I have a factory overhaul one one side about 500 hours on it no problem changing oil, don't even need to fill oil filter first. I have a RAM on the other 75-100 hours. When I first got it it was losing prime had to pressurize the system if it sat for a week and oil changes were an automatic pressurize each oil change. But it was just a pain in the a$$ to go anywhere with the thought it was going to lose prime. We bitched to Ram and they said btw we had sent them a core that was bad and made us pay for that before they would do any warranty work, so that was a quick $9,000 payment we had to make first. Then they finally sent us a replacement pump that we installed. It seems to have fixed the problem but we were doing oil filter changes every 10 hours and inspecting to see if we were making metal until we got a comfort level that we had no damage. They did pay for the labor for the oil pump exchange. I just am glad that we saw we were not getting oil pressure befor we had run the engine too long.

Yes. Watched for indication and when it was not there after a few seconds the engine was shut down.

Don- The responses below thus far from Twin Cessna

1 A few of questions:
What grade of oil are you running in the engine?
How long between engine runs/flights?
What is the average temp of the aircraft when stored between flights?

It sounds like you have oil pump gears with too wide of clearance either between the housing and gears or the gears themselves. The answer to the questions above might help prove or disprove my theory.

The company I work with has a fleet of aircraft equipped with radial engines. We have to run the aircraft every two weeks or pre-oil the engines before starting if they sit longer than two weeks. This is due to the oil draining out of all the little passages over time. The wider the tolerances in the engine the faster the oil will drain from those passages.

2. I just did this to my new GTISO520 2 weeks ago ! I primed it before we spun the engine over for several cycles to purge the fuel pump and build some oil pressure before we started it up . I just took of the oil pump hose going to the oil filter from the engine and filled it with oil and kept it full while rotating the engine backwards a few turns and with the oil filter already full with oil when we installed it we had oil pressure as soon as we started purging the fuel pump . The GTISO 520 has a history of loosing it's oil prime but I think if you have an air pocket in the filter or a small leak some where in the system it looses prime more often , That's what I have been told by a few APs and a few old 421 corporate pilots. The most my 421 has sat without starting was 2 months when it was getting painted and both engines had oil pressure when I stated them to fly it back . Good luck ! Doug

I've endured many 421 woes, but have mostly avoided this one.

On my old factory remans, I lost prime once on one engine when in avionics for 3 months. I could drain the oil for an oil change and leave it set overnight, and still not lose prime.

On my factory new engines (3+ years and 400 hours), I have not ever lost prime, even when in avionics twice for one month periods.

As a side note, 421s seem unusually prone to engine failures due to spun bearings. I hypothesize that many of these failures are due to pilots not promptly recognizing theabsence of oil pressure on startup. With a GTSIO, watch this like a hawk. Also, when in avionics or paint for months, try to avoid letting the shop start your engines when you are not present.

I have been told "they do that"

This is a known issue at RAM. I have two friends who smoked young motors as a result.

Man. So even if you do everything right when acquiring and operating one, you still have no idea if a previous owner of mechanic ran an engine at some point in time without oil pressure.

...and there goes the happy feelings about 421s beginning to fade.

I would not let that deter you on getting one. I have had my 421 since 1999 and never had a prime problem until I put on a RAM motor and now that has been fixed with an oil pump replacement. Mine can sit for a long time and not lose prime.

Thanks for the replies and discussion. We heard back from Ram that the oil pump was out of round. They are making noises as if they may cover some of the cost for this low time issue. The repair will include replacement with a new rather than overhauled pump. As it develops I will keep you guys posted.

Still no real progress on identifying the underlying problem other than perhaps the out of round allows oil to drain easier setting the pump up to loose prime. I wish I had access to an engine oil system so I could see what happens to allow oil to drain in the first place. Perhaps having the filter mounted directly to the pump rather than remotely a foot and a half or so below supplies enough to keep the pump chamber full. Maybe it has something to do with the orientation of the check valve in the filter. Maybe the oil is draining out of the oil galleries as air seeps past bearings and finally gets into the gears of the pump. Apparently no engineering involvement is available to answer a pretty serious question that occurs almost predictably. Does seem to be a very dim link to Ram, but perhaps it is just use of lapsed tolerances on overhauled pumps from anybody assembling engines with other than new pumps.

Seems like 421s are a prime candidate for a preoiler system.

No need for a preoiler system. If you have Ram engines just install factory new oil pumps.
If your 421 is parked for an extended period of time watch for oil pressure on start up. I have factory new engines with 1300 hours on them. This plane has been parked for periods up to 90 days with no oil pressure problems on start up.

Just another data point: I've never had the "loss of prime" issue in my 421...

Robert

Who did the last OH?

Robert

Who built your engines and when?

My experience is the same as Roberts. I have read about this on TTCF forum but fortunately never experienced it in over 400 hours of use. We bought the plane in December, 2012 with matched 300 SMOH Ram Engines that were purchased/installed in December, 20008.