2003 detroit 12.7 question

I had that same type of noise thru filters on a 3406, pulled valve cover some rockers were broke dug deeper and head was shot too, caught it in time where nothing messed up motor, id pull top cover off and look around

 

my detroit sounded like that had the ecm retuned and went away so i have no clue what it was mines a 05 14 liter

 

If it's kind of a chunk, chunk, chunk sound, you may have some intake valves not seating because they're too tight. Series 6o just about has the market cornered on tightening up intake valves. If it hasn't had the overhead ran in a long time, just hope you don't have a carbon build up and have to do it about three times to beat the carbon loose so they'll seat.

 

I would agree with what beenjammin says.

 

X3 in checking the valve adjustment. The intakes tighten up on them.

 

Run the over head. It's a very simple job that won't take more than two hours. Only special tools needed is the injector height one. Can get it at Detroit for under a hundred bucks. Other than that it's just a few wrenches and a feeler gauge.

 

Wow, he must be a great mechanic. I've been doing this 25 years and I can't tell a bad harness by listening to it. It could be a harness issue, but if the check engine light is not coming on, I'd say probably not. You're probably best off bring it to a reputable Detroit shop and and for a overhead adjustment and ask them to check everything really close under the valve cover while they're in there.