Exhaust Stud

[grizzly]

Goodmorning,

I started removing the heat exchangers. As suggested, I have been soaking the nuts with PB Blaster for the last few days. Going strictly on feel, I was able to remove 2 of the barrel nuts without a problem. The 13mm nuts did not feel like they would crack before snapping the studs so I applied more solvent and I will be using the torch next.

The third barrel nut came out but with the stud attached!

Should I just use the stud/nut combo like a bolt?

Any thoughts?

Thanks,

Brian

[cds72911]

Nope, replace the stud. Then use a new nut with antiseize.

Charlie

[grizzly]

Thanks, Charlie.

Any thoughts on where to get the stud? I already got the nuts from Pelican but I do not see the stud.

Brian

[cds72911]

Hi Brian,

I'm not an expert or anything, I just removed my own about a week ago, so it is fresh in my mind.

They're just regular 8MM 1.25 thread pitch studs. If you do a quick search you can even get the length on this bulletin board (I think it was Warren who posted it recently).

I'd recommend replacing it because you may not be able to fully tighten it if the rusted stud/nut bottoms out before you get it fully tightened.

I'm sure Pelican has them or can get them. Your local auto parts store should have them too.

Charlie

Just did a search and found this:
http://www.pelicanparts.com/cgi-bin/vb/showthread.php?s=&threadid=33712&highlight=stud+length

Todd says the factory info says 35mm studs.

Also:
http://www.pelicanparts.com/cgi-bin/vb/showthread.php?s=&threadid=4016&highlight=exhaust+stud

jmcleod used 55mm studs from an auto parts store and a mercedes dealer.

And:
http://www.pelicanparts.com/cgi-bin/vb/showthread.php?s=&threadid=7323&highlight=exhaust+stud

Warren says:
"You should be able to get them from a dealer, pn 900.061.006.01 ...

They are an M8 x 20 mm, grade 8.8 stud, so you could also cut and dress a standard bolt to make a replacement."
(sorry for the confusion, I was quoting the old post at the above link.)

Or, you could just measure yours for length and get a matching length M8 stud locally too.

[yelcab1]

Porsche has plenty of those studs at the dealer. And chances are you only need a few any way. I did the same thing when I rebuilt my top end.

[beepbeep]

Brian:

Studs are cheap, replace them *all*. Nuts too...
Theese are always snapping off and it's generally better to fix it once for all than to use old parts.

Actually, last time i had a leak i got *issed and replaced all studs and nuts + helicoiled *all* holes....

Now it's tight as drum.

[boyo]

You should never replace a stud with a bolt!

Maybe it's common sense, but I finally figured out why studs are used instead of bolts. Swapping in a bolt for a stud may seem like it's doing the same thing, but there is a big difference.

Both the fastener (stud/bolt) and aluminum/magnesium/cast iron pieces are "strong", meaning they hold up well to compression and tension forces.

But the stud/bolt metal is "hard" in the sense that it is resistant to wear, unlike the cast pieces. If you've ever felt a hot bolt after removing a rusted nut, that's friction between metal - if one of those metals is softer than the other, there's a lot of wear including the possibility of pulling out threads completely.

On the other hand, installing a stud then torquing a nut onto it still causes tension stress on the cast piece, but it's strong enough to hold. The friction is between the nut and the stud, two pieces with equally high hardness.

So there ya have it.

-Boyo

[ChrisBennet]

cds72911 posted:
They are an M8 x 20 mm, grade 8.8 stud, so you could also cut and dress a standard bolt to make a replacement.
To which boyo responds:
You should never replace a stud with a bolt!

Just so there is no confusion, cds72911 was suggesting making a stud from a bolt i.e. cutting the excess amount off (including the head) and dressing the end.

[marcesq]

Brian:

I believe one thing that is being assumed by all of the prior posts is that everyone it talking about studs that are threaded top to bottom.

Since I can not tell from your post the year of your 911, I will add that the original studs, and in some cases replacements, were threaded on each end with the center of reduced diameter.

No reputable Porsche wench would install the old type, but they may be sitting around in a parts bin somewhere and should he avoided.

For what it is worth.

[Early_S_Man]

The 20 mm stud I gave the length on was for a 2.4/2.7 engine with the thin exhaust flanges.

The longer 35 mm length was for the 'thick' flanges on SC exhaust systems.

Depending on what type of system is going back on ... early-style heat exchangers would need shorter studs, and thick-flange SSI's would need the longer studs.

Most hardware stores have all-thread M8 rods these days, but it isn't DIN 8.8 strength, so that is why I recommend cutting a longer-threaded DIN 8.8 bolt to make studs. Red Loctite should be used on the threaded portion in the heads ... after chasing the threads with a tap, and degreasing thoroughly with brake cleaner/degreaser. Anti-sieze compound should be used on the nuts!