chooch Posted August 18, 2020 Report Share Posted August 18, 2020 Help! As mentioned in another thread, I've been facing prop overspeed beyond 2700 rpm red line - on the ground all seems fine but when airborn and oil gets warm the prop overspeeds (noticed 2 times during initial climb). I had governor overhauled but it did not solve the problem. So I did the test described in Lycoming SI 1462A and...it failed (I did it with engine at ambient temperature but I dont think it impacted the results anyhow). So, I got the prop dismantled and inspected plugs at the crankshaft end - seems like they both sit tight. Next, I machined tight plastic cap with gasket, bolted it to the prop flange and made Lycoming pressure test again - still no pressure buildup and distinc oil gurgling heard inside the engine case. Then, I disconnected hose delivering oil from the governor to front of the engine case, pluged the fitting in the engine case and supplied air pressure through the plastic cap bolted in place of the governor - also no pressure buildup and oil gurgling inside the engine :-( Any ideas what else I could check to find cause of the issue other than worn front bearing requiring splitting the engine?! Any suggestions more than wellcome! thanks in advance, Marek Quote Link to comment Share on other sites More sharing options...
EricJ Posted August 18, 2020 Report Share Posted August 18, 2020 It's not looking good, but your reference gauge should be at 40psi and it's only showing about 32. You can also spray a little soapy water or soapless bubble fluid around your flange seal (which is pretty cool and a nice way to isolate this sort of thing) and put a cap on the oil fitting near the front of the case (and spray that for bubble check as well). If you get no bubbles and the leak is in or around the crank, then get somebody to check the crank plug, because those leak sometimes and my understanding (no personal experience) is that that can be serviced in place. I've heard of cases where the plug gets moved back too far and leaks. I just did a bunch of this myself. Good luck with it. Quote Link to comment Share on other sites More sharing options...
N201MKTurbo Posted August 18, 2020 Report Share Posted August 18, 2020 All I can think is you have a damaged front main bearing. Quote Link to comment Share on other sites More sharing options...
chooch Posted August 18, 2020 Author Report Share Posted August 18, 2020 7 minutes ago, Jeph357 said: Cf. M ? Quote Link to comment Share on other sites More sharing options...
N201MKTurbo Posted August 18, 2020 Report Share Posted August 18, 2020 The front main bearing has three parts. The front and rear parts are to support the crankshaft like all the others. The middle part transfers oil from the prop governor oil line to the port in the crankshaft. The air must be leaking past the bearings to the ports and blowing air back through the oil system and gurgling in the sump. If the plug was leaking, it would just blow the air into the crankcase without gurgling. Quote Link to comment Share on other sites More sharing options...
carusoam Posted August 18, 2020 Report Share Posted August 18, 2020 There is lots of tight space between all of the bearing surfaces... If using air to test the seals... expect that air is going to by-pass some of the seals and leak back in all directions... Air has tiny molecules compared to oil... If you have verified the shaft seal to work... this is a plus! Next verify that the OH’d govenor is delivering oil to the prop... The gov has a gear pump to move oil from the sump to the prop.... and a control valve that allows the oil to flow... Are you sure oil pressure is being delivered by the gov? Are you sure the oil pressure is activating the prop properly? PP thoughts only, not a mechanic... Best regards, -a- Quote Link to comment Share on other sites More sharing options...
Jeph357 Posted August 18, 2020 Report Share Posted August 18, 2020 Reading thread had to put phone in pocket and thats what my thigh had to say apparently.. Apologies...haha Quote Link to comment Share on other sites More sharing options...
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