Engine knock at 3,000 rpms

[jmiller789]

Ok, I just recently I was fighting the wind on the highway of course and was driving in 3rd gear pretty much the entire drive home for about an hour. Now when I am driving, I get a normal rhythm loud knock at about 3,000 rpms, but is not heard at lower revaluations.

It’s coming from the engine compartment and you can hear it when the windows are down. It's pretty loud.

This just started after that drive. The engine has about 135,000 on it. It is a strait 6.

I just dumped 1,200 into the transmission, so I’m hoping for the best.

Any thoughts?

 

[SteelHeadz]

Possibly a piston knock, rod bearing or wrist pin bearing. One way to verify for metal is change the oil and filter. Cut the filter open and see what's trapped onto the filter element. Chunks of metal would indicate that the engine needs to be dis-assembled for further analysis. Also make sure that you have an adequate oil pressure @ idle and @ 3000 rpm. Are you sure it's an engine knock and not a valve train noise like a colllapsed lifter?, does it misfire at all?..

 

[jmiller789]

There is no misfire, it seems to run just fine. Its just that knock at 2500-3000 rpm. I can check on the oil pressure.

 

[jmiller789]

I checked the oil pressure everything seems to be fine. It doesn’t make noise until its warmed up, no backfire and the engine runs pretty smooth as it always has, even when the noise comes around it runs pretty good.

 

[Saddle Tramp]

The only other option not mentioned above is a sticky lifter. Not sure about that though.

 

[xt master]

Normally lifters will rap all the time not just at certain rpm.I can't think of anything that would only make noise at 3k rpm..if it was always there but got louder I could understand a lifter problem.

 

[SteelHeadz]

Lifters MAY still cause the noise only at higher rpm's. I've seen them make a knocking noise when the lifters couldn't expand fast enough to keep pressure on the rod and rockers above the curb idle. If you have access to a mechanics stethoscope to isolate the knocking noise, that will give you a better idea where to look for the problem.