Front Seal Tool

How many of you have replaced the front crankshaft seal on a Lycoming engine? Yeah....I see a lot of hands up, which is what I figured. These seals can last the life of an engine, or be problematic children that seal and leak and get replaced a bunch of times in a short number of hours. My hypothesis is that it all has to do with how clean you get the bore. Or what adhesive you use. Or how you hold your tongue when you apply the sealant. Or... well, you get the point - probably a lot of things.

One of those is what tools you use. Removing the old seal means finding the right combination of picks and other implements of destruction. They have to be small enough to fit behind the prop shaft, but big enough not to bend when you stab them in to the seal. Oh - and don't scratch the crankcase bore!

Installing the new seal also needs the right tools, and I recently found what I think it perfect. Trying to push it carefully in to place without damaging it, I started looking for a tire iron - but they are all too large. Except... the "irons" I carry in my bicycle tools! Made of nylon, small, smooth, not damaging to rubber - the perfect thing to grab. And the best thing is - it worked! They usually cost a couple of bucks each, or a set of three for five dollars or so, and are often right on the counter of your local bike shop. Definitely something to add to your tool box.

We'll have a feature article in Kitplanes on the entire process of replacing a front seal sometime in the future.

Paul Dye

Paul Dye, Kitplanes® Editor in Chief, retired as a Lead Flight Director for NASA’s Human Space Flight program, with 40 years of aerospace experience on everything from Cubs to the space shuttle. An avid homebuilder, he began flying and working on airplanes as a teen, and has experience with a wide range of construction techniques and materials. He flies an RV-8 that he built, an RV-3 that he built with his pilot wife, as well as a Dream Tundra they completed. Currently, they are building a Xenos motorglider. A commercially licensed pilot, he has logged over 5000 hours in many different types of aircraft and is an A&P, EAA Tech Counselor, and Flight Advisor, as well as a member of the Homebuilder’s Council. He consults and collaborates in aerospace operations and flight-testing projects across the country.

2 Replies to “Front Seal Tool”

  1. While you are talking about replacing the prop seal on a Lycoming engine, I always use the advice given in the Continental Service Bulletin SB-M76-4 regarding prop seal replacement . In particular, the part about lightly sanding a helix into the crankshaft where the seal rides. I find that it works incredibly well to break the polished surface of the crank shaft to get the seal to seat and seal properly on Lycoming and Continentals whether they are Cad plated or not.

    I also always use a stretch over type seal. Put it in a cup of water and into the microwave until the water boils. As soon as the waer boils, pull the seal out and stretch it over the prop flange. It's kind of like watching your wife give birth as you just can't believe that thing will stretch that far, then retain it's original shape. But in my experience, this method works well and I have had a 100% success rate with fixing leaky front seals with this method provided the crankshaft doesn't have a groove worn into the sealing surface or some other similar damage.

    I agree. A set of tire spoons are a good way to seat the seal once you get things started going together.

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