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Engine basics => Engine set up tips => Topic started by: frank mccune on May 27, 2019, 09:04:31 AM

Title: Burned on oil deposits on engine and head after 3 flights. Is this normal?
Post by: frank mccune on May 27, 2019, 09:04:31 AM

      Hi All:

      After three flight with my "new" tongue muffler equipped OS FS .40 I would like to know if this is normal.  Is this a sign of too much muffler heat and/or restriction?  I have not had burned on oil deposit on engines that were used sans mufflers.


                                                                                                                                                                              Tia,

                                                                                                                                                                              Frank

                                                                                                                                                                   

Title: Re: Burned on oil deposits on engine and head after 3 flights. Is this normal?
Post by: FLOYD CARTER on May 27, 2019, 11:27:34 AM

Burned oil?  Something is leaking.

Title: Re: Burned on oil deposits on engine and head after 3 flights. Is this normal?
Post by: Dave Hull on May 28, 2019, 05:23:10 PM

More info:

https://stunthanger.com/smf/engine-set-up-tips/muffler-gasket-sealant/msg554538/#msg554538

Title: Re: Burned on oil deposits on engine and head after 3 flights. Is this normal?
Post by: Steve Helmick on May 28, 2019, 06:32:27 PM

It's a 4 cycle OS with a tongue muffler? I'd like to see a picture of that.

A picture might not be a bad idea anyway, as it would show the setup, cowling if any, and hoses. Most guys that ran 4 strokes hooked the pressure tap on the muffler to the crankcase drain...not saying that's a good thing to do, but many did. Personally, I think it makes more sense to hook the muffler tap to the tank and a drain tube to the blow-by drain fitting. If it's cowled, maybe it needs more cooling air.

I'll admit that I've never run a 4 stroke glow engine, but it just doesn't seem right to have the bottom end lubed by the fuel. Doing that is just crazy...it does work for awhile, but sometimes the plastic backplate melts and messes up an official flight at the NATS.  ;) Steve

Title: Re: Burned on oil deposits on engine and head after 3 flights. Is this normal?
Post by: FLOYD CARTER on May 29, 2019, 12:30:00 PM

The crankcase drain fitting is there for a reason.  Since crankcase pressure isn't used to move fuel up to the cylinder, fany uel pooled down there has no place to go.  Not much drains out, but over time the crankcase could a load of fuel.  Since there is equal up and down motion of the piston, crankcase pressure cycles from + to - to
+, etc. in a sinusoidal fashion.  Average crankcase pressure is zero, so no good for a pressure fitting.

I'm running a Saito 61 upright with a hose to drain crankcase drippings out the bottom of the plane.  People who seem to know about these engines recommend a plastic "clunk" tank with no pressure.  Works for me.