Exhaust Nut Torque

[CranelakeMN]

Seems to be lots of opinions and ideas out there. The Lyc book I have shows exhaust studs at 40 inch lbs minimum. Does anyone out here know or suggest what the hold down nuts should be torqued to? Thx

 

[mike mcs repair]

As loose as they will stay on. Or else the flanges bend(with no blow style gaskets). You can sand the flanges flat again a few times before the must be replaced


Sent from my iPhone using SuperCub.Org

 

[stewartb]

A good place for Nordlock washers.

 

[bob turner]

Interesting. We smaller Cub owners use brass nuts. Over-torquing results in stripping. But Clint has these neat stainless steel flanges he welds on, and it would take way, way more than 40" lbs to make one banana-shaped.

 

[Steve Pierce]

I have not found a current torque value for the exhaust nuts in any current publication from either Piper or Lycoming. The best thing I have found was in the Jan 1973 Table of Limits that has been superseded which gave a value of 160-180 in-lbs.

 

[mike mcs repair]

A good place for Nordlock washers.

and for those who haven't seen them... cool stuff, order some samples and try them...

I stock them now... no comparison!!!

 

[mike mcs repair]

spruce has them too...

https://www.aircraftspruce.com/catalog/hapages/nordlockwedgewashers.php?clickkey=106103

 

[stewartb]

Thank goodness. Spruce has simplified the ordering process a great deal! I just spent $150 on lock washers ahead of my engine install. Worth every penny, too.

If you haven’t tried them? You ought to. They work.

 

[SD cubman]

Steve is correct. 160-180 inch lbs is what I recommended for many years.

 

[RVBottomly]

Thank goodness. Spruce has simplified the ordering process a great deal! I just spent $150 on lock washers ahead of my engine install. Worth every penny, too.

If you haven’t tried them? You ought to. They work.

Timely for me. I've been working on a hardware order for the last week and was trying to figure out which way to go.

Thanks,
Vic

 

[stewartb]

My order was quickly filled and shipped from Spruce’s Alaska warehouse. That’s my second order of parts, hardware, and gaskets that have come from the local warehouse recently. Very handy for Alaskans!

 

[skywagon8a]

Interesting. We smaller Cub owners use brass nuts. Over-torquing results in stripping.

I use these nuts on the Lycomings as well. They are deeper than the steel Lycoming nut, lock washer and flat washer and they don't rust from the heat. Just run a course thread tap through them, since they are intended for the fine threaded Continentals. They are long enough to cover the entire stud preventing heat and rust erosion of the stud.

 

[Steve Pierce]

The STD-1410 factory Lycoming nuts Aircraft Spruce Part# 08-13229 are stainless and I have nut had any rust issues. Their studs are the same and no issues.
https://www.aircraftspruce.com/catalog/eppages/lycomingstuds_08-13229.php?clickkey=45483

 

[skywagon8a]

I Have seen a lot of rusted studs over the years. Some rusted so much that the nuts will not back off and pull the studs out with them.

 

[Steve Pierce]

Same here, that is why I replace with the stainless. No fun doing the Piper Exhaust AD every 50/100 hours

 

[bob turner]

I insisted on the muffler terminating that AD. Nobody was doing it except me, and I hated the job. Never seen a Super Cub without stainless nuts - but have the Heicoil kit ready anyway.

 

[AkPA/18]

I also recommend the stainless nuts and I also put a little dab of hi temp RTV inside the nut. This coats the stud as you install the nut.

 

[mike mcs repair]

..and I also put a little dab of hi temp RTV inside the nut. This coats the stud as you install the nut.

that's what I heard also from a Cordova guy too....he slathers the studs too.... says it helps...

 

[stewartb]

Thread resurrection since I helped a friend with exhaust stud replacement. I did some research, including here, and finally found the Lycoming info from a reference in my IO-390 maintenance manual to the linked document. My take is the driving torque for the studs in 40 lbs/inch. Torque for the exhaust nuts is 17 lbs/ft. I hope that’s right. We used standard studs because the had just a few foot pounds of resistance. Oversize studs would have been tighter, but there’s no upper limit in the torque specs for these studs, just a minimum.

https://www.lycoming.com/sites/default/files/SSP-1776-5 Table of Limits - Complete.pdf

 

[Steve Pierce]

Funny, I just pulled a 100 hr inspection on an IO-390 and had this document opened on my computer.
906 ALL 5/16-18 Exhaust Port Studs (Driving Torque) 40 in. lbs. min.
ALL 5/16-18 Nuts to Attach Exhaust Stacks to Cylinder Head 160-180 in. lbs.

 

[stewartb]

Where did you find exhaust nut torque? I’ve looked a few times and don’t see it so I used standard values for 5/16 nuts, 17-19 lb/ft. Exhaust studs are in special values. That’s what I was most interested in. Mike gave me an assortment of oversize studs and I had no idea how to determine what to use or why. Now I do.

 

[Steve Pierce]

Item 906 just under the stud torque.

 

[stewartb]

What’s the date on your instructions? I posted mine and it’s different. No exhaust nut torque.

 

[Steve Pierce]

That particular page is April 2018. It is SSP-1776-5. The -5 is the revision number.

 

[stewartb]

Huh. I wonder why they dropped it. Mine’s 2020.

 

[Steve Pierce]

April 2020 is the date on the title page.

 

[stewartb]

Make’s ya wonder….

 

[Steve Pierce]

Yours is correct, I was on Part IV Vertical Engines and you are on Part I Direct Drive Engines. I kept part ! in my paper copy and threw the other sections away for this very same reason a long time ago. I had forgotten about that.

 

[stewartb]

Ahh, I get it. I was looking at the geared engine chart at first. Not the most intuitive document. I was thinking while torquing those bolts that I wouldn’t have been much different if I was doing it without a torque wrench.

Those aluminum interference threads are interesting. I had enough torque feedback to stay with standards. How much harder would .030 over have been? That has to be a decision you make from experience, and I had none. The project was a result of a loose nut and a missing stud on one flange. When I dropped the stacks I found the one remaining stud wobbled. I removed it with very light pressure and found the stud was about 2/3 as long as the correct part and didn’t have the interference threads. I suspect the missing one was a match. Who does that crap? After chasing the holes with a bottom tap the new studs went right in. In this case I like a little more nut torque to keep the studs in place, because 40 inch pounds isn’t much torque. I enjoyed the project, and the opportunity to learn something new.

 

[Steve Pierce]

I keep a couple of oversized studs on hand just in case. Back in the day did a lot of helicoils and studs but mainly factory new engines or at least cylinder so don't get into it much. Got my but
t kicked by a transient Super Cub resently that I had to drop the exhaust on and every nut I torqued pulled the stud out of the head. Reminded me why I don't normally take on new customers.