O Rings

It’s Tech tip time again! I apologize for taking the summer off, however it was a great summer for flying and the need to fly like a bird surpassed my need to sit at a computer and type! From time to time in the next few months I will alternate between writing short simple Tech tips and more in depth tips complete with photos and maybe even a few graphs. I have decided to pass along this months tip after Bob Payzer mentioned I should print this one. I had just completed a great night of flying with friends and noticed that there was a lot of commotion in the hanger next to mine. It seems that Bob’s new Rans on floats is home and there were a swarm of people looking it over and working on the engine. It was determined that Bob needed a new intake manifold boot as his old one had somehow been damaged in the building process. His new manifolds had arrived and it turned out that the sealing “O” rings between the boot and intake manifold would no longer fit inside of it’s groove. It appeared to be much too large? How can that be Bob asked? Well here is the skinny and the tip of the month. Rotax engines use many “O” rings in their construction rather than old-fashioned gaskets. This ensures a precise no leak, and no need to retorque, seal wherever they are used. However these “O” rings are either a Neoprene or Flouride type of rubber, these materials have a tendency to “grow” or “swell” as soon as any hydrocarbon touches their surfaces. This means any fuels, oils, or solvents, and even antifreeze can cause them to swell up. They tend to absorb the liquid and will no longer fit its desired location. What ever you do, do not attempt to shorten the “O” ring by cutting it and re-gluing it. There is a very simple resolution to this situation. Simply lay the offending “O” ring on a low temp, stable heat source such as a heat shield from a trouble lamp and the “O” ring will dry out and shrink before your eyes! It will fit like a glove with no need to keep the UPS man busy one-day airing parts across the country. Hope this months tip helps someone some day, and next month I will give you a great story and some tips on how to rebuild your Mikuni vacuum operated fuel pump. Happy flying