This weekend was spent in changing out the seals in the main gear legs of the Stearman. This is the third time that we have faced this task, and would like to pass on to you some of the things we’ve learned.
The first question is how high do you have to raise the plane to get the strut out of the bottom of the leg. With the brake assembly off, the bottom of the gear leg has to be 22 inches off the floor. That’s not really so much, and the other wing is still two feet off the floor. Make sure that there is nothing under the other wing before you start to lift.
Jack up the wheel using the jack point on the inside of the knuckle. Remove the wheel, then remove the brake plate assembly.
When you get the six nuts off of the bolts that hold the brake plate to the lower knuckle, three of the bolts are held in by the brake springs, and are hard to get out. So leave them in place. You can slide the brake assembly off of the axle without disconnecting the brake line.
Now the biggy. How do you lift up the plane so that the leg is 22 inches off the floor. It could be done with wing jacks provided you tie a couple of hundred pounds of weight to the lift handles at the rear of the fuselage. Otherwise it will go over on it’s nose. You have to have a jack with the right min and max height,. Then there is the worry about lifting up one side and having the top of the jack, at an angle, put a half moon dent in the underside of the wing.
In the past we have removed the 1/2 inch bolt from the top scissor mount, and pulled the scissor back. Then forming a loop in a nylon sling, replace the bolt to capture the sling. Then with an engine lift, you can lift up that side of the plane with the sling.
The problem with this method is that when the sling lifts straight up to take the load of the plane, it runs into the gear fairing, and damage may be done. So to use this method you have to remove the gear fairing and the lower support for the fairing. Not a happy thing.
This time we looked at the problem in greater depth and came up with a much better solution.
Using 1/4 inch steel plate, we made a lifting strap about 1 3/8 inches wide and 3 1/2 inches long. There is a 1/2 inch hole in one end and a 7/16 inch hole in the other. About an inch up from the end with the 1/2 inch hole, bend it over about 22 degrees
Again, removing the bolt from the top scissor, and using a longer substitute bolt (4 1/2 inches) put the bolt through the 1/2 inch hole in the lifting strap, then about four 1/2 inch washers, (They hold the strap away from the fairing) then back through the scissor and the nut back on.
Remove the bottom scissor 1/2 inch bolt and swing the scissor out of the way.
Now with a clevis connecting a chain to the lifting strap, and the other end of the chain fastened to an engine lift, that side of the plane can be lifted up the required amount without removing the fairing.
Remember that when removing the bolt from either end of the scissor, the strut is free to turn, and one must guard against it spinning off the jack. A small jack stand placed under the end of the axle taking some of the load from the jack should prevent this.
Remove the large brass nut and start coaxing the strut down and out of the leg. There are two quarts of red hydraulic oil in the leg. A very large pan or bucket will catch only part of it. The strut and spring are heavy, so two people have a better chance of maintaining control when it finally exits the leg.
Put some blocks under the end of the leg that will support the leg if the hydraulic ram on the engine lift starts easing the load down while you are busy with the seals.
Now when the strut and the new seals are ready to go back in, reverse the procedure, reconnect the scissors, and put the brake plate back on. (don’t forget the large spring that goes over the metering rod and the large washer that goes on top of the spring. Only tighten the brass gland nut enough to keep the seals from leaking. No tighter, or the seals will bind.
Also be sure the spacer that goes over the axle is in place and seated through the hole in the brake plate, before you tighten up the six bolts in the plate.
When the full load of the plane is back on the wheel and tire, put two quarts of 5606 oil in each side. Just up to the level of the fill plug.
There is opportunity for injury or damage to the plane in this type of operation. So it must be done by someone totally familiar with such lifting operations.