A Stitch in Time ....

[old man emu]

Here's a tip that may save you, or someone else down the track, a lot of frustration and time.

 

We recently had to change the starter motor on a Lycoming engine. Nothing too difficult about that, we do it all the time. However, ......

 

The starter motor has two steel locator pins that go into holes in the crankcase. These pins stop the motor body rotating out of alignment. Usually, the pins just slide out of the holes when you want to remove the motor from the engine. But one of the pins in this motor decided to slide out of the motor body and remain in the crankcase. That meant we couldn't fit the replacement motor until we removed the pin. As usual, this happened on Friday afternoon and the plane was needed for a lot of flying over the weekend.

 

It took us nearly two hours to work the pin free. What had happened was that the pin is made of case hardened steel and the crankcase is cast iron. There was a bit of a dissimilar metals reaction that froze the pin in the hole. We had to grind some flats into the pin and twist away with a pair of vice-grips. We finally got the old pin out and fitted the new starter and all was well with the world.

 

Now. Here's the tip: If you are going to put dissimilar metals together, and they will be a tight fit, apply some anti-seize paste to the thing that is going into the hole.

 

You are not likely to be changing starter motors very often, but remember this when you are putting the spark plugs into your engine.

 

Old Man Emu

 

 

[Guest Maj Millard]

Good advice OME. It is amazing how often we come across this occurence working in the industry, as you do. Even applying a light film of grease to two different metal types in many cases, would save a lot of grief come removal time.

 

Add to this with salt-water amphibous operations as we do here in the Whitsundays, where aircraft are sitting in salt water for several hours a day, and all types of dissimiliar-metal corrosions are rapidly amplified !!....

 

We have over the years developed a special 'paste' which is made up of four different compounds. Everything is put together using this paste to act as a 'buffer' between all items. This goes a long way toward eliminating the 'battery' effect which is kicked off when moisture enters the equation. Where we can't use our special paste, standard grease is used, and we go through roughly a small box of grease a week !...spread over (literally) four busy aircraft.

 

As you mention, steel spark-plugs going into alloy cylinders is the perfect situation for this type of corrosion and yes, anti-sieze please !!............................................................................................Maj...