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Case splitting tool explained

Mconner7

Well Known Member
To split the case you need to push on the case half through bolts. I went to Home Depot and bought a piece of medium strength angle iron. At Ace Hardware, I also bought four 1/2x20 female couplers. Then I bought six 1/2x20 nuts and 2” bolts (I had to use grade 8 as that’s all they had), about 15 or 20 large washers that would fit over the 1/2’ bolts.
I had a small length of wooden 2x2.

The goal is to extend the hold down bolts through the angle iron and the wood. You drill holes in the angle iron and the 2x2 to match the cylinder hold down bolts (that are not through bolts) large enough (3/4”) to allow the coupler to pass. Thread the coupler onto the hold down bolts. Add washer and thread the bolt through the other side of the coupler.

Put a nut on the actual through case bolts to protect the threads When you start moving the nut down, the undrilled part of the angle iron presses on the through case bolts forcing the halves apart. If you run out of thread, unscrew and stack more washers.

Go slowly, do not force anything, if the case halves do not immediately start to part, you missed something. Keep the gap even as you go.

Here are some photos.
 

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Interesting tools. Just for info, the way that they split the case at the factory (and the factory school) is to pull the through-bolts with a slide hammer (a modified slide hammer that can be threaded on to the through bolt). You just wang on the bolt with the slide hammer until it comes out. When they are all out, the cases come apart pretty easily - if they don’t you have probably left a bolt installed somewhere on the periphery…or under the cam gear.

Paul
 
Just to help others, there are two styles of Lyc case through bolts. The older ones (mostly narrow deck) and the type Mconner is discussing have the through STUDS threaded into the left side of the case. These studs have two sets of threads on one side to accomplish this. With this type, you need a tool like he mentions to push the case apart by applying pressure to these captive bolts on the right side. There were also two different styles of through stud used through the years.

The more modern style on the wide deck uses through BOLTS with an interference fit in the center of the case and these bolts are NOT threaded into either side of the case. With this style, like paul mentions, you just drive the through bolt out and the case falls apart, though if it has dowel pins it may need just a bit of persuasion.

During installation differing procedures are also required for tightening. The later style requires much more care in torquing the through bolts down as it can move in the case. You don't want the interference fit resistance to be confused as torque that creates bolt stretch. There is an SI for this.

Don't trust me on the left vs right, as it has been a while and not sure I got it correct. BUT, be sure you know what you are working with BEFORE attacking it with a slide hammer.

Larry
 
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Thanks Larry,
Yes my case is a narrow deck that has the through studs threaded. The aft 6 studs are in the right hand case half. There are two more threaded into the left half that do not hold down a cylinder base. Pressing the aft six worked fine to split my case.

Mark
 
During installation differing procedures are also required for tightening. The later style requires much more care in torquing the through bolts down as it can move in the case. You don't want the interference fit resistance to be confused as torque that creates bolt stretch. There is an SI for this.
Larry
Thanks for explaining this, now it makes sense as why Lycoming requires the through bolts to be torqued simultaneously on both sides.
 
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