Norton Offset Crankshaft
- Thread starter lkleppe
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Why do you want one?
Different power output? Smoother engine?
Different power output? Smoother engine?
Take a look here crankshaft-t2741.html?hilit= crank
To answer a few of your questions, I think my friend likes it, the cam was modified by the guy who made the crank and the ignition is a modified Boyer (the ignition rotor has the magnets at the proper angle). When I did the electrics on the bike, I also timed it which is a bear to do and I am still not 100% sure it is OK because I find the bike very hard to start, but some of that may be due to the carburators which were not completely dialed in. My friend is back in Toronot so I don't know if the bike is used on a regular basis. It does sound very different from any Norton you may have heard though.
As for things to look out for, as mentionned, ignition and start out with either stock dual Amals or a single Mikuni before trying anything really wild like the FCRs. For an Ignition, if it was my bike, it would be an Ignitech with a pickup for each cylinder (dual channel) run off the crank.
Another thing to consider would be lighter rods and pistons in addition to the ofset crank.
Jean
To answer a few of your questions, I think my friend likes it, the cam was modified by the guy who made the crank and the ignition is a modified Boyer (the ignition rotor has the magnets at the proper angle). When I did the electrics on the bike, I also timed it which is a bear to do and I am still not 100% sure it is OK because I find the bike very hard to start, but some of that may be due to the carburators which were not completely dialed in. My friend is back in Toronot so I don't know if the bike is used on a regular basis. It does sound very different from any Norton you may have heard though.
As for things to look out for, as mentionned, ignition and start out with either stock dual Amals or a single Mikuni before trying anything really wild like the FCRs. For an Ignition, if it was my bike, it would be an Ignitech with a pickup for each cylinder (dual channel) run off the crank.
Another thing to consider would be lighter rods and pistons in addition to the ofset crank.
Jean
Thanks a lot for your comments Jean.
Expect a lot of accuracy is required for this to really work. For sure the modified crank offset angle must be precise, and must match the camshaft offset and the ignition perfectly. I will be putting a lot of faith in the guy who is modifying the crank, I believe one of your countrymen - a Canadian - and maybe the same guy who did your friends crank [now in Toronto].
I'm hoping to get more power, faster acceleration and of course less vibration.
Assume the Norton pictured on your reply is yours - mmmm very nice.
Best Regards,
Leon
Expect a lot of accuracy is required for this to really work. For sure the modified crank offset angle must be precise, and must match the camshaft offset and the ignition perfectly. I will be putting a lot of faith in the guy who is modifying the crank, I believe one of your countrymen - a Canadian - and maybe the same guy who did your friends crank [now in Toronto].
I'm hoping to get more power, faster acceleration and of course less vibration.
Assume the Norton pictured on your reply is yours - mmmm very nice.
Best Regards,
Leon
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I would try the lighter pistons/con rods before going to the expense of the offset crank. Don't know why the offset crank would give you any more power.
lkleppe said:
The lightweight pistons can be ordered from http://users.gotsky.com/jimschmidt/nortonrods.html as for the ofset crank, take a look here http://www.offsetcrank.com/ if you haven't found him yet. There is no more power from an ofset crank, but the motor should be a lot smoother and since there is less change in crankcase volume, there should be fewer leaks and less pumping losses. The crank my friend used came from the same guy. The only way to get faster acceleration from the engine itself, is to reduce rotating and reciprocrating weight, in other words, the lightest crankshaft possible, as well as everything attached to it (rods, pistons, drive pulley, clutch...) Then consider more power, (higher compression, carbs, exhaust...)
Jean
The bike on my reply is my friend's bike, for my bike, take a look here cafe-racer-all-finished-t4710.html
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It would be a lot less expensive to go with the Jim Schmidt solution and a good breather (like the one from Jim Comstock/CNW). Then you could use existing cams and other parts and make a seriously fast bike.
Of course the other reason for offset cranks is to have something different.
Of course the other reason for offset cranks is to have something different.
Danno said:
What do you mean by that :?: Usually a twingle or split single ( http://en.wikipedia.org/wiki/Split-single ) is done on two strokes sharing a common combustion chamber, that is not easy to do on a four stroke, unless you mean pairing two Norton engines like TC Christenson did with his Hogslayer dragster ( http://motorbike-search-engine.co.uk/cl ... g-bike.php )
Jean
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Jeandr said:
I've never heard of anyone twingling a Norton but it was done on Yamaha 850 twin TDM / TRX? dirt tracker so should be doable. Reason was, If I remember correctly, they were looking for traction. Big bang.
Side note, I think Bob said he had Megacycle do a minimum run , ( 6 ), cams for the 80 offset.
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Dunno if one of the old Norton grass Track outfitts didnt try it. Still running 828s against the Japper fours,
they were trying 'twingling ' those - fireing cylinders as pairs for dig in the dirt . British ' Grass Track ' could
be 'mud hole track ' in the rain , M-X style not flat.
The 'Fancy' crank is " tangentaly Disposed '" in regard to the Rod centerline to Crank Throw , with piston at
half stroke. theory in a V-Twin , 90 dg , is that one piston is at full speed while the other is at an'awkward'
time, stoping going that way , and going back there again. So the Inirtia of the flat out piston helps the other
stop dithering. Ordinarily the Flywheel would be doing this on a 180 or 360 deg. crank. So with our cranked
crank with the alternative piston supplying the energy , it isnt nessesary to have the weight that'd be doing
it in the flywheel there.Without it its lighter . term , Parrallel (Cylinder) V - Twin, Pick your angle .
But theres bigger forces around in there than the weight of one little piston , so a real look at the mathmatics
involved starts leading to some intresting possibilities, Like a Twi-V-ingle .
good camera shots of the odd dirt tracker , show the little puffs of dust from the tyre as Ea. cylinder Fires on
some old 70s shots of Twins. Dick Manns thoughts were the single Had Better Traction than the 45 deg. H.D.
which was better than the triumph. The TZ had real problems with traction with the even fireing impulses ,
and only really accelerated uprightish on the dirt .Though they all said it was the HP and peaky power band
it wouldve been the lack of kick and dig, halt , kick and dig , etc ., it was kick , kick , kick . S L I D E .
Anyone fancy hanging on to a Commando Chair on their ' english Holiday ' , I think they classic race them
they were trying 'twingling ' those - fireing cylinders as pairs for dig in the dirt . British ' Grass Track ' could
be 'mud hole track ' in the rain , M-X style not flat.
The 'Fancy' crank is " tangentaly Disposed '" in regard to the Rod centerline to Crank Throw , with piston at
half stroke. theory in a V-Twin , 90 dg , is that one piston is at full speed while the other is at an'awkward'
time, stoping going that way , and going back there again. So the Inirtia of the flat out piston helps the other
stop dithering. Ordinarily the Flywheel would be doing this on a 180 or 360 deg. crank. So with our cranked
crank with the alternative piston supplying the energy , it isnt nessesary to have the weight that'd be doing
it in the flywheel there.Without it its lighter . term , Parrallel (Cylinder) V - Twin, Pick your angle .
But theres bigger forces around in there than the weight of one little piston , so a real look at the mathmatics
involved starts leading to some intresting possibilities, Like a Twi-V-ingle .
good camera shots of the odd dirt tracker , show the little puffs of dust from the tyre as Ea. cylinder Fires on
some old 70s shots of Twins. Dick Manns thoughts were the single Had Better Traction than the 45 deg. H.D.
which was better than the triumph. The TZ had real problems with traction with the even fireing impulses ,
and only really accelerated uprightish on the dirt .Though they all said it was the HP and peaky power band
it wouldve been the lack of kick and dig, halt , kick and dig , etc ., it was kick , kick , kick . S L I D E .
Anyone fancy hanging on to a Commando Chair on their ' english Holiday ' , I think they classic race them
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Matt Spencer said:
Hey Matt, do you mind posting an introduction to yourself in a new thread? You seem to know a bit about bikes. Perhaps add your location to your profile? Thanks!
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Yes Matt, I seek your insights in handling extremes too. Please try to include the effects of Commando isolastic mounted power-unit drive train on high power pulse traction hook up dampening. Also consider the rpm effects on power pulses. Big bang of 2-4 hits in a row, 14,000 times a minute might upset tire hysteria too much.
What I've found is only place un-linked Commando can demo their superior hook up is hill climbs because they get so out of control in held leans before traction limits.
Crank mass has gryo resistance to lean, but also resists lean changes once leaned.
This can be a good thing when sliding, helps just drift and not tip over further.
Low mass speeds up and slows down more per piston hits to tire, more mass dampens the power strikes on tire. Whats best compromise?
Twi-V-ingle is a new concept to me, thanks a lot for more restless pre-sleep as that flashes back and forth in my minds eye.
hobot
What I've found is only place un-linked Commando can demo their superior hook up is hill climbs because they get so out of control in held leans before traction limits.
Crank mass has gryo resistance to lean, but also resists lean changes once leaned.
This can be a good thing when sliding, helps just drift and not tip over further.
Low mass speeds up and slows down more per piston hits to tire, more mass dampens the power strikes on tire. Whats best compromise?
Twi-V-ingle is a new concept to me, thanks a lot for more restless pre-sleep as that flashes back and forth in my minds eye.
hobot
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- Jul 25, 2010
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- 5,947
Trying to dig a few photos out today , appears I dug them out last week and put them ' somewhere ' , And itll take a bit to scan + post them , so hold your hats .
Was a RGV ? 250 Honda in Aus. built about 95 or so , BSA lightning mill , Commando Crank ,
Think thats about 920. Was staggered offset , 90 Deg. ish . Flywheel was 3/8 steel plate ,
mayve had counterweights bolted on . Pics of that tucked away to . Was at eastern creek
at a classic meet , 2000 .
Was a RGV ? 250 Honda in Aus. built about 95 or so , BSA lightning mill , Commando Crank ,
Think thats about 920. Was staggered offset , 90 Deg. ish . Flywheel was 3/8 steel plate ,
mayve had counterweights bolted on . Pics of that tucked away to . Was at eastern creek
at a classic meet , 2000 .
I have been reading all the posts about offset crank for Norton twins and am interested in pursuing the concept.
Not wanting to re-invent the wheel, I have been looking at all Prof. Google has to offer.
The first thing I have noticed is that some individuals have rotated one crank clockwise & others have rotated the same crank anti-clockwise. (all viewed from the same end, obviously).
Does either option have advantages /disadvantages, or is it purely a matter of preference?
Not wanting to re-invent the wheel, I have been looking at all Prof. Google has to offer.
The first thing I have noticed is that some individuals have rotated one crank clockwise & others have rotated the same crank anti-clockwise. (all viewed from the same end, obviously).
Does either option have advantages /disadvantages, or is it purely a matter of preference?
Possum said:
Its also noticeable that some folks have used 90 degree rotations, and others a 76 degree.
Which is also supposed to have advantages.
All we can say is that the cam and ignition systems used had better match up to whatever configuration is selected !!!!
I haven't been following closely, is all the advantage for racing use only ?
We notice someone on the NOC Forum enquiring about balance factors for a s-m-o-o-t-h road use.
That really threw them, balance factors get somewhat complicated about then (?).
Fast Eddie
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Possum said:
It is quite a lot of 'proper' engineering work to do this. Irving was the first to present the benefits I believe.
New Nortons and the new 2106 Bonneville range use them, so one assumes there are good reasons for this. Nourish Racing Engine offer there range of racing twins in a 90 degree option and they are definitely the smoothest variant.
However, as aleady mentioned, balance factors seem to be an area of debate and, frankly, guess work, so you should be warned that getting it right may involve a lot of trail and error.
Scramble types used them a lot as the uneven firing is supposed to give greater traction under acceleration. Some road racers use them for the same theoretical reason, but having ridden such, I do not believe their is any advantage to be gained from that on Tarmac.
They are, of course, inherently smoother. But Commandos are smooth anyway. So I really struggle to see how one could have any bennefit over a well balanced 360 Commando with properly adjusted ISOs. For a rigid mounted engine, there may be some benefit, but then we come back to the difficulties regarding balance factor... So whether or not it will actually be any smoother than a well balanced 360 degree crank will be down to good fortune!
Personally, I don't like the sound of them. Its the only thing I do not like about the new Bonneville range, I don't think you can beat the sound of a crisp 360 four stroke twin!
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