Interpretation Service Bulletin 1172a Lift Strut Bolt

[Binty]

Hi all.

Unless I’m mistaken, this SB specifically states our Strut bolts MUST HAVE bolt head markings
13241 or NAS 464P

How is it that UNIVAIR, Spruce and AIRFRAMES ALASKA sell U13241 with only X marked heads for Strut Bolts??

Im having a discussion/argument with my Certifying engineer about what is acceptable….

regards

 

[Binty]

 

[Eddie747]

9 years since I bought my plane and I am almost up to 400 hours, another 3 years and I might be getting close to the 500 hour limit. I have the NAS464p6-11 bolts now, comparing them to the univair 13241 bolts, they look about as different as a standard and metric crescent wrench

 

[Binty]

Problem is…. UNIVAIR bolts are not marked with 13241…! They are marked with an X….. so as far as I can tell are NON-COMPLIANT…. .??!

someone Please correct me?!

 

[Steve Pierce]

The Univair bolts which are a PMA replacement of the Piper part # 13241-00 bolt is easily identified because it has a shorter thread grip length. Those NAS bolts need to be installed upside down because of the long thread grip length with contact the gear leg. The whole idea is to keep threads out of the shear area of the strut fuselage intersection. Piper quit making these bolts and wrote SB 1172A to approve the use of the NAS bolts. Had to take a Super Cub apart years ago that hit a chemical tote. Major pain because you have to remove the gear to get the strut attach bolts out. Had an issue with a couple of Carbon Cubs when Cub Crafters didn't have proper fixture alignment for the strut attach bolt holes for the strut/gear attach fittings when they were welded together. Guys on the shop floor fixed the problem with a drill. Well that made an hour glass shaped hole allowed movement in the strut. Cub Crafters fix was an oversized fork and NAS strut bolt installed upside down so it doesn't contact the gear.

When you change something it usually effects 2-3 other things.

https://www.supercub.org/forum/showthread.php?58448-Question-on-strut-fork-bolts

 

[bob turner]

Dunno about Canada, but service bulletins are not mandatory in US part 91 operations. NAS bolts are lots stronger, but my impression is that all failures have been either strut or strut fork.

Another perhaps mistaken impression is that the originals were just AN bolts with some of the threads cut off and re-drilled. Easily done in the field.

My question is why can't we use stop nuts on these?

 

[Eddie747]

The NAS464P6-11 bolt in fig 1. is about 1/8 inch longer than the 13241 bolt, the thread lengths are same, the NAS464P6-11 grip is 11/16, the 13241 bolt is grip is 9/16. Installed it's hard to tell the difference, the 13241 bolt is only 1/16 inch shorter on the underside of fork.

An AN3 bolt would probably have to be installed upside down, but the NAS464P6-11 being only 1/16 inch longer on the bottom of the fork than the 13241, seems overkill to replace it.

 

[Steve Pierce]

The NAS464P6-11 bolt in fig 1. is about 1/8 inch longer than the 13241 bolt, the thread lengths are same, the NAS464P6-11 grip is 11/16, the 13241 bolt is grip is 9/16. Installed it's hard to tell the difference, the 13241 bolt is only 1/16 inch shorter on the underside of fork.

An AN3 bolt would probably have to be installed upside down, but the NAS464P6-11 being only 1/16 inch longer on the bottom of the fork than the 13241, seems overkill to replace it.

Do you have a picture of the two? I can't find a spec sheet on the NAS464P6-11 and the last I dealt with this was in 2006.

 

[Eddie747]

Just the Textron parts link with the specs. Compared the 2 side-by-side couple years ago, same bolt other than the 464p6 grip being 1/8" longer, the an960 washer on the top and bottom make the bolt fit

https://ww2.txtav.com/Parts/PartSearch/PartsDetail/NAS464P6-11

NAS464P6-11

 

[stoldriver]

I have access to the nas464 spec. It is a "Bolt, Shear, Close Tolerance". It has also been obsoleted and is superseded by the nas62xx series. The 62xx series is almost identical and where it is different, the 62xx series is a better bolt. Both are 160-180 KSI. Both are close tolerance
Wayne

 

[Eddie747]

8 bucks at Wag Aero

Was $8.43 3 weeks ago, went up to $9

 

[Eddie747]

Piper 13241 and NAS464P6-11, bought the Piper 13241 to replace the NAS464P6-11, the difference is incredible

Almost identical bolt, PA 13241 top and NAS464P6-11 bottom

.


13241 no washers

.

NAS464p6-11 with 960 lite washer

 

[Steve Pierce]

Looks like you need a standard thickness washer instead of a L thin washer. I would swing the landing gear shock system to it's maximum throw and check the clearance between the strut hardware and the rear gear leg tub attachment.

 

[jrussl]

How about putting the washers under the head of the bolt? Just need to take up the space. Shouldn’t matter which side you do it from.

 

[Eddie747]

The Service Bulletin shows the standard thickness AN960 washer Steve recommended, not the AN960L washers I used in the pictures. Using the thicker standard washer under the top of the bolt would make the threaded end of the NAS464p6 bolt the same length as the Piper 13241, my brain hurts trying to understand the change from the NAS464p6 to the Piper bolt. I see why they let you continue using it for 500 hours.

 

[Eddie747]

Put a standard an960 washer on the bolt head of the 464p6 bolt so it is as Fig 1 in the SB, and looks about 1 thread longer than the Piper 13241 bolt. Will swap them out since I got them, but would not do it again, the NAS464p6 bolt is rated higher in shear than the Piper bolt.

 

[Steve Pierce]

I have never seen a strut bolt failure.

 

[sj]

So a little bird told me this afternoon that the FAA is focusing in on this SB again as there have been some other situations where improper bolts might have played a role. They are really wanting owners and people inspecting aircraft to make sure to check these bolts.

I'm just the messenger!

sj

 

[Steve Pierce]

It is pretty simple in my opinion. Univair has the Piper original bolts under the Piper part number and it fits correctly. Yea, you can follow a Piper Service bulletin where they call out a different bolt because they don't make the correct one any more. Then on extended gear you have to put the bolt in upside down so it doesn't contact the landing gear. Makes pulling wings fun cause you have to pull the gear first. I will still with the approved bolts from Univair and I believe Wag Aero.