Knock in engine?

[wargle]

I have a 92 XLT with about 10k miles on a complete rebuild. All of a sudden I have developed what sounds like a knock around number one cylinder. When the engine is reved up the knock seems to go away. It idles smooth but has the knock. It is not a "tick" like with a lifter, it more of a "solid" type of knock. Could it be a loose rod cap, wrist pin. Could it be anything in the head?
Does anyone have ideas for narrowing down he possibilities. I appreciate any help.

 

[Michiganbear]

I also have a 'knock' in 1 cylinder, and I KNOW mine is a collapsed lifter. with the valve fully closed, I have a good 20-30 thou of play in that one pushrod.

now, mine does not go away (my lifter is totally dead) with increased rpm. YOurs does sound like a failing lifter to me.

mine does not sound like a normal lifter tick, it is very heavy in sound, due to the amount of motion and how hard the pushrod hits the rocker.

I am not in a hurry to fix it, been this way for 100k miles, and I am not pulling the head to swap out 1 measly lifter,

 

[Masterd]

Get a sound clip if possible...

 

[wargle]

When I rebuilt my engine I got a bad lifter (new). It would never pump up and gave me a "tick". I had to go bacK in and replace all the lifters on the side with no. one cylinder. I was sure the tick was on no. one, but changed the all to be safe. The lifters were replaced free of charge along with new head bolts and head gasket for that side by my parts guy. Now I have the "knock" and it sounds like it's on #1. You think it could be another lifter going bad, huh?

 

[Blacksheep Josh]

I've heard of running slightly higher octane fuel and sometimes the knock will go away, but I'm not sure why. Someone may be able to explain it, I just can't recall my vocabulary at the current moment..

One of my lifters was ticking horribly a few years ago, a local mechanic said he's used transmission oil to fix sticky lifters. He'd drain a quart of oil from the engine, then replace what he drained with transmission oil, then run the engine in park for a few minutes, and most times because the transmission oil is lighter, it can get into that lifter and free it up. He'd then drain everything out and replace it with regular oil. Not sure how accurate or safe this is, but it's a definite idea... Someone with more experience and knowledge might want to chime in on this.