Has anyone else experienced small amounts of oil leaking around the Hall/RPM sensors on the back of the engine block?

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Update: after running the engine for about 3 hours, no leaks.

If you get new O-rings, measure the outside diameter of them installed on the sensor, and compare it with the inside diameter of the hole. The new O-rings should be a little larger than the hole so it squeezes down to create the seal. The O-rings I bought from Wicks were the same size as the sensor hole, which is why they leaked to begin with.

The ones that don't leak for me are 11/16" inner diameter X 1/16" thickness. Metric size is 17.17 mm inner diameter X 1.78 mm thickness. 

Thanks, I installed new (larger) O rings a couple of months a that fixed the problem...

Did you use RTV on the larger O rings or just bare?

Yes, I little bit.  I also discovered that I had a 2nd smashed "O" Ring on it that was not letting it seal properly.  Once I cleaned them up and installed the new "O" rings I haven't had any leaks at all...

I tried the black RTV, once using a little (no luck) and again with more effectively adding a gasket to the beveled area of the bore and the sensor. The silicon seemed a bit grainy even from a fresh tube so the next time I used the copper with same results. I’ve used new 1.78mm O rings each time.

May try it again with the grey silicone (a little smoother?). If that doesn’t work I’ll try the 2mm O rings before I resort to siliconing the whole recessed sensor area of the backer plate. That’s what UL is suggesting I try,

Me too.  Got the new o rings from Wicks and put some red rtv around them and the area is now dry. 

O-ring update. After about 30 hours the larger size O-rings that I used (mentioned in an earlier message) started seeping again. Not badly, but zero leaks is nice. This time I used slightly larger 17mm X 2mm O-rings from the same kit. The sensors were a little harder to push in, but so far so good. If they leak again I will use RTV on them.

Finding indications of small oil leak in my engine compartment. Where/how did you notice the leak from the Hall sensors? I mounted a tool box behind my engine and it gathers a light sheen of oil after about an hour of flight. My breather hoses have oil on them, but I cannot see how they could leak. I am not seeing any oil around the sensors.

Replaced my front crank seal. Found a “nick” on the crank. Shipping engines, even in original create is a rough endeavor. Smoothed it out and so far, about 5 hours, it has not started leaking again. This leak may have hidden rear engine leak.



208 680-2561

Hey Eric, are your O rings still good? Did you end up having to use some RTV?

How did you get the 2mm ones in? 

Still no joy after using 2mm o rings with silicone. Really don’t understand it. The bores are a wee bit larger than spec (21.69mm) but the 2mm O ring should compensate. 
anybody have some advice other than replacing the backing plate?


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