TX7A

TX7A

Well Known Member
Van's supplies four 1/4-20 (gr. 8) bolts that are used to attach the FAB mount plate to the bottom of the carb.
Instructions say to use the locking tab washers or safety wire. I prefer the safety wire, which means that I need to drill the bolt heads.

As another option, can these be used? Acceptable?

AN500-A416-10
They are fillister head 1/4-20 with drilled head.

http://www.aircraftspruce.com/catalog/hapages/an500.php

Of course using flat washer & torqued accordingly.


...and on a slightly related note: I bought the Avery bolt head / nut drill jig and I am disappointed in the results. It just drills across a point and doesn't leave much meat. Maybe I'm doing something wrong.??:confused:

Thanks for any help.
 
Uneducated SWAG

It is an area where I would not experiment. I'm told that anything that gets loose in this area will get sucked through the carb to the intake valves and cylinders. There is a lot of stress there. I just replace my mounting plate that I found to be broken in my annual condition inspection. I drilled and safety wired my bolts in the original installation. It was not a big deal, probably easier with a small drill vise on a drill press.

Bob Axsom
 
You're probably right, Bob.
No jackin' around in that area.

Guess I'll just suck it up and start drillin'! :eek:
 
I used the Fillister Head Screws

TX7A said:
Van's supplies four 1/4-20 (gr. 8) bolts that are used to attach the FAB mount plate to the bottom of the carb.
Instructions say to use the locking tab washers or safety wire. I prefer the safety wire, which means that I need to drill the bolt heads.

As another option, can these be used? Acceptable?

AN500-A416-10
They are fillister head 1/4-20 with drilled head.

http://www.aircraftspruce.com/catalog/hapages/an500.php

Of course using flat washer & torqued accordingly.


...and on a slightly related note: I bought the Avery bolt head / nut drill jig and I am disappointed in the results. It just drills across a point and doesn't leave much meat. Maybe I'm doing something wrong.??:confused:

Thanks for any help.
Click to expand...

I found no reason not to use them. Have you reviewed the specs compared to Van's standard 1/4 20's Grade 8's? I think you will find the AN500's to be superior in tensile, clamping, and shear strengths. Perhaps one of our engineering buddies has that info at hand?
300 hours, no issues here.
 
Last edited:
Weird,

I used Van's FAB kit and did not drill or buy any additional bolts for attaching it to the carb. Van's must have included pre-drilled bolts as I know I did safety wire em.....
 
Brantel said:
Weird,

I used Van's FAB kit and did not drill or buy any additional bolts for attaching it to the carb. Van's must have included pre-drilled bolts as I know I did safety wire em.....
Click to expand...

Sitting at home, I guess I better check with my Van's FAB kit, maybe they are drilled. I don't think they are though. I know I have them temporarily installed now with the self-locking washers that cam in the kit.
 
When I called Van's...

...about a related issue, I asked the tech about the screws. The pick list specs 4, 1/4-20 x 1/2. He said that a 1/4-20 bolt and with drilled head wasn't (readily) available. That's why the locking tab washers are supplied. Maybe the bolts were drilled at one time. To me, they look to have the markings of grade 8 bolts.
I have an AP friend that suggested the fillister screws with drilled heads and safety wired would be fine. I just wanted other opinions or experiences.
 
Follow advice on other threads to avoid cracking....

TX7A said:
...about a related issue, I asked the tech about the screws. The pick list specs 4, 1/4-20 x 1/2. He said that a 1/4-20 bolt and with drilled head wasn't (readily) available. That's why the locking tab washers are supplied. Maybe the bolts were drilled at one time. To me, they look to have the markings of grade 8 bolts.
I have an AP friend that suggested the fillister screws with drilled heads and safety wired would be fine. I just wanted other opinions or experiences.
Click to expand...

I used a large area washer, backed up with a lock washer, to help avoid cracking of the plate. I am hopeful the larger surface area might help although the source of cracking has not been conclusive. Some crack, some dont. I replaced mine at around 230 hours. Thus far, no signs of cracking on the new plate. We shall see.
The Fillister contact head area appears to be slightly smaller than the 1/4 20 bolts.
 
JonJay said:
I used a large area washer, backed up with a lock washer, to help avoid cracking of the plate.

The Fillister contact head area appears to be slightly smaller than the 1/4 20 bolts.
Click to expand...

Great Idea on the large washers.

I looked at the contact area also and saw what you saw. But with the large washers and lock washer and safety wire......well it sure sounds good from here.

Where's them engineers when you need'm ?? Hello?
 
TX7A said:
...and on a slightly related note: I bought the Avery bolt head / nut drill jig and I am disappointed in the results. It just drills across a point and doesn't leave much meat. Maybe I'm doing something wrong.??:confused:Thanks for any help.
Click to expand...

A drill jig for the corner of the head works fine on aluminum flare nuts. Drill bolt heads straight through, flat to flat. No jig required, just a good drill press clamp. Bet I did 1000 of them (metric) back in the racing days.
 
Just watch you filter clearance

TX7A said:
Great Idea on the large washers.

I looked at the contact area also and saw what you saw. But with the large washers and lock washer and safety wire......well it sure sounds good from here.

Where's them engineers when you need'm ?? Hello?
Click to expand...

If your FI you have to offset the FAB. This may not leave enough room for the larger washers without interfering with the filter. Each installation is different.
 
Safety wire + the bend over lock washer + locktite = it's not coming lose.

Laugh if you want but as mentioned if one of those screws come out it is at minimum an engine overhaul. Worst case a fatal crash.

Looking in the nose wheel well of a boeing some critical fasenters have the following:

Big bolt with a castle nut + AN bolt keeper with a castle nut + roll pin for that castle nut + safety wire through the roll pin + gob of seal on the second nut/roll pin/safety wire.
 
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