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. I have had carb problems recently also. It's been flooding and I hadn't had a chance to replace it. Could it be related to the knock? Any suggestions on tracking down the problem without causing more problems in the process? Any help is much appreciated.

 

Welcome aboard, pal.
I would suggest that you crawl under and look for an exhaust leak. When you hit the limb you might have cracked a header weld or jarred a gasked.
It is unlikely that running over a branch could cause internal damage to moving parts.

 

Also look at the engine's oil pan. That limb you ran over might have dented the pan up to the oil pump's pickup screen. Choking off the oil pump. What is your oil pressure gauge reading?

 

Thanks for the welcome and replies. I don't believe the limb caused internal damage either. It happened a short distance from leaving the house so checking the modulator line seemed easy and and a likely candidate. The knocking began 2-3 miles later. Oil pressure was ok the short time I ran it afterward and I saw no damage underneath but will look closer. It wasn't a big limb or a hard hit but was enough to get my attention. I was more concerned about the tires than anything else. This definitely sounds like an engine knock and I think the limb deal was just coincidence, not the cause.

 

I hope you are correct. Please let us know what you find.

 

Correct about what? I'd prefer it was one of the reasons you or CougarJohn suggested. I believe it's very likely something's wrong internally, I just don't think it was caused by the limb.

 

I misunderstood you. I hope it turns out cheap and easy.

 

Thanks Jeff. I did start the motor a while ago and used a hose to listen. It seemed loudest around #7, near where the manifold meets the pipe. Maybe tomorrow I'll have time to get under there with a light and see if there are any visible problems. I do have a leak at the connection but it is not what's causing the knocking.

 

As long as oil pressure still OK start it back up and pull the plug wires off the close cylinders one by one and see if the knock changes or goes away. As long as you insulate yourself from the metal of the truck you won't get jolted. This is checking for rod/main bearing knock.

 

You said you had been having flooding problems lately. How bad did it flood? Did you get gas in the oil?

I would check your oil see if it is over full and if it smells like gas. If so then more then likely you have a bearing that's gone bad. It don't take long to ruin a bearing with gas in the oil. I hope this ain't the case. Let us know what you find.

 

That's good thought Phantom but didn't happen. I had a carburetor do that to me before on this truck. I think I'm probably looking at a bearing but never had gas get in the oil on this go round. Thanks for the idea though.