Exhaust stud size?

[markjs]

My exhaust on my '84 GL Wagon isin AMAZING good shape, just only seperated at back of cat and one stud dropped out, IDK form unscrewing and falling or stripping.  What size is the stud and the hole and what pitch?  Im figuring it for a diameter of 4-6mm, maybe 8 tops, and coarse pitch?

 

I had another '84 GL once, nearly identical except only fwd, much worse shape, IIRC it lost more than one exhaust stud and I used bolts and lockwashers to replace them, which worked fine till the pipes themselves rusted through, and the lip at the top opf the pipe where it goes into manifold no longer held the pipe to the mount.  Any reason not to go with a bolt and lockwasher?

[markjs]

I used this stuff called "Fiber Fix" thinking as temporary for between the cat and muffler system, but I'll be damned if it don't look, feel and according to the auto store guy, is, solid enough to last quite some time.  I have welders and can buy clamps later if need be, but IDK if I ever will....

[DaveT]

The studs are 10mm x 1.25 pitch.

 

Studs are better, the entire length of the thread is engaged in the head before any load is applied. I've used helicoils to fix mine. Others have used 7/16" threaded rod or studs, since all you need to do is tap the head with that size.

[idosubaru]

A stud or a bolt? “Exhaust stud” usually refers to the exhaust manifold bolts in the head.

 

All Subaru bolts in the mid-range are 1.25 pitch metric threads. 6 mm bolts are 1.00 but they’re not used for parts that see stresses so I can’t imagine seeing one holding exhaust together.

 

Can you mic the diameter?

 

It’s going to be one of the following:

M6x1.00 (I’m doubtful of this I onky include it because you said 6mm)

M8x1.25

M10x1.25

 

If there’s two then use the other one to copy from. Take it into the store, or at home run a few nuts on it and see which one fits and take that nut to the store to check thread there if you can’t meausre at home.

 

Run that nut onto Store bin bolts until it fits and then whatever that bolt is is what you need. Stores usually have a thread measuring board hanging somewhere to make that easy.

[markjs]

Honestly I'm thinking bolt, cuz it's just one, and cuz a stud is more money and I sunk spoob tons in it already and am tapped for a bit, plus just ease of sealing it up for a while till I can get down there and hget everything right.  Just a temporary fix really, but may hold up to permanent (the life of the exhaust at least?)

[Gloyale]

Honestly I'm thinking bolt, cuz it's just one, and cuz a stud is more money and I sunk spoob tons in it already and am tapped for a bit, plus just ease of sealing it up for a while till I can get down there and hget everything right.  Just a temporary fix really, but may hold up to permanent (the life of the exhaust at least?)

 

Your talking about a $2~$3 dollar difference to fix.

 

Studs are way better for this.  The reason is that you don't want to have threads disturbed every time the exhaust has to be tightened.  And you don't want the force of clamping hte exhaust to be applied to moving threads in teh head, you want them stationary, and the "pull" happening at the steel stud threads instead.  These engines are prone to stripping out threads in exhaust, very soft aluminum.

 

The way to install the stud properly is to stack 2, non-shouldered nuts onto the stud and lock them together using 2 wrenches.   Then using a socket, drive the stud into the head.  Once seated, using the 2 wrenches again, unlock the 2 nuts from each other, take the top one off, then the other. 

 

If your head has stripped out holes, you will need to repair.  Cheapest/quickest way is to tap the hole to 7/16 and use 7/16 GM exhaust stud.  Otherwise you will need to do a helicoil or similar thread repair.

[idosubaru]

Studs are way better for this..... Then using a socket, drive the stud into the head.  Once seated, using the 2 wrenches again, unlock the 2 nuts from each other, take the top one off, then the other.

 

he says "studs" but is referring to "behind the cat" so i'm not sure exactly what issue he is having, but i don't think he means the head studs.

[markjs]

OK now I am BAFFLED, (get it, baffled?), anyway....

 

I put a bolt and lock washer on, torqued it good, and no change in the exhaust!  It's loud as ever.  The cat and muffler not the issue, issue on passenger side head.  There's a warm air pipe on that side leading to the air cleaner?  Why?  How can the exhaust, straight off the head go into the cold air intake and how can that pipe "y"out anjd bypasss the cat and muffler and how can it still be quiet?  The heat hose is the flimsiest of foil and wire.  Is there even a hole or is it just air warmed by the pipe?  Is it possible that a hole rottred through?  You feel a steady leak down there, but nothiong like a busted manifold gasket, not as strong but loud as hell, what gives?

[idosubaru]

http://www.ultimatesubaru.org/forum/topic/119550-can-i-get-rid-of-these/

[DaveT]

Ok, I got mixed up by the terms used. Studs are used in the head to y pipe. Bolts are used in the flanges.

 

There are gaskets between flanges.

 

The I use 10mm or 3/8" stainless steel nuts and bolts on the flanges.

 

It's pretty common for a flange to rot out on the second cat. If the gasket was damaged, a new bolt won't stop the leak.

 

The flimsy hose going up to the air cleaner is not carrying exhaust gasses, only air from around the shields on the exhaust pipes. It's preheat to help warm up the engine and avoid icing in the carb.

[markjs]

Behind the cat is fixed with fiber fix, I'd swear I posted that? Sometimes people don't read past the gist?.  Yes I am talking about on the head, but now it has a bolt has torque applied and is still just as loud, what gives?  I'm thinkinking I might need to remove the bolt and nut and look inside, but the nut looks perma seized....

 

Is there a gasket in the head to exhaust? As I recall like a motorcycle, a simple one shouldn't ever wear out?  Its been almost 15 years tho, since I toyed with an EA81 ewxhaust.  That rotted the flare end of the head pipe, only fix I could afford at time was muffle goop and lots of support wirebut it worked.....

 

But to be clear, my noise problem is 100% from the head on passenger's side.  Fiber fix is amazing stuff, for now, we'll see for how long.

Edited April 10, 2018 by markjs

[markjs]

he says "studs" but is referring to "behind the cat" so i'm not sure exactly what issue he is having, but i don't think he means the head studs.

No, you read part of what I say, and interpret it before reading for comprehension.  Sorry but it's necessary to read all of the two posts, not just skim through and start thinking it's me who is unclear, though admittedly I could have been clearer....

Edited April 10, 2018 by markjs

[markjs]

Oh and as for why not spend $3 on an exhaust studf? Maybe I can affor one tonight, but why, till payday, if a bolt does no good now?  There is a deeper issue clearly.

Edited April 10, 2018 by markjs

[DaveT]

There is supposed to be a gasket between the head and the y pipe flange.

 

They do not usually survive being loose or removal unless pretty new.

[markjs]

There is supposed to be a gasket between the head and the y pipe flange.

 

They do not usually survive being loose or removal unless pretty new.

OK, well I could not remember, the motorcycle ones never die, just two half cirle pieces of metal softer than the pipes and head, but not by any stretch truly "soft".  On driving, after warm up, I have to amend my earlier judgment, but it's still not right and somewhat loud, but much better.  Not right tho which bugs me, but easily fixable at payday and surviveavly until.

 

I guess just being under choke and high rev at cold temp it's extra loud until full heat expansion....

[idosubaru]

Gasket. They are typically reusable but after 30 years things happen. clean surfaces and repair any fasteners that are compromised. The threads often strip in the heads. Clean, Chase, repair as needed.

 

I wouldn’t be worried about using a bolt. In the rust belt the nuts all seize to the shaft and end up functioning like bolts on any repairs all the time anyway and I never see issues.

 

Fiber fix sounds interesting, good to know though I hope to avoid rust altogether as much as possible.

 

Did you use it over existing rust?

 

No, you read part of what I say, and interpret it before reading for comprehension. Sorry but it's necessary to read all of the two posts, not just skim through and start thinking it's me who is unclear, though admittedly I could have been clearer....

i did read all of it, I owned the confusion with “I’m uncertain” rather than “you’re unclear” - you’re assuming way too much by thinking I’m trying to critique. I’m here to help not play games. Also - because I read the posts through I pointed out to someone else that what they typed didn’t line up with what was decribed and described that “stud” was going to confuse people due to well known and common issues there.

 

It hardly matters. If the goal is to critique every online post then we have a lot of work to do!

[DaveT]

They way to avoid the nuts seizing to the studs is to use anti size compound.  The only time I have had to deal with those stuck nuts is the first time I had to pull the header off.  New studs, Stainless nuts [if available] and anti seize, no problem with later work.

[markjs]

Gasket. They are typically reusable but after 30 years things happen. clean surfaces and repair any fasteners that are compromised. The threads often strip in the heads. Clean, Chase, repair as needed.

 

I wouldn’t be worried about using a bolt. In the rust belt the nuts all seize to the shaft and end up functioning like bolts on any repairs all the time anyway and I never see issues.

 

Fiber fix sounds interesting, good to know though I hope to avoid rust altogether as much as possible.

 

Did you use it over existing rust?

 

i did read all of it, I owned the confusion with “I’m uncertain” rather than “you’re unclear” - you’re assuming way too much by thinking I’m trying to critique. I’m here to help not play games. Also - because I read the posts through I pointed out to someone else that what they typed didn’t line up with what was decribed and described that “stud” was going to confuse people due to well known and common issues there.

 

It hardly matters. If the goal is to critique every online post then we have a lot of work to do!

Well I justt screwd up but not being clear in first post, but the second shouldhavew cleared the confusion some.  Nobig, it happens, I appreciate the help.  Gonna sit on it a while drive as it, hate getting under.  Notr so much cuz it's big deal, it's not, don't even need to lift car to access, but it's the weatrher and mud at home that keeps me unenthusiastic lately, and lack of funds.