns. On the modern V-twin and inline 4's I've rode, I detest their valve train buss getting to me after 20 miles.
 
I've got to agree with Tim on this in that a more reliable way to reduce vibration on the Commando is to reduce the reciprocating mass. You can knock off 1/4lb without getting too radical about it. Make more power and less wear and tear. Then again, the rocking couple may not cause the problems that one might think. Has anyone ever tried it?
 
Tim said

Tintin said:
it is far more reasonable to reduce the source of the vibes - and this is the weight. Slipper pistons with reduced compression height and longer rods are far better than playing around with the crank which only redirects the forces instead of minimising them.

Tim
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Boy do I ever agree with you Tim.

See the post "Commando at Speed" with Kenny in the saddle and able to concentrate on the track instead of having his butt vibrated off the bike. He's using the longer rods and short lightweight pistons. And I love them in my own Atlas.

But if the 270 crank is an improvement - then its another step in the right direction.
 
swooshdave said:
john robert bould said:
3264 Forum members, No one as seen one ,none had one ,or rode one?
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Sure but he's Canadian and mourning the loss last nite. :mrgreen:
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The Canadians have been out of contention for ages, I heard that there was some commotion in Vancouver last night....

Jean has seen one, ( he wired it), as have I. Would have loved to get a ride. Put my hands on the cases while it was running and it was smooth. Would like to have more to say but that's it.

I'm broke now but if I had some cash, I would put one in my P11, but want to run a Mag as well, don`t know how that would work, custom points-cam. Definitely saving my pennies for Jim's lightweight stuff though ....
 
WOW!!! Break through at last!!! You put your hand on a 270 engine that was running and it was smooth. This News caused a movement in my lower regions.....SMOOTH, I will going to Darleymoor...not been in ages...last time it was Star's at Darley...Bob Heath was racing!
 
Friday 06-16-2011
Geoff,
Seek feedback on the uses and feelings of 270 crank in both isolatic and solid mounts for the NortonCommmando forum. Mainly want to know if they go totally smooth silent like 360 crank on isolastics or if there is still detectable horizontal or other vibration if isolastic mounted or solid?
Steven hobot
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I've felt those so called dead silent cycles and they transmit buzz from lots of stuff other than major engine orbitals which still annoys a Princess on a Pea me.


Steve,

I have an 850 Commando with a 270/90 degree crank. Balanced at 50% the bike is as smooth as an air-head BMW. You hear the bike but do not feel anything through the footpegs, handlebars, gas tank or seat. You can feel vibration in the primary chain case which has more to do with the imbalance of the drive line. Some people balance the clutch and drive sprockets to make things even smoother or add a belt drive. Dead quiet.

Some of my customers have solid-mounted Commando engines with my cranks in featherbed frames or even BSA A10 frames and have reported the same 'dead' feel; all sound, no vibration. Not as smooth as an Isolastic-mounted engine but still vibrationally quiet. With a belt drive and balanced driveline you get rid of more vibration. Its also worth balancing the rear sprocket separate from the rear wheel on the rear drum-brake bikes.

For street use the 50% balance factor works best, isolastic or solid-mounted. For racing and other constant high RPM riding a balance factor of 40% makes the bike smoother above 6000 rpm but brings back some vibration at low RPMs. Not as bad as stock, but noticable.

Over the past ten years I have played with various balance factors from 40 through to 66% in various increments and found that 50% is still best. On an isolastic Norton you can play with the balance factor a bit more then you can with a solid-mounted engine hence 50% is still good for the occasional high RPM work or racing. The important thing to note about balance factors is that the engine is like a V-twin hence any balance-factor and frame combination that has been published for a normal 360 crank engine won't work (I get constant arguments on this subject).

Geoff Collins
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John, I passed on your good words to Geoff to savor. Even Geoff admits nothing so far is as smooth as a well balanced 360's isolastic Commando. But I encourage trying all combo's, just not me thankyou.
 
hobot said:
John, I passed on your good words to Geoff to savor. Even Geoff admits nothing so far is as smooth as a well balanced 360's isolastic Commando. But I encourage trying all combo's, just not me thankyou.
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Steve reading Geoff's mail to you...There is a probem in is statement he says the 270 cranks are "dead" with no vibration, then states Not as smooth as a isolastic 360? I assume he means the well set up iso mounts reduce the engines effects on the chassis, But the engine still shakes? Plus compareing the engine to a air head BMW ...well i have had a few of them and tick over "shake"is just as bad as a Commando! But nice when reving...
The post as been interesting...Mixed view's , i would still like the hear from someone who is riding a 90 degree on a daily basis, looks like none of the 3000 forum members as one.
Best regards
John http://www.lansdowne-engineering.com
 
Haven't ridden one as stated before but would expect the level and type of vibration to be similar to what you feel riding a Duc, you know the engine is working but it isn't intrusive or bothersome such as an inline four,(buzz), or 360 parallel twin, (shaker).

Just my 2 cents
 
New Norton 961's are solid mount parallel twins with 270' cranks and new age contruction, but they ain't no real isolastic Commando ...

http://www.cycleworld.com/motorcycle_ro ... _se_page_2
The 270-degree crankshaft gives the bike requisite character, although it’s more Ducati than old-time 360-degree-crank Norton. A Twin, however modern it is, isn’t supposed to be glass-smooth or buzzy, and the Norton isn’t either of those. The counterbalancer quells the strongest of the vibes and leaves the rest for you. Output is a claimed 79 hp at 6500 rpm, and it feels like it on the road. Claimed torque is an equally welcome 66.4 ft.-lb. at 5200 rpm. Healthy enough figures for an air-cooled Twin.
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Don't improve the handling either ...
And while the engine is right on the money in comparison with similar-displacement, modern, air-cooled Twins, the handling of the SE is shocking. Not bad. Shocking, as in unexpected. The appearance of the new Commando is a mixture of British history, rose-tinted familiarity and trusted modern blue-chip brands. But grab it by the bars and wring its neck and any nostalgia trip is over. The bike twitches and shimmies like a stripped-down streetfighter. The bars kick as the front end goes light on the throttle. Perhaps it’s the superlight South African-made BST carbon-fiber wheels (non-SE models will be equipped with alloy-rimmed wire-spoke wheels) that help it feel so frisky. The new Commando doesn’t go AWOL but gives the impression it’s up for a fight or fun, whichever comes its way.
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Again to me its just evidence the whole rest of the world is mis guided down dead end half fast solutions to handling and pilot comfort.

My '00 'curvy' 90' crank SV650 feels tight smooth and secure, till on it ~20 minutes, then the buzz of valve train annoys. Yet its as smooth as is acceptable to new age world. After Code's Corner School where I learned to fly inline4 buzz bombs off the surface I did it on SueVee too to find she smoothed out while in the air but for /slow' suspension oscillation, then we'd land and the buzz hits again. ugh. Ms Peel when flown suddenly shakes with the crank shaft and the valve train and suspension plus shimmies with wind eddies, till she lands on pasture grass or THE Gravel and disappears again but for surface texture inter face. Same on tarmac, but that level of handling is beyond comprehension here or by the world most elite racer craftsmen.

About half dozen rear linked plus 2 helper rod 360' Cdo in the works with eager seasoned skilled riders, till then just ole hobot's word that all's ya all's don't know what you are missing out on, hehe. When the going gets tough on oldest Cdo's or newest moderns, they go off shopping, with twitches, shimmies, shakes, rattles and rolls alerting pilot to back off or lose it, not on Ms Peel she just enters next level-phase change of energy handling and stays on accelerating smooth glee, till the next higher level-phase change of energy handling threshold crossed, for 3 more funner ways around than anyone but hobot enjoys in refreshing low effort sensation.

Handling and smoothest have been totally solved in the Ozarks, just don't know how long it'll take rest of the Cdo world to catch up. We have one other example of supremesty of 360' isolastic in Doug McRae's rub plate tri-angulated racer but he's not described any further handling phases than plain old boring phase 2 counter steering. But he' and chassis are not annoyed by the vibes.

Smartphones have app's that use accelerometers to graph vibes, so want to get one and pass it around, but most want to record a fully loaded two up Goldwing as I think Ms Peel unloaded one up is smoother yet.
 
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