engine noise in '69 F-250 390

[69er]

I have maybe 40-50k on a rebuild. New crank and bearings, new cam and bearings, high pressure oil pump.It had been running great and the oil pressure was good. Oil level was good. After about a 4 mile drive to church it began a tapping that got louder as I pulled in the lot. It was the first convenient place to stop after it began. It's loud and will make the noise from start up. I didn't run it long after that but it did seem to be coming from the lower end on the passenger side. We pulled it back to the house that night and I haven't looked into it any further. I had run over a limb on our dirt road that hit loudly under the truck so I climbed under hoping the tranny vacuum line had gotten disconnected but no such luck. Any suggestions on tracking down the problem without causing more problems in the process? Any help is much appreciated.

 

[m78]

See if you can't buy a stethoscope with a tube on the end. Harbor freight has one for cheap.
Start the engine and start pointing that tube around different places.
You might get lucky and find an exhaust leak. Or locate where the tap is coming from.
I often wonder if those high volume oil pumps are more of a problem then a benefit.

 

[Fellro]

It would help to know what the noise sounds like, is it like a hammer banging on the block, or more of a dull knock, or a tap, or what? That helps narrow down the possibilities.

 

[BuzzGun79]

Sounds like a wrisk pin has worn to me..if it is loud and persistant,through my experience with the FE engine...The wrisk pin holds the piston to the rod.Marks suggestion will pinpoint which one.

 

[m78]

Sounds like a wrisk pin has worn to me..if it is loud and persistant,through my experience with the FE engine...The wrisk pin holds the piston to the rod.Marks suggestion will pinpoint which one.

You must be talking about a "wrist" pin.

 

[Fellro]

I have had the snap rings that hold the wrist pin in place give out and let the pin ride in the cylinder wall... It was accompanied with extra crank case pressure and high oil usage.

 

[BuzzGun79]

You must be talking about a "wrist" pin.

Yes Mark...wrist pin.. sorry man thank you!!!

 

[69er]

Sorry I didn't reply, I wasn't notified you'd posted. I had a wrist pin go out on a rebuilt Chevy before and there was no noise except for the sound of pouring oil in it! I had bought a short block and it always used oil. I finally tore it down when I was working out of town and bought another one there. The rebuilder made good on it so that was good.

I finally tore this one down and discovered the culprit. Very odd one too in my opinion. The motor had apparently backfired enough to cause the bolt holding the air cleaner to the carburetor to strip out of the carb. Somehow the end of that bolt broke a piece off and was sucked into #7 cylinder. It was big enough to close the gap on the plug but not damage it. I probably could have gapped the plug and run it for quite a while longer. The top of the piston is a little beat up but the cylinder was ok. Small scratches that honed out. I am glad took it apart though because #8 had the middle compression ring broken. It also was just lightly scratched and honed out fine.Overall I was pleased with the motor wear. I'm putting in new rings and bearings of course and also timing gears and chain. Most important is the carb is getting replaced.

Probably about half the people I know understand why I keep the old beast and wish they could do it too. The other half think I'm crazy. Thanks to all of you that replied and tried to help. It's not easy to diagnose on the net. Most of all Merry Christmas to you all.