Rod_Montana

This is in my friend's 04.5 CTD

Best way to describe the sound is this:

At an idle, engine at operating temperature. Hood up and standing near passenger battery.

Standard thump, thump, thump, thump of all cylinders firing evenly. BUT:

A rather loud knock, knock, knock that is timed exactly with the thump, thump, thump.

What's strange is that the knock goes away for about 3-4 beats every four or five seconds.

This truck was recently in a Cummins service shop where they had to adjust all rocker arms a LOT.

I pulled a Blackstone sample kit out of my 05 glove box and drew a sample. 1000 miles on his oil. Report not back yet.

He says the truck drives fine.

Any thoughts?

papaduck

Sence they adjusted the valves a lot, sounds like he has valve seat dropping and the thump is the piston hitting the valve and seat. Might be something else but worth checking as it could destroy the engine.

Rod_Montana

Wouldn't that effect drive-ability? Power is smooth, just noisy, especially at idle.

Spooler

Pull the valve cover and see if all the valve stems are at the same height. He may have a seat about ready to fall out. It is very hard to say from here though. He may have some carboned up injectors. Does he pull heavy or just drive around like grandma for fuel mileage?

Rod_Montana

Got a 14k 5th wheel that's gone a few places, but most of the 80k miles is empty-daily driver stuff.

Good idea on pulling the valve cover. That would be me though, he is not so good with wrenches.

Sur5er

Can you feel anything thru the VC while it is running? If it sounds like metal on metal, he could have something flopping around, like a feeler gauge, or a wrench Whatever it turns out, I wouldn't recommend running it until you can determine what it is.

Rod_Montana

Didn't try that. Oil report should be here tomorrow or the day after. Assuming it doesn't show a ton of iron from a bad cam lobe, or super fuel dilution from a bad injector, we'll proceed on the likelihood of an errant valve seat. The truck is "grounded" as of tonight, according to Larry, the owner. I'll get down there on the weekend and we'll pop off the VC and take a look.

I kind of interviewed him today about his towing trips. He has Smarty, was running SW2 (towing), but keeping his foot in it a bit on some long grades over the continental divide. He always tows with Tow/haul engaged, so the overdrive was locked out. His wife is a bit of lead foot and at times he'd wake up from a nap and she would be pushing 70mph or more, in the passing lane. Towing the fiver.

No gauges, so we had this little lecture today about EGT and RPM and fueling. He might have got it hot enough to loosen a valve seat. Easy enough to check for that.

Assuming so, how is that repaired? I mean, I know the head has to come off, but are oversized valve seats pressed in? What's the typical cost of something like this? And who would you trust to do it? Truck's in Kalispell, MT.

jhenson

My dad has an old Mack truck with a 237 in it and twice now, on two different heads, the intermittent thump, thump, thump has reared it's ugly head. The first time it happened we pulled the heads off and low and behold, a loose valve seat. The thump we were hearing was the valve slapping the seat back into the head. He's lucky it never got hung up crossways....would have been nasty at best. I'd definitely pull the head and do a thorough inspection of the valvetrain.