All,

I recently did cams (57h) and heads on my bike. I also replaced the lifters, pushrods etc and have autotuned the bike with the Powervision.

The bike runs really, really well right up to the redline and the valve train seems to be pretty quiet and sounds "right" to me (after I stopped the front exhaust pushrod from hitting on the tube).

But when I park the bike after riding it, if I leave it running at idle I can hear a strange hollow "tonk" kind of noise that seems to overlay on top of the regular engine noise.

The bike only does this when it's warm idling - not when I fire it up from cold.

I have used a mechanic's stethoscope to listen to all parts of the motor and everything sounds absolutely fine - whirring and purring with absolutely no sound of the "tonk" and nothing sounding out of place. No bangs, clatters or clangs. I have checked the rocker boxes, heads, cylinders etc and cannot hear the noise at all there....

It's a bit difficult to describe, but as I said above it's kind of a hollow sounding "tonk", regular with the engine. It's pretty quiet, but I can hear it over the valve train noise. It also disappears if I bring the throttle above idle.

I have rocker lockers in the bike already. I also have a DK customs Outlaw 636V open elbow type air filter on the bike. Exhaust is a D&D BobCat.

Any thoughts on what this could be?

 

What you're hearing is reversion, it's normal when running certain cams. I had it when I was running a Wood TW555 in a 2010 Trike, drove me nuts at first till I figured out where the noise was coming from. Open element air cleaners seem to make it a whole lot easier to hear, something as simple as the cover over a normal stage 1 air cleaner will mask the sound.

 

Thanks, I was reading up on that and kind of thinking along those lines.

Any idea why it would only be noticeable at idle, but disappear as the revs go up - and also why I can only hear it at a warm idle not a cold one?

 

A lot of times it depends on the cam where and when the reversion is heard, cold idle is going to a little higher than warm idle which may make it less noticeable.

 

I had the same noise in my Roadking. It turned out to be a loose compensater bolt . The bike only made the noise at idle when warm . I had to replace the bolt and compensater to get rid of the noise .

 

Good point. My cold idea starts off around 1200 RPM whereas warm idle is around 1000 RPM.

 

Thanks - guess I will check that just be sure, but it's definitely a right side of the bike noise and seems to come from the air filter more than anywhere else...