Engine Mounting holes missaligned

[DanielGelinas]

Hello,

I have misaligned my mounting holes on my profile super clown   
Was wondering if I should fill the holes with 30 minute epoxy or JB weld and redo my drilling 
Any other options?

Thanks,

-Danny

[Randy Powell]

Replace the mounts are the only other option I can think of.

[Dick Pacini]

You might consider Brodak's mounting system.

http://www.brodak.com/shop_productdetail.php?ProductID=6629

[W.D. Roland]

At one time I was expert at this missed hole thing.

When this happens or new holes made for engine change I make the hole to be abandon the same size as closest hardwood dowel. Roughen up dowel and epoxy with 30min working time epoxy(no quick stuff here!)
After cure trim flush and redrill. If new hole is in edge of old a pilot hole with small bit in a pin vice helps keep new
hole on track.

On .35 size and smaller profiles have been using sheet metal screws in place of bolts to mount the engine.


David


PS
Dick just checked out the unit you posted.
Looks like it clamps the engine down by the lugs. That works good! Have used that method on .60 size R/C
in the past with no problem. benefit is able to adjust location and angle of engine and in a crash there hopefully is some movement to do less engine damage.

[jim ivey]

geeeze dave thats really clever.  It sounds like s great and easy solution.     jim

[DanielGelinas]

Dick,

Seems like a good system. I'm a little worried about weight though

David,

Thanks for the trick. I think using a smaller drill is the thing to do...thing  I should have done.

THanks,

-Danny

[Dick Pacini]

That mounting system is aluminum for the most part. I don't think it would add that much weight.  The nice thing about it is it will accommodate different engines, regardless of bolt pattern.  It also allows you to tweak in a bit of up or down thrust if needed.  I have also heard that a crash will not rip the engine mounting holes out of the crankcase, like a bolted down installation might.

[DanielGelinas]

Hmmm,

Sounds like that engine mounting system might be the ticket to some futur projects

I think I fond a solution to my problem. As david mentioned. a dowel with epoxy would work fine.
I went to the kitchen and found the perfect dowel: 1/8th inch shish Kabob barbique Brochetts!!
Just gluew them in (perfect fit) and wait 24 hours before redrilling!

-Danny

[Balsa Butcher]

I've used the plug with dowel and re-drill method on more than one profile. It works well. 

[jim gilmore]

As an ex aircraft mechanic I vote to drill the holes to 3/16 and plug them with wood dowels if you have the room.
If you do not have the room use what ever dowles you can get to fit the hles as they are now....
Use metal plates under the lugs on both sides of the fuse and make sure to tighten it all up.
No need to do anything beyond that. If it is just some holes are mis aligned then just plug those ones and still use plates to secure the plugs in the holes.

[jim ivey]

danny. I'm going by memory here. I think the o.d. of a 4x40 screw thread is .089 (thousandths)". use a 3/32nds drill for a clearance drill thats .0935" maybe # 42  would be less clearance #43 is tap drill size .078? like i said going by memory. so good luck. jim

[Randy Ryan]

You might consider Brodak's mounting system.

http://www.brodak.com/shop_productdetail.php?ProductID=6629

Ooch ouch!! Sorry, I would advise against these strongly. I'd go for the dowel idea and if that didn't work I'd be doing surgery.

[Dick Pacini]

Ooch ouch!! Sorry, I would advise against these strongly. I'd go for the dowel idea and if that didn't work I'd be doing surgery.

What is your objection?

[Brett Buck]

What is your objection?

  Because they loosen up. I have seen that pretty frequently with the clamp mounts, and there aren't that many around here.

    Brett

[Serge_Krauss]

My only objection to the dowels and re-drilling is compromised strength. If the holes are not very far out of line, you can bore them out in the direction you want them moved, until the engine aligns as you want it. Then lubricate your 4-40 screws with vaseline and partially fill (coat) the holes with 30-minute epoxy, pushed through with a toothpick, and bolt the engine back on in alignment. wipe off the excess epoxy and let it set. When the epoxy has cured, unscrew the 4-40's. You can now either drill out the new epoxy threads, or if you have already installed blind nuts, leave them in or remove as preferred.

You can also plug the holes with medium density wood of some sort (it isn't that difficult to just cut and sand to apprximate diameter), glue or epoxy in, and re-drill. You need a drill press, clamps, and very slow pace downward through the mount, or the drill will wander. I have done the first method with good results and the added bonus of fuel resistant holes.

SK

[jim gilmore]

How can you think filling the holes and redrilling is compromised strength ?
Aircraft engineers do it all the time !

[Randy Ryan]

  Because they loosen up. I have seen that pretty frequently with the clamp mounts, and there aren't that many around here.

    Brett

Precisely, and they scar up engine cases too.

[Randy Ryan]

How can you think filling the holes and redrilling is compromised strength ?
Aircraft engineers do it all the time !

I think you should consider cross sectional area of the bearer. If its 1/2 X 3/8 and you drill out to 3/16, you've effectively reduced the cross section 50%, meaning you now have the equivalent of a 1/2 X 3/16 bearer. Probably would be acceptable at the front hole, but at the rear it screams "BREAK ME HERE!!!!". I'm all for the epoxied dowel, but only at minimum drill size.

Just re-read the post, this isn't as critical with a profile.

[Ted Fancher]

O.K.  Just thinking out loud here but...isn't the best idea of all?

Drill out the existing holes for as big an oversize dowel as possible and still stay within the existing mount (i.e. don't let the drill slip into the open space between the mounts where the crankcase will reside).  Glue in that over size dowel so it extends a fraction on both sides and then sand flush with the doublers so you've got a nice flat mounting surface.

Now, the Piece de resistance!

Drill the new holes (accurately this time!) completely within the dowels so that the holes are surrounded by the dowels with the dowel grain going in the same direction as the holes.  The result will be substantially stronger than the normal "sandwich" of plywood and maple and almost impossible to compress by over tightening the mounting screws (because you would be trying to compress "end grain") as so often happens on profiles allowing the engines to come loose.

If there's something wrong with this plan forget where you heard it.

Ted

Edited p.s.  Oh, I first thought of this because of the potential for screwing up a redrill that ends up half in the old mount and half in the (usually softer) end grain of the dowel.  The drill will try very hard to slip sideways into the end grain.  If the whole hole is in the end grain that can't happen.  For that same reason, by the way, try hard to find a truly "hardwood" dowel.

[W.D. Roland]

Using a large dowel on front hole might be ok., Not on the rear holes. Disrupting the length of the grain in the maple at rear hole probably is not a good idea.

The skewers will split and are softer than the dowel.

So far I have had good luck with dowel close to bolt size and pilot hole made by hand then followed with larger
and then final size bit.

At one time I was an expert at missed hole and when lazy still do fairly well at it! or should that be HB~>or

When not lazy on the profiles I locate the holes by:

Rubber band engine in place,. Couple of good rubber bands from glow plug around fuselage and back to glow plug.
Set it down and level wing incidence then same for thrust line.
When all lined up a drop of super glue at the lug to mount on top one and when cured pick airplane up, turn it over
and drop of super glue on bottom lug.

Now our bolts are usually smaller dia than the hole in the lug so I find a bit that fits hole in lug snugly.
With this bit turned with fingers until  basically a center punch has been made. Do all 4 holes.
Then pop the engine loose and get after it with the drill press or hand drill.

I use this way most of the time on all my airplanes. Comes in handy when using r/c radial type mounts.
 Glue mount to fire wall , drill holes, install bolts and nuts.
Line up engine (with rubber band trick) side thrust then super glue and a bit in hand to make 'center punch' marks.

Remove it all, drill , block sand glue off if needed. a knife will pop it off the engine lugs.

36 inch long drill bits from harbor freight come in handy for marking when the sizes match up( brass tubing over bit sometimes works)
These are the lowest quality bits I have ever seen ,But their long! 4 holes in maple will do them in but still good for marking.

If you use the sheet metal screws use some silicone to prevent fuel seepage, I do this even with bolts. airplanes last longer.

Just this long haired country boy's weird ways. That reminds me, time for another haircut!

David

Ted, I can teach you how to miss the holes more often!!! ( only if you keep helping me learn to make these things I build fly right!)

[Andrew Borgogna]

At this years VSC Jim Lee was selling drill jigs for many of the most popular engines that makes this problem go away.  Having said that, I use the drill and dowel plug method it works for me. 
Andy

[Steve Helmick]

I've never used the dowel plugged hole method. I've always drilled one hole, bolted the engine on, drilled one diagonal, bolt there, then do the others. Seems to work. Stubby drills will do a much nicer job of getting the holes on location, as will pilot drilling, and stepping up in size. Also, if you put a small pilot hole in there and try the engine, maybe you'll see that it's wonky and you can fix it before it's both big and wonky. 

Here's a neat tool to help eliminate the problem, from Tower Hobby. Actually, Great Planes, I think. Storing this thing so you don't lose it, or parts of it, is the job for a long capped tube, shown in the background. I've used it, and it works slick, unless the exhaust stack hangs over the bolt holes (OS .40/.46LA's do...one of mine does no longer). 

The ubiquitous 4-40 machine screw is .112" major diameter. For a normal (cutting) tap, the drill size is #43 or .089". For a clearance hole in wood, which you'll want to seal with epoxy or at least CA, .120" (#31) is about right.
  Steve

[Randy Ryan]

I've never used the dowel plugged hole method. I've always drilled one hole, bolted the engine on, drilled one diagonal, bolt there, then do the others. Seems to work. Stubby drills will do a much nicer job of getting the holes on location, as will pilot drilling, and stepping up in size. Also, if you put a small pilot hole in there and try the engine, maybe you'll see that it's wonky and you can fix it before it's both big and wonky. 

Here's a neat tool to help eliminate the problem, from Tower Hobby. Actually, Great Planes, I think. Storing this thing so you don't lose it, or parts of it, is the job for a long capped tube, shown in the background. I've used it, and it works slick, unless the exhaust stack hangs over the bolt holes (OS .40/.46LA's do...one of mine does no longer). 

The ubiquitous 4-40 machine screw is .112" major diameter. For a normal (cutting) tap, the drill size is #43 or .089". For a clearance hole in wood, which you'll want to seal with epoxy or at least CA, .120" (#31) is about right.
  Steve

I have one of these and they do work pretty slick, but holding the engine in place can be a pain sometimes. And you're so right Steve, keeping it all together is a challenge, the plugs won't stay in the tube anymore so I have a special place for the tool on my bench shelf.

[L0U CRANE]

Ted, to your Post #18...

Usually available dowels are not as hard as even cross-grain maple, so there can be a 'crush-strength' difference. It should not be critical in the ply-maple-ply sandwich... And the dowels ARE loaded along the grain, not across it. Even so.

This is a problem that no one would have even considered 30+ years ago... If the spinner does not line up? - ream the mount holes and torque the engine in so it does... Not enough/too much offset? ream the engine and mount holes and torque it in as needed.

Are we getting too persnickety? (Not if it works, we're not...)

[W.D. Roland]

I have one of these and they do work pretty slick, but holding the engine in place can be a pain sometimes. And you're so right Steve, keeping it all together is a challenge, the plugs won't stay in the tube anymore so I have a special place for the tool on my bench shelf.

[but holding the engine in place can be a pain sometimes]

Ah! all that's needed is a new supply of rubber bands and super glue!

Something that works good if the engine doesn't move around while drilling^^^^......
Music wire( Ok spring steel) of the right dia , Anvil, Hammer, Grinder.
Hammer wire flat on anvil. equally flat on 2 opposing sides.
trim the width of flattened area back to wire od and grind a point on the end.
Drills wood decently.
Need new one each time as old one is probably landing gear now.

David

EDIT
Lou
George Cleavland, My Dad, Several others-- 40+ years ago would threaten bodily harm if I did that reaming!
Now, If no one was looking unless it was a Fast Rat or Combat.

[Ted Fancher]

C'mon Lou.  I told you to forget where you heard it if it was screwy!

Ted

I will add, however, than many a Boeing passenger floor was built from vertical grain balsa with thin sheets of aluminum on the top and bottom because it was light and resistant to compression.

Now, if that's wrong, Mrs. Rush will correct me!  She peddles such things as options at the Boeing store.

Ted

[Serge_Krauss]

How can you think filling the holes and redrilling is compromised strength ?
Aircraft engineers do it all the time !

Jim-

I don't know whether you were referencing my post, but I saw no other that mentioned compromized strength. All I can say - if you were - is that my post advocates "filling the holes and redrilling", with the advantage that the fill is smaller than a dowel. As someone else implied later, the dowel or anything else that breaks a significent part of the bearer grain is inviting a fracture there, since the grain is not continued through the dowel. That was why I did advocate "filling the holes and redrilling", but with a convenient way to achieve accuracy, without wandering drills.

SK

[builditright]

Might I suggest

http://www.brodak.com/shop_productdetail.php?ProductID=7784

Description:
These brass threaded insets are the perfect way to put threads into wood and mount engines to wood mounting rails. A simple & effective way to make Wing Hold Downs. Can be used where blind nuts are hard to fit. Pkg of 4.

http://www.brodak.com/shop_search.php?productsearch=INSERTS

[Brett Buck]

Might I suggest

http://www.brodak.com/shop_productdetail.php?ProductID=7784

Description:
These brass threaded insets are the perfect way to put threads into wood and mount engines to wood mounting rails. A simple & effective way to make Wing Hold Downs. Can be used where blind nuts are hard to fit. Pkg of 4.

http://www.brodak.com/shop_search.php?productsearch=INSERTS

      I know people swear by them but I think this is a much worse solution than the dowels. You have to drill a *huge* hole in the motor mounts just like with dowels, but you get essentially no recovery of the strength of the wood you remove.

     Brett

[EddyR]

I just keep drilling the hole bigger and bigger till it lines up with the motor bolt hole.  ~^NOT
Ed

[DanielGelinas]

Thanks for all the great ideas!
I finally used the bamboo dowels I had on hand with epoxy. Worked great
The problem stemmed from the fact that the mounts were spread apart more than the mounting holes (arf super clown) of the LA 25 I want to mount on it.
I will use a faster drill speed (drill press) and smaller drill bit to start off the holes straight this time.
-Danny

[john e. holliday]

Next time make the mounts fit the engine.   I know the Goldberg kits have it set up to insert spacers or not to get the hard wood the same as the width of the engine.