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How to Make an Oil Seal Installation Tool


By Bill Craft, EAA Chapter 287, EAA 597436, for Experimenter

When a special tool is in need, all isn't necessarily lost. You're building an airplane, right? So how hard could it be to build a tool? It's not very hard at all is what I discovered when tasked with replacing his my seal on the front of his Lycoming engine. A little trip to the plumbing section of the hardware store, a little crafting in the shop, and voilą, a tool is born.

While conducting the annual condition inspection on my aircraft, I discovered that the front crankshaft oil seal was leaking, so it needed to be replaced.

There are two different types of replacement crankcase front oil seals used in Lycoming direct-drive engines. One is a two-piece split seal, and the other is a single-piece solid rubber annular seal that's designed to stretch. The reason for this should be obvious; the inside diameter of the seal is considerably smaller than the outer diameter of the propeller flange. The solid seal is made from a highly elastic material that allows the seal to be stretched over the crankshaft propeller flange during assembly.

Lycoming crankshaft propeller flange tool ST-383 shown during the installation of the stretch version of the oil seal

I wanted to use the solid seal but didn't have the Lycoming tool ST-383 (seen above). The FBO at the field had one when it was in business. But it's gone now, and the nearest tool was at an airport 45 miles away. I remembered an article in an old EAA Sport Aviation issue on how to make one, but it required welding and bending tubing.

So, during a visit to the hardware store, looking at plumbing parts, I came up with a simple, low-cost replacement for the Lycoming tool that doesn't require welding or bending tubing. It's constructed out of PVC pipe and fittings available at most hardware stores.

PVC parts

Parts list:

  • ½-inch PVC elbow
  • 6-inch length of ½-inch PVC schedule 40 pipe
  • 90-degree ½-inch PVC schedule 40 sweep (large radius elbow).

The sweep needs trimming down to about 6 inches in length, and it also requires cutting a slot into the inside radius, as wide as the thickness of the prop flange. The prop flange rides inside this slot to keep everything aligned.

Elbow slot

Assemble parts as shown, and make sure to use PVC cement on joints prior to use.

Final assembly

To see the specific instructions on how to use the tool, check out this Lycoming PDF.


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