Let's Talk Engines...
 

This is something I was wondering today as I was riding my bike. Up until 2300 RPM, the motor sounds fine. Get past 2400 RPM, and the rattling and clattering starts. It does it under load, and is quieter (but still definitely there) at coasting.

What's changes in the engine between 2300 and 2400 RPM to bring this on? My tuner doesn't add any timing to the original Harley map. Oil pressure would come up a little more. Engine turns another 100 RPM faster...

I am at a loss to figure out why it is quiet below one engine speed, and noisy above. It is almost as if the bike says "Oh, 2400 RPM... start loosening up."

EDIT: 500th post!!!

Could be harmonics starting. Could be valvetrain or maybe primary chain whipping around causing the compensator to rattle.

After much work trying to figure the same thing out I lean toward harmonics also.
Depends on all the things put into the valve train I am thinking.

Mine is whisper quiet at 2000RPM. Clatter builds at 2050 then goes mostly away at 2200 RPM. Comes on again around 3000 a little.

Is your engine stock??:icon_steer:
Scott

What really helps me to understand what noises and engine makes is.......taking it apart and almost studying ever part and what it does and what it will do when in movement.

Think of all thats going on. From crank spinnin, to chains and tensioners spinning the cams, to lifters going up and down while pumping, to valve slamming open and shut under a ton of pressure...etc..not to even mention combustion...Add to that, the motor is open, not under a hood and about 3 inches from your nuts...lol

Whenever i change the oil in my wifes honda with a Vtec motor, i say to myself, this highly refined motor is louder than my 650 lift built harley...lol

Thats right.
I have taken the top apart several times for one thing or another and I have looked very closely for and sigh of something and there is nothing to see.

My night train has a rattle sound when you get on it hard that sounds like pinging. I dont think that it is because when I put the bike it a high gear and open it up I dont hear the sound. I think that it is the primary chain whipping because it only happens when going through the gears wot and when I took my primary cover off there are chain marks in the case. So the only thing I can think is that the noise is the chain is hitting the cover and making that noise.

absoluty true

For the record... my motor is stock... for now. I am planning on changing over to geardrive cams. I have a Stage 1 A/C and Exhaust... w/ a PCIII USB with just fuel mapping.. no timing changes...

As for the primary chain... I was planning to change the engine oil tomorrow, but now I am going to do the primary as well, and check the chain adjustment. Another quart of 20w-50 and a new derby & inspection gasket.

Well, I did the oil change.... used 20w-50 in both the engine and primary. Primary chain was a little loose, but not enough to touch the chain case.

One thing that worries me a little. I saw some coppery colored flecks in the oil. Not big pieces, but more like powder. So that has me wondering... could be cam bushings, rocker bushings, or <gasp> rod bearings. I am not thinking rod bearings because you can get on it and you don't hear any knocking from the bottom end. All my noises are coming from the top end... and it seems to come more from the front cylinder, and more from the intake side.