I have a 1996 12 valve with nv4500. Truck has 248k 2wd. Home cut 100 fuel plate slid forward afc housing at middle stage and star wheel light tension on stock spring. It has mrbp 4 inch turbo back and bhaf. Sitting on 33s 2 inch level. Truck rattles pretty good at around 1 thousand rpm in any gear.but it cleans up as i get higher in rpm. So on the freeway doing 60-70 mph 2000rpm the engine makes a really good chattering noise you can hear when the radio is off. It sounds like lose valves combined with a load compression noise. Iv done 3 valve adjustments physically rechecking each valve each time and still does it. Doing 80 mph at 2100rpm the engine sounds much smoother but at 65-70 it's pretty loud. No performance loss whatsoever as it drives perfect. My question is, is this common in 12 valves? Is it just all those mechanical parts making noise. Diesel engines arnt really designed for high rpm especially an old mechanical one. Would love to hear some input on this please and thank you. And the rattling in just about every gear change drives me crazy i started shifting at 2100 rpm just to shut it up.

 

few things it could be. did you ever get egts hot enough to score a cyl.

 

Not that i know i dont have a gauge. But i drive it easy. Previous owner may have tho. Iv nerrowed it to a possible exhaust manifold leak. 2 bolts for cylinder 1 are brand new the others are really old. Iv read up on manifold shrinking maybe that happened before me. Im going to try gaskets . But does what I mentioned sound like a exhaust leak? Funny thing is I build boost no problem and it only occurs at highway speeds climbing? Thanks

 

Has the Killer dowel pin been addressed? it may be a damaged gear or gear lash, IP fuel timing problem, if its intercooled maybe a boot leaking making the compression sound, hard to say for sure. Do you feel any vibrations, could it be not engine related?

 

Im not sure if the kdp has been taken care of but it's definitely engine. Thr truck runs amazing pulls really hard my power is all there throughout all rpms. But just in the high speed rpm section on the freeway you can hear it thumping. Ill post a video soon.

 

https://youtu.be/68MM6Y6u5EA

 

I thought I heard a loose rocker arm or lifter sticking could be a broken/weak valve spring (floating valve). I listened to it a few more times and about half way through the video it sounds like an exhaust leak at a cylinder flange hard to tell.