Rusted Exhaust Studs & Other Issues

[V1]

I have a 2004 Mazda 6 3.0L with about 140,000 miles. It's a beater, but I want to keep it. There are cases where the exhaust system on this car caused engine failures. So I am considering to remove my exhaust headers and address this problem.

More specifically, the catalytic converters are what cause the issue. There are are all made of ceramic - 2 per bank, 4 total. Eventually the "pre-cats" begin breaking apart from heat cycles, age, etc. Those broken pieces of ceramic are ingested through the EGR system causing engine failure.

The ideal solution is to either
A) Replace the headers with aftermarket, or
B) Remove exhaust headers and physically remove the ceramic "pre-cats"

Both require removal of the headers.

As you might imagine, the exhaust bolts and studs are completely rusted. The only way those headers are coming off is if I cut the stud at the header flange. My concern is that if I do cut them, I may not be able to remove the remaining portion of stud that is left over. Whether it's seized, rusted or otherwise toast.

If I decide to attempt this operation, is it likely to have problems with the studs? Or will heat, penetrant oils, and other persuasive techniques do the trick?

 

[mva]

I would try to undo the nut/studs. Because they are rusted the stud will likely unscrew from the block. Install new studs and nuts when you put it back together.

I have done this job on a nissan but not a mazda.

 

[eljefino]

You may find they put tons of anti sieze on them and they'll come right out. This operation is a success on many engines older than an 04.

 

[Trav]

Use kroil a few days before and let it soak, use nut extractors instead of regular sockets if they are seriously rusted and undersized.

These are available at most places, Advance has them and you can use a coupon to get the price down if you need some other stuff. Sears also has them branded as Craftsman.
They work slick on this job.

http://www.amazon.com/Irwin-Industrial-394001-Bolt-Grip-Extractor/dp/B0000CCXVZ

If they wont budge don't break them, stop and heat the nut only with a very small tip on a oxy acetylene torch and try again.

 

[The_Eric]

Originally Posted By: Trav

If they wont budge don't break them, stop and heat the nut only with a very small tip on a oxy acetylene torch and try again.



THIS. Biggest time (and part) saver invented.

 

[mechtech2]

Then comes the problem of using the old rusted studs again.
They still may need replacement.
Exhaust manifolds are hard to get to, and prone to horrid little problems.

 

[1 FMF]

i just did the exhaust on my truck- 2006 gm 8.1L. everything was factory original and had no antiseize on them. Had 3 exhaust manifold studs sheared on passenger side. The nuts on the studs coming out of the cylinder head were rusted and looked like they would be a problem but all the studs backed out when trying to remove the nuts. on the sheared studs, one was protruding and was able to get a vice grip on it and that backed right out. the others i had to drill into and use a screw out and those backed out with minimal effort. I think I put my oxy-acetylene torch to one of the sheared studs to heat hit and it removed easily. the hardest part was undoing the studs/bolt at the manifold collector flange where it connects to the exhaust system. Those I had to heat cherry then use 1/2 inch which breaker bar, sometimes it was the nut that came off leaving the stud other times the stud came completely out. And for the studs left screwed into the manifold, i had to heat those on garage floor then got a work out removing those.
best advice i can give is have an oxy-acetylene kit and be able to reach in to heat what you need to. I had used penetrating oil for the previous 2 months, didn't do squat on the flange nuts. Be aware on stuff you do heat, you will harden the steel and make it harder to drill through should you need to drill it out. So don't heat stuff first and fail then decide to drill it, drill it first prior to heating. And if you use a screw out, use it with a small tap T where the T handle is only 2-3" long. If you can't back out the screw with that, then you'll most likely break off the screw out in the drilled stud using a bigger handled device with more torque. another trick is if you're ready to heat something to back it out is to put candle wax on it as a lube prior to backing off the nut over rusted threads or removing a stud. good luck. I had mail ordered a left handed drill set with screw extractors and when i used the small bit on my lawnmower engine it failed miserably, but on the 1/4" bit i drilled right though 1" worth of stud that was stuck in the cylinder head. They sell what looks like the same screw extractor kit on the shelf at autozone, partamerica, etc.

 

[V1]

Yeah, this exhaust system issue is definitely a horrid problem. Either you roll the dice and hope the cats never break, or go in there and take them out before your engine commits suicide. Most 6 owners who know about this will agree that the threat should be eliminated. Even though taking the headers off of this car is a total pain. Subframe has to come off, tight spaces. It's nasty.

The exhaust studs on this thing are so rusty that you can barely make out the threads anymore. They will not have a second chance in life. I will not even give them one.

If unscrewing the bolts is possible with penetrant, candlewax, and heat, I'll definitely try that route first before cutting. I have my doubts though. My biggest fear is having a stud bust off at the head and having to drill, or re-tap. But what I'm gathering from you guys is that even a badly corroded stud should back out fairly easily if done correctly. This is encouraging to me.

 

[Trav]

If they are that bad i have been successful this way.
Blow the nuts of with a torch if they don't come easy. This will leave enough to get vice grips on.

Remove the manifold and heat gently around the stud with a small torch tip.
Remove the rest of the stud with vice grips, most of the time they come right out.
Its a lot easier to mess around with the torch and grips with the manifold out of the way.

 

[V1]

My car is getting new headers. They've been ordered, so I'm going ahead with this.

I purchased a Mapp / Oxygen torch from home depot. It was $60, and says that it's good for welding, cutting and brazing. The burner tip is very small and concentrated. Maybe a 1/4" opening. Is this the correct type of torch to heat up those rusty nuts?

 

[Trav]

It sounds like it will work although not ideal for cutting.
This kind of torch will beat you to death keeping it fed with those little bottles if you use it more than a few min at a time.
If you are going to be doing more than this job in the future you would probably be better served with a small portable oxy/ac set, it will be a lot cheaper in the long run.

 

[V1]

I like this idea. Any suggestions on where I might find a decent setup? I've never had to deal with this stuff.

 

[MarkM66]

Have you even tried to remove them yet? They might come out easier then you think?

Soak them, and hammer on a one size smaller socket, they might come right out.

 

[V1]

I really hope so. Just taking every precaution I possibly can here. The nuts are 12mm, but I tried a 1/2" socket on for size the other day, and it fits snugly.

To my surprise, 3 of the nuts were already a tad loose! But I think I know why. A few years back, I had exhaust fumes coming into the cabin. Turned out to be loose spark plugs that I figured out later, but before that I brought the car to Midas to ask their opinion. They were dickin around under my car for about 30 minutes before they came out and told me I had a manifold gasket leak. It never leaked - still doesn't actually. Pretty sure they cracked those 3 nuts loose...

Anyway, I brought this subject up with a friend of mine. He suggested I make the nuts 1/8 turn tighter before loosening. Does this make sense in any way?

The other thing, did I catch somebody say to use candle wax to treat the exposed threads?

 

[Trav]

This is a Genuine Victor and really nice torch set. It cost a Little more but will last forever, worth every dime i guarantee it.
Get the bottles swapped out at any airgas or gas service when empty. Once you own one you will wonder how you ever lived without it.

I own one similar to this (slighly bigger tanks on a cart) and its been great over long term use, i couldn't live without this tool living in the salt belt, its like a magic wand of fire.

Original Victor Torch set

You can find Victor style sets for a bit less and use Victor parts to repair it, they are also okay.

 

[Kestas]

I only used candle wax once or twice to wick wax into the gap. Yes, it works!

Tightening a tad is one technique of breaking the rust bond to get the fastener moving. When I get it moving I'll sometimes use a back-and-forth motion in combination with penetrant to prevent snapping the stud.

 

[MarkM66]

Did you ever get them out?

 

[V1]

Well, I decided to go ahead with this project. Last month, I purchased a new, aftermarket exhaust system for the car. Today I started the operation. So far, so smooth - kind of.

I was able to remove every exhaust component up to the headers. Then it got late, so I decided to resume tomorrow. The headers and said rusty bolts are still on the car at this time.

Before I started today, I drowned every rusty bolt with PB Blaster. The header bolts were targeted repeatedly. Also, the oxy/acetylene torch I got worked wonders. Made things unbelievable easy!

Everything was going so smoothly that it was too good to be true. When I took one of the downpipes off, it revealed a header stud that had been snapped off flush with the engine. Pretty sure it was Midas that did it, because they're the only ones who ever came in contact with that area. But that's water under the bridge at this point.

Looks like I'll be getting myself a drill & tap kit for at least one stud. We'll see how the rest of them go tomorrow.

I'll follow up with the results, and possibly some pics. All the advice has been very helpful so far. Thank you!

 

[Donald]

Some mechanics weld on a bolt or nut to a snapped stud and get it out that way.

 

[V1]

Here is what I am dealing with:

This is a transverse V6, and you're looking at the rear (right) portion of the engine. Notice the snapped stud on the far right. It is flush with the engine case at best. At least there is some room to work with on this side of the engine.