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Old 07-16-2012, 12:17 PM   #1
Hiatt OP
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Camshaft to Crankshaft Ratio

Can anyone help me locate the information on the EXACT rotational ratio between the crank and cam? This would be particularly for a /5 model. Is this value different for the different airhead models, or the same across the board? Will a /5timing chain/sprocket work on other models?

Thanks for the help.

JH
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Old 07-16-2012, 12:25 PM   #2
helion42
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if you mean for the gearing or whatever, it's just 2 to 1. in all gas engines, the cam is spinning at half the rate of the crank.
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Old 07-16-2012, 12:30 PM   #3
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I think he means the actual number of teeth on the sprocket, i.e did it change between the years ? Like the single row vs the double row.

Correct me if I'm wrong OP.
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Old 07-16-2012, 12:39 PM   #4
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Actually I am looking for all of the above. Is there a universal timing chain set up that will work on all airheads? That is what I am trying to find out. Not necessarily single or double row but is the math the same? Sprocket diameter, teeth, etc.

Thanks for the help.

JH
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Old 07-16-2012, 12:56 PM   #5
disston
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The crank rotates twice for every single rotation of the cam shaft. This is an absolute part of the design of the 4 stroke engine.

In the Airhead 247 engine design there are two cam chain designs. The double row on early bikes and the single row on later editions.

I thought of putting a later single row chain on a double row engine once but never got around to doing this so can't say for sure it would actually work.
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Old 07-16-2012, 04:15 PM   #6
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Quote:
Originally Posted by disston View Post
The crank rotates twice for every single rotation of the cam shaft. This is an absolute part of the design of the 4 stroke engine.

In the Airhead 247 engine design there are two cam chain designs. The double row on early bikes and the single row on later editions.

I thought of putting a later single row chain on a double row engine once but never got around to doing this so can't say for sure it would actually work.
Number of teeth on single and double are the same. On a side note, some cams are advanced 3 degrees (actually 6 degrees but this is cut in half by the 2 to 1 ratio). There is some debate over wether it is the slot in the gear that is advanced or in the camshaft. I'm in the camshaft group. I stacked a single and a double sprocket together from an early 0 degree bike and a later 3 degree bike. The slots lined up when the teeth were aligned.
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Old 07-16-2012, 04:52 PM   #7
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Quote:
Originally Posted by mattcfish View Post
Number of teeth on single and double are the same. On a side note, some cams are advanced 3 degrees (actually 6 degrees but this is cut in half by the 2 to 1 ratio). There is some debate over wether it is the slot in the gear that is advanced or in the camshaft. I'm in the camshaft group. I stacked a single and a double sprocket together from an early 0 degree bike and a later 3 degree bike. The slots lined up when the teeth were aligned.
Was that an emissions driven change ? Or, god forbid, performance ?
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Old 07-16-2012, 05:12 PM   #8
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Quote:
Originally Posted by mattcfish View Post
Number of teeth on single and double are the same. On a side note, some cams are advanced 3 degrees (actually 6 degrees but this is cut in half by the 2 to 1 ratio). There is some debate over wether it is the slot in the gear that is advanced or in the camshaft. I'm in the camshaft group. I stacked a single and a double sprocket together from an early 0 degree bike and a later 3 degree bike. The slots lined up when the teeth were aligned.
There you go. I guess you showed that cam is advanced crowd.

I'll bet it is an emissions issue. The more I hear about this kinda stuff that BMW did over the years the happier I am with my older Airhead. But then if you look at performance and the machines on the road, my bike really shows her age.

I owned a K75 for a few years. Was nice on the road but talk about no seat of the pants performance. That's a bike that can't get out of it's own way. I talked to a guy yesterday on a K1200. He said they still don't have any torque.
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Old 07-16-2012, 07:10 PM   #9
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Was that an emissions driven change ? Or, god forbid, performance ?
Well let's see. With the 308 the story is they did it for emissions. With the 336 they did the exact same thing for performance. It depends on what cam you are talking about. That and who is telling the story.
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