Exhaust header torqued down but two threads are not showing

[lndwarrior]

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

[Auburntsts]

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?

[drill_and_buck]

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.

[rvbuilder2002]

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).

[jetjok]

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

[lndwarrior]

Originally Posted by jetjok

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

Yes it is. The photo is a little deceiving due to shadow.

[alpinelakespilot2000]

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.

[scsmith]

Originally Posted by rvbuilder2002

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.

[aerhed]

Yah Scott. I've seen more than one IA have a hissy about this over factory bolt stacks.

[JonJay]

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