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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Yes,  just checked mine prior to heading to Mexico this weekend.  Have you talked with the UL power guys yet?  Fix? Recommendations?

Dr Fred 

150 hrs 


I was able to talk with Ray Lawrence this morning.  He said that the factory is aware of this problem.  They have not got a complete solution yet.  Possibly they are trying to come up with a different O-ring to help seal this area off.  He said that I can take the units off apparently there is a clip that holds him in a couple more nuts to take off, clean him put a little bit of high temp RTV and seal them back into place.   hopefully, I can get this done tonight so I can still make it in Mexico on Friday.

I removed the nuts and sealed the pickups last pm.  Wasn't hard.   No obvious leak with engine test.  Will see if this helps. 

I tried to help seal it with silicone as noted above.  After about 5 hrs, started leaking again.  New o rings ordered. Will replace and report. 

I did order the new "O" Rings from Wicks.  Followed the SB directions and let it set for 72 hours before starting and it is still leaking...don't know what else to do...

Here is the service bulletin (last one in the list, Oct 1, 2020). 

Service bulletins | ULPower Aero Engines

WIcks has new O-rings, part number is in the service bulletin. I noticed mine leaking right after I bought my 701. Pretty easy to replace.

I fully satisfied the SB and it is still leaking...

I haven't had a chance to run the engine yet, but it seemed like the O-ring wasn't snug enough. I wouldn't be surprised if the O-ring they provide isn't the correct size.

I thought the same thing...

After buying the "new" replacement O-ring from Wicks, they seemed to be the same size, same loose fit. I bought an O-ring kit and found O-rings that fit much better, the sensor pops in and pops out with about the right amount of resistance. They are green EDPM material, made in China, so may look for better quality ones.

The size that works better is 11/16" inner diameter X 1/16" thickness. Metric size is 17.17 mm inner diameter X 1.78 mm thickness. The old ones were about 17 mm inner diameter X 1.5 mm thickness, using a cheap Verner caliper, so don't take my measurements as absolutely correct.

The hole diameter is about 21 mm. The Hall sensor outer diameter is 20 mm.

The inner groove is 18 mm. 

Groove width 2.5 mm.

The old O-ring installed on the sensor was 21 mm outside diameter, same size as the hole itself. No wonder it leaked.

The new O-ring installed on the sensor is 21.5 mm outside diameter, which squeezes it down a bit for a better seal. I haven't had a chance to run it yet. 


Thanks for the information I will research as well...

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. 


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