That's a fairly normal vibration pattern for all the rubbermounts. Shakes at idle, smooths out some by 1500, gets rough again, smooths out over 2500. Putting at 1500 should be fine.

Minimum safe rpm is idle speed.
Contrary to old wives tales which get repeated over and over on the internet, low rpms don't place any extra stress on rods or bearings. Quite the opposite, stress on rods, rod bearings and pistons increases with the square of the rpm, so it's high rpms that put the most stress on these parts.

Another load factor, aside from rpm, is how hard the combustion in the cylinder is pushing on these parts. Combustion pressure is highest around the torque peak, not at ultra-low rpms, so that's another strike against those who claim that low rpm operation is hard on engine components.

I've oversimplified some of this a little bit, but that's the gist of what's going on.

 

I'm calling BS on this. If you are putting along at 1500 RPM you should expect excessive vibration because you are Lugging your engine and there is potential damage.

Here is an article on Bearing failure and they specifically mention damage from lugging. http://www.knowyourparts.com/technic...earing-damage/

 

low rpm's or "idle speed" at operating temp is a point at which the oil pressure is at it's lowest! metal to metal contact is at it's most likely window of opportunity. add the inherent "twin lope". "lugging" is absolutely the worst thing you can do to your motor, compensator, primary chain/tensioner, and absolutely rod bearings, piston pin, mains. don't lug for fun/show.

 

The article is talking about a completely different kind of bearing (which is called a "bushing" in the bearing business). The rolling element bearings in a Harley bottom end are a whole different animal. Just like ball and roller bearings in a wheel, they can handle high loads and low rpms. Keep in mind that low rpms aren't a problem for wheel bearings.

However, many cars with plain bearing bottom ends are going down the freeway now at about 1500 rpms, for emissions and fuel economy reasons, and these engines hold up much better than engines of the past which were spinning much faster.

 

Yes, oil pressure is at it's lowest, but high oil pressure isn't needed at low rpm, even on a plain bearing engine. An old rule of thumb on plain bearing racing engines is 10 pounds oil pressure for every 1000 rpm.

But Harleys are roller bearing bottom end engines, and roller bearings don't need pressure like a plain bearing, nor will they hold pressure like a plain bearing. What they need is adequate volume.

By the way, my supercharged Corvette is turning 1200 rpm when cruising down the freeway at 65 mph. That's with original factory gearing. Someone should have told the engineers at GM that "lugging" destroys engines.

A lot of this stuff about "lugging" comes from the old days, when a combination of low rpm and high throttle opening was likely to result in detonation. Detonation is an engine killer, for sure, but computer engine controls and detonation sensors (which Harleys have) have pretty much taken care of it.

 

Jc, your problems could describe mine perfectly. If you want to save yourself a lot of work go read my "evo shake" thread in the evo section. I have replaced or checked everything and some things triple and along the way I've found a lot of damaged parts that needed replacement but did not fix the 2000 rpm shudder shake or vibration and I've put a crazy amount of hours and effort into it. PM me or post here if you have specific questions as if you think of something I'll tell you if I've done it already and save you the time.

What I've learned is that I still find stuff wrong but what has made the bike rideable for me is the vibratechnics front mount made it more manageable. It was better than the stock mount by far and made it more stabile both straight and in corners. 12 " apes with 5" lead rolls in the ends absorb enough that I can hang on and ride it. With the stock short bars it's not rideable and will shake so hard you can't see straight. I didn't want apes but it is what it is for now. You still feel it in the seat and pegs but until I figure it out at least it's rideable.

Most recently, not in the thread, is a new ignition, jetting and plug wires. The wires and carb were faulty as well. Basically everything I check has an issue but isn't the one making the problem! I've been told it's the crank and it probably is. Mine smooths out up high as well and is like glass on the highway, I just don't ride the highways.

 

Yes, I get that this is a different type of bearing, but did you miss this part?

Engine lugging can distort the crankcase and/or crankshaft, affecting the connecting rod and/or main bearings.

 

I didn't miss it, but it's basically B S, unless they're assuming that the engine is detonating. If so, that's basically antiquated "old school" thinking.

As I explained before, combustion forces are highest around the torque peak (around 3-3500 on a stock Harley), and inertia forces are highest at the highest attainable rpm. What is the source of these forces which supposedly distort the crankcase and crankshaft at very low rpms?

Sure, we've distorted blocks and crankshafts pretty badly on things like blown alcohol automotive-style engines (and slightly crowned crankshaft journals or bearing inserts are sometimes use to deal with this distortion to keep from wiping out the edge of the bearing), but this has nothing to do with low rpm operation. It was because they were making about 1500 ft/lbs of torque, making around 4 horsepower per cubic inch, and turning mega rpms.

 

I beg to differ sir, and must respectfully disagree. Ive heard my pop explain it a dozen times, but I didnt really understand until he tore his FLH apart, and explained it in great detail, as he cross referenced an article in sum HD mag that he had xeroxed. Ill be damned if I remember everything, but I saw and understood at that time, that basically when u "LUG" ur hog, the mixture in proportion to your speed/load is such that the explosion is eventually going to work its way thru the piston rings.

I started off about 6hrs ago, searching for why my 98 wide glide, after a ruff road with a passenger, now feels like its gonna rattle apart at idle, and wants to pitch a little from side to side over the littlest bump or groove in the road. Pop lowered the rear a bit when he had it, but Its none of his mods, cuz it ran perfect until that raggedy cratered shortcut. Ill admit that im not the most gentle rider, but its a little scary to ride now, and Its gotta be something simple. I saw this, and had to respectfully object. Thank you tho, cuz it dawned on me, that being the hardcore old school biker that will always rides apes, jockey shift and suicide clutch, and wont have a starter on his bike but will always kickstart.. not to mention it was his bike first.. recollecting the whole LUG lesson, I know just where to take the ol glider. Thanks guys!

 

It's taken you six years to get here and solve the problem. Thank you and welcome!