Exhaust Manifold Bolts

[husker boxster]

I'm hoping to change out the driver's side exhaust manifold today (bad cat). When removing the exhaust manifold bolts going into the engine block, should I...

1) Give 'em the beans and hit them with an impact wrench

or

2) Carefully hand loosen them

I'm really afraid of breaking them off so I'm wondering if either of these approaches is better. I'm leaning towards #1. I've been squirting them with AeroKroil several times over the last 24 hrs in preparation of the extraction.

[method]

I've received the advice to use an impact wrench since it's supposedly less aggressive on the bolts than using a wrench. I managed to break 8 out of 12 bolts but then I didn't use enough penetrating oil and/or heat and used wrenches.
If you have a map gas burner I'd suggest you use it to heat the bolts, thus hopefully breaking the bond between bolt and head.

[RobT987]

I took a more conservative approach by repeatedly applying penetrating fluid and tapping the exhaust bolts with a punch to loosen them up over a 3 day period. All the bolts came out easily with a socket wrench.

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[blue62]

Originally Posted by husker boxster

I'm hoping to change out the driver's side exhaust manifold today (bad cat). When removing the exhaust manifold bolts going into the engine block, should I...

1) Give 'em the beans and hit them with an impact wrench

or

2) Carefully hand loosen them

I'm really afraid of breaking them off so I'm wondering if either of these approaches is better. I'm leaning towards #1. I've been squirting them with AeroKroil several times over the last 24 hrs in preparation of the extraction.

I have found over the years that a 50/50 mix of Acetone and ATF (automatic transmission fluid) works better then any over the counter products. Use it the same way you use AeroKroil just shake hell out of it each time before you apply it.

[ike84]

Originally Posted by husker boxster

I'm hoping to change out the driver's side exhaust manifold today (bad cat). When removing the exhaust manifold bolts going into the engine block, should I...

1) Give 'em the beans and hit them with an impact wrench

or

2) Carefully hand loosen them

I'm really afraid of breaking them off so I'm wondering if either of these approaches is better. I'm leaning towards #1. I've been squirting them with AeroKroil several times over the last 24 hrs in preparation of the extraction.

Please, for the love of all that is holy, do not use an impact on these.

I agree that repeat oiling and whacking over several days is the best first step.

I watched an interesting video a mechanic made about removing seized header bolts. He would actually tighten them until you could feel the cracking of the rust, then loosen quarter of a turn, then tighten again, then loosen again, etc. Take your time, don't force it, and don't actually remove any of the bolts until they are all cracked free. Start with the front and rear ones first as they are usually the hardest ones (and will only get more difficult if you save them for last). This was the technique I used in mine and 11/12 came out fine. The integrity of the metal on the rear most bolt on driver's side was so poor that I could actually feel it twisting but not breaking free. That one had to be drilled out.

Do yourself a favor - when you replace them, don't use standard hardware. Go with SS studs (tightened with hex key for your toque wrench) followed by copper plated nuts. Using dissimilar metals will reduce the risk of contact welding as corrosion and heat cycles do their damage.

Let me know if you need part numbers for the studs and bolts. There are "porsche specific" kits that will run you well over $100 but I bought universal parts for $25 and they worked just fine.

Btw, when I dismantled mine, I found that the top not on the triangular flange between header and midpipe were spot-welded by the factory. I'm not the only one to have found this, but it doesn't seem to be universal though.

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[jdavis8361]

Blaster PB Penetrant

[elgyqc]

Originally Posted by ike84

... Do yourself a favor - when you replace them, don't use standard hardware. Go with SS studs (tightened with hex key for your toque wrench) followed by copper plated nuts. Using dissimilar metals will reduce the risk of contact welding as corrosion and heat cycles do their damage.

Let me know if you need part numbers for the studs and bolts...

I just finished drilling out 3 broken bolts and installing helicoils on the spare engine I bought. So would appreciate the part numbers you mentioned.

[Dave80GTSi]

-- STUDS !!! --

See my pictures and commentary in this thread, starting with post no. 11:

Tune after Headers only?

[ike84]

Originally Posted by elgyqc

I just finished drilling out 3 broken bolts and installing helicoils on the spare engine I bought. So would appreciate the part numbers you mentioned.

M8 x1. 25 x 50mm studs. I got mine on Amazon but they're currently out of stock, but are oem for ford 4.6 and 5.4 L V8s. You could get by with a 45 mm length if you can find it but the 50s are fine. The ones I found were fully threaded but a lot are only threaded in each with a blank in the middle where the header sits. The block depth is 24mm, so just keep that in mind if you go with that type. Also, not all of them have the slot for the hex head. This is important since they should be torqued to spec. The nuts are just m8*1.25 13mm copper plated flange nuts, again procured on amazon I'm sure that I shouldn't have, but I used antisieze on the threads.

I've never heard of helicoils before! Do they really work? I stripped out one of my rear sway bar bolt holes recently and there wasn't enough left to retap, so I've got a longer bolt with a nut on it for now. The OCD in me would love to try make it all match again though lol.



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[ike84]

Originally Posted by Dave80GTSi

-- STUDS !!! --

See my pictures and commentary in this thread, starting with post no. 11:

Tune after Headers only?

Dude, where did you find those headers?!

My metal guy and I actually schemed up a nearly identical design in case the china headers I have don't work out. Ford used a similar design on a bunch of headers in the 70s. Theoretically you don't actually need a collector with this style of header since there isn't really a merge point, as long as the lengths are calculated out correctly. Anyway, super cool setup. How have they worked out for you?

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[Dave80GTSi]

Originally Posted by ike84

Dude, where did you find those headers?!

You mean these?



These are simply early OEM non-cat factory manifolds which I bought used (and way cheap) and then had high temp coated.

I REALLY like this set-up. For a street car, I feel that they flow every bit as good as aftermarket headers which seem to have hit-or-miss fitment and quality. Since they are OEM parts, quality and fit are perfect.

Compare these to their cat brothers and ask yourself which one should perform better:



By the way - I went to my local hardware store and bought a dozen M8 full thread bolts, and then cut off their bolt heads at home with a Dremel cut-off wheel in order to create studs. Cheap to do, supporting a local business, and perfectly acceptable for the need.

[ike84]

Originally Posted by Dave80GTSi

You mean these?



These are simply early OEM non-cat factory manifolds which I bought used (and way cheap) and then had high temp coated.

I REALLY like this set-up. For a street car, I feel that they flow every bit as good as aftermarket headers which seem to have hit-or-miss fitment and quality. Since they are OEM parts, quality and fit are perfect.

Compare these to their cat brothers and ask yourself which one should perform better:



By the way - I went to my local hardware store and bought a dozen M8 full thread bolts, and then cut off their bolt heads at home with a Dremel cut-off wheel in order to create studs. Cheap to do, supporting a local business, and perfectly acceptable for the need.

Very nice. Where did you find the heads? Ebay?

How did you torque the bolts? Double nut? Or did you cut off the head of the bolt after you torqued then to the block?

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[Dave80GTSi]

Originally Posted by ike84

Very nice. Where did you find the headers? Ebay?

How did you torque the bolts? Double nut? Or did you cut off the head of the bolt after you torqued then to the block?

a) Yup, eBay.
b) Double nut, worked great!

[elgyqc]

Originally Posted by ike84

... I've never heard of helicoils before! Do they really work? I stripped out one of my rear sway bar bolt holes recently and there wasn't enough left to retap, so I've got a longer bolt with a nut on it for now. The OCD in me would love to try make it all match again though lol...

Thanks for the info on the studs.
Yes helicoils work, I have used them a couple of times before. My engine won't be installed for awhile so I have not yet installed and torqued the header bolts. I bought a kit on Amazon with several sizes of helicoils including the proper drill bits and tools needed for the installation.

[Gilles]

+ 1 on the studs.. combined with brass nuts, I used them on the Fiat and Alfa engines and are great.

https://www.vickauto.com/ALFA-ROMEO-PARTS/Alfa-Romeo-Spider-Parts/Exhaust/Brass-Exhaust-Nut-SKU-27-0840

[elgyqc]

Found this on Amazon (Canada) with SS nuts. Is there a problem using the SS nuts on SS studs or are the brass nuts a lot better?
https://www.amazon.ca/Big-Autoparts-Stainless-Exhaust-Manifold-Manifolds/dp/B074J3VT1X/ref=sr_1_6?dchild=1&keywords=M8+stainless+studs&qid=1613910587&sr=8-6

[ike84]

Originally Posted by elgyqc

Found this on Amazon (Canada) with SS nuts. Is there a problem using the SS nuts on SS studs or are the brass nuts a lot better?
https://www.amazon.ca/Big-Autoparts-Stainless-Exhaust-Manifold-Manifolds/dp/B074J3VT1X/ref=sr_1_6?dchild=1&keywords=M8+stainless+studs&qid=1613910587&sr=8-6

SS should be less likely to seize since it is very resistant to oxidation, but copper is theoretically better. The problem with using similar metals is that heat cycles can create immense pressure and this can result in a type of welding (called cold welding in reference to the fact that it happens in the presence of a true vacuum). In addition, the products of oxidation of similar metals in contact with one another will be able to form a solid crystalline structure which will effectively bridge the two structures. Cold welding cannot happen with dissimilar metals, and dissimilar metals will have different oxidative byproducts. Hence the theoretical advantage of copper plated nuts. In the real world does it really work? I don't have the experience to tell you. But I can tell you my kit came with SS nuts and I still went with copper plated ones.

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[-tWv-]

Originally Posted by Dave80GTSi

-- STUDS !!! --

See my pictures and commentary in this thread, starting with post no. 11:

Tune after Headers only?

Definitely take your time with these... I had an absolutely terrible time as detailed in that thread and would never wish it on my worst enemy. I thought I was being careful/going slowly and still ended up snapping 10/12 bolts.

If I were to do it over I would definitely try the tightening/loosening technique someone else mentioned. I used tons of penetrant and went straight to loosening and it did not go well...

[husker boxster]

For 3 days I've been squirting the bolts with AeroKroil and tapping them with a hammer and punch. I got the 3 post cat nuts off (2 snapped off and the only way to get to the 3rd was with a dremel) and the O2 sensors were broken loose but still in. It was finally time to attack the 6 engine bolts. Was not looking fwd to that because if even 1 snapped off, it ratchets up the project.

I used a 6 pt socket on a 1/2" drive ratchet. Began with steady pressure. 4 of the 6 popped loose. I shot some AK on the 4 and tightened them back up. The 5th bolt came loose, so I oiled it up and tightened. The 6th had me worried. I sprayed it a couple more times between attempts. I changed my attack by 180deg and she popped loose. Oiled it up and retightened. All 6 then easily came out.

Thanks for all the suggestions. I was very concerned about this project but you got me thru the hard part.

[Raider]

Would an induction gun be safe to use? I know they are OK on all steel/cast iron, but what about these bolts into the aluminum heads?
Hope this image works!