My best friend Marvin bought a 421 last year. We are learning its peccadilloes as the months go on. We have just experienced the above. It seems obvious there is some mechanism that allows oil to leave the pump gears, and given time the pump will not pick up oil from the pan when starting. The general "fix' seems to be pumping new oil backwards into the pump to establish operation. We have done that successfully.

It seems we are using a bandaid rather than fixing the underlying problem, which does not satisfy our mechanical senses. Does anyone really know what causes the problem on this particular engine? These pumps are ubiquitous, but the problem seems to occur only on the GTSIO-520s on this plane. Is the problem one of engine assembly/overhaul specs? His engines are Ram engines with less than 200 SMOH? Does the same problem appear on factory overhauls?

This may or may not be remotely similar, but a friend had a similar issue after overhauling his O-200. I have no idea if the oil pumps are similar or not. He ended up having to get into the accessory case and change something. It was many years ago and I'm sorry I don't remember the details.

I'd go with your gut and dig into the problem to fix it permanently. Have you talked to RAM yet?

We have talked with Ram. They are used to band aids. They have offered to remove the pump and inspect it at our cost. We will probably do that, but even with them it seems we are in the land of the blind.

I a perfect world, the oil pump, whether gear type or lobe type should stop the flow of oil in either direction when stationary. I guessing the oil pickup to accessory case connection is leaking, o-ring or gasket, idono on a GITSO.

That is what I'm leaning toward as well. Did find a very little oil on outside bottom of casting. Makes me also suspect the oil pressure relief valve housing that must be removed to change the spring if needed.

Seems like it happens frequently and I'm hoping to uncover the smoking gun without shooting a lot of blanks.

Bad oil pump. I have seen and heard of this problem on other. Ram overhauls.

Thanks Gerald. So you're thinking it might be linked to lose overhaul spec? I have noted frequent occurrence of accessory problems on the Ram engines I am familiar with. In fact this plane had several fuel pumps in the first 100 hours that failed. Ram did change their vendor for the last fuel pump put on, which has lasted a year so far.

Yes I thinks it's the oil pump. I am not a fan of Ram overhauls.

We had a bad oil pump and RAM replaced it under warranty. No more loss of prime. They claimed it was a 'manufacturing deficiency'. You will still lose prime if the plane sits idle a long time or during annual. It is recommended to fill the filter and line to the pump with oil in order to get it to the pump gears.

So from your 3rd party perspective, has "learning its peccadilloes" been worth the benefits of the 421 for your friend? I lust for one but also have very little time for peccadilloes. Fortunately for me, Tony Saxton is just right around the corner from my home base.

Don - call Juan Oviedo at DFW Aeromechanix (+1 (972) 250-2403) in Addison or Tony Saxton in Ohio at TAS Aviation. They are probably a better resource than RAM.

Don- I'll post on the Twin Cessna forum and see what responses are given and report back. I'm interested in this too.


How long doe the aircraft have to sit to experience the lo issue?

I can't contribute any advice, solution, etc......but I did have the same problem in March of this year. Completed some structural repairs to a 421C which sat in the hangar about 5 weeks during repair ops. One engine started and oil pressure came about normal. The other, we shut down and "primed" the pump as the OP did. We did this after discussions with owner, operator, and their regular mechanic. They obviously had this issue before. It was also an engine with brand recognition

Alex - Thanks. I know Juan and we will call him tomorrow.

Tim - Actually have two data points. First time after 2 weeks it had the problem, but motoring the engine with plugs pulled restored prime. This time the plane set 2 months and nothing worked except pumping oil backwards through the pump from the filter line. Ergo, it becomes really bad somewhere between 2 weeks and 2 months. The worry is it will get more frequent and with shorter periods. Would hate to be left high and dry on a ramp after a long vacation. Thanks for posting on the Twin Cessna board. It will hopefully appear before more owner/operators there.

Don C. - So far he is happy, but this type stuff needs to end.

Further talks with Ram this afternoon revealed that they recently decided to no longer use overhauled oil pumps, but instead go with new on this engine.

Don- What was your indication of this problem? No oil pressure at start up?