FAB Plate Screws...acceptable?

TX7A · #1 05-17-2010, 09:01 AM

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.??

Thanks for any help.

Bob Axsom · #2 05-17-2010, 10:27 AM

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

TX7A · #3 05-17-2010, 11:47 AM

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

Guess I'll just suck it up and start drillin'!

JonJay · #4 05-17-2010, 11:59 AM

Quote:

Originally Posted by TX7A

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.??

Thanks for any help.

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.

Brantel · #5 05-17-2010, 12:08 PM

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.....

apkp777 · #6 05-17-2010, 12:10 PM

They look good to me. I am ordering 4. I am not a fan of self locking washers.

apkp777 · #7 05-17-2010, 12:12 PM

Quote:

Originally Posted by Brantel

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.....

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.

TX7A · #8 05-17-2010, 01:43 PM

...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.

JonJay · #9 05-17-2010, 01:51 PM

Quote:

Originally Posted by TX7A

...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.

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.

TX7A · #10 05-17-2010, 01:58 PM

Quote:

Originally Posted by JonJay

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.

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?