I've got a slight noise coming from the top end of my motor. It's a 502, about 140 hours since a rebuild.

The noise goes away when I hit about 1500-2000 RPM. It's only there at idle, when I increase the revs, she purrs like a kitten.

The noise is there whether the motor is cold or hot. It's hard to say if it's more pronounced when cold, it might be. The motor runs fine, the exhaust sounds great, oil pressure is good. Oil pressure near 60 lbs at idle when cold started, probably 20-30 lbs when idling hot.

Thinking it might be piston slap since it's got forged pistons, but since it doesn't go away when warm i'm wondering.

I did a search and someone suggested a similar noise might be a broken return spring in the fuel pump. I just replaced the fuel pump (dumping fuel into the water pump / fuel pump drive housing) and neither had a bad return spring. It did this last year too.

You may have a little debris in your lifter. This is quite common and if that's the case it will most likely flush out with more time on the motor. If you have no tick at a higher RPM you are most likely just fine...The worst case sounds like you may have a worn or collapsing lifter. This can happen but not likely at your hours on the motor. Possibly the lifter was not adjusted down enough at build also, again, run it for a while and if it does not go away, pull the valve cover to check it out.

Could it be an exhaust leak? I had one between head and manifold, sounded just like ticking, and went away at increased RPM

Had the same issue.

If you have the internal flappers in the exhaust those will make a ticking sound at idle also

I think it's been doing it long enough that it won't just go away with hours.

Where are the internal flappers in the exhaust located? I don't know if i have them or not. Are they needed, is that something i could remove?

if it's an exhaust leak it would have to be multiple cylinders. I suppose i could check the torque on the exhaust manifold bolts.

I may pull the valve cover tomorrow to check it out. Is there a possibility of loose rocker arms? are the rocker arms adjustable?

Do i have to pull the risers off to get the valve covers off?

I bet it is your flappers. Take a screwdriver put it to your ear and the exhaust riser to see if the sound is coming from the flappers. I had my boat in the shop, and the tech called me to tell me that he was afraid to start my motor until I told him about the flappers. He also though it was a problem inside of the valve covers.

So the flappers are inside the riser? I've been searching the site all morning trying to learn about them. That does sound like a reasonable explanation.

Check this out.

http://www.outdriveshop.com/shutters.html

So that says they're in the y-pipe (good link by the way, thanks). What component exactly is the y-pipe?

I have quick and quiet exhaust. There's the manifold, then the riser, then the switchable diverters that will either send the exhaust straight out through the transom (mufflers with external flappers) when open or they'll close and divert the exhaust down into the (y-pipe?) that goes down under the back of the engine and sends the exhaust out through the outdrive.

I get the noise whether the exhaust diverters are open or closed, but with the diverters open, the exhaust is still free to go down through the outdrive (there's just more restriction that way).

Thanks for all the help guys. Hopefully it is something as simple as an exhaust flapper.