Engine mounting hardware

[Peter Nevai]

Hi Guys a quick question

I have a OS 46 VF to mount. 4-40 bolts and blindnuts are just too light weight for this. I recall using 5/32 hardware in the past but can not find any sources for the blibd nut , allen screw sets. Brodak only supplies 4-40 stuff. RSM size is 6-32 I think that would be too large for the engine mount holes. Any Ideas? Want to place an order with other CL related items so I really dont want to go to a seperate supplier for this.

[John Stiles]

Did a search in ebay, ther term I used was "blind nuts" and there's great plains and dubro items all through the lists. Didn't search the slot-head screws because I know they're there too. 

[Pat Johnston]

Peter,
We used to use soft 4-40 bolts for mounting Formula I Pylon Racing engines like the old ST X40's.  The thought is that the soft bolts would sheer and save damage on engines.  For Stunt applications, the standard socket head 4-40's offer more than enough strength and the mounting holes do not have to be hogged out.  That is very nasty and annoying to get an engine which the holes need to be shrunken.
Pat Johnston
Skunk Works

[Garf]

I use 4-40 screws on my fast combat engines and have yet to break one. I had 4-40 on the BassMaster when I crashed into the coral rock at Tamiami field. It broke both mounting lugs on the OS 35S and slightly bent the screws. You NEVER need more than 4-40 on 35/46 size engines. Of course, if you use screws made of pressed dog manure...........

[Gordan Delaney]

Peter,
I use 6-32 on anything larger than a 40 size engine.

Gordy

[Peter Nevai]

I understand about having to enlarge the mounting holes. But I am equally spooked by having a sloppy fit between the bolts and the engine, it allows for creep in the engine offset or more accurate a deviation from zero engine offset. A nice low clearance bolt to engine hole fit is optimal. I need to research the hole diameter of the engine to see perhaps I need to go to a metric size, finding metric blind nuts will be a challange though.

Oh BTW,

Wheels! I always used Dubro Low Bounce wheels but they tend to be on the heavy side. The foam stuff from back then disintegrated badly. Are the new ones any better? Any input on DB wheels (Dave Brown) or any other suggestions. THe Robart Wheels are real nice as they hide the wheel collar but again are heavy.

[Randy Cuberly]

Grade 8 Allen Head 4-40 screws (will be black oxide finish) are more than ample to hold any of the engines we use in stunt.  6-32's are bigger but not necessarily better unless you want to use stainless screws...then I would reccommend 6-32's because Stainless is about 15-20% lower tensile strength than the High carbon grade 8 screws.  The main problem with 6-32's is that the blind nuts are so large that they usually have to be trimmed to fit inside typical engine mounts.  Also the larger holes in the mounts weaken the wooden mounts unless you usi 1/2 square mounts...All this adds up to more weight!  UNNECESSARILY!

Randy Cuberly

[Steve Helmick]

THE most important thing is to get Dubro blind nuts. The Great Planes ones tend to pull apart. You don't need that. I'm in favor of 4-40's for a .46, but would use 6-32's for a .60 or .75. My PA .51 is mounted with 4-40's.  Steve

[Peter Nevai]

I was thinking of orderint them from stunt supply. They do not state the manufacturer. I know the deal with no name blind nuts as Ive had a few thet seperated at the flange and pulled through.

Any input on wheels?

[Bob Reeves]

4-40 socket head screws with Dubro blind nuts and Dave Brown wheels.. Works everytime...

[Peter Nevai]

The mount holes in teh VF accept 3.5 mm screws. that works out to .137 inches. Which is a #6 screw. So It's 6-32 cap allen heads with blind nuts. That will minimize the free play between the screw and the engine mount holes.

No input on the wheels? Foam or standard dubro low bounce. Durability?

[Allan Perret]

I use 6-32 on 60 engines and bigger.  Some 60 engines come with holes big enough for #6 screws.
  
I got a used engine that one of the previous owners had really butchered the holes in the mounting lugs.  They were a loose sloppy fit even ffor 6-32's.   Came up with a solution that worked out really well.  Built the motor crutch, but before it was glued into the fuse sides, took great care to get the motor perfectly aligned and clamped into the crutch at zero offset.  Using a 6" long drill bit I drilled two locater holes, one in each lug centered between the 2 mounting holes, thru the engine lugs and into the motor crutch.  Epoxied 1/16 wires into holes in crutch, let them stick out top of crutch just the thickness of engine lugs to work like dowel pins.  This keeps the motor properly aligned even after many times it is put in and out during building process.  You need to have the long bit to keep it perpendicular.  I like to use the longer bits whenever I can because they give you more of a reference for keeping holes straight and square.  

Blind nuts, stay with Dubro.

[Larry Fernandez]

Hi Guys a quick question

I have a OS 46 VF to mount. 4-40 bolts and blindnuts are just too light weight for this. I recall using 5/32 hardware in the past but can not find any sources for the blibd nut , allen screw sets. Brodak only supplies 4-40 stuff. RSM size is 6-32 I think that would be too large for the engine mount holes. Any Ideas? Want to place an order with other CL related items so I really dont want to go to a seperate supplier for this.

Hello Peter, I have never used anything larger than 4-40 hardware on my large piped ships, (.65 RO Jetts) I purchased a large quantity o Grade 8 4-40 screws a while back from McMaster Carr and have never had a problem with them. They are plenty strong and I would also add that I NEVER use a split lock washer more than once. If I remove the motor for any reason, I toss the slpit locks and replace with new ones.

Larry, Buttafucco Stunt Team
 

[Mike Greb]

I used to use 6-32 bolts in my slow rat planes, but the motor mounts kept breaking at the hole, and when that happened that was the end of the airframe.  I dropped down to 4-40 and that problem went away.  I have bought a couple of stunt planes that had 6-32 bolts in them, and for some reason the blind nut seem to crush the bottom of the motor mounts more than 4-40 blind nuts.  Over the years I have had a few 1/8 to 1/4 outside loops with my race planes and the 4-40 bolts have not broken.

[Claudio Chacon]

Hi,
4-40 bolts are perfectly OK for a .46 but if you are looking for something larger in between 4-40 and 6-32, try here with metric sizes (M3.5 or M4):
http://rtlfasteners.com/RC/index.html

Claudio.

[john e. holliday]

If you look close at my P-47 you will see i eliminated the blinds nuts(T-nut).  I stay with 4-40's as they break easier when I put a plane in.  By the way there are littlesbolts holding the plates in place.   So far I have not stripped the threads in the aluminum plates.  The plates on the top and bottom of the motor mounts.

[Allan Perret]

If you look close at my P-47 you will see i eliminated the blinds nuts(T-nut).  I stay with 4-40's as they break easier when I put a plane in.  By the way there are littlesbolts holding the plates in place.   So far I have not stripped the threads in the aluminum plates.  The plates on the top and bottom of the motor mounts.

Do you tap threads in both the top and bottom aluminum plates for the engine bolts ?   What thickness are the plates

[john e. holliday]

Tap holes only on the bottom plate.  Holes on top plate match the holes on the engine.   The plates are a little over an 1/8th inch thick.  Don't know the type of aluminum, but it is hard to cut and thread.   Have not had one strip out yet.  Knock on wood.

[Allan Perret]

Tap holes only on the bottom plate.  Holes on top plate match the holes on the engine.   The plates are a little over an 1/8th inch thick.  Don't know the type of aluminum, but it is hard to cut and thread.   Have not had one strip out yet.  Knock on wood.

Thats why I asked if you tapped both plates.  I would not think threads in a single 1/8 alum. plate would be strong enough. 

[Peter Nevai]

Lots of good input here.

I am sure that 4-40 hardware is plenty strong for the OS 46 VF. Srength is not my main concern. If I was mounting directly to the maple mounts I would not hesitate using 4-40. However I am mounting to aluminum plates. When you mount directly to wood the maple deforms to a degree creating a pocket in which the engine lugs fit. This pocket helps keep the motor from twisting along its vertical axis (Inverted and upright configs.)  Aluminum to aluminum contact is much harder little or no deformation occurs and if the engine lug hole size is much greater than the screw then under vibration the engine can creep along its vertical axis. Metal to metal interfaces are more prone to vibration than the wood to metal interface. Vibration is concentrated more in a smaller diameter screw with a loos fit than a larger diameter screw with a tighter fit in the hole.

Of course the larger bolt with a tighter tolerance will be far tought to shear incase of an impact but it tighter tolerance within the hole that makes it a far superior mounting mechanism. As it is far easier to use a larger screw than to reduce the size of the holes in the engine lug by a couple of thousands, I figured I'd go with  a larger screw.

Or am I completely off base with this line of thinking?

[Allan Perret]

Lots of good input here.

I am sure that 4-40 hardware is plenty strong for the OS 46 VF. Srength is not my main concern. If I was mounting directly to the maple mounts I would not hesitate using 4-40. However I am mounting to aluminum plates. When you mount directly to wood the maple deforms to a degree creating a pocket in which the engine lugs fit. This pocket helps keep the motor from twisting along its vertical axis (Inverted and upright configs.)  Aluminum to aluminum contact is much harder little or no deformation occurs and if the engine lug hole size is much greater than the screw then under vibration the engine can creep along its vertical axis. Metal to metal interfaces are more prone to vibration than the wood to metal interface. Vibration is concentrated more in a smaller diameter screw with a loos fit than a larger diameter screw with a tighter fit in the hole.

Of course the larger bolt with a tighter tolerance will be far tought to shear incase of an impact but it tighter tolerance within the hole that makes it a far superior mounting mechanism. As it is far easier to use a larger screw than to reduce the size of the holes in the engine lug by a couple of thousands, I figured I'd go with  a larger screw.

Or am I completely off base with this line of thinking?

You are not off base.  So you have a couple of options.  Use 4-40's and add the locater pins as I suggested above, or drill out motor for 6-32's.