Can't get oil pressure

Larry DeCamp · #1 10-02-2015, 09:40 AM

Priming the system for first start.

Pushed one quart through the oil pressure sensor line to fill galleries.
Confirmed cooler and sensor are plumbed correctly per Dan H diagrams .
Oil comes out pressure sensor port by hand and starter cranking ( plugs out).
Installed mechanical gauge known to work.
No pressure cranking by hand or starter

Concerned about a lot of cranking without pressure. Engine was inverted for cam oil before install, but what to try now ?? All suggestions appreciated.

Kahuna · #2 10-02-2015, 10:12 AM

Larry,
Little confused. You said you have oil coming out the pressure port during cranking but no pressure on the mechanical gauge? I assume you mean the mechanical gauge hooked up to that pressure port that you see oil coming out of during cranking?

krw5927 · #3 10-02-2015, 11:18 AM

You probably did this but it's worth asking: are there at least a few qts of oil in the sump?

Larry DeCamp · #4 10-02-2015, 11:22 AM

Yes kahuna, the Fligtlines flex hose going to the sensor will drip oil when the engine is cranked by hand or with starter. When the mechanical gauge that is known to work is connected to the line, pressure does not register cranking by hand or with starter. Conclusion is the oil must have low resistance path somewhere.

Past threads have commented to fill the cooler, but when cold, the vernatherm should shunt oil direct to the galleries ? Thanks for your response.

Russ McCutcheon · #5 10-02-2015, 11:34 AM

When I built my engine in 2006 we cranked it by hand and starter about a million revolutions (slight exaggeration) and never got an oil pressure reading. I gave up and started the engine and had oil pressure immediately after start up.

Larry DeCamp · #6 10-02-2015, 11:46 AM

It appears your experience is where I am at. There were 5 qts in the sump plus the 1qt. I pushed through the oil pressure sensor line. If I don't get other ideas to try, I will just start it with the mechanical gauge and hope. I wanted to avoid troubleshooting more than necessary at the airport because it is starting to cool off in Indiana.

ABRV4 · #7 10-02-2015, 12:02 PM

Larry,
There is a plug in the oil pick-up line of the case right where the sump joins up in the back. You leave the plug in for a bolt-on, sump centered pick-up and take the plug out for a sump with a built in sump pick-up. Accidentally leaving the plug in when switching to a sump with the built in pick-up doesn't work too well. Don't ask me how I know. You might want to double check that.
Alan
RV-4

jrs14855 · #8 10-02-2015, 12:10 PM

I never prime the oil line or fill the cooler. Just pull one set of spark plugs, hook up the oil pressure line and crank with starter. No more than a minute or so at a time to avoid overheating the starter. Pressure usually comes up within 30 seconds or so.
What is the history of the engine. If it is built by someone who is not building engines all the time it would be very easy to leave out one of the pipe plugs inside of the accessory case. There is also a pipe plug in the oil pump housing which IIRC is only on some of the newer PMA pump housings.
Would you email me regarding Parakeets jrs14855@hotmail.com

Jesse · #9 10-02-2015, 12:45 PM

I have had this happen before. The engine just wouldn't prime. Allen Barrett told me that when that happens, he pulls the accessory case and the oil pump and packs the pump full of Vaseline. That created more suction that air and it primed right away with that trick.

jrs14855 · #10 10-02-2015, 03:15 PM

One recent recommendation, can't remember the source, is to lube the pump gears and cavity with lubriplate. I did that and had near instant oil pressure with the starter, no filling the oil line or cooler. The recommendation may very well have come from Alan, I attended an engine assembly forum that he did years ago.