PA12 Short mount won't fit my 2+2 fuselage, fuselage holes off a bit

[Marty57]

I hit a snag working on my fire wall forward on my 2+2. I bought a PA12 short mount to save some time rather than fabricating one my self. When I welded up the fuselage I jigged the mount bushings up well (I thought) but as with any 4130 welding, things crept out of alignment. Hindsight being 20/20, I should have had the engine mount to use as the jig. Anyway, the mount won't fit.

Now, to solve the problem. The short mount is a lot stiffer than the lighter long mount and has a lot less flex than I anticipated. The holes are off about 1/8" on one side, of the fuselage maybe 1/16" on another, and the angle of one of the bushings in the fuselage isn't perfectly straight. What to do? I have an unused case that I can use to jig up if I need to weld up a completely new mount but ...... any thoughts on getting the short mount to work? I also have a stock long mount that has a bend upper tube so plenty to work with. What are the pros and cons to heating the mount and bending to fit? My brain screams no to that option but maybe I'm way to picky as to the ways and means of adjustment on all things Cub related. I've heard the line "built with a yard stick; adjusted with a sledge hammer" So I'm way out of my comfort zone on this one. Suggestions?
Thanks,
Marty

 

[mike mcs repair]

Make new fuselage mount lugs


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[mike mcs repair]

Swing mount like an -18? Right?


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[Marty57]

Swing mount like an -18? Right?


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No, I don't have a swing out mount, stock bolt on mount.
Marty

 

[aktango58]

Make it a swing mount and adjust lugs as needed?

 

[Gordon Misch]

Marty, I think I'd be inclined to make the fuselage right. There's no telling about possible future need for a different mount.

Would it maybe be possible, rather than rebuilding the front end, to cut and re-weld tubes and sleeve them IAW 43.13 to get the proper lengths?

Is it also possible that the tube lengths are correct and the front end is racked? If so, might it be possible to heat joints and adjust the geometry?

 

[Marty57]

Marty, I think I'd be inclined to make the fuselage right. There's no telling about possible future need for a different mount.

Would it maybe be possible, rather than rebuilding the front end, to cut and re-weld tubes and sleeve them IAW 43.13 to get the proper lengths?

Is it also possible that the tube lengths are correct and the front end is racked? If so, might it be possible to heat joints and adjust the geometry?

I think heating the mount and adjusting might be best idea. Rewelding the fuselage pretty much out of question with everything assembled , painted, etc. Without a jig, no guarantee it won’t happen again when rewelding. With scratch built fuselage, I think a custom mount to position the engine correctly is necessary. I had a similar recommendation from a Cub rebuilder/IA to use some ratchet straps to try and cold bend the mount to fit, heat and slow cool if necessary . I’m leaning toward that followed by hanging case and checking for alignment and proper down angle (4 degrees). Lots of hind site learning here, heavy short mount should have been used to jiggup fuselage when building and welding. Curious to see what others think of food bending as first attempt at fix.

I could cut the mounting tubes off the short mount, bolt them to the fuselage, and then attach mount to case and posation properly and reweld the mounting tubes with everything properly positioned. Thoughts on that? As I have said all along, scratch building everything is not for the faint of heart!
Thanks and keep the ideas coming.
Marty

 

[mike mcs repair]

I would be more inclined to just cut off a leg or two & reweld, than to try heat & bend....

you might also have issues getting the bolts through also...

you will probably end up having to put the bolts through from the front......one at a time...

 

[jimboflying]

You might check to see if the problem is the fuselage or mount. Could be either or both. Converting the mount to a swing out version as Mike suggested would be nice for working on the engine and also solve the current issues.

 

[Marty57]

You might check to see if the problem is the fuselage or mount. Could be either or both. Converting the mount to a swing out version as Mike suggested would be nice for working on the engine and also solve the current issues.

Something has to give here; adjusting the existing mount isn't going to solve the problem. The lower holes are off; they are narrow by 1/4". I was able to get three holes to line up using ratchet straps but I'm not happy with the stress on the mount that way. I would need to cut out the lower tubes on the right side and reposition the mount bushing and the two tubes. Then, I'm not sure how the alignment actually will be. Right now, I'm leaning toward making an entirely new mount; something I really did not want to do. How hard would it be to modify the standard bolt on mount to a swing out? Needless to say, this is a very discouraging set back; not sure how best to solve the issue safely and in a timely manner.
Marty

 

[mike mcs repair]

http://www.fadodge.com/engine-mount/
Should be easy to convert, considering your dilemma.


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[cubdriver2]

Javron might be able to help?

Glenn

 

[Marty57]

http://www.fadodge.com/engine-mount/
Should be easy to convert, considering your dilemma.


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Mike,
I'm leaning that direction; looking at converting my short mount to a swing out mount. I'm working on a few fittings to see what I can fabricate vs what I need to buy.
Thanks,
Marty

 

[mike mcs repair]

Mike,
I'm leaning that direction; looking at converting my short mount to a swing out mount. I'm working on a few fittings to see what I can fabricate vs what I need to buy.
Thanks,
Marty

can you just convert one side of it???

 

[Marty57]

can you just convert one side of it???

I suppose that would be a solution but If I'm going to modify the mount to swing out, I'll go all the way. I'm working on making the swing out mounting attachment brackets to bolt onto the fuselage. I know I can buy the mounts but if I can make them easy enough, I will. If I order the brackets, I won't see them till next week and I'd like to get something on the fuselage so I can look at modifying the mount. I also don't want to buy the brackets incase I decide to fabricate a new bolt on mount rather than doing the swing out mount.
Marty

 

[Marty57]

Yesterday, I decided to make lugs to support a swing out mount. The idea was to modify the short mount I have to swing out, eliminating the issues I have with the lower bolt holes being off. As with everything related to this mess, I discovered a snag.

On a swing out mount, the stock attachment lug holds the head of the AN6 bolt and the nut is torqued from the back; that's what I have been able to figure out from the drawings and making a few lugs. In my case, at the lower engine mount bolts, the nut at the back is not accessible with a socket. The reason is the diagonal brace runs from the lower corner up toward the instrument panel; opposite a stock PA14 14. That restricts access to the nut at the lower attach point. I can hold the nut with an open end wrench and torque the bolt head on the front of the firewall only. Since a socket will not fit inside the stock lug, the stock setup is not an option for me. I realized this issue today.

Here's my options as I see them. If I want the swing out mount, I can make bigger lugs to accommodate a socket inside the lug and than make bigger brackets to fit the oversize lugs. I can cut the bolt mounts off the short mount I have and weld the larger brackets to the mount with the proper reinforcing straps as per Piper drawings. The other option is to try to cut and modify the short mount I have to fit with standard bolts from front of mount. The third option is to build a completely new mount with stock bolts to the fuselage, no swing out.


I don't mind making the bigger lugs, can anyone see any issues that with the corresponding bigger brackets necessary on the mount? I know no parts will be interchangeable with stock mount parts down the road, but I am way past that option. The lug will need to be about 1/8 to 3/16" or so larger inside to fit the socket for torquing.


I attached some pictures. The first one shows the diagonal brace that causes the issues (stock PA14 runs diagonal from upper corner down toward lower door area). Second shows the nut and bolt and how tight the area is. The third shows the lugs that I have made; one stock size with a bolt in it and the other lug with a socket in it as needed for my application.

Has anyone else run into this type of a situation? I realize this would be just exp. Cubs but wondering anyway.

For any scratch builders out there; decide on engine mount early on in the build; purchase the mount first or build a very strong jig for the mounting holes. I relied on the 2+2 drawings and wood jigs and have learned the hard way that that set up wasn't strong enough to hold everything in place during the welding process ....... live and learn.

Thanks, lets see what ideas and experiences you have out there.

Marty

 

[Gordon Misch]

Marty, from the middle pic it looks like you might be able to turn down a socket, i.e. thin the socket wall, to fit on that lower-left nut. Maybe an option???

 

[mike mcs repair]

You put vise gripes on nut and spin the lugs. The head of the bolt shoul lock in lugs


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[Marty57]

You put vise gripes on nut and spin the lugs. The head of the bolt shoul lock in lugs


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I've noticed a large, fiber washer under the lug on sone Super Cubs; is that the purpose of of the washer? Gordon pointed out an option of cutting down a socket, that or universal socket may fit with some floor trimming. I'm going to revisit this option.
Thanks guys,
Marty

 

[mike mcs repair]

I've noticed a large, fiber washer under the lug on sone Super Cubs; is that the purpose of of the washer? Gordon pointed out an option of cutting down a socket, that or universal socket may fit with some floor trimming. I'm going to revisit this option.
Thanks guys,
Marty

There should be 3 fiber washers. None on upper door side, because your tab to mount limiting arms is there. You WILL want limit device or you will have engine swing to far and dent boot cowl. Also be careful if you are on narrow shop gear to not swing engine and tip your plane over


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[Marty57]

There should be 3 fiber washers. None on upper door side, because your tab to mount limiting arms is there. You WILL want limit device or you will have engine swing to far and dent boot cowl. Also be careful if you are on narrow shop gear to not swing engine and tip your plane over


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I wasn't aware of the limit stop; thanks for pointing that out. Any pictures of the limit stop? I do have full gear on the plane but thanks for the warning; that would be a ugly mess if that happened.
Marty

 

[Gordon Misch]

I can get you a pic of that tomorrow. As a practical matter, everything can be done without swinging the engine, but it's tight. I didn't put service loops in my wiring, so I do everything with the engine in its operating position. Mags are a pain, but doable.

 

[Marty57]

I can get you a pic of that tomorrow. As a practical matter, everything can be done without swinging the engine, but it's tight. I didn't put service loops in my wiring, so I do everything with the engine in its operating position. Mags are a pain, but doable.

Tomorrow I'll check the bolt access behind the mount, or see about doing it Mike's way. Either with the swing out or bolt in mount, I need to re-do the fit. I'm not happy having the bolts fit so snug that they gall up the threads tapping the bolts through the mount into the fuselage. I have two mounts to work with, the short mount and a long mount that needs repair anyway so I can do some experiments. I need to see If I can remove the bolt bushings and weld on the brackets for the swing out mount. If not, than there may not be any advantage to the swing out if I need to make an entire new mount.

Marty

 

[RVBottomly]

Marty, no advice here, but thanks for the heads-up. I'm finish welding a 2+2 fuselage and am taking notes....

Providentially, a day before you started this thread I was looking at Christian Sturm's photos dealing with his engine mount and this scenario was on my mind.

Vic

 

[tarnold]

Ran into the same problem scratch building a wag-aero super sport trainer. The engine mount came off a pa-18 0290d2. I cut and spliced the two lower legs to match the bushings on the frame. Have over 500 hours on it and no problem.

 

[Marty57]

Marty, no advice here, but thanks for the heads-up. I'm finish welding a 2+2 fuselage and am taking notes....

Providentially, a day before you started this thread I was looking at Christian Sturm's photos dealing with his engine mount and this scenario was on my mind.

Vic

It would have been nice to have a mount prior to welding the bushings in the fuselage. My suggestion is get the mount you are planning on using or decide now that you will fabricate from a mount from scratch. Surprises aren't fun but it's difficult to completely plan ahead. I now have two mounts, need to decide if I modify or build from scratch; leaning toward modify I think.
Marty

 

[Gordon Misch]

Personal opinion - I would prefer very rigid fixturing, with angle iron or similar, of the fuselage mount locations to Piper dimensions. My reason is that an engine mount isn't very rigid; if used as a fixture it can deflect some due to welding-induced stresses. Also, close fit-up of joints and keeping fillets from getting too large can help reduce weld distortion.

 

[RVBottomly]

Personal opinion - I would prefer very rigid fixturing, with angle iron or similar, of the fuselage mount locations to Piper dimensions. My reason is that an engine mount isn't very rigid; if used as a fixture it can deflect some due to welding-induced stresses. Also, close fit-up of joints and keeping fillets from getting too large can help reduce weld distortion.

I've got 15 feet of 2X2 angle iron up in my loft, looking for something to do. This looks like a good use of it.

 

[Marty57]

Personal opinion - I would prefer very rigid fixturing, with angle iron or similar, of the fuselage mount locations to Piper dimensions. My reason is that an engine mount isn't very rigid; if used as a fixture it can deflect some due to welding-induced stresses. Also, close fit-up of joints and keeping fillets from getting too large can help reduce weld distortion.

I agree; the heaver the fixture the better. Having the finished engine mount to build the fixture and than to check the fuselage would be the best set up. Looks like I'll be welding up a new engine mount. Removing the bushings to modify to swing out mount will leave a large gap between the two tubes that would be difficult to modify. Time wise, building new makes more sense. Looks like I have a spare short mount.
Marty

 

[Marty57]

I spent a lot of time this past week building up a steel jig for the engine case side of the engine mount and used the firewall lugs for the rear of the jig and fabricated a mount ........... but I'm not happy with it at all. I'm gas welding, no TIG and the high heat needed around the front case side lugs against the heavy steel frame made it very difficult to weld. My fillets had to get very big and not sure of the penetration of the weld so it's kind of back to square one.

The measurements of the firewall show that the lower lugs are off by 1/8" each side, and the left lug is set back 1/8" from being perpendicular to the firewall so either a new mount must be TIG welded with my fuselage as a jig or I need to re think modifying my bolt on short mount.

Here's an idea to run by the group. A stock swing out mount has a .065 "U" bracket welded to the end of the mount tubes and a .065 finger strap is welded to the tubes on the top and bottom of the bracket. This makes up the attach point to the lug bolted to the fuselage, making the hinge. My thought would be to remove the round plate (and underlying fillet) at the end of the tubes where they bolt to the firewall and simply weld the "U" bracket in place of the round plate; positioned correctly to compensate for the issues on my firewall. Than fabricate the finger straps as shown on the swing out drawings to weld over the top and bottom of the "U". I would leave the bolt bushing attached, welding over one end with the "U" bracket and closing up the other end. When finished, I would have the same set up as a standard swing out mount with the bushing still attached. I feel pretty confident that I can do that welding with gas without distortion. Everything would be jigged in place to the fuselage and I would use an engine case bolted to the front of the mount for proper location.

I attached a few pictures to show how this might work. what are your thoughts on this type of modification?

Thanks,
Marty