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  #11  
Old 12-31-2017, 08:37 PM
jrs14855 jrs14855 is offline
 
Join Date: Apr 2008
Location: Lake Havasu City AZ
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Default Bolt

I built my first Wittman Tailwind to an old set of plans that did not specify the gear bolt size. I don't remember how I made the decision but I used an AN6 bolt. 1000 hours when I sold the airplane it now has at least 1700 hours.
The AN 6 is the simplest fix. A welded fix would be better but will require removing the engine and mount.
There is an example of a simple drill jig in either Kitplanes or Sport Aviation. Build the drill jig and get an assortment of hardened bushings starting 1/64 undersize, then .371, 372 and maybe .373 depending on the exact diameter of the bolts. What you are trying for is a moderate drive fit. You absolutely do not want the bolt to push in place easily or next time you will be starting with new gear legs.
Jig the gear securely in place with proper toe and start with the 1/64 undersize drill. The titanium bits may work or you could even use carbide tip drills. Slow r/m and moderate pressure, lots of lubricant and stop occasionally to keep everything cool, heat is your enemy. The reamers should be high speed steel, I prefer straight flute. A 1/2" capacity drill motor is optimal, it allows slower rotation speed with more power. PM me for some more info.
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  #12  
Old 12-31-2017, 08:59 PM
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ronschreck ronschreck is offline
 
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Might it be possible to drill another hole in the tube and gear leg at a different location, assuming there is a place on the tube to allow sufficient clearance?
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  #13  
Old 12-31-2017, 09:29 PM
jrs14855 jrs14855 is offline
 
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Default Gear

That is not possible on the Wittman Gear. The upper portion of the gear leg where the bolt goes is only about 3/4" in length, the gear then steps down in diameter to 7/8* diameter on most RV's and I think 3/4" on some or all 3's. No place to drill an additional hole.
On an A model an artist/contortionist can weld up the holes without removing the gear support structure. I have never heard of anyone doing that successfully on a taildragger.
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  #14  
Old 12-31-2017, 10:34 PM
CAVU Mark CAVU Mark is offline
 
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Location: San Diego, CA
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Thanks for all the suggestions. To add some detail, this is a 24 year old 3. Wings were built buy a factory person in OR and the owner did the rest. The wings are great, the rest of the plane is a 6. The wing spar mode has not been done nor do I plan on doing it since acrobatics are not on my list. I lost my 170 so this is the only plane I have to fly and that is what I want to do.

The gear already has a AN6 and the other gear (right) has a bolt and what appears to be an AN4 threaded into the side. That gear seems solid but so did the left side.

It sounds to me that the most correct solution would be to remove the gear and the engine mount and put some new collars on the top of the mount so I can drill new holes. But then I will need to match drill to the gear while being jigged correctly for alignment.

I bought the plane for a good price... moral, a deal is not always a deal.
Ohhhhh the pain.
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  #15  
Old 01-01-2018, 02:21 PM
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Ed_Wischmeyer Ed_Wischmeyer is online now
 
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Quite some years ago, I decided to bite the bullet and realign the landing gear on my RV-4 due to excessive tire wear. (The toe out was extreme, don't remember where is was measured from, but I do recall that it was almost 5/16" instead of 0.00 - 0.050")

Anyhow, I pulled the engine mount and had plugs welded into the gear legs and the motor mount holes were reduced in diameter, IIRC. Then everything was jigged up, the holes were drilled out in 1/64" increments on the drill press, and that got things in perfect alignment.

But the other thing I did was to have the motor mount magnafluxed to check for cracks. Sometimes poor workmanship goes along with poor flying skills, and who knows what might be lurking in your airplane. And who knows what the other gear leg looks like, even if it's not (yet) loose.

Yes, this suggestion is over-cautious... unless it turns out that it's not.
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Last edited by Ed_Wischmeyer : 01-01-2018 at 02:59 PM.
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  #16  
Old 01-01-2018, 07:02 PM
DNeufeld DNeufeld is offline
 
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Location: Coeur d Alene
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If the bolt is a decent fit through the gear leg, how about spot facing the motor mount where it's peened, make a bushing out of 4130 and tack the bushing to the motor mount with the bolt in and tight. Remove the bolt and leg and finish the weld. The bolt would have more bearing surface than the original motor mount tube. The repair would be above the cluster. I don't see how this repair would compromise the mount??

Might leave the bolt in for the weld and replace when finished.

If the leg is oversize, a decent machinist should be able to ream out the leg and fabricate a press in bushing into the leg to get it back down to size. Could carefully be done on the average drill press if you are comfortable with it.
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Last edited by DNeufeld : 01-01-2018 at 07:51 PM.
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  #17  
Old 01-01-2018, 08:10 PM
jrs14855 jrs14855 is offline
 
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Location: Lake Havasu City AZ
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Default Bushing vs flat doubler

I considered that but prefer the flat 4130 doubler shaped to match the socket. My reasoning is that welding a bushing in place produces a lot of scale on the inside which means the bushing must be reamed a second time. This is not the case with the flat doubler. A heavy wall bushing would help but considering the tight area the bushing is harder to weld.
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  #18  
Old 01-01-2018, 08:22 PM
DNeufeld DNeufeld is offline
 
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Location: Coeur d Alene
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Default Bushing vs. flat doubler

I am not a certified welder so I didn't see that coming. I get it. The problem I see with a plate is there will be a unsupported area between the plate and the gear leg the thickness of the tube. Might not be a big deal??
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  #19  
Old 01-01-2018, 08:32 PM
jrs14855 jrs14855 is offline
 
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Default Bolt

Quote:
Originally Posted by DNeufeld View Post
I am not a certified welder so I didn't see that coming. I get it. The problem I see with a plate is there will be a unsupported area between the plate and the gear leg the thickness of the tube. Might not be a big deal??
Not a big deal. The shaped flat doubler is pretty much the standard repair. I think there are a lot more of these repairs than people realize, just not many talking about it. My proposed doubler would be oval on the outside and would be just large enough to extend outside of the peened area. Actually the optimum doubler would be a section of .120 wall tubing cut from a tube with od 1/4" larger than od of socket.
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  #20  
Old 01-01-2018, 08:38 PM
David Paule David Paule is offline
 
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Quote:
Originally Posted by CAVU Mark View Post
....It sounds to me that the most correct solution would be to remove the gear and the engine mount and put some new collars on the top of the mount so I can drill new holes....
I disagree. The next solution is what I think ought to be done:

Quote:
Originally Posted by rvbuilder2002 View Post
....My recommendation is that you contact Harmon Lange at Langair machining.

http://www.langair.com/

Langair has made the RV gear legs for decades and Harmon has helped many people resolve loose leg and alignment issues with some very creative fixes in the past.....
My first mentor had a saying,

"If you want it done like downtown,
Take it downtown."

In this case, that means Langair.

Good luck!
Dave
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