Exhaust nuts keep coming loose

FDchief · 09-10-2011, 10:20 AM

On my Workhorse with 8.1, I had the exhaust donuts replaced because a WSC said that they were slightly worn and causing the system to the loose at the manifold / pipe connection.

Since then, I have had the system loosen up on me from time to time. Have lost two studs, and 3 nuts. Installed new donuts thinking the there could have been a defect in the old ones. Installed all new studs and nuts and torqued to specs (25' lbs). Checked after each trip, usually every couple hundred miles and they were loose again

Each time I re-torque the system, the exhaust is tight and I say to myself "got it this time" yet to no avail. I have recently replaced the standard aluminum nuts with interference (pinch) nuts. Seem better but still not perfect. The studs are still tight, but I am wondering if the threads are stretching? I just thought I would share my findings with the group. If I find a cure I will post further. It is a work in progress.

EDALLSAILS · 09-10-2011, 12:10 PM

Question? do you retorque after running the engine long enough to reach normal operating temp? are you [pressing the studs in or screwing them in. check the holes to see if you need to have them fixed. If you have room at the stud you could go online and find a source for "BELLVUE WASHERS" these washers are made of spring steel. figure how many you need for each stud at 25 lbs. The idea of these washers are to keep constant load on stud and bolt thru hot & cold temps. I'd also use premium Nuts. Oh, one last thing are your studs course of fine threads?

M&EM · 09-10-2011, 12:17 PM

I've noticed my exhaust system on each side is slightly movable(rotation) when cold. This observation came after the time WH had a recall on the catalytics. I questioned the WHSC about it and was told it was normal. This has been the case since new(8yrs). I see/hear no signs of exhaust leaks at the donut. Can't say I've tried to move the pipes when hot though..

FDchief · 09-10-2011, 07:13 PM

Quote:

Originally Posted by EDALLSAILS

Question? do you retorque after running the engine long enough to reach normal operating temp? are you [pressing the studs in or screwing them in. check the holes to see if you need to have them fixed. If you have room at the stud you could go online and find a source for "BELLVUE WASHERS" these washers are made of spring steel. figure how many you need for each stud at 25 lbs. The idea of these washers are to keep constant load on stud and bolt thru hot & cold temps. I'd also use premium Nuts. Oh, one last thing are your studs course of fine threads?

I have tried torquing when warm. Doesn't seem to make much difference. The studs are course threads, and are screwed in. They should remain tight. If I must I will check them routinely, but I shouldn't have to. Not enough threads available to double nut. The interference nuts should work as well as lock washers.

jimbo16720 · 09-10-2011, 07:18 PM

Double nut them. After you torque the first nut screw a second one on and tighten it against the torqued one with a lock washer between them.

FDchief · 09-10-2011, 08:20 PM

Quote:

Originally Posted by jimbo16720

Double nut them. After you torque the first nut screw a second one on and tighten it against the torqued one with a lock washer between them.

Good suggestion, however not enough thread showing to even get a nut started. I could go with longer studs, but not my first choice.

falcor · 09-10-2011, 09:05 PM

Had a BB (348) Chevy. All the bolts and nuts on the left side of the engine kept coming loose and I just kept retightening. Finally an uncle of mine saw what I had been doing and told me to replace the harmonic balance. Never had to tighten another bolt. Good luck.

FDchief · 09-10-2011, 10:06 PM

The harmonic balancer, who would have thought.

Midniteoyl · 09-10-2011, 11:46 PM

Stage 8 locking bolts....

Or AN bolts and safety wire...

Ding-a-ling · 09-11-2011, 08:31 AM

At 62K miles I had the worn donuts replaced at Brazel's Performance RV in Centrailia, WA. They tack-welded a piece of angle iron, as a brace, between the exhaust pipes just aft of the connection to the manifold.

I also like the safety wire idea.

FJF

DriVer · 09-11-2011, 09:45 AM

Both left and right exhaust manifold gaskets failed on my engine. The timeline was approximately 1 year apart. The right side was replaced first and the left side was replaced last.

The repair was accomplished using upgraded studs and hardware - believe some type of stainless. Holding well as of today and hoping that the fasteners stay tight.

The gasket failure was evident by a rapid blow-by sound from the engine just before the engine started. While the engine was running, the exhaust manifold leak was lost in the engine noise.

93,175.2 and counting ...

falcor · 09-11-2011, 12:04 PM

Also had a 84 Georgie Boy which kept breaking the exhaust pipe behind the manifold. Turns out the drive shaft was out of balance. Memphis Trailer was able to balance both shafts (harmonicly) Not even GM does that. Point I'm trying to make is that, if things loosen up anywhere on a drivetrain, harmonics is at work. It may take some searching , but something on the drivetrain is causing it. The effort is well worth in if you intend to keep the vehicle. Again, good luck..

rvjimmy · 09-11-2011, 08:08 PM

As DriVer says go with stainless steel studs and stainless flange nuts, problem solved.

DAN L · 09-12-2011, 03:05 AM

Quote:

Originally Posted by FDchief

I have tried torquing when warm. Doesn't seem to make much difference. The studs are course threads, and are screwed in. They should remain tight. If I must I will check them routinely, but I shouldn't have to. Not enough threads available to double nut. The interference nuts should work as well as lock washers.

how about some trying loctite medium blue or green thread locker? they are rated for 300 deg f.

http://www.loctiteproducts.com/threadlockers.shtml