Oil pressure relief valve

·         Rob Turk

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The latest installation manual JEM3302-6 lists significantly lower maximum oil pressure values when compared to previous manuals. It used to be 76psi all the way back to my original manual from 2000. In this new manual the maximum oil pressure has been reduced to only 2/3rd, just 51psi. I'd love to hear the background on this change.

As the upper pressure limit has gone down this much, what are the partnumbers of the matching pressure relief valve and/or spring? Are they available for ordering?

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·         Doug Smith

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Hi Rob,
The new limits are only applicable to hydraulic lifter engines... I'm double-checking my facts and should have the full story for you shortly.
The new spring is Part Number PX4A002D.
Regards,
Doug.

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·         Doug Smith

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Hi Rob,
We only recommend changing the spring to the new lighter version if the oil pressure on a hydraulic engine when measured by a mechanical gauge is above 350 kpa. We like to see the oil pressure operating between 250 – 350 kpa for hydraulic engine; this is the “sweet spot” and tends to give better valve actuation.

If your engine is running well, has good leak-downs and valve seals, it's not something you need to rush and fit.

Regards,
Doug.

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·         Ross Clarke

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Hi Doug
My J170 was purchased new in March last year and has just clocked 98 hours. I have the Hydraulic engine.
On recent short flights, usually less than 45 mins, ive noticed the oil pressure sitting around just under 400 psi. CHT is always at the bottom of the green and the engine is performing very well.
Would you expect to see the pressure reduce on longer flights, say over an hour as the oil gets hot.?
Most of my recent flights have been short duration so I havent been able to check the pressure on a longer flight.
The Annual is due in March next year so I could get the lighter spring installed then but in the meamtime, i will just monitor the pressure as suggested by other owners.
I live in Sydney so dont have any really cold temp variations.
Would appreciate any comments, thanks a lot.

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·         Rob Turk

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Thanks for following up, Doug. Mine is a solid lifter engine. In cruise it runs around 390kPa. The only reason for wanting to lower the pressure is that I have a small, annoying leak in the sump/oil pump area that I can't get rid of. Only happens after full throttle take-off. almost impossible to induce on the ground. Therefor I though a slightly lower max oil pressure may keep the oil in.

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·         Doug Smith

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Hi Ross,
Depending what oil you're using and what temperature the oil is running the pressure will vary (I'm assuming you mean 400kpa by the way!).

Particularly if you're using a single grade (W100) oil the pressure will tend to be a little higher while the oil is cool and drop when it warms: it's not unusual to see seasonal variation in oil pressure along with oil temperature. You can sometimes also see the same effect on a cross country flight: if you change altitude and the oil temperature drops the pressure will sometimes change visibly too.

If the engine is running well and your leak-down results are good I would leave it alone!
D.

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·         Doug Smith

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Hi Rob,
Can you see where the oil is coming from? What sort of propeller are you using? It's strange that the leak is power dependent - if that's the case it'd be worth checking carefully to see if it's coming from the crank seal.
Otherwise, as you say, a solid lifter engine is going to be pretty oblivious to oil pressure variations (within limits).
D.

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·         Rob Turk

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Hi Doug,

My prop is a 2-blade fixed pitch wooden GT propeller. Back in August I have made a cardboard mock-up cowl to be able to observe the front while ground running, and without the prop wash spreading the oil everywhere. After a good warm-up and a short full power run I was able to catch the first indication of the leak. Attached is a picture of the leak, take from below, looking upward at the oil pump and sump ridge. You can clearly see the oil droplet at the left side

I have re-cleaned and re-mounted the oil pump several times, thinking I messed up the seal somehow. Tried Loctite 515 and Hylomar, no luck.

The only thing I can think of is that the sump seal is leaking. That's why I asked earlier about the hidden sump screws. I don't mind taking the sump off, but removing the back plate and messing up timing is something I'd like to avoid.

Note that this leak started after the engine was taken apart to inspect why it had low oil pressure when hot and idle. Suspicion was bad sealing between the case halves. At that time, the through-bolt upgrade was also performed. The engine came back producing much better oil pressure, but this tiny leak has been bothering me.

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·         Ross Clarke

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Thanks Doug
I forgot to mention i use Shell W100plus Oil

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·         Doug Smith

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Hi Rob,
If you've had the oil pump off a few times and not cured it chances are the leak is elsewhere... but it might be worth one more try using Loctite 518: it's a variation of 515 that allows a bit more gap and irregularity between the parts. I'm assuming you left it overnight to cure before starting the engine again.
D.

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·         Ross Clarke

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Hi Doug
Just had a 50 hourly oil change, and the leakdown test came in at 70,70,70 and 72.
The Engine ,a 2200, has just clocked up 105 hours since new and im using Shell 100plus oil.
Can you advise what is considered an "excellent" and a "problem" test result?
Im hardly using any oil at all between oil changes and running avgas with 25 hourly oil changes.

Thanks and regards

Ross

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·         Doug Smith

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Hi Ross,
The manuals recommend corrective action when leak-down results are worse than 80/60, which is the simple answer. The great thing about leak-down results is the trend monitoring ability it gives you: comparing the results from one service to the next can tell you if you've got something which is gradually getting worse, so you can act before anything gets critical. Results in the 70's are pretty typical for a normal engine running on AVGAS.

I find that the results from my engine are usually better if it's done a good session of circuits recently (compared to if it's just come back from a long cross-country). My theory is that all the variations in the circuit - different power settings, different engine temperatures and pressures - tends to loosen up the rings in the piston and clean up the valve seats.

Regards,
Doug.

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·         Ross Clarke

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Doug, thanks for that info.
The Engineer has written 70/80, 70/80,70/80, 72/80 in the Logbook and the engine hadnt been flown for about a week before the test.
The next scheduled maint is the Annual next month and i will be having that done at Jabiru.
Brst regards
Ross

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·         Steve Bennett

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Hi Rob

I have what seems the same niggling leak. Bizarrely I'd also been chasing low pressure at idle when hot which is now sorted. Not sure what sorted it if I'm honest as it seemed to rectify itself in the process of taking things apart and refitting them. I've had the oil pump off and, like you, refitted again as I thought it was the cause of the leak. I did it a third time when I changed the crank seal. The crank seal seems to have stopped the small amount of oil that would sit around the front of that seal but there is still oil coming from somewhere up front.

I wouldn't say it was only at full power as it does seem to leave more residue around relative to length of flight rather than at a particular stage of flight. But it is a pain in the butt trying to locate it.

Doesn't help your cause I'm afraid but at least you're not alone 🙂