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Prop Lug Installation Problems

Posted By:
David Scott
IAC MemberHomebuilder or Craftsman
#1 Posted: 3/25/2010 09:56:01

Hi Guys.  I'm planning to mount a lighter Catto 2-blade propeller (Kevlar w/wood hub) on my Pitts S1S to compensate for the extra 45 lbs running the 200hp Lyc. AEIO-360.  Craig Catto sent me to Saber Manufacturing to purchase the ½" prop bolts and the recommended longer lugs intended to help distribute the sheer loads on the wood hub.  The original lugs sent to me were 3/4" too long to fit into the 1-1/8" gap between the heavy flange and the case sweet spot.  The next batch of lugs were still too long to insert.  Saber is currently shortening the lugs further.  The lugs currently installed in the hub are very short and only extend an 1/8" into the back of the prop.  When the new lugs are installed, they will only extend about 5/16" into the hub, but as Saber says, that's better than what I currently have.

Here's the problem: Installing/pulling the lugs through the flange without any clearance behind the lug will have to be done by threading a 1/2" all-thread bolt into the lug and pulling it through using the socket routine on the face of the flange.  When there's enough clearance behind the lug for a nut, we'll switch to a smaller bolt (take the load off the lug threads) and pull the lug through the rest of the way.  That's probably the easier part...
Our big problem is how to remove the existing lugs when there is only 1-1/8" clearance behind the flange (actually, there's less than an inch clearance outside of the 3/4" dia. sweet spot on the front of the case). If I trim a socket to fit behind the flange with room for a nut and washer, we'll only be able to back out the lugs approx. half way, and then there's no way to remove the socket.  But that can probably be solved by cutting away some of the wall of the socket beforehand so that it can be slid past the lugs.  So, how do I remove the lugs the rest of the way?  One guy suggested heating the flange, then dripping liquid nitrogen into the lug (we have a source) and hopefully freeing up the lug enough to tap it out with a plastic mallet.
Any input that you can give me will be greatly appreciated!!!


Files Attachment(s):
Lug issue.jpg (94163 bytes)
Brian Vasseur
Homebuilder or Craftsman
#2 Posted: 4/30/2010 00:09:18

I also changed the studs on my O320 from 3/8 to 7/16 so I could use a different prop. My solution was to get a short fine thread bolt and thread it into the bushing from the front, same as if you were bolting on a prop.

The next step was to get a very large C clamp and one part behind the prop flange, about where you're holding the bushing in the picture. the threaded end of the C clamp goes over the head of the bolt. You're already saying that this doesn't line up and you're right. I used a short piece of tube over the head of the bolt and the threaded part of the C clamp to keep it from slipping off. 

Screw the C clamp down as though you were trying to press it out. Nothing will happen yet but now take a small hammer and tap on the handle part of the C clamp that you were just using to tighten it. The bushing will move 1-2 mm. Repeat the process about 10-15 times and the bushing should be all the way out.

If you know how to weld you could modify the C clamp to have a Y at the back which would fit around the bushing and allow you to line it up straight. This will help it stay aligned on the head of the bolt a little easier.

Light taps with a twist of the c clamp each time is all it takes.