4-Stroke: to vent or not to vent?

May 09, 2011 No Comments by

I am a long time reader of your column, first time writer. I have learned a lot from your column, and I appreciate the service you provide with your engine wisdom.

 I have been running four stroke model engines since my first OS FS 40 in about 1983. I have always “vented” the crankcase out of the cowling with fuel line from the back of the crankcase. I recently bought the non-pumped version of the OS FS 200. OS has the crankcase combustion by products routed back into the intake. It just doesn’t seem right, to run that “stuff” back through my engine. That would not only put combustion by products back into the engine, but would put more oil back into the charge as well.
In your opinion, can I just run those crankcase products out of the cowl like I have always done? I can’t imagine that it is gonna’ be detrimental to the engine. I have an OS FS 120, twin rocker model, bought new in 1981-2, it has been vented out like always. I run that engine “dry” at the end of each flying day, put about 12-15 drops of Marvel Mystery Oil in it, turn it over for about 30 sec’s, it is still running on the factory installed bearings, piston and ring, all I ever do is check and adjust the valve clearances. I think I know the answer to my question, but I spent a lot of money on the new “200″, so wanted a second opinion. I consider your advise very valuable, so will wait to hear from you.
Thanks Clarence for your column, and all your wisdom.
Mike

Dear Mike,
I’m with you regarding drawing the crankcase slop back through the engine. I conferred with my contact at O.S. when they first came out with this system and they felt that there shouldn’t be any problem. However, I don’t see any problem venting the case as you have been doing, Just be sure to plug the intake tube fitting. If you do run into any problems, be sure to let me know.

Good flying,
Clarence Lee

Clarence Lee, Editors Blogs, Glow

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