Io-360-l2a Manual

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Jackie Bullinger

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Aug 3, 2024, 4:36:56 PM8/3/24

to parkcorrivest

Pilot_DAR wrote:
Yes, very true, even Lycoming will tell you that the airframe POH prevails over their own engine operating manual for operating their engine in an airplane. But, I doubt that Lycoming will recommend an oversquare power setting for their normally aspirated engines. I asked them recently, and the answer was they do not state any procedure for this.

I suppose an engine with really large cylinders would be challenged to drive a fixed pitch prop that requires high MP with relatively low static rpm for takeoff and climb. Even worse if it were a high speed plane with a very coarse prop, something like the old Schneider Trophy racers would be the worst.

I was reading the Lycoming IO 360 maintenance manual and doesnt give any hint on how much to adjust the pressure relief valve, meaning, I dont know if I should do 1 turn, half turn, 2 turns, whatever.

I know this is an iterative process, but would like to get as close as possible in my first attempt. Does anyone know how much the oil pressure increase/decrease with each full turn of the pressure relief valve adjustment screw?

The oil pressure relief valve can get some small piece of junk caught in it that keeps the ball from seating. According to instructor for the Lycoming factory class, 90% of pressure problems can be corrected by replacing the spring and staking the ball in the valve. Lycoming also has a service instruction 1172

Even if the GI275 and the OEM gauge agree, I'd triple check the gauge accuracy with external instruments for both oil pressure and temperature before adjusting anything.

And +1 to also check the suction screen. There are a number of things to check before adjusting the relief valve, not that that's a big deal, either, but you may just be masking a symptom of something else.

The temperature was between 175F and 180F. The GI 275 gauge is new (the previous one was INOP), and the OEM is a completely independent system. How likely is it for two systems without any common parts from different manufacturers to fail in the same way? I think the odds of that happening are extremely low. Or am I missing a relatively common failure mode that could affect both gauges?

My understanding of the GI-275 is that it has multiple pins for interfacing various transducers. So it depends entirely on how yours was installed and it appears possible that it was wired in parallel with your existing transducer, i.e., the same transducer may be driving both instruments. I wouldn't assume anything just because you have a new instrument installed. The first step is still to verify that the instrument(s) are reading correctly. I'd check to see whether the GI-275 has a separate oil pressure transducer from the stock instrument.

Edit: Just to add a little bit, the GI-275 installation manual has a procedure for adjusting the marks on the instrument, but not a calibration procedure that I can find. It may be possible that it was just adjusted to match the existing gauge, in which case it would match the existing gauge.

When I had high OT and low OP issues during cruise (IO360A1A), we tried many things over several years. If I remember correctly, we overhauled the oil cooler, reseated the vernatherm valve, adjusted the pressure regulator, tried multi-weight and single weight oils to see which worked best, even installed a fixed center cowl flap (I was flying in AZ desert temps a lot). Can't remember if we checked the suction screen but I'm guessing we did. Got used to climbing and cruising in the upper edge of yellow. Finally overhauled the engine for other reasons and magically, all the temps and pressures have been perfect ever since. So.... what would have been the remaining potential causes? Oil pump or ???

The transducers are not in parallel, I have two different transducers, one connected to the OEM oil pressure gauge and the other to the GI 275. When the GI 275 was INOP, the OEM was working. I personally (with the supervision of an AP) changed the oil pressure transducer for the GI 275, so I know that the only thing in common between the OEM and the GI 275 is the hose with the tee at the end where both transducers connect.

The display may need to be properly configured (or at least matched) to the transducer, though. There's a list of different transducers that can be used with the GI-275, with different voltage ranges and different inputs for the GEA24 or 110. There may still be opportunities for misconfiguration. While I agree that with separate transducers the likelihood of error decreases, imho there's still reason to verify they're both correct before adjusting the relief valve on the engine.

This is in the last 18 months. The outlier that is showing a high value is when the transducer broke. Also, the third dot from the right was after 5 months of the aircraft being grounded, and the last one was after 10 months since the last "long" flight.

There is no such thing as a Lycoming service manual. Traditionally, Lycoming produced an overhaul manual, an operator's manual, and all additional information was contained in service literature (letters, instructions, bulletins). Many, many years ago, the FAA mandated a requirement to create maintenance manuals that included airworthiness limitations. Because of the shear number of products involved, Lycoming got the FAA to delay the requirement. A few years ago, the FAA finally made Lycoming begin creating maintenance manuals, but they are only available for some later models. The only IO-360 maintenance manual that I'm aware of is for an IO-360-N1A. It's probably very similar to what a maintenance manual for an IO-360-A3B6(D) would be if there was one, but there may be differences. I believe that the overhaul manuals must be purchased, perhaps with a subscription.