Quote:
Originally Posted by rotorwrench
Air compresses and oil doesn't. Air can cause a shaky needle movement. I usually purge the air out of the gauge line while the motor is running by cracking the fitting to the gauge inlet. The King Seeley electrical set ups was relatively accurate since there isn't much to purge there.
I use all sorts of gauges for testing different aircraft systems and I have to take them to a metrologist at least once a year for calibration. We end up replacing a lot of the cheep gauges that won't calibrate to specs. It's best to have a good quality instrument that is within the range of movement needed. I have 0 to 30 psi all the way up to 0 to 2000 psi and most of the good quality metal case & glass lens instruments last a long time if they were made by reputable companies. The cheep plastic ones last about two years or so before they are no longer serviceable.
The old 41A oil pressure relief springs do fatigue with time. I would replace the spring and see what happens. If it needs shims after that then shim it up but 15 psi is within the range of normal operation for the pre-8BA engines. The 8BA engines generally have a bit more but not a lot more. I would rather see anything above 5 psi on a hot engine for the older ones at idle. Those old floaters were some good con-rod bearings but I wouldn't like to see the gauge at 0 psi anytime.
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Not trying to be critical but got a chuckle and a vision of little yellow birds using "cheep" gauges.
