I have had a knock in my engine at a very specific rpm(2800+/-100). I have checked and readjusted the rockers, there are no bent pushrods. You can hear the knock continuously if you keep the engine rpm at that level but it quickly goes away above and below that. However, the noise doesn't correlate with a decrease in power or an engine stutter. The crank, rod, and cam bearings have been replaced and when the engine is warm I'm running about 30psi oil at idle and 50-70psi at speed. I thought about exhaust leak but it sounds more mechanical. Any ideas?

 

I have been doing some research and have decided to put some pushrod guideplates on to see if that helps. Has anyone heard of a specific rpm rattle being caused by rockers?

 

There used to be such a thing as fuel pump knock in small block Fords, The 1964-1970 Motor Repair Manual mentioned it and the fix for it, however I don't have mine handy, I'll look for it and get back to you.

 

It has an electric fuel pump on it now. I have been listening to knocks on youtube and haven't heard anything exactly like it. I doesn't sound like a spun bearing as far as I can tell, plus I have been successfully ignoring it for a while so I hope its nothing too major.

 

You can't put guideplates on these motors without machine work on the heads and it's a complete waste of time and money anyway you're just replacing one perfectly good alignment mechanism with another, so I don't see this as being your problem. It sounds to me like you have eliminated internal engine problems as the source of this noise so the logical thing to do is start looking externally at the exhaust or those belt driven parts on the front of the motor. I have seen alternators and AC compressors make funny noises at times or you could have a tensioner pulley on the way out.. if so equipped. Divide and conquer.

 

I had a knock in the 5.0 in the 92 F150 I resurrected last weekend, it turned out to be the dipstick tube hitting something in the crankcase. I know this isn't going to be the case in your 72, but just goes to show you what can happen. The fix was I bent the tube slightly up top and that redirected the bottom of the tube inside the crankcase, that ended the contact point in there.

 

Possible wrist pin.

 

Ugh, I'm pretty sure critter is right. The Rotating assembly is the only thing i haven't changed on this engine. If this is the case what do I need to do to fix it? Should I go ahead and change all the pistons and rods? The engine is already bored .040 over. So, in the case of swapping them all would I need to have it honed and put in more .040 over, bore it out, or is it new short block time?

 

To help in the overall decision given that this is the problem here is a picture of the block. It looks like it was rebuilt because someone threw a couple rods and broke some iron off an cylinder sleeve. 302 Crank

 

What are the casting numbers on the block ? Those look like Hi-Po main caps from the angle the picture.

 

Don't have them handy, I know I checked them once and the code said the block was from a 1972 Fairlane or Torino and the heads were from a 1969 f100.