Noise in new 390

[Blue Cloud]

As some of you may recall I got a rebuilt 390 for my F250 4x4. The engine had sat after being rebuilt, still crated up and wrapped in plastic for 13 years. When I uncrated it I squirted oil on all the moving parts, then rotated it with a breaker bar several times. It started up fine, no noises and ran good. Now after 200 miles I've got a knock. It only knocks at higher RPMs (I don't have a tach). I can't hear it at idle and only notice it right before I shift gears and over 45 or 50 MPH. At first I thought I had a rod knock but after reading and listening to videos on you tube I don't think thats it. It's not real loud or steady. I retarded the timing and leaned up the carb thinking that was the problem, didn't help. Today I went and bought a mechanics stethoscope and probed all over the engine and it sounds like the noise-knock is coming from the rear of the engine and is loudest right on the flywheel cover and the very back of the block. From what I've read a cracked or broken flywheel sounds different but I'm not sure. I didn't want to post on here until I knew for sure what this noise was but this has me baffled. Any ideas?

[DuckRyder]

Although it is odd that it would only do it at higher RPM, check the torque converter bolts...

[Blue Cloud]

It doesn't have a torque converter, it's 4 speed. I thought of the clutch, but it works OK, no noise or chatter. The knock is the same with the clutch in or out.

[DuckRyder]

Ah, probably not the torque converter then...

Hard to diagnose a noise over the computer any chance of a recording of it?

Is the clutch new?

[Blue Cloud]

The clutch was new 3 years ago when I put the used 390 that the wrist pins went out on a couple of months ago.

[ezernut9mm]

there is a thread like this over on the slick60s site. the pressure plate seems to be getting alot of attention on that one. is it the type with three prongs or a bunch of little fingers? can you change the noise with the clutch pedal? just throwing ideas out there.

[Blue Cloud]

The noise don't change at all. Now that you asked about the prongs, I can't remember. It was the standard Napa clutch kit, never had a problem with it. I've decided that tomarrow I'm taking it to a mechanic shop and let them listen to it. It might be the flywheel but I'm not sure.

[Blue Cloud]

After looking at it closer this morning again with the stethoscope, then pulling spark plug wires, It seems I have isolated the knock to the #8 cylinder. I checked all the cylinders by pulling the plug wires and when I pulled #8 there was no knock what so ever, which pretty much tells me the connecting rod bearing is out.

[willowbilly3]

It could also be piston slap or a wrist pin.

[Blue Cloud]

I got to go to work today and won't get a chance to pull the pan and look at it until fri or sat. I'm hoping it won't be a major repair. I have a weeks vacation next week so we'll see then.

[Blue Cloud]

Just got home from work. I'm going to drop the oil and pull the pan in the morning, then check out the rod bearing and take a look at the wrist pin. Hopefully it's an easy fix.

[Blue Cloud]

Friday morning I got the oil pan off (glad it was a 4x4!) and removed the cap and brearings on the #8 cylinder. Just as I suspected the bearing was bad. The journal looked OK at first glance but when I ran my fingernail over the surface I could barely feel 2 or 3 tiny grooves. I probably should have pulled the crank and had it turned but decided to just replace the bearing and see how long it lasts. A mechanic buddy of mine said it could last an hour or it could last for years, I guess I'll find out. The guy I bought the long block from had a short block stored too, I'm thinking of seeing what kind of deal he'll give me on it and use it and the old 390 to build a new engine to have on hand for my next project or if this one starts knocking again. This time I'll take it apart first and make sure everything goes back lubed up right. I imagine I could have prevented all this if I had spun the oil pump with a drill before I started it the fist time. Oh well, live and learn!

[Blue Cloud]

I've put around 20 miles on it this afternoon and so far no noises.

[fomocoguy]

Glad to hear you figured it out so easily. What a sinking feeling it is when something is new and you spend hundreds of dollars on it and it malfunctions . Anyways, hopefully it was just a fluke!

[Jake11]

Glad ya got it fixed. You only pulled 1 cap? I would have gave some thought to replacing all the bearings
since the pans off. Good luck, Jake