Check your T-6 next annual

[Chris]

I was doing the annual on our T-6 and I noticed on the left LG retract cylinder that one of the mounting bolts was missing. Fortunately the nut was still there as was about a half inch of the bolt where it had sheared. The bolt was a drilled bolt and had sheared right at the cotter key hole. We pulled all the bolts and they were all drilled shank bolts. Needless to say they are being replaced. You may want to pull one or two of yours next time you do the annual. Just a heads up.

[Jack Cook]

Another good one to check closely.
JCW was landing his SNJ when the bolt connecting the scissors on the right
main sheared cause the wheel and bottom part of the leg to turn leading to loss of control.
Pulling the gear up and mixture off left the a/c settle on the runway with minimal damage.

[bdk]

I am a little cornfused. Are those AN bolts? If the nut was only threaded on as far as the cotter pin hole (where it failed), how could you have three threads protruding from the end of the nut? That would have to be a bolt with extra long threads AND a cotter pin hole drilled close to the shank. Never seen anything like that in a fastener catalog!

[Chris]

I should clarify the picture a bit. The bolt that was attached to the nut with the end of the bolt still protruding was gone. It may or may not have been an aircraft bolt. The nut was wedged in there pretty good. The bolt that was sheared in the picture was one I removed from one of the other mounting holes. The other bolt was still intact but was there just to show that it was a drilled bolt. Good point though BDK. That's why I'm throwing out the heads up deal.

[bdk]

Does the book call out standard AN bolts or something special? I don't have the actuators installed on my T-6 project yet...

[Matt Gunsch]

if I recall correctly, is ia a standard AN bolt, but it is a long sucker. It has to go thru the retract cylinder mounting blocks, the mounting flange, and nut. The nut is captured, otherwise it would be a royal pain to get it out.

BDK, since you are restoring your plane, make sure you replace your hose fitting with AN hardware. Chris, it appears yours has AC hardware, so watch your mixing of fittings. a bad AN/AC mix is what put Sentimental Journey into the blast fence and dumpster.

[Hal B]

All good points!

And you shouldn't use drilled shank bolts with locking nuts, especially Nylocks as the holes tend to cut the locking material out.

[Broken-Wrench]

I would use a bolt next time without the hole if your using self locking nuts. You are techniccaly supposed to use self locking once. If you are going to use bolts with the hole at the end use a castleated nut and cotter pin.. You probably allready know this but just in case

[skymstr02]

You are techniccaly supposed to use self locking once.

Sorry, that is an old wives tale. They may be reused if they meet the minumum prevailing torque values (drag torque).
This is unless the manufacturer states that they cannot be reused, which is very rare.

In this instance, the drilled shank bolts were incorrect for this installation. I've had many T-6 MLG actuator cylinders out, and those back two bolts are a "rectal ripper" even without having to pin them.

[t28pilot]

The bolts are the wrong ones per the parts book, so is the nut. Also anyone using an AN363 on a drilled bolt are just asking for exactly what happened.
Check your parts manual, I just OH both gear actuators in a G model and yes the nuts are semi captured. They will not come out unless the bolt is removed.
Last, I would double check your gear rigging per the manual. Looks to me like the throws on the Actuating cyl were off causing a constant load, thus over time the vibration simply cut thru the weak point, the drilled hole.
Once again, use the correct hardware, if you dont have it, GET IT !!

[Chris]

I ordered the correct bolts this morning. AN 5-33A. I'll check the rigging too but in the picture, all of the bolts have been pulled thus making it look like the cylinder is out of whack. Thanks for the tip

[t28pilot]

Chris,
When I said
"If you dont have the right hardware, GET IT"
That was not a personal attack, it was ment to be a general recommendation for anyone.
Sorry if you took that the wrong way.

And reference your comment, you need to check the alignment of the cyl shaft. When I recently rebuilt 2 gear sets, the washers used as spacers on the gear cyl were not correct, probably due to wear or hard use thru the years. Dont assume the washers will be re installed as before. Measure everthing per the manual as if it were a new install.
Chuck Wahl

[Chris]

No problemo T28pilot. I didn't take it in a bad light at all. I agree with you %100. In the long run it's ALWAYS cheaper to do it right anyway. I'll check the rigging like I said before just to make sure there's no side load on the cylinder. I know exactly what you're talking about. I guess the jist of this thread was to let everyone know what I found. Had one of the bolts not been missing, I never would have checked the others. I just think it's a wise idea, especially with the knowledge that floats around on this forum that if someone finds something on their plane, pass it on to others. These planes are very old and if the one of you fly hasn't gone through a ground up restoration by a reputable group, then to paraphrase Forrest Gump, It's like a box of chocolates, you never know what you gonna find!!!!

[Matt Gunsch]

Chris,
When you check the rigging, the uplock roller should be in the middle of the hook when pressure is on the system, niether touching the top or bottom of the hook. If there is upward pressure, it will bend the pivot bolt on the uplock hook.

[bdk]

BDK, since you are restoring your plane, make sure you replace your hose fitting with AN hardware.

Thanks for the tip! This is all great info.