Exhaust manifold change question - JeepForum.com
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post #1 of 17 Old 07-31-2020, 04:52 PM Thread Starter
ej1920
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Exhaust manifold change question

Any reason why I should use studs rather than bolts on the outside holes?
Drilling out and extracting the rear stud and wanted to just pick up all new bolts.

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post #2 of 17 Old 07-31-2020, 06:26 PM
IRQ
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The studs are just there to guide & hold the manifold during installation, I replaced mine with bolts a number of years ago with no issue.

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post #3 of 17 Old 07-31-2020, 06:39 PM Thread Starter
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The studs are just there to guide & hold the manifold during installation, I replaced mine with bolts a number of years ago with no issue.
Thanks...that's what I was thinking as well but wasn't sure if it relieved expansion stress
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post #4 of 17 Old 07-31-2020, 06:52 PM
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there is more to it than that, do not get mislead - there is reasoning behind the studs on either end. That said, i do know of a few members who have replaced them with bolts.

But, Studs = finger tight to get in and the torque is applied to the nut. For instance, in porsche 911s you can often find factory used ALL studs. The in and outs when servicing over time can booger the threads - sure, in their case, aluminum is used and the hardness of the externally threaded bolt would be greater than the hardness of the material the internal threads are cut into.

I believe there are some expansion stresses in those locations the stud/flat based nut redirect/deflect to the expansion cup washers used in the bolt locations.

I'm sure one of our local geniuses will chime in with more information on some of the reasoning... perhaps @Boojo35 will chime in here. Seems like a topic he'd have a great insight about.

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post #5 of 17 Old 07-31-2020, 07:09 PM
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Here’s an interesting article on the subject
https://www.autoserviceprofessional....and-tips-on-ac

1995 Rio Grande • 2.5L • AX5 • Stock • 58k miles
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post #6 of 17 Old 07-31-2020, 07:19 PM Thread Starter
ej1920
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Thanks for the feedback I was going to order the bolt kit but it didn't come with enough bolts. It was show 7 Bolts and 2 studs and I have 9 and 2
Was gonna just go to the parts store or hardware store and pick up some 8 grade bolts.
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post #7 of 17 Old 07-31-2020, 08:07 PM
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Originally Posted by bruinjeeper View Post
there is more to it than that, do not get mislead - there is reasoning behind the studs on either end. That said, i do know of a few members who have replaced them with bolts.

But, Studs = finger tight to get in and the torque is applied to the nut. For instance, in porsche 911s you can often find factory used ALL studs. The in and outs when servicing over time can booger the threads - sure, in their case, aluminum is used and the hardness of the externally threaded bolt would be greater than the hardness of the material the internal threads are cut into.

I believe there are some expansion stresses in those locations the stud/flat based nut redirect/deflect to the expansion cup washers used in the bolt locations.

I'm sure one of our local geniuses will chime in with more information on some of the reasoning... perhaps @Boojo35 will chime in here. Seems like a topic he'd have a great insight about.
You sound like the resident expert yourself Bruin. You have a lot of truthful and valid points about studs.

I am not 100% sure about why Jeep used studs on the ends of the manifold. The expansion cupped washer point is very valid. There are engines that commonly break exhaust manifold bolts. Some LS motors, some of the Hemi's and lot of others over time. The very end bolts on manifolds are the more common ones to break.

Metal expands and contracts when heated and cooled, a lot. You can heat a connecting rod in an oven and drop a press fit piston wrist pin in place. When it cools it takes a lot of force on a press to remove it. You can install a manual trans flywheel ring gear buy heating it and dropping in on the flywheel. When it cools it holds enough tension to not slip on the flywheel with the starter engaged and turning the engine.

When an exhaust manifold grows or expands it grows from the center outward. The ends of the manifold are where it suffers the most. Shoot, there is actually a couple of tools in my box that are exhaust manifold spreaders for older small block chevy manifolds. It is like they designed their manifold to have to be stretched a little when cold so it put a little stress on the bolts inward to kind of not have so much outward stress when hot. Bolts are made for clamping force and do not withstand sheer stresses well. Studs are subjected to the same properties in that sense. They are made to clamp and not withstand too much lateral force. This is why body lifts are unsafe if too tall. (Body mounts are overrated anyways )

Studs are inherently stronger. The stud is not and does not have to be installed more than finger tight into its base. When the nut is torqued the stress on the fastener or stud is only in one direction. It stretches it. With a bolt the stress is both stretching it and twisting.

I don't fully know all the science and physics but will state that in many diesel applications, high performance applications, etc. stud upgrade kits for cylinder heads, main bearing caps, etc. etc. increase reliability and clamping pressure. With some diesel tunes for instance, you will f some stuff up without them. They are still the same size fastener so to speak. They are just superior.

I KNOW 110% FOR POSITIVE that a stud provides a more accurate torque reading. By far. When you torque a bolt your accuracy relies on the cleanliness and perfectness of the threaded hole AND also the friction of the base of the head of the bolt or washer against what is being bolted down. Think about it. Some bolts can be screwed in by fingers forever. No problem. Too easy.... The next bolt cannot be turned in by fingers, or catches every so often.... blah blah blah. I don't care how much you tap, die, clean, etc. A burr , chip in an internal thread, piece of poop in a hole makes inconsistencies. This effect goes up exponentially when fastener torque is being reached. What made that sucker hard to turn with fingers only gets worse when more torque is applied. A stud reduces this by making the only friction at the base of the nut against whatever it is torqueing.

In the end. Would I be afraid to put bolts in the end of my exhaust manifold in a pinch? NOPE. Would I be surprised if my repair did not last as long as the original configuration did? NOPE.

At least buy some decent grade fasteners whichever way you decide. Zinc plated, stainless, grade 5, grade 8..... Don't use dime store grade stuff ever, especially where exhaust parts are concerned. The corrosion/oxidation factor and loss of strength factor goes up exponentially on bolt that get superheated.... Like exhaust bolts... It gets worse with turbos.

BTW bruin. You suk. I thought this would be a quick reply and my old mind got to thinking. You made me ramble. It is all your fault.
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If you cannot fix it with a hammer then it has to be an electrical problem.
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post #8 of 17 Old 07-31-2020, 08:33 PM
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Studs on the ends to hold the gasket in place as the manifolds are installed.

Whats over that next ridge?
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post #9 of 17 Old 07-31-2020, 08:54 PM
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Quote:
Originally Posted by 4Low2G0 View Post
Studs on the ends to hold the gasket in place as the manifolds are installed.
the gasket can get held in by the pegs/locator pins casted on the block itself, or, simply putting the top center bolt through your manifold and the bolt end through the gasket itself as you place it.

Have you seen some of the things AMC/Chrysler engineered for our YJs? impossible to reach bolt locations and the dash speaker replacement process, the HVAC air box removal/re-install and the like? Everything on this YJ can be a tedious task, albeit one of the easiest vehicles to troubleshoot and work on because of it's simple design.

My point is, i don't think AMC and Chrysler had a lightbulb moment and thought: "Hey, i know what we can do to make holding the manifold gasket on while our clients and/or service mechanics a much easier task than it already is - we'll add studs and nuts on the ends!".

I could be wrong. But i'd definitely be surprised.
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post #10 of 17 Old 07-31-2020, 08:58 PM
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BTW bruin. You suk. I thought this would be a quick reply and my old mind got to thinking. You made me ramble. It is all your fault.
...it's Friday night and i needed a good read.

you got played, sir.

~YJOTM MAY '16, JULY '19~


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post #11 of 17 Old 07-31-2020, 09:25 PM
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Quote:
Originally Posted by bruinjeeper View Post
My point is, i don't think AMC and Chrysler had a lightbulb moment and thought: "Hey, i know what we can do to make holding the manifold gasket on while our clients and/or service mechanics a much easier task than it already is - we'll add studs and nuts on the ends!".

I could be wrong. But i'd definitely be surprised.
I guess that could be true, ever worked on any of the K-car variants? lots of parts held on with
sharp sheet metal screws, if you where working on the other side of that panel you where sure
to end up with bloody hands.... Thanks Mr Ioccoa!
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Whats over that next ridge?
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post #12 of 17 Old 08-01-2020, 07:17 AM
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I don't have any valid opinion on studs vs bolts but I can say for certain after much experience the most important things are using the cup washers, (I think they are called breville) and proper torque. My manifold has not had a hint of a leak for many years after getting the correct fasteners. Meanwhile most of the rest of the group has a random handful of bolts and washers and leaks

.
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post #13 of 17 Old 08-03-2020, 06:03 AM
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Crack the block, break off a bolt, or constantly having thermal loosening of the outside manifold ‘bolt’ and no engineering degree is necessary to understand why they are studs.

A lot of people put bolts there. I won’t.

[size=“3”]Shackles & D-rings are different things.
Cranking IS turning over
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post #14 of 17 Old 08-03-2020, 08:26 AM
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If you had to drill and extract the rear stud like myself and others have had to do, check for interference between the stud/bolt and the hole in the manifold. (I'm guessing you have a 4.2L engine). I'm convinced that either the rear stud was positioned slightly off or the the hole in the manifold was drilled slightly off. The lateral pressure on the stud and repeated heat cycles eventually cause that stud to break. I felt the interference after replacing the stud and using a die grinder ovalled out that hole a few hundredths until the manifold slipped right onto it.

To extract my stud I first welded a nut on but it twisted off so I welded a washer on to get the MIG wire right down to the broken stud. Then backed it out with vicegrips on the washer.


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post #15 of 17 Old 08-03-2020, 09:06 AM
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I used ALL studs. And that's what I would do again. Have had zero issues since that job was done. 5 years ago (dang, time flies)

https://www.jeepforum.com/forum/f12/...stall-3314361/

Bill

1988 Wrangler,4.2L I-6, Howell EFI JP-1,CRT HEI Ign,AX15 ext slave conversion, Zone 2" lift + 1" BL + 1/2" booms, BFG 31 x 10.5, Bestop.
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