Threaded brass inserts for engine mounting good bad ??????????

[frank mccune]

        What are your thoughts on using threaded brass inserts for mounting engines?

                                                                                                                    Tia,
       
                                                                                                                     Frank McCune

[john e. holliday]

I tried them on a profile plane and they split the motor mounts out when I tried to install per instructions.  They are in the shop some where with other stuff I have tried in the past.

[Tim Wescott]

Good quality T-nuts (DuBro, Sig, RTL -- not no-name eBay crap) work fine.  I have planes that have hundreds of flights.

My main ride for about five years was a Fancherized Twister with a 46LA held on by 4-40 screws into T-nuts.  It has somewhere between 300 and 600 flights on it, and I've had no signs of problems.  You'll wear out the airframe before you'll wear out a plain old T-nut.  If you want to do something to extend the life of your engine bearers, put aluminum pads under the engine mounts to spread the load on the bearers.

[Brett Buck]

I tried them on a profile plane and they split the motor mounts out when I tried to install per instructions.  They are in the shop some where with other stuff I have tried in the past.

    I had the same issue, and I can't see a situation where something similar wouldn't happen, if nothing else, because the insert has to come very close to the edge of the mounts. I can think of ways around that, but, even if you succeed and they are fully enclosed by the wood, you still have 4 giant holes cut in the mounts right at the point of the most stress, taking your 1/2 x 3/8 maple mounts down to about 1/2 x 3/16. The inserts themselves add nearly nothing to the integrity of the mount even if you glue them in with epoxy.

   Given all that, I would actually prefer using either 4-40's threaded directly into maple, or, properly-installed wood or sheet-metal screws (i.e. appropriate pilots holes, etc), than the brass thread inserts. I have used the thread inserts on other projects where they didn't have to be right at an edge and there was no way to put in a nut plate or blind nut, and it worked OK, but there is almost always a better solution.

    I know people have used these inserts successfully, so it can be done, but I never had any luck at all with them, and the reasons seem pretty obvious to me. I *have* used conventional thread inserts (Heli-Coils) into maple when I had a blind nut strip out, and it seemed pretty solid, but it would probably also work with just three mounting bolts, so who knows what sort of load it was under. It tightened up OK.

      Brett

[Larry Fernandez]

    I had the same issue, and I can't see a situation where something similar wouldn't happen, if nothing else, because the insert has to come very close to the edge of the mounts. I can think of ways around that, but, even if you succeed and they are fully enclosed by the wood, you still have 4 giant holes cut in the mounts right at the point of the most stress, taking your 1/2 x 3/8 maple mounts down to about 1/2 x 3/16. The inserts themselves add nearly nothing to the integrity of the mount even if you glue them in with epoxy.

   Given all that, I would actually prefer using either 4-40's threaded directly into maple, or, properly-installed wood or sheet-metal screws (i.e. appropriate pilots holes, etc), than the brass thread inserts. I have used the thread inserts on other projects where they didn't have to be right at an edge and there was no way to put in a nut plate or blind nut, and it worked OK, but there is almost always a better solution.

    I know people have used these inserts successfully, so it can be done, but I never had any luck at all with them, and the reasons seem pretty obvious to me. I *have* used conventional thread inserts (Heli-Coils) into maple when I had a blind nut strip out, and it seemed pretty solid, but it would probably also work with just three mounting bolts, so who knows what sort of load it was under. It tightened up OK.

      Brett

I have been using Heli-coils for quite some time now.
After the mounts are drilled and tapped with a Heli-coil tap, I wick thin CA down through the threaded holes and let it completely dry. Run the tap through again, just to clean up the threads.
Install the Heli-Coils and again wick thin CA into the threads. After the CA has dried, run a standard 4-40 tap through.
I had a t-nut spin on a Macaluso Tomcat around 2001. I had to cut up a very pretty airplane to get the motor out and Ill never be doing that again.
I have never considered the brass inserts as, the large hole drilled into the motor mounts dramatically weekens them.

Larry, Buttafucco Stunt Team

[bob whitney]

I have been using them mostly in full body ships for over 6 years I like that u set them up to touch the bottom of the engine lug and it is solid ,Tnuts pull from the bottom and squeeze the moto rmount

the bad to me is that they are too short .I put 2 in each hole and it will take up the whole mount
4/40 and 6/32 both have the same OD size  once i get the pilot holes started i lightly wedge  a piece of hard wood between the  mounts it keeps from walking out the side of the motor mount

my Big Job (S/T 60) is over 5 years old and has the 6/32 Brass inserts. 

for 35 size ships sometimes i will get some 12-18 brass or steel bolts from ACE and drill them out to 4/40 , they dont get as close to the edge of the motor mount

[Perry Rose]

I've installed Du-Bro 4-40 and 6-32 inserts into wood bearers with no problems. In one plane I installed both sizes to fit an ASP .51 and an OS .46LA with no problems. The inserts for the OS have it's threads poking out the side of the bearer. The # 4 and 6 inserts are the same o.d.  I use a .1700 or number 18 pilot drill. (Made in China) That is a few thou. larger than the insert barrel. Which gives me .0437 of grip with the insert outer threads. Or .0218 each side. Theoretically there is no stress on the wood from mounting the engine. As long as the engine mount holes are smaller than .1700 dia. and the inserts are perfectly positioned. 

[kevin king]

I use roofing nails.

[Tim Wescott]

I use roofing nails.

The ones for asphalt shingles, or the ones for metal roofs, with the rubber gaskets?  I could see the gaskets providing some vibration damping, particularly if you set the motor on a sheet of rubber.

[BYU]

I use roofing nails.

Always, and great for nose weight

[Geoff Goodworth]

I have 4-40 inserts from Micro Fasteners.

The one place where I used them was in a Brodak ARF Oriental. It is one of the first production batch and I considered the bearers to be too soft. The bearers are quite wide so I left the inserts very slightly proud of the bearer mounting surface.

Once the epoxy cured, I sanded the inserts back level with the timber so the engine bolts down onto the brass inserts rather than the timber.

As others have noted, there is a risk of splitting the timber so I do not use them with 3/8" wide bearers

[Scott Richlen]

Maybe try ring-shank nails instead of roofing nails.

Just to be safe, hammer them over where they come through...

[Larry Fernandez]

I have been using Heli-coils for quite some time now.
After the mounts are drilled and tapped with a Heli-coil tap, I wick thin CA down through the threaded holes and let it completely dry. Run the tap through again, just to clean up the threads.
Install the Heli-Coils and again wick thin CA into the threads. After the CA has dried, run a standard 4-40 tap through.
I had a t-nut spin on a Macaluso Tomcat around 2001. I had to cut up a very pretty airplane to get the motor out and Ill never be doing that again.
I have never considered the brass inserts as, the large hole drilled into the motor mounts dramatically weekens them.

Larry, Buttafucco Stunt Team

Another reason I like using Heli-Coils, is that the bolts do not go through a profile fuselage so there are no unsightly nuts on the inboard side, giving it clean, well finished look.

Larry, Buttafucco Stunt Team

[Scott Richlen]

Another reason I like using Heli-Coils, is that the bolts do not go through a profile fuselage so there are no unsightly nuts on the inboard side, giving it clean, well finished look.

So, where do you get them?  I'll consider using them so my unsightly nuts don't show....

[Brett Buck]

So, where do you get them?  I'll consider using them so my unsightly nuts don't show....

  Any good hardware store should have them. Even though I used them and Larry has been successful, this is a rather radical application that is definitely not what they were intended to do - which is stripped thread repair in metal -  and more or less, you are mounting the engine with what amounts to a 6-40 machine screw into wood (in this example, hardened with Hot Stuff). I am not entirely convinced that this is a good idea compared to the alternatives. I used mine only in what I would consider an emergency and I had 3 other real bolts with a steel nut plate.

     Brett

[Doug Moisuk]

I have now used them on the last three or four Stunters I have built. I think they are way better then blind nuts that always seem to pop out on me. On the first one I did, I did a test on a a piece of motor mount.  I used the suggested drill size and the mount spit. So I experimented and used larger drill sizes until the insert went in without splitting. When I finally do the motor mount I screw the insert in then take it out and install with JB Weld. So far I think they are great.

The other use is if you want to change a motor in and existing plane. I have done this as well. I fill the old holes with epoxy and filler then re-drill for the new motor and install the new brass inserts. Works great.

[Larry Fernandez]

So, where do you get them?  I'll consider using them so my unsightly nuts don't show....

Great reply, I got quite a chuckle from that.
You can get the Heli-Coils from McMaster Carr. You will also need the install kit which comes with a drill, Heli-Coil tap and installation tool. The longest 4-40 Heli-Coil is .400 long. These are the ones I use.

[Dave Harmon]

I have been using Heli-Coils for a long time for motor mounts and on engine muffler mounts.
The metric cap screw head hex seems to be shallow causing the head to strip....so I just use the 4-40 H/C from the start and get it over with.
I have never had a problem with the H/C in plastic, wood or metal....and I have been using the shorter coil too....gonna get me some of those .400 coils though.
No...the tool is not rounded off either...

[Doug Moisuk]

So, where do you get them?  I'll consider using them so my unsightly nuts don't show....

4/40 brass inserts. Local hobby shop or online hobby dealer. No special tools require.

[Dave Hull]

The TR guys use various custom threaded sleeves. Often titanium. Sometimes flanged. Bonded in. But the engine lugs sit right on the lapped ends, so there is no compression of the bearers. Imagine a DuBro T-nut that goes all the way thru the bearers and you see the possibilities.

One thing to remember about a helicoil that is very different from a solid threaded insert, whether it is a Du-Bro brass job or a Keensert: the only loadbearing coils are those engaged by the screw. If your bolt does not go all the way thru, then only those threads touching the screw are considered active on the wood side. A threaded insert will distribute the load over the whole insert. You may have been taking advantage of this without realizing it.

I also wonder how the bonded joint between the helicoil and the wood bearing will tolerate the use of a thread locker, say Loctite Blue. I have not looked at that chemistry there before,  because there was no need....

One thing that puzzles me are the types of wood some guys use (and some ARF factories use) for engine bearers. I really dislike ring porous woods like oak (ugh) or ash (yuh), because they have built in tendencies towards splitting. And if the grain is in an unfavorable orientation, well....   Save the oak for your rendition of Old Ironsides.  My favorites are tight grained birch, or the old standby, hard maple. Not big leaf maple or western maple which is much softer.

Dave

[L0U CRANE]

Some of the available 4-40 T-nuts are iron or steel. Much better - easy to check with any kind of magnet.

I also "counterbore" the hole with a bit just about the diameter of the 'tube' surrounding the threaded section, and to a depth that matches that. NOT all the way through...

The 'counterbore' should be a snug, but NOT forced, fit. Acetone air-dried on the metal; fine wipe of 15- or 30-minute epoxy, and drawn home by a bolt (and washer) from the 'head side.'

The barbs on the T-nut will dig in - no spinning. The joint makes no splitting pressure on the wood mounts. Can't recall any manner of failure or loosening since I went with this method. (Who said, "bad memory...")

[phil c]

I bought 1000 4/40 brass die inserts quite awhile ago.  They are still available online.
They worked fine on combat planes and stunt planes.

A couple of tricks that help, although I never had a plane break the wood.  A few failed when they weren't epoxied in.  That's a must.

As mentioned above, measure the OD between the threads and try to drill the hole just a thousandth or so oversize.  The insert is supposed to cut a thread into the wood, not press fit in place.

Drill the mounting holes in the center of the beams.  That's the strongest although I never had any motor mounts break with off center holes. Get the whole spacing right and then use a hand grinder to relieve the mounts so the motor will fit.  Try to minimize the grinding, although for stunt a little extra relief won't matter.
The holes don't have to go all the way through.  Just remember to clean any sawdust out before installing.

Seal the inside of the hole with epoxy. No harm done if you get too much in.  Just drill it out after it hardens.

To install die inserts I used a 4-40 cap screw with a nylon lock nut screwed on backwards.  Add a washer and then thread the insert on and lock it tight to the nut.  The insert should be just a few thousandths above the wood.  Installing the motor will pull things into alignment.

Once the motor and mounts are mated you can square the outside of the mount up the fuselage or motor block. 1/64 ply works well for shimming in place if needed.  Use epoxy.

If I was going to build a new stunter I'd use aluminum for the mounts now.  If you have the tools and technique down it would be stronger and stiffer.  I think Scott Dinger, or another Scott worked at Boeing and has good instructions for epoxying aluminum to things that he's posted here.

The Du-Bro inserts have a cross cut for a screw driver, but even with them the screw-nut-washer trick makes installation easier.

[Neil Rogers]

The cross cut in the brass insert is not for a screw driver.  That end goes into the wood first to aid in cutting the threads.  The correct drill size is 11/64.  I CA them in place and haven't had a failure in the 20 years that I've been using them.

They work especially well in the Chinese hardwood in Brodak ARFs where the wood will crush using T-nuts.

Neil Rogers

[Ara Dedekian]

The cross cut in the brass insert is not for a screw driver.  That end goes into the wood first to aid in cutting the threads. 

Neil Rogers

I bought 1000 4/40 brass die inserts quite awhile ago.  They are still available online.
The Du-Bro inserts have a cross cut for a screw driver, but even with them the screw-nut-washer trick makes installation easier.

      Just got off the phone with DuBro because I couldn't find on-line instructions on the the proper way to install the inserts. Dubro gets their inserts from the furniture industry and come with and without the cut outs. Strangely enough, the person I spoke to had to check to see if the inserts sold to the modelers had the slots.(??) The correct way to install them, I was told, is to use the 'screw driver slot'.

      I've found they go in much easier and with a lot less stress on the wood when the cut-out goes in first, cutting a path down through the wood.

      This may fall into the RC servo mounting debate. Does the grommet flange sit on the mounting surface or under the mounting screw head. Answer: it un-intuitively should be installed upside down with the flange sitting on the mounting rail. I see a fair number of them mounted with the flange up.

       Inserts save the day for me in replacing RC engine mounts when I can't access the back side of the firewall.

      Ara

       

[bob whitney]

I agree 100% with neil

[Curare]

      Just got off the phone with DuBro because I couldn't find on-line instructions on the the proper way to install the inserts. Dubro gets their inserts from the furniture industry and come with and without the cut outs. Strangely enough, the person I spoke to had to check to see if the inserts sold to the modelers had the slots.(??) The correct way to install them, I was told, is to use the 'screw driver slot'.

      I've found they go in much easier and with a lot less stress on the wood when the cut-out goes in first, cutting a path down through the wood.

      This may fall into the RC servo mounting debate. Does the grommet flange sit on the mounting surface or under the mounting screw head. Answer: it un-intuitively should be installed upside down with the flange sitting on the mounting rail. I see a fair number of them mounted with the flange up.

       Inserts save the day for me in replacing RC engine mounts when I can't access the back side of the firewall.

      Ara

     

There is no debate about servo grommets, go and read the instructions! Flange upside down, and wide flange screw head at the top makes an isolated mount for the servo, the other way round will cut a hole through your servo rail and hard mount the servo for you.

[RandySmith]

In Rock maple  the best is  T Nuts, but you have to make sure you have high quality nuts, The CHEAP stamped ones are very thin where the edge is rolled over to make the flange, they are VERY weak at that point and will break very easy, Good ones like DuBro and Goldberg  are whoppingly stronger, I have never had one break or split, I have seen the cheap ones cause people a lot of problems, So take care what you use, The inserts are excellent in other hardwoods, that are softer than maple, and you need take care to use the  exact drill size specified and follow instructions to the letter, make sure you drill the holes for the inserts dead in the middle of the wood beam, adjust engine hole size to induce offsets.  In my kits I include T nuts for the engine mount, and Brass inserts for the  landing gear mounts.
They also make a  steel product that works just as the brass inserts do, but are much stronger, these are excellent but hard to find, I would use these over helicoils . They come with a  blue dry locking substance on the outside of them, remove it for wood, keep it for metal. I also have used both the steel inserts in muffler luggs on engines in both 4-40 and 3mm  to hold mufflers on.

Randy
These are available many places in different types below is just a  sample of what is out there

https://www.albanycountyfasteners.com/Threaded-Insert-Stainless-Steel-4-40-x-0-250-p/11700000.htm

[qaz049]

I've been using 3/16" solid round head Aluminum Aircraft rivets as inserts on .15 size models. I just drill a suitable hole down the centre in a lathe chuck and tap 4:40 UNF. Drill the Beech bearers 3/16" and tap in from the other side with a small hammer. Saturate rivet with thin CA all round, and file the rivet end till it's flush with the bearer.

Works fine!