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Oct 05, 2017, 03:25 PM
Registered User

First kit build, SIG four star 40

Hello! I'm trucking along on my first kit build. A bit frustrating here and there, but I'm learning a ton and getting through pretty well. I'm now to the drilling of the engine holes on the glass filled-nylon motor mount that was included in the kit. I bought my engine second hand and it didn't come with screws to mount the engine to the black mount, what should I buy to mount it securely? I bought a blind nut kit but the nuts keep coming out and I flattened the back end so now they won't even stay in. Is there a locking nut I could use instead?

Thanks a lot
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Oct 05, 2017, 05:16 PM
Oh...that's gonna leave a mark
capt kurt's Avatar
Yes, a nut would work fine. I use a washer and a nylon nut on my glo stuff. Your gonna love the 4 star!
Oct 06, 2017, 05:38 AM
Registered User
With a nylon mount I've used round-headed (not countersunk) coarse self-tapping screws in the past. So long as you get the hole size right, the nylon seems to grab a hold of them after you've screwed them in.

Otherwise use long bolts with nyloc nuts. The problem with this solution is the engine mount usually has tapered arms, so the nut is bearing onto a sloping surface and will probably bend the bolt as it tries to lie flat against the mount. The solution is tapered washers, or heat the nuts so that they melt into the nylon a bit.
Oct 08, 2017, 09:17 AM
A man with a plan
Balsaworkbench's Avatar
Dave Brown nylon mounts have always had coarse self tapping screws included. I have always used them with excellent results, even at 120 size. If your holes are still small enough you can use a self tapping screw. But if they were drilled for machine screws to slide through you will need a lock nut on the other end, preferably the kind with the nylon insert.

Incidentally, when you buy a new engine it never comes with mounting screws. That's considered part of the mount.
Oct 08, 2017, 12:39 PM
Registered User
burlesontom's Avatar
You picked a really good plane to build.

I usually drill and tap my mounts for a 6-32 bolt and that way no locking nuts are needed. But the #4 sheet metal screws will also work fine. I just grew up working in my dads machine shop and tapping holes comes natural to me. By the way, the machine I operated the most was a tapping machine. I averaged tapping 2500 holes each day.
Oct 14, 2017, 07:20 PM
Registered User
I like machine screws and I drill and tap black plastic mounts for them. Someone suggested running the tap most of the way, but not all the way through. Then the last part the threads go through acts like a lock nut. I've found it really works great, but I had to learn the right amount. Just about when the tip of the tap emerges, stop and try it.

Oct 14, 2017, 07:40 PM
A man with a plan
Balsaworkbench's Avatar
I just thought I should mention that if you have taken a bad turn with your current mount, you can always get a new one. Making mistakes and then vowing to never make the same mistake again is a big part of the fun. If you don't feel like using lock nuts, don't sweat it. There are lots more mounts out there.
Oct 19, 2017, 11:02 AM
Registered User
Drill through the motor mount so 6-32" socket head bolts slide in comfortably. Use a flat #6 washer on each side and secure with nylock nuts. Available at your local hardware store.

Easy and almost fool-proof
Oct 19, 2017, 11:15 AM
Registered User
It's OK as long as you just have cheek cowls so you can get to the nuts on the bottom of the mount, and if you don't mind juggling a screw driver or allen key from the top and a nut driver from the bottom. That's why I like drilling and tapping, and leaving some untapped at the very end to keep it tight. Works great and you only screw and unscrew the mounting bolts from the top. You can use a side mount without having an access hole on the other side, or upright you can close up most of the bottom.
Nov 06, 2017, 08:34 PM
I'm a pilot, 100 yrs too late
Thermalin's Avatar
Just picked up a verrrrrry old kit of this on ebay just because I wanted an "old" one to build . Built one several years back and it's a great flying plane.

Are you making mods to it?

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