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post #1 of 7 (permalink) Old 06-30-2016, 08:28 PM Thread Starter
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crank angle

any know the crankshaft angle on a vstar 650 is it 90 or 180 or 360? no guesses please

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post #2 of 7 (permalink) Old 07-02-2016, 07:08 AM
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If the cylinders share the same crank pin, the crank angle is zero. If there is only one crank pin, it is pretty difficult to have an angle. If there is an angle between the cylinders that angle will determine any difference in firing time. The two cylinders cannot be at TDC at the same time. The firing order will be uneven. If the cylinder angle is 70 degrees, the rear cylinder will fire (360 - 70) 290 degrees after the front; the front will fire (360 + 70) 430 degrees after the rear. I do not know how the ignition system handles that difference, if it uses a single ignition pickup. It would be possible to have two magnets on the flywheel. but I do not know.
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post #3 of 7 (permalink) Old 07-02-2016, 08:05 PM
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Originally Posted by pauli466 View Post
you don't understand engines. if the pistons share the same pin both pistons are up or down at the same time. one will at TDC on compression and the other will be at TDC on exhaust. it's a four stroke engine each piston only fires once for every two crank revolutions. compression stroke (bang) =1/2 revolution of the crank.. power stroke= 1/2 revolution of the crank.. then comes the exhaust stroke= 1/2 revolution of the crank and finally the intake stroke= 1/2 revolution of the crank then the whole process repeats. no such thing as a zero degree crankshaft. old triumphs used 270 degree crank shaft, check this link out it show some of the more common angles and why they were used. note there's not one zero degree crank on the list.. https://en.wikipedia.org/wiki/Big-bang_firing_order the angle between the cylinders is meaningless in relation to the crankshaft angle or firing iterval... the v- angle and the crankshaft angle are two very different and separate things... in this image A= the crank angle, the cylinder or (bore centerline) can be anywhere along the radius and the angle won't change https://upload.wikimedia.org/wikiped...n_geometry.png
Perhaps you need to look at the drawing of a radial engine as used in aircraft. If we use a five cylinder engine for example, we see that there is one crankpin with five rods operating pistons in five cylinders separated by 360/5 degrees, 72 degrees apart. The animation in the Wikipedia article shows a five cylinder radial moving. Any two adjacent cylinders are pretty close to the 70 degree separation of the single-pin crank Yamaha 650 engine. Watch the animation and see that the pistons on any two adjacent cylinders are never at TDC at the same time. https://en.wikipedia.org/wiki/Radial_engine
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post #4 of 7 (permalink) Old 07-03-2016, 10:34 AM
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I am clearly illiterate and clearly do not understand the intricacies of either V-twin or radial engines. I must defer to the expert. But I look forward to the video in which you place soda straws in the plug holes of a V-Star 650, then rotate it slowly so that all of us can see both straws showing TDC occurring in both cylinders at exactly the same point in engine rotation.

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post #5 of 7 (permalink) Old 07-03-2016, 08:57 PM
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The V-Star 650 uses a single-pin crankshaft. There can be no measurement of angle between a single pin and itself. But in terms of piston timing a 0-degree crankshaft is identical to a 360 degree crankshaft, so the point is moot. If you go back to my first post, you will see I said essentially that. True, I added more information, but you can ignore it if you like.
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post #6 of 7 (permalink) Old 07-04-2016, 06:34 PM Thread Starter
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The V-Star 650 uses a single-pin crankshaft. There can be no measurement of angle between a single pin and itself. But in terms of piston timing a 0-degree crankshaft is identical to a 360 degree crankshaft, so the point is moot. If you go back to my first post, you will see I said essentially that. True, I added more information, but you can ignore it if you like.
believe me i get what your saying and it is correct with 0 and 360 being the same thing but if you look a degree wheel that's used on a crankshaft for dialing in cams and such you'll see the zero is in very light print and 360 is very bold and obvious that's because when setting up things like camshaft advance the 360 is always used as a reference, i'm not saying that zero can't be used it absolutely can, but i just don't see it used on internal combustion engines. maybe you know why the 360 is used and not the zero, maybe it's industry standard for engines but i really can't say, here's one for ya if the front cylinder is at TDC compression and rear cylinder is rising on the exhaust stroke, how far behind is that rear cylinder compared to the front one on a 70 degree cylinder bank angle, would it be correct to assume 70 is degrees less than 90 so the rear cylinder would top out 70 degrees after the front tops out. what i'm saying is once you have the front cylinder on TDC if rotate the crankshaft 70 degrees will the rear piston be at TDC. i get what you meant that both can't arrive at TDC at the same moment but i think the closer the bank angle is the closer the piston positions will be to each other, see i can admit when i'm wrong i'ts the only way to keep learning, thanks for the help. what looks weird to me is the timing marks on the flywheel for the 650 don't look like they're 70 degrees apart they just look a lot closer that for some reason

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Last edited by pauli466; 07-04-2016 at 06:49 PM.
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post #7 of 7 (permalink) Old 07-05-2016, 07:24 AM
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Without a 650 to look at I can't actually look at the marks. But on my 250 there are two timing marks close together and another set elsewhere. The two close-together marks are probably the TDC mark and the ignition timing mark, which will usually be separated by the amount of ignition advance at idle speed.

Most of the old British vertical twins (Triumph, BSA) used a crank with two crank pins positioned so the pistons moved exactly together, almost like a "split single." The valves were so timed that the cylinders fired alternately, or at 360 degree intervals. That gives even power strokes, one per engine revolution, but also gives vibration problems with both primary and secondary imbalances. That is likely where the term "360 crank" came from. The other common crank was a "180 crank" with crank pins 180 degrees apart resulting in one piston up and the other down. That was the configuration used in two-cylinder John Deere tractors for many years. It gives perfect primary balance, but an uneven firing order with firing intervals at 180 and then 540 degrees. It also considerably reduces crankcase pressure pulses and helps reduce oil leaking.

On a V-twin with a single crankpin and a 70 degree bank angle, the front piston will "lag" the rear piston by 70 degrees, or "lead" it by (360 - 70) or 290 degrees. That is the mechanical configuration. If the front piston is at TDC and the cylinder has just fired, beginning its power stroke, the rear piston will be about a third of the way down on its intake stroke.

You are correct that the narrower the V angle the closer the pistons are to moving together. Harley uses a 45 degree V, about the closest of any maker. Ducati and Moto Guzzi use 90 degree V angles. 90 degree V angles give some advantages in balance, but become harder to package in motorcycles. Harley's 45 degree V let them use a single carburetor and a "Y" manifold. Wider V angles make it easier to put two carburetors between the cylinders. The compromises never end. Cruisers also have the really serious constraint of style. It it ain't pretty, it won't sell.

Last edited by Charon; 07-05-2016 at 03:33 PM.
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