kbailey

Ok guys I'm looking for some help before I give up and head to the local cummins shop. I had the head gasket changed on my '98 12valve and now it makes a terrible noise starting around 2000 rpm. The noise gets louder as rpm increases. The noise is also worse when the truck is driving as opposed to being revved. I first thought maybe the turbo had something wrong with it but after listening harded to the noise I can hear the turbo spool up and it sounds normal. My second thought was maybe the valves were out of spec seeing as it just came from a head gasket change. I took it back to the mechanic and he readjusted all of the valves and said the #5 and #6 cylinders were a little off. This helped a little but the noise is still there. Really, it still sounds like the valves are out of adjustment but I'm no diesel mechanic.

eyoung429

Last time I had that happen was with my Duece and a half in the military...adjusted the valves while the motor was cold and had the noise once the mill warmed up as they were a bit too tight. Is it a whistling noise or almost a constant rattle?

kbailey

It definitally isn't a whistling noise, but it could be a constant rattle.

eyoung429

Sounds like the exhaust valves may be adjusted too far and not closing all the way but then this is speculative and not being there to hear it, I would get the specs and pop the vc's off and check them before driving it any further.

John DiMartino

Is it RPM sensitive or load sensitive.I ask because you said its when your driving,not revving it.2000RPM is the same under load or revving in N,so I am guessing its load sensitive.It sounds like you may have a boost leak to me.Check all your connections,and the intake horn to intake gasket first.

kbailey

OK, let me clear this up a little. When I rev the engine, with no load, the engine does make the noise. The noise is just louder when under load. The difference in volume is noticable but it isn't huge. I hope this clears everything up a little. I'm going to try adjusting the valves saturday but please keep the suggestions coming.
Thanks for the ideas eyoung and john!

XLR8R

Sure sounds like the valve lash.

dpuckett

I have a similar rattle in my 92- sounds like a valve adjustment problem or maybe an injector knock. Being I dont have a tach, I cant give you exact RPMs, but it seems to start at about 35mph in 3rd (manual), and 50ish in 4th. Definitely load related. I readjusted the valves to .010 and .020 (stone cold first thing AM) as per the book. I had set them to .009 and .019 when I put the pump on 2 weeks ago, then reset them yesterday, to no change, except slightly higher EGT at cruise. Guess it's time to pressurize the intake system and look for leaks.

DP

kbailey

I spent most of the morning re-adjusting the valves and sure enough that was the problem. All of the valves were adjusted too tightly. I backed them off a little and now the truck runs pretty good. Thanks for all the help guys.

XLR8R

Same thing happened to my '98 the first time I adjusted the valve lash - according to the instructions... engine wouldn't even start, so I went back and did them again my way (@ 75K miles ago).