Engine Fastening Best Practice

[Kafin Noe’man]

What’s the best practice of fastening the engine to the mounting so the engine won’t move due to vibration.
My last setup was:

Bolt
|
Engine lug
|
Aluminum pads
|
Hardwood Engine Bearer
|
Locknut

I’ve got:
- [ ] Flat washers
- [ ] Spring washers
- [ ] Steel nut (normal nut)
- [ ] Locknut

Looking forward to hearing more from you!


Best,
Kafin

[Brett Buck]

What’s the best practice of fastening the engine to the mounting so the engine won’t move due to vibration.
My last setup was:

Bolt
|
Engine lug
|
Aluminum pads
|
Hardwood Engine Bearer
|
Locknut

I’ve got:
- [ ] Flat washers
- [ ] Spring washers
- [ ] Steel nut (normal nut)
- [ ] Locknut

Looking forward to hearing more from you!

     This is on a through hole (like a profile)?  You have a (presumably thick/hard) aluminum pad under the engine, but I think you need something to spread the load on the other side of the mount. The reason they come loose in these situations is that the wood compresses, so you can have all the jamnut/locknuts in the world, and it still comes loose.

   You also show no doublers over the hardwood mount - presumably you do have those. That is the usual part to collapse/compress and make it come loose. At the very least, you want a flat washer between the nut and the wood, the aluminum doubler is far better.

    The net assembly has to be stiff enough that you can count on slightly stretching the mount bolts, so that you have some positive pressure pulling it all together. If the wood compresses, it usually says compressed. It also depends on *which* hardwood you have, you need something at least as hard as sugar maple ("rock maple"), which means sugar maple or some exotic wood like cocobolo, etc. (which are typically difficult to glue since some of them are pretty oily).

    Brett

[Motorman]

bolt
spring washer
flat washer
engine lug
aluminum pad
wood
flat washer
nyloc nut

[Dan McEntee]

What’s the best practice of fastening the engine to the mounting so the engine won’t move due to vibration.
My last setup was:

Bolt
|
Engine lug
|
Aluminum pads
|
Hardwood Engine Bearer
|
Locknut

I’ve got:
- [ ] Flat washers
- [ ] Spring washers
- [ ] Steel nut (normal nut)
- [ ] Locknut

Looking forward to hearing more from you!


Best,
Kafin

      What you have listed there is pretty much typical these days. The only difference is that most often we use a blind nut or what some call a T nut in the hard wood mount if it's a full fuselage model and you can't get a wrench or socket on a nut. Otherwise, I think you have it pretty much correct. I use blind nuts on profile models and sometimes run a nut onto the bolt after all have been tightened to my satisfaction to act as a jam nut and it is worth the effort. But again, what you have described is pretty much correct but you should have a flat washer under the nuts on the back side of the wood mounts also..
    Type at you later,
    Dan McEntee

[Dennis Toth]

Kafin,
Pretty much what everyone has said, you could use a drop of Loctite blue to secure the threads at the blind nuts. Also remember when using aluminum pads the engine mount lugs need to be flat. Older engines had a mold release draft angle cast in (very small) that when using maple mounts would just crush in. With the AL pads it can cause stress in the case (particularly the FOX 29/35) that can cause binding in the piston/cylinder and really mess up the engine run. For these older engines either don't use the AL pad or put a 1/32" ply pad between the engine lug and the AL pad to absorb the draft angle.

Best,   DennisT

[Kafin Noe’man]

bolt
spring washer
flat washer
engine lug
aluminum pad
wood
flat washer
nyloc nut

Can I do this with the spring washer on both sides?
Bolt
Spring washer
Flat washer
Engine lug
Aluminum pad
Wood
Flat washer
Spring washer
Nyloc nut

[Brett Buck]

Can I do this with the spring washer on both sides?
Bolt
Spring washer
Flat washer
Engine lug
Aluminum pad
Wood
Flat washer
Spring washer
Nyloc nut

  You can but it's probably unnecessary, if everything else is right. You just need the lockwasher on one side, in this arrangement, it should be the nut side. You do need a flat washer under the screw head.

     I emphasize again, check that the nuts or washers are not digging into the wood and progressively crushing it. That will guarantee that it will come loose later, it has nothing to do with the fasteners backing out.

   Brett

[Kafin Noe’man]

  You can but it's probably unnecessary, if everything else is right. You just need the lockwasher on one side, in this arrangement, it should be the nut side. You do need a flat washer under the screw head.

     I emphasize again, check that the nuts or washers are not digging into the wood and progressively crushing it. That will guarantee that it will come loose later, it has nothing to do with the fasteners backing out.

   Brett

Thank you Brett, forgot to mention that it is for the Vector setup

[Brett Buck]

Thank you Brett, forgot to mention that it is for the Vector setup

   Blind nuts, then. With an aluminum pad under the engine, use a socket cap screw with a lockwasher and a flat washer, tighten, should be no issue. With no blind nuts, a steel nut plate maybe 1/16" thick with regular steel nuts soldered to it, glue to engine bearers on the top side. I have considered going back to nut plates when several people had problems with the stamped steel blind nuts breaking, but I have never had an issue with them.

     The downside to a nut plate is that it takes up extra space where you want to shape the nose. I usually come very close to or hit the blind nuts on the inboard side of the airplane when shaping the nose. If you do that, grind that edge off with a Dremel tool so make sure it is below the surface, then use SuperFil  or a balsa insert to fill the groove. If you try to blend in the metal, I guarantee it will show.

    Brett

[Jim Hoffman]

A picture is worth 1000 words.  Here is a very traditional installation, consistent with what is described by others.

Maple motor mount
1/16-inch alum pad.
4-40 blind nut (steel) on maple motor mount side (not visible in photo)
Steel 4-40 socket head screws
Washer under the screw head.

No loc-tite.
No lock nuts

Do Epoxy blind nuts to maple mounts - caution to keep epoxy out of the threads

[Steve Helmick]

Personally, I wouldn't use "lock washers" aka "Spring Washers". If I really felt the need, I'd use "Star Washers", but would prefer Loctite. If you decide to use "lock nuts" (aka Elastic Lock Nuts), remember that they're a throw-away item and should not be used a second time. In the last few years, I've run across lock nuts that sort of have a buggered spot on the top side of the steel nut...same rule...use once and dispose of.  Steve

[frank williams]

I've been doing this for a while now and so far have not had to fish around in frontend for a blindnut that got pushed out the backside while cheking the system at the Nats.  The steel inserts I get from Grainger are slightly smaller than the standard 4-40 brass inserts from DuBro or such.  The inserts hold tight no problem with coming loose.

Bolt
Spring washer
Flat washer
Engine lug
Aluminum pad
Steel insert in wood motormount

[fred cesquim]

micro fastner have this great schnorr washers
what usually looses bolts are unballanced sets. a flat washer with a drop of blue loctite will hold a properly ballanced set for ages
if you want redudancy the schnorr washers will do and looks cool

[FLOYD CARTER]

I was always taught the locking device (split washer, etc.) always goes under the part you turn to tighten.  That means under the nut, and not under the bolt head.  A flat washer under bolt head is OK to spread the load.

[Brett Buck]

I was always taught the locking device (split washer, etc.) always goes under the part you turn to tighten.  That means under the nut, and not under the bolt head.  A flat washer under bolt head is OK to spread the load.

   In the case we are discussing, there is not access to the nut and it does not turn. The lockwasher goes under the screw head in that case, because that is what you are turning.

     Brett

[Motorman]

I use the Dubro billet blind nuts not the stamped sheet metal ones from Great Planes. I drill the hole for them just deep enough so the blind nut bottoms out in the hole the same time the shoulder hits the wood. This gives it a double register.
Then I use a little epoxy on 1/32" wire and swirl it around in the holes. Just enough so it soaks into the wood and doesn't block the hole. A little heat gun helps. Then I put some epoxy on the blind nut and press it in. Helps protect it a little longer from fuel soak.

I like the split washer under the bolt head when using blind nuts as there's no other place to put it and it's bigger than the head and helps spread the load on the flat washer that always seems to cup. We need thicker/harder #4 flat washers.

Hope that helps,
Motorman

[Bruce Shipp]

I have overdrilled the holes to the OD of the blind nuts, installed the engine to set the blind nuts, and removed the engine. I covered the bolts with mold release, filled the holes with slow set epoxy and installed the bolts.  Remove the bolts after the epoxy sets and you have a fuel proof, threaded, self locking hole.

I got his from either a magazine column or stunt news in the 90s. Not new.

[Dave Harmon]

Anyone else notice that the Du-Bro 4-40 blind nut threaded hole is off center?

I like the holes in the wood to be right sized for the bolt and when the DB net with the off center hole is installed....it becomes difficult to install the bolts.

Thinking I might have received some defective blind nuts I called DB and asked about it.
They were not concerned.

I like the Great Planes nut better anyway because of the bigger footprint.....I have not had any problems with them.

[doug coursey]

micro fastner have this great schnorr washers
what usually looses bolts are unballanced sets. a flat washer with a drop of blue loctite will hold a properly ballanced set for ages
if you want redudancy the schnorr washers will do and looks cool

I used those on my helicopters and they work really good...i dont think it matters if you use the spring washer next to the nut or under the head of the bolt it will accomplish the same thing....

[Perry Rose]

Putting a spring washer between the bolt head or nut and flat washer you have no security as the spring washer grabs the flat washer and the flat washer will slide as it has more area and less force.

[Steve Helmick]

I use the Dubro billet blind nuts not the stamped sheet metal ones from Great Planes. I drill the hole for them just deep enough so the blind nut bottoms out in the hole the same time the shoulder hits the wood. This gives it a double register.
Then I use a little epoxy on 1/32" wire and swirl it around in the holes. Just enough so it soaks into the wood and doesn't block the hole. A little heat gun helps. Then I put some epoxy on the blind nut and press it in. Helps protect it a little longer from fuel soak.

I like the split washer under the bolt head when using blind nuts as there's no other place to put it and it's bigger than the head and helps spread the load on the flat washer that always seems to cup. We need thicker/harder #4 flat washers.

Hope that helps,
Motorman

Agree with MM 100% on this, especially the use of Du-Bro blind nuts. Also, I'd wonder if maybe #4 washers might be available in "SAE" grade...they're harder and have a smaller hole in larger sizes. When I bust out another OS LA engine, first thing I do is throw away the prop nut and replace it with a 1/4-28 SAE nut, and I have replaced various prop washers with SAE spec washers...mostly because the hole is not such a loose fit on the crank. They look to be heat treated to some degree or other. Steve

Ah, it looks like #4 SAE washers are a "thing". 
https://www.grainger.ca/en/product/WASHER-FLAT-SAE-PLTD-NO-4/p/PFSFW4P

[Brett Buck]

Putting a spring washer between the bolt head or nut and flat washer you have no security as the spring washer grabs the flat washer and the flat washer will slide as it has more area and less force.

  The purpose of the spring wascher is not entirely  to "dig in" to the other parts, it's to make sure it keeps tension on the assembly to eve if it starts to come loose, there is still friction keeping it from unscrewing completely.

    Brett

[Colin McRae]

One other thing that I don't think was mentioned.

Any wood (hard-wood, plywood, etc) will compress over time which will lower the bolt tension. It is a good idea to check and snug up the fasteners now and then. Just don't assume they are tight.

[Istvan Travnik]

I think, some components are enough. See:
https://www.flickr.com/photos/171504164@N04/48094471777/

(plus the next 4-5 photos in gallery)

[kevin king]

My bad. This post was for Kafins airplane storage post. Sure do miss that "Remove" button. But heres my storage rack. Its at the 2:35 minute mark.

Kevin

[Lauri Malila]

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