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Exhaust header torqued down but two threads are not showing

lndwarrior

Well Known Member
This is on an O-235.

This occurs on two of the nuts. I've installed new gaskets, new lycoming exhaust nuts, washer and star washer per the parts manual. Everything looks right - but I don't have two threads showing after torquing to spec..

Opinions, ideas?

https://goo.gl/photos/UATRNEj5zhtBqAM8A


TIA
Gary
 
I can't see the pics at work but based upon your description is it possible the studs have been inserted just a bit too far?
 
I wouldn't consider that to be acceptable.

On my TMXO360 install I just used a split ring lock washer. Try that and see if you can get some threads exposed.
 
First thing is to understand what the actual requirement is, and why...

1. The requirement is not for 2 threads it is only one.

2. The requirement is for when using self locking nuts. To assure that enough of the threaded portion of the fastener shank penetrates through the self locking feature of the nut to assure that it develops the proper prevailing torque to keep the nut in place.

The nuts for attaching the exhaust system are not self locking nuts so the rule does not apply. Lock washers are used for the locking/safety function.

As long as the threads of the nut are fully engaged with threads on the stud (which it appears to be), you are good to go.

If you personally don't like it, you could remove and reinstall with a light washer, but that will require new lock washers as well (internal tooth lock washers are single use only).
 
Is the...

gasket seated fully against the cylinder boss? It does not look like it in the photo.
 
2 washers?

If this is a Vetterman exhaust, check if you need both a flat washer and a lock washer. IIRC, a phone conversation with Larry Vetterman indicated that only a stainless lock washer was to be used here without the customary flat washer. Unusual, yes, but that's why I remember it.
 
Thanks Scott!

First thing is to understand what the actual requirement is, and why...

1. The requirement is not for 2 threads it is only one.

2. The requirement is for when using self locking nuts. To assure that enough of the threaded portion of the fastener shank penetrates through the self locking feature of the nut to assure that it develops the proper prevailing torque to keep the nut in place.

The nuts for attaching the exhaust system are not self locking nuts so the rule does not apply. Lock washers are used for the locking/safety function.

As long as the threads of the nut are fully engaged with threads on the stud (which it appears to be), you are good to go.

If you personally don't like it, you could remove and reinstall with a light washer, but that will require new lock washers as well (internal tooth lock washers are single use only).

Thanks, Scott,
I'm so glad you wrote this out. It is such a mis-understood pseudo-requirement.
The rationale is that the first thread is a starter thread that has a taper, so if the end of the bolt is just flush with the end of the nut, that last thread isn't getting gripped by the locking feature as much as it should.
 
I assumed you torqued the stud to the correct range? What's wrong with going with the next size stud?
 
The "thread rule" is a much understood bit of hogwash. There are many factors that can, but typically don't apply. I wont go into all the details, but thread protrusion is a mix of bolt/nut type, and shear/tension application. At the end of the day, anything protruding from the end of the nut has nothing to do with retention or safety. As a general rule, it validates if the bolt is long enough, or too long..a much more important factor in stressed applications. With a stud, the threads are infinite, and anything flush or better is 100% of need.
 
Maybe an engineer should jump in here; not all studs have 'infinite' threads. It might not be a factor on an exhaust system, but my understanding is that studs loaded in shear have an unthreaded portion that actually extends into the parent material so that the shear load is on the unthreaded portion of the stud.

I ran into this while designing a motor mount for my alternative engine. My engineer buddy kept working me over if it looked like I was going to violate that rule. If I understood my engineer friend correctly, that's the reason studs are used instead of bolts in highly shear-loaded applications.

I hope this isn't nitpicking...

Charlie
 
I assumed you torqued the stud to the correct range? What's wrong with going with the next size stud?

Yes, they are properly torqued.

Didn't know that changing out the stud was an option. How hard is this to do and how do you do it?
Thx
Gary
 
Yes, they are properly torqued.

Didn't know that changing out the stud was an option. How hard is this to do and how do you do it?
Thx
Gary

Excuse me for sounding a bit snarky, but this is the point in the story (and it repeats it self over over over here and on other internet forums) where the poor builder has to choose from all of the well intended advice in an on line forum.
He does choose, and attempts to do some work he knows nothing about (and was totally un-needed). He then ends up spending a bunch of money having someone who does know what they are doing, repair the threads in their cyl head that are now damaged.
 
Excuse me for sounding a bit snarky, but this is the point in the story (and it repeats it self over over over here and on other internet forums) where the poor builder has to choose from all of the well intended advice in an on line forum.
He does choose, and attempts to do some work he knows nothing about (and was totally un-needed). He then ends up spending a bunch of money having someone who does know what they are doing, repair the threads in their cyl head that are now damaged.

+1 here. This is a 5/16" nut holding a 3 pound exhaust pipe. I don't see how one could recommend removing and replacing an exhaust stud because one or two threads are not exposed. That is a potential costly mistake waiting to happen for the inexperienced. As mentioned previously, there is no locknut and therefore no need for solid thread engagement in the locking mechanism.

To the OP and others, this is great forum with a HUGE wealth of information. I can't even count the invaluable guidance and tips that I have received. However, just like any other public forum, not all of it is accurate or appropriately applied. Take in the wealth of information, but don't ever stop using your judgement and common sense. Also, there is a much larger source of information out there to help you make good judgement calls if your experience is limited. "trust but verify" is one of my favorite sayings.

Larry
 
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I did not like the condition of my studs so I changed them out, do not want a chance of a pipe coming loose and one of those fire breathing dragons loose inside the cowl, That would be a very bad day!
 
Excuse me for sounding a bit snarky, but this is the point in the story (and it repeats it self over over over here and on other internet forums) where the poor builder has to choose from all of the well intended advice in an on line forum.
He does choose, and attempts to do some work he knows nothing about (and was totally un-needed). He then ends up spending a bunch of money having someone who does know what they are doing, repair the threads in their cyl head that are now damaged.


That's funny - and probably all too true! Definitely not looking to get in over my head.
 
Remove the thick flat washer leaving nut/lock washer only, if you have one thread thru the nut you are good to go. End of story.
 
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So let's score this.

The pros (Walt, rvbuilder2002, aerhed ++) say leave it, it is fine.


The risk of leaving it is - possible argument with the inspector? Most guys leave the engine alone. There are even a bunch of nylocks there and even the most picky pass them.

Or remove the studs - the risk is a broken stud, or pulling some threads out with it. A dark possible path of things can happen here. Is an exhaust stud, not a "cold one" that has fewer risks.

Hmmmmm.
 
1st, Need a better picture, at a lower angle.

Most likley, remove the flat washer, install brass nuts, DONE !

From the picture, my attention would be more focused on, if that is a spark plug lead routed thru and touching the exhaust pipe :eek:

If the engine has much time, inexperienced persons removing those studs will most likely result in?? :mad:

Enjoy
 
Maybe an engineer should jump in here...
Charlie

OK, I will. This is correct:

First thing is to understand what the actual requirement is, and why...

1. The requirement is not for 2 threads it is only one.

2. The requirement is for when using self locking nuts. To assure that enough of the threaded portion of the fastener shank penetrates through the self locking feature of the nut to assure that it develops the proper prevailing torque to keep the nut in place.

The nuts for attaching the exhaust system are not self locking nuts so the rule does not apply. Lock washers are used for the locking/safety function.

As long as the threads of the nut are fully engaged with threads on the stud (which it appears to be), you are good to go.

If you personally don't like it, you could remove and reinstall with a light washer, but that will require new lock washers as well (internal tooth lock washers are single use only).

Tim
 
Excuse me for sounding a bit snarky, but this is the point in the story (and it repeats it self over over over here and on other internet forums) where the poor builder has to choose from all of the well intended advice in an on line forum.
He does choose, and attempts to do some work he knows nothing about (and was totally un-needed). He then ends up spending a bunch of money having someone who does know what they are doing, repair the threads in their cyl head that are now damaged.

It was a question asked about what would be the harm. I take it, the harm of putting in the next size stud could, potentially, be driving it into the head farther than intended ruining the threads?
Sorry you took it as advice, rather than a question, as it was worded. We all appreciate your experience and knowledge, snarkiness aside. I know you. Your not that snarky ;)

PS - under the guidance of a very well known local RV mechanic (you know him) this is exactly what we did to correct an issue on the 0320 on my Bucker. Just sayin.....

PS-PS - this is one reason why I don't show up on here as much anymore.... to much jumping on people without reading what was said.....
 
It was a question asked about what would be the harm. I take it, the harm of putting in the next size stud could, potentially, be driving it into the head farther than intended ruining the threads?
Sorry you took it as advice, rather than a question, as it was worded. We all appreciate your experience and knowledge, snarkiness aside. I know you. Your not that snarky ;)

PS - under the guidance of a very well known local RV mechanic (you know him) this is exactly what we did to correct an issue on the 0320 on my Bucker. Just sayin.....

PS-PS - this is one reason why I don't show up on here as much anymore.... to much jumping on people without reading what was said.....

Please don't jump to the conclusion that I was singling you out Jon. I wasn't.
My comment was to the whole vibe of the thread in general.
My main point was to get people to analyze whether there really is anything wrong with the OP's installation (I say there is not), and if not, is it worth the risk (at the very least the wasted effort) to change the studs if it is not really needed?
 
Please don't jump to the conclusion that I was singling you out Jon. I wasn't.
My comment was to the whole vibe of the thread in general.
My main point was to get people to analyze whether there really is anything wrong with the OP's installation (I say there is not), and if not, is it worth the risk (at the very least the wasted effort) to change the studs if it is not really needed?

No offense taken Scott. Your too good of a guy. Sorry I concluded incorrectly.
Nobody wants anybody to do any extra work for no reason, let alone damage something out of ignorance from a suggestion in a forum.

Carry on, and again, thank you for continuing to chime in.
 
Exhaust

1st, Need a better picture, at a lower angle.

Most likley, remove the flat washer, install brass nuts, DONE !

From the picture, my attention would be more focused on, if that is a spark plug lead routed thru and touching the exhaust pipe :eek:

If the engine has much time, inexperienced persons removing those studs will most likely result in?? :mad:

Enjoy

never heard of brass nuts on Lyc exhaust.
Plus one on removing flat washer and proceed. I have never used the flat washer on Lyc exhaust on EAB, never a problem.
 
My final solution - was to do exactly what I was supposed to do in the first place.

I realized I had torqued the bolts to the stud torque setting of 40 in. Lbs and not the recommended torque for the 5/16" nuts - 204 in. Lbs. (As per my copy of the overhaul manual for my engine). When I did do this all bolts had more than one thread showing.

I appreciate all of the comments on my question. I think a big part of the learning process is to learn the wrong way to do things, so the right way gets impressed into your brain. After this I believe I will always remember the difference between torquing the studs and torquing the nuts - and the correct values for both!

Thank you all for the responses.
Gary
 
My final solution - was to do exactly what I was supposed to do in the first place.

I realized I had torqued the bolts to the stud torque setting of 40 in. Lbs and not the recommended torque for the 5/16" nuts - 204 in. Lbs. (As per my copy of the overhaul manual for my engine). When I did do this all bolts had more than one thread showing.

Whose exhaust is this? If it's Vetterman, don't his instructions call for something like *120* in-lbs?

If it's not a Vetterman exhaust...then "never mind". :)
 
Whose exhaust is this? If it's Vetterman, don't his instructions call for something like *120* in-lbs?

If it's not a Vetterman exhaust...then "never mind". :)

Vetterman used to show those low numbers, I believe they've revised their documents to show the correct higher torque of 180-200.
 
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Vetterman used to show those low numbers, I believe they've revised their documents to show the correct higher torque of 200.

I know they showed somewhat lower numbers originally (maybe something like 100-110) and then revised their documents to slightly higher numbers (120-140 or something like that).

I haven't seen one showing torques that high (and if it exists, I'd like to, because mine are torqued at the 120-140 or whatever it said value).

ETA: His site shows

What is the correct torque on the exhaust flange bolts?
We recommend 140 to 180 inch pounds.

I'm pretty sure that's crept up from what is stated in the paperwork I have, so I'll have to double-check this at upcoming annual. (Again reminding me why I'm less-than-thrilled with various vendors ways of communicating changes...this is just stuck way down on the website somewhere...nothing like word-of-mouth on the internet to communicate changes to critical systems, eh? :( )
 
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I know they showed somewhat lower numbers originally (maybe something like 100-110) and then revised their documents to slightly higher numbers (120-140 or something like that).

I haven't seen one showing torques that high (and if it exists, I'd like to, because mine are torqued at the 120-140 or whatever it said value).

So this in my mind leads to the question as to which authoritative source to use as the reference for things like torque values: the engine manufacturer (e.g. Lycoming) or the component manufacturer (e.g. Vetterman)? :confused:

The RV-10 plans call for a torque of 100-140 in-lbs for the Vetterman exhaust which is a lot lower than Lycoming's spec of 204 in-lbs for a 5/16-18 nut. Interestingly, the plan spec is closer to the recommendation out of 43-13 for a 5/16 coarse thread fastener. FWIW, I went with the 140 number in the plans.
 
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Who owns what

So this in my mind leads to the question as to which authoritative source to use as the reference for things like torque values: the engine manufacturer (e.g. Lycoming) or the component manufacturer (e.g. Vetterman)? :confused:

The RV-10 plans call for a torque of 100-140 in-lbs for the Vetterman exhaust which is a lot lower than Lycoming's spec of 204 in-lbs for a 5/16-18 nut. Interestingly, the plan spec is closer to the recommendation out of 43-13 for a 5/16 coarse thread fastener. FWIW, I went with the 140 number in the plans.


Lycoming always says "use the general torque values unless stated otherwise".

BUT - in this case the exhaust system "belongs" (per the FAA definitions) to the airframe manufacturer and not to the engine manufacturer, so Lycomings numbers don't really count for the torque on these studs...:)

The certified Grumman Tiger/Cheetah manual calls for 110-130 inch-lbs for Lycoming O-360/O-320's.

There are a lot of heat related effects going on at this particular joint. :D
 
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