Crankshaft Question
- Thread starter Diablouph
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No less vibration as the reciprocating weight stays the same. The vibration then becomes a higher frequency rocking couple which is not possible to control with isolastics. Try a Honda 450 or a Yamaha 650. A 360 degree twin shakes and a 180 twin buzzes. Jim [ps I tried it on a Norton}
You will lose some flywheel inertia of the heavier stock crank but not that's not torque. The rephased crank with less mass will accelerate faster and slow down quicker off throttle. It loses no torque, and if anything feels like it gains some with it's V twin feel.
I fitted one into a commando that had repop mk3 iso's that never worked as well as the originals. It still bounces at idle but then smooths out just like the original setup and stock engine. Rick
I fitted one into a commando that had repop mk3 iso's that never worked as well as the originals. It still bounces at idle but then smooths out just like the original setup and stock engine. Rick
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Torque is just how much fuel is being burnt, how fast and hard that's felt depends on the mass being spun up or slowed down. Ms Peel had 5 lb lighter crank and it was wonderful once I leaned reflex to grip bars hard and plant but harder before throttle snaps. If anything the change in power pulses may help or hinder tire grip, don't know which way. I'm glad to know horizontal imbalance is tolerated enough by isolastics. Smoother is the sales pitch of those offering off set cranks in various 360's twins.
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cash said:
Also when the majority of British vertical twins were developed, twin carbs would have been regarded as an added complication and an unnecessary expense, and a 180 degree crank four-stroke vertical twin really needs twin carbs.
Well according to Leo Goff , my MK3 had about a 358 degree crank :shock: And the rods were significantly different in length too . After replacing those with items from his parts cache and installing an offset bushing in the DS cam bore to line it up with the TS , he now says I have one of the most blue-printed 850 bottom ends on the planet 8)
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comnoz said:
All the available information I can find suggests the "Rebel 250" had a 360 degree crank?
http://cgi.ebay.com/ebaymotors/CMX250-C ... 439b7ce924
http://cgi.ebay.com/ebaymotors/CB250-CB ... 439c536b14
http://www.cheapcycleparts.com/model_ye ... blies/6408
http://answers.yahoo.com/question/index ... 235AAaO2nF
comnoz said:
But those "million Harleys" had narrow angle Vee twin engines with both conrods sharing the same crank pin, so the firing cycle is closer to that of a 360 degree vertical twin than a 180 degree twin?
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You may be right about the Rebel. I never worked on it and there was no kickstarter to find out. But I rode it once and decided it must be a 180. and my Honda parts guy agreed. I never looked any further.
I am not sure that having the Harley intake pulses closer together makes a single carb better or worse than a 180. Harley suffered a lot from charge robbing.
A buddy of mine had a 650 Yamaha with a single carb conversion on it and he rode it for years. He always said it was better than stock carbs but I never rode it.
I never thought much of the idea but obviously it can be done. Jim
I am not sure that having the Harley intake pulses closer together makes a single carb better or worse than a 180. Harley suffered a lot from charge robbing.
A buddy of mine had a 650 Yamaha with a single carb conversion on it and he rode it for years. He always said it was better than stock carbs but I never rode it.
I never thought much of the idea but obviously it can be done. Jim
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comnoz said:
Well the XS650 Yamaha certainly had a 360 degree crank!
http://en.wikipedia.org/wiki/Yamaha_XS_650
http://www.sense.net/~blaine/270.html
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That is correct. But Harley still suffers from charge robbing. I know we had a tough time keeping the front cylinder from stealing the rear cylinders charge on the last twin cam motor I built.
Are there any examples of 180 motors with a single carb?
I don't know what I was thinking. I had it stuck somewhere in my head that a xs650 was a 180. I knew better.
Are there any examples of 180 motors with a single carb?
I don't know what I was thinking. I had it stuck somewhere in my head that a xs650 was a 180. I knew better.
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