Why does HD make their engines like this?
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Tourer
Joined: Feb 2011
Posts: 410
Likes: 1
From: Portland, ME
Why does HD make their engines like this?
Hello all,
On my continuing quest to understand all things HD in preparation to buy my first Fat Boy, I am doing a lot of research. I've never been into working on cars or anything, but I understand that doing some of your own work on your bike adds to the enjoyment, and I want to understand more about what I am riding than just how to stay upright.
So, here are a couple questions I hope some of the more learned folk might be able to help me with:
1) The HD is known for having a 45 degree V (except for the V-Rod, which is 60). Why is this such a big deal that it is mentioned at the beginning of every description of a HD engine? Does this have some sort of effect on how the engine operates? If it is so well established, why did they go to a 60 degree V on the V-Rod?
2) I understand that the unique HD sound comes from having a single pin connecting the pistons, and that rather than having a synchronized firing, it causes a pause between each pair of firings, giving it the HD sound. Can anyone tell me why they do this? Is there any reason, other than the sound? I can imagine that they may stick with it today to maintain the sound, but I doubt the original design was to get the sound. Is there any other advantage to this design?
Thanks for any help!
On my continuing quest to understand all things HD in preparation to buy my first Fat Boy, I am doing a lot of research. I've never been into working on cars or anything, but I understand that doing some of your own work on your bike adds to the enjoyment, and I want to understand more about what I am riding than just how to stay upright.
So, here are a couple questions I hope some of the more learned folk might be able to help me with:
1) The HD is known for having a 45 degree V (except for the V-Rod, which is 60). Why is this such a big deal that it is mentioned at the beginning of every description of a HD engine? Does this have some sort of effect on how the engine operates? If it is so well established, why did they go to a 60 degree V on the V-Rod?
2) I understand that the unique HD sound comes from having a single pin connecting the pistons, and that rather than having a synchronized firing, it causes a pause between each pair of firings, giving it the HD sound. Can anyone tell me why they do this? Is there any reason, other than the sound? I can imagine that they may stick with it today to maintain the sound, but I doubt the original design was to get the sound. Is there any other advantage to this design?
Thanks for any help!
Tourer
Joined: Jan 2009
Posts: 494
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From: Reno/Tahoe
Tourer
Joined: Nov 2010
Posts: 342
Likes: 0
From: South Florida
It's a trade-off between the nostalgic sound vs performance. There is something visceral about the sound, it hits something deep down and not many other sounds have the same impact on me, especially in the middle of a pack of HD's just idling.
Wikipedia has some good stuff on the V-twin...here is an excerpt from one of the pages. Hope this helps some. They have even done physch studies on how thier sound effects the brain...
http://en.wikipedia.org/wiki/Harley-...vidson_engines
The classic Harley-Davidson engines are two-cylinder, V-twin engines with the pistons mounted in a 45° "V". The crankshaft has a single pin, and both pistons are connected to this pin through their connecting rods.[6]
This 45° angle is covered under several United States patents and is an engineering tradeoff that allows a large, high-torque engine in a relatively small space. It causes the cylinders to fire at uneven intervals and produces the choppy "potato-potato" sound so strongly linked to the Harley-Davidson brand.
To simplify the engine and reduce costs, the V-twin ignition was designed to operate with a single set of points and no distributor. This is known as a dual fire ignition system, causing both spark plugs to fire regardless of which cylinder was on its compression stroke, with the other spark plug firing on its cylinder's exhaust stroke, effectively "wasting a spark". The exhaust note is basically a throaty growling sound with some popping. The 45° design of the engine thus creates a plug firing sequencing as such: The first cylinder fires, the second (rear) cylinder fires 315° later, then there is a 405° gap until the first cylinder fires again, giving the engine its unique sound.[76]
Wikipedia has some good stuff on the V-twin...here is an excerpt from one of the pages. Hope this helps some. They have even done physch studies on how thier sound effects the brain...
http://en.wikipedia.org/wiki/Harley-...vidson_engines
The classic Harley-Davidson engines are two-cylinder, V-twin engines with the pistons mounted in a 45° "V". The crankshaft has a single pin, and both pistons are connected to this pin through their connecting rods.[6]
This 45° angle is covered under several United States patents and is an engineering tradeoff that allows a large, high-torque engine in a relatively small space. It causes the cylinders to fire at uneven intervals and produces the choppy "potato-potato" sound so strongly linked to the Harley-Davidson brand.
To simplify the engine and reduce costs, the V-twin ignition was designed to operate with a single set of points and no distributor. This is known as a dual fire ignition system, causing both spark plugs to fire regardless of which cylinder was on its compression stroke, with the other spark plug firing on its cylinder's exhaust stroke, effectively "wasting a spark". The exhaust note is basically a throaty growling sound with some popping. The 45° design of the engine thus creates a plug firing sequencing as such: The first cylinder fires, the second (rear) cylinder fires 315° later, then there is a 405° gap until the first cylinder fires again, giving the engine its unique sound.[76]
Thread Starter
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Tourer
Joined: Feb 2011
Posts: 410
Likes: 1
From: Portland, ME
My google-fu is not so good. But reading that, it looks like 45 degree angle is simply a traditional thing from the first bikes, with no other mechanical purpose. So why did they change to a 60 degree V for the Revolution engine?
It also doesn't mention anything about why they use the single pin thing that leads to the sound.
It also doesn't mention anything about why they use the single pin thing that leads to the sound.
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Thread Starter
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Tourer
Joined: Feb 2011
Posts: 410
Likes: 1
From: Portland, ME
Thanks, I think that confirms my suspicions, that it doesn't really mean a better running machine, but sticks to the tradition of the sound. I guess I am just not used to how important that sound is (I like the look of the bikes), because it reminds me of how my first car sounded when it was about to croak.
Thanks for the links, too, that will give me some more study material.
Thanks for the links, too, that will give me some more study material.
Last edited by Wabbit; Mar 7, 2011 at 02:30 PM.
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