Q: I have a mid-time O-235-N2C. I recently pulled the engine from service due to low power reports from our renters. Initial troubleshooting revealed two cylinders with low compressions. One was 55 and the other was 62. Decided to do a top overhaul.
Put it all together, including an overhauled carb, and I still cannot get more than 2200 static on the ground.
All compressions are 77 or better on the overhauled cylinders.
I also performed the Lycoming valve lifter clearance procedure recommended after cylinder replacement.
The engine is installed in a 2004 AMD Alarus and the TCDS indicates 2550 min and 2750 max static. I also noticed the oil temperature was higher than usual.I would appreciate any ideas or troubleshooting steps you can recommend!
John Sidorek
A: John, let me begin by telling you I really don’t think you have any issues here. If the TCDS for the AMD Alarus indicates a minimum of 2250 static RPM on the ground, my bet is you’re right in the ballpark with what you’re seeing on your tachometer.
This startling fact may not come as a surprise to you, but one of the most common situations is for an aircraft tachometer to provide an erroneous reading and, typically, they read low.
My suggestion is that you check the calibration of your tachometer or locate a local maintenance facility that has a Vue-Thru or other instrument to calibrate your tachometer.
I do have one question for you though and that is what RPM does the engine turn in straight and level flight? How does this compare to what you read prior to doing the top overhaul? Oh, and did you ever happen to check the static RPM prior to doing the top overhaul? Just had to ask this!
I haven’t provided very much information for you here, but I feel it may give you something to compare and find out exactly whether your engine is, in fact, producing less power than you think.
Yes, for a three blade prop the number is 1,200 rpm.
Which I guess is a good excuse to buy a three blade prop for my 150, right?
Best Regards,
Or my Pober Pixie!!
Thanks. Jim
Define low power and what are the cylinder head temps? Is the carb adjusted correctly? Is the timing correct? What is the density altitude? What is the real RPM? Is the muffler coming apart internally? Is the carb heat functioning properly? Did you borescope it? Not enough info.
Suggest reading “Mike Busch On Engines” to help address the cause of the initial lower compressions (which really weren’t that bad) and the current high oil temperature. His book and knowing the CHT’s with an engine monitor will assist with preventive maintenance.
Renters and airplane engines make certain body parts of mine shrivel. Bad combination.
The type cert is here:
https://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/08a3d1c788abb00b862579300051f0ac/$FILE/TA5CH%20Rev%209.pdf
The min static RPM is 2550. Sounds like he has a serious problem to me.
Check for plugged/restricted exhaust.
Free tachometer calibration test:
Wait for dark, park airplane under ramp lights. Hold brakes, start engine, and manipulate the throttle so the “strobe shadow” of the prop stops. (It is easy to see). Tach should read 1,800 rpm.
Best Regards,
Mike, will this also work for a 3 blade prop? Thanks, Jim
I would think for a 3-bladed prop it would be 1200 rpm for the shadowing, but I’m not 100% sure.
I’m slightly confused by this post; the question said TCDS gave a static range of 2550 to 2750, while the reply talked about 2250.