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Let me first say that I am not a Bike owner but have always found Bikes fascinating . So, I pulled up to this stoplight and there was a beautiful looking H.D. RoadKing Bike driven by a fella who looked to be about 60 . Aside from the beauty of it, I immediately noticed while it was at idle that the entire Bike was shaking violently -- everything from the fenders to the handlebars ; he had both hands on the grips and both his arms and torso were shaking pretty good. Ive never seen this before quite frankly, and wondered what was up with that ? Is this normal, or, does his motor need some work ?
As he gave it some throttle and began to pull away, the bike all of a sudden smoothed out with no more shaking. It was only at a stop.
I cant say ive ever noticed shaking to that degree on a Bike . Please forgive me of my ignorance regarding this issue, but I am curious. Thanks.
P.S. Which H.D. model is the best seller today out of all of them ? Ive wondered that too.
I google'd a study once of various engine configurations for a motorcycle class I was teaching awhile back ... can't find it now in my files ... but I'll bet it's still online. They had animations of the running dynamics of various motors ... singles, twins, in-line multi's, parallel twins, radials, and various angle V twins and flat opposed motors. Pretty interesting to see the differences of the forces on the crankshaft at low RPM and then higher RPM's.
For the V twins, it's interesting that the narrow angle ones, like the 37 1/2 degree or 45 degree ones never smooth out, while the 90 degree V twins (such as Guzzi, Ducati, and Honda, to name but a few) start at low RPM with a slight primary inbalance but smooth up the more the RPM's increase and the secondary forces prevail.
H-D (and others) have spent a lot of engineering time to isolate the rider from the motor vibration, so it's not so bad at cruising speeds ... but it's not inherently smooth like a lot of other configurations. At idle RPM, many of them are so out of balance on primary forces that they can shake the whole bike, sometimes pretty violently. If the motor had been "modified" with different pistons or other mods affecting the balance, and the crankshaft not rebalanced correctly, it could have a lot more vibration than factory stock. I bored a lot of HD cylinders years ago for a shop I worked for that was the importer for Covmo pistons ... a performance all alloy piston (as opposed to the steel reinforced factory piston) of higher compression ratio's than stock. Many of the shops that installed those cylinders only worked on the top end of the motor and didn't work inside the crankcases, so the resulting motors shook a lot at idle RPM. I guess their customers accepted that was the price they had to pay for having a "hot" performing motor, although it didn't have to be that way ... or maybe it was their way of showing off that they had a built up HD motor. I only did the cylinder boring and piston fitting, I never worked on the complete motors ....
From what I know, the motor mount cushions allow the whole bike to shake at idle, but they are 'tuned' to work at higher RPM. Makes sense to me, I guess.
The intent of the later HD's (post 1980's, IIRC) with the rubber motor mount set-up was to isolate the strong motor vibrations at idle RPM. Apparently, HD has been having premature failures of these along with the top isolation mount ... enough so that "aftermarket" manufacturers are selling "improved" parts, at substantial prices. I've seen some of the motor mount "kits" selling in the $250 range, with just a top and bottom mount.
I'd call that pretty expensive for a small flange with a center tube piece bonded into it with rubber for the bottom mount, and the top mount is a fairly simple piece, too. Even my airplane motor mounts aren't a fraction of that price, and they are FAA certified parts which quadruples their retail price.
The reason why they shake so much is that Harley has two motors out one is a non-balanced motor which they put in the touring bikes i.e. road kings, classics, baggers etc... the other is a balanced motor which is put into all the solid mount bikes which are softails, dynas, fxds etc... I have a built stroker motor in my bike that i built, and it does not vibrate at all because it is balanced. this motor of mine puts out 115 hp and 117 ftlbs of tourqe to the tire. If you want to do more research look up on any harley tech forum and they will have more info on this.
Let me first say that I am not a Bike owner but have always found Bikes fascinating . So, I pulled up to this stoplight and there was a beautiful looking H.D. RoadKing Bike driven by a fella who looked to be about 60 . Aside from the beauty of it, I immediately noticed while it was at idle that the entire Bike was shaking violently -- everything from the fenders to the handlebars ; he had both hands on the grips and both his arms and torso were shaking pretty good. Ive never seen this before quite frankly, and wondered what was up with that ? Is this normal, or, does his motor need some work ?
They are designed to do precisely that. It's not that they have to, but many of the old hard-core Harley riders wouldn't even consider buying a motorcycle that didn't shake at idle.
They are designed to do precisely that. It's not that they have to, but many of the old hard-core Harley riders wouldn't even consider buying a motorcycle that didn't shake at idle.
Where's that BS flag? They aren't designed to do that. They do it because of a old inherent design drawback, but it is marketed as "character".
No bike should be a paint shaker, but there isn't much room for engineering advancement at the old Bar and Shield, that is unless it involves chrome.
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