Loss of Prime

[edidin]

Although I have rarely lost prime in my C-85, it has happened twice after sitting for about six weeks in very hot weather each time. The first time was attributed to use of Victory oil, since other long sits with Phillips X/C did not result in loss of prime (a friend changed the oil, and since his other plane has a Lyc, he had lots of Victory around). Second time may have been due to using Camguard which I go on and off of like whiskey and cigarettes.

I found that if you have a pump oiler can with a tip as shown in the attachment, it is very easy to reagin prime. Simply remove the oil temperature bulb from the screen housing and insert the tip shown. Its OD is about the same as the bulb, so once inserted you can pump away and fill the screen and oil pump cavity easily. When you've pumped enough remove oiler, plug hole with thumb, and then quickly replace oil temp bulb. Oil pressure should come right up, and seems to work even in a three point attitude, though the amount of back flow on removal will be less if you first lift and support the tail.

The second time it happened I used a borescope in the screen cavity and saw that the oil pump gears were just very dry. My oil pressure is at the upper end of allowable, so it's not clear to me that losing prime is always a fault of a poorly performing pump, though suspect that the greater the pump gear to plate clearance is, the less oil has to dissipate before prime is lost.

Oil is Lubrimatic 50-337 available many places including Amazon

https://www.amazon.com/Handled-Oiler-10 ... B00478EFMA

Lubrimatic Pump Oiler Tip.jpg (110.71 KiB) Viewed 525 times