turbo noise or exhaust leak?

[JimT]

well, things have been pretty good for a while now with no major engine issues at a little over 200,000 miles since my inframe, 789,000 total miles on this 2012 Pete 587 CM2250. So it's not entirely surprising to see one pop up now. Just yesterday while driving to my delivery I started getting an odd metallic whining sound under hard acceleration only. Hard to describe exactly it sounds kinda like the whine from a bad power steering pump on a car when your turn the wheel all the way. Or an electric motor under a heavy strain. Clearly from the right side of the motor it only occurs under hard acceleration and is not tied to boost pressure. If I slowly get into the throttle I can get the boost up to at least 28psi with no issue. I didn't try going higher at the time since I was driving first and foremost, loaded, and not looking to break down before understanding what's wrong. So I took it easy, delivered my load, cancelled today's pickup and got home just before dinner after a nice 14 hour day.

The turbo was my first suspect and after some searching on here I decided to check for exhaust leaks before jumping to conclusions. Well I found them, but not at the turbo mounting gasket as I thought. No, I found 3 broken exhaust manifold bolts with only the slightest sign of soot around the #1 exhaust. #1 had both top and bottom bolts broken while #6 had just the bottom broken. That's gonna be a fun job... not.

Replacing bolts is one thing and if that's all I need to do I'll be thankful. But what I'm wondering is why they broke. Is there something else I need to address? I don't run hard. I rarely push boost levels above 21-ish psi, even loaded uphill and I operate almost exclusively between 1450 and 1800 rpm with the low end only for flat cruising at low boost. The only thing I did differently immediately prior to the whining was allow the engine to wind up to 1900 at about 18psi boost going up the hill on I-84 east just pas the PA border. Then I stayed in gear using the engine (not the engine brake) to limit my decent speed. Engine temps never went above normal and the fan only kicked in once or twice during the climb which is typical for the conditions.

I don't know exactly when the bolts started to break. Last time I thoroughly inspected the exhaust manifold was a month or two ago when I replaced the IMAP and exhaust sensors. It's possible at least one was broken at that time and I missed it, but I know for a fact that there was absolutely no sign of an exhaust leak at that time. The area around the manifold has been exceptionally clean since the inframe.

So, in absence of feedback from you fine folks, my current plan is to replace the broken bolts and put it back together to see if that solves my issue. Am I on the right track? Is there anything else I should do?

[JimT]

Some pics. The bottom bolt at #1 is broken and sounds but won't come out. The top bolt was nowhere to be found. #6 was just the bottom bolt and it was just laying there as seen in the picture.

[Rawze]

that is a lot of rust.

[JimT]

(04-19-2024 )Rawze Wrote:  that is a lot of rust.

I'm up in the Northeast, coastal and salt happy in the winter. The major difference in the picture is the exhaust manifold. Unlike the bolts, the manifold got a nice coating of corriseal before installation when I did the in frame at your house in 2020. Despite some of it burning off on the initial drive home it has clearly resulted in almost no rust buildup on the exhaust manifold. It was an interesting experiment and I think the results speak for themselves. So the bolts were not treated or painted in any way.

[JimT]

so I've been reading up on other's posts regarding broken bolts. I now understand Rawze's comment about the level of rust on the bolts. It also seems like a possible cause for #1 and #6 bolt failures could be a failure of the expansion joint(s) on the manifold. I wasn't even aware they were separate pieces when I did my inframe. Should I consider replacing them or just attempt to take them apart and clean up the connections? I don't want to needlessly replace parts, but I also don't want to just throw new bolts on if there's an underlying cause that could lead to repeated failure. Local Cummins isn't open until monday and I'd like to have my shopping list figured out since it's over an hour trip each way.

[Rawze]

just make sure they are not rusted up, and are able to move a bit to allow for expansion.

on the bolts...
I also always use liberal amount of anti-sieze on the bolt shanks under the sleeves, etc. and a light bit of it on the threads when I do them to help too.

[tree98]

The reason the bolts break is usually because the bolt holes in the manifold aren't big enough. There's an ancient TSB regarding this and also mentioned on this forum somewhere.

Don't try to take the slip joints apart that isn't your problem. The only way I've ever been able to get them apart is with a LOT of heat and then they don't ever like to seal back up again.

[JimT]

(04-21-2024 )tree98 Wrote:  The reason the bolts break is usually because the bolt holes in the manifold aren't big enough. There's an ancient TSB regarding this and also mentioned on this forum somewhere.

Don't try to take the slip joints apart that isn't your problem. The only way I've ever been able to get them apart is with a LOT of heat and then they don't ever like to seal back up again.

Center holes were reamed by Rawze in 2020 during inframe. Required/recommended anti-sieze applications were performed then as well. There have been absolutely zero exhaust leaks in the last 3.5 years and now only #1 is leaking slightly with 2 broken bolts. #6 has one broken bolt and shows no signs of leaking.

Correct me if I'm wrong, but from what I've read on this forum, lack of movement in the slip joints IS the leading cause of broken bolts on #1 and #6, like I have. I was going to order new seals for the slip joints, all new bolts and spacers, along with all new gaskets (they may be reusable, but the cost is minimal compared to my labor should a used gasket not reseal properly).

Seriously, I'm trying to learn, not argue. If I'm misunderstanding something please correct me. My only real automotive knowledge has come from hands on experience working on this truck/engine and reading this forum (and youtube, though that's not so much for information as it is for a visual reference to descriptions on here and quickserve).

-

One complication I ran into this morning is the pressure tube that connects to the #1 pipe is stripped. Best I can tell the threads in the pipe are messed up and chewed up the tube threads. Can this be reliably fixed with the correct sized tap run through the threads or will I be better off replacing that section?

[JimT]

A few questions:

* Does anyone know the thread size for the exhaust pressure tube on the elbow of the exhaust manifold? The threads inside are visibly good but full of rust/dirt/debris causing the threads on the pressure tube to partially strip/flatten the final 30% in. All my taps are imperial and wouldn't work on this application anyway.

* One of the studs on the turbo mounting also snapped on disassembly. I haven't tried removing it yet and there's still about half of the upper threads remaining. Any tips / tricks / recommendations to aid in removal?