Claythomas Posted March 23, 2020 Report Posted March 23, 2020 I have a 1967 M20 E with 2170 hours on a smooth running engine with good compression on all cylinders. 988 hrs since top overhaul in 1982. In 1973 the engine received new main bearings @ 529 hours to comply with Lyc SB 3200. The engine oil pressure on the gauge after warm up shows 55 psi at 900 rpm ( lowest it will run with throttle back to the stop) 65 psi at 1200 rpm and 70 psi at 1700 rpm. I normal idle at 1200 rpm. I purchased the plane 2 1/2 yrs ago and have only flown 25 hours. What could be done to access the health of this engine? I know I could do a soap sample and have it bore scoped. Any thoughts would be appreciated. I realized I may be looking at an overhaul but not sure since in runs good. Thank you Quote
carusoam Posted March 23, 2020 Report Posted March 23, 2020 Welcome aboard Clay... I think I understand most of your details... If you can clear up one or two... you normally idle at 1200 rpm? If I release the brakes while idling that fast... I may be traveling across the field at 35mph.... in a short period of time... If I hold the brakes... I will have drawn every piece of sand from the pavement through the prop... Lowest rpm of 900rpm isn’t slow enough to land at my airport... Check with your mechanic for setting the proper idle speeds and rpms... There is a document that can help you determine what they are supposed to be... Often Mooneys use numbers closer to 700 and 1000... 700 provides good runability with out stopping... or roughness... 1000 provides good oil distribution via splash lubrication... and an excellent starting setting... If the engine is known to be in good condition an ordinary pilot can do some flight testing and collect his own data... a healthy power plant can achieve T/O distances that meet or exceed book values... Same with vertical speeds... If you have limited experience with this beyond TBO engine... it is hard to have a baseline to go forwards with... Many people flying beyond TBO have a long record of performance and maintenance history... oil analysis records show how well things are progressing... Anyone that owns a Lycoming IO360 for a couple of years knows what is bad for the engine... Not flying... The best way to assess the engine is to get a look at the individual failure points it has... Search on cams and cam followers and lifters... Rust likes to form on metal surfaces... and destroy the hardness layer... then grind away the parts they contact... no oil can protect a missing hard layer... from rough surfaces... Overall the method of assessing an unknown engine’s status... is called a tear down.... if all is well... nothing else is needed... But, with such high time are you expecting anything less than an OH? A few times...around here people buy a plane at a bargain price with a run-out engine... (sound familiar?) they plan to run it until it needs an OH... the first line of defense... is changing oil often... and doing due diligence on screens and filters... expecting metal parts to show up... a flake or two in the filter isn’t metal parts... a cam going away leaves enough on a kitchen utensile you won’t want to swallow it... the second line of defense... using a dental camera to check the health of the cylinders... healthy cylinders have a good cross-hatch pattern in them... all valves have a nice pizza look... Start your oil analysis as soon as practical... read up on how this gets done, how to get the most of your money being spent... What are your thoughts? PP thoughts only... not a mechanic... Best regards, -a- Quote
PT20J Posted March 23, 2020 Report Posted March 23, 2020 The thing that seems to kill Lycomings is corrosion — rust — of the lifters and camshaft and, to a lesser extent, nitrided cylinders. What keeps them going is frequent flights and oil changes and living in a low humidity part of the country. Oil analysis is good. Camguard may be helpful. Borescoping cylinders is easy. There’s no non-invasive way to check the cam. If it were mine, I’d change the oil every 25 hours or at least a couple of times a year and get oil analysis and just enjoy it until something shows up, Skip 1 Quote
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