Bravo Oil Pressure

[tls pilot]

Owner of a Bravo since 1993, just did a complete engine OH.

All brand new genuine Lycoming parts/kits, accessories OH

Lycoming in the last two years have gone to parabolic tappets and camshaft

Issue: as I climb oil pressure goes down, as I descend oil pressure climbs back to same values.

Have dual oil pressure gauges, ships and direct reading. Both indicate same values.

On surface have 85psi, climb at 3000 is 78psi, 7000 is 69, 9000 is 70, 11000 is 60

DID not climb further as bottom on green is 55-58.

MP and RPM is consistent and steady, oil temp is 205' on dual gauges.

Descent shows same values as listed.

The oil bypass valve spring was also changed to the heavy duty Lycoming spring

All lines/hoses checked and fittings. No leaks no kinks on lines or breather.

Oil filter changed and oil.

Exact same issue of decreasing oil press with climb and inverse increase with descent.

Have had previous engine changes without this issue.

Anyone with experience on this specific issue?

Thank you in advance.

[tls pilot]

sorry slight typo

surface is 85 at 440ft msl,

3000ft is 78, 7000 is 70, 9000 is 65, 11000 is 60

This is the trend, again climb decreases oil pressure and descent increases oil pressure.

Thanks again...

[KSMooniac]

I don't know definitively, but I've read a lot of anecdotal reports that the parabolic lifters result in lower oil pressures and many shops won't use them.  At least your Bravo has the wet head design so you don't have to depend on high oil pressure to squirt oil thru the pushrods to get to the head!  I think lower pressure on most Lycomings = badness in terms of lubricating and cooling the valves.  You should climb higher and see if it continues to decrease.  And you should probably call a Lycoming engineer as well.

[carusoam]

What would alt or air pressure have in common with oil pressure?

Sounds like the two pressure gauges may be sharing a blocked vent?

Are the two oil gauges using the same sensor? How independent are they?

Best regards,

-a-

[tls pilot]

Totally independent. One transducer, other direct reading

[BuzzProc]

I'm still new to this forum having owned my 99 Bravo for 5 weeks. I could have typed nearly the exact same OP and altitude numbers.

The difference being I have been up to 14,000 and OP is 54, OT was 199.

I was told as well this is a characteristic of this engine. I have had the oil pump turned up some and it has helped just a little but now concerned about higher OP on start. This engine has only 150 hrs.

Just yesterday I sent my initial note to the Lycoming engineers and got a reply that just asked the exact engine type.

I responded but it was past east coast closing time.

Anxious to hear more from more experienced folks.

Thanks for putting this topic out

Regards

[tls pilot]

when was the engine installed, is it factory new lycoming or an overhaul

Please indicate when it was built.

All previous engines installed had NO issue with Oil Pressure all the way up to FL 240.

Caution, if indeed your oil pres is 54 at 14000 ft that is BELOW the green and in the yellow

it also limits your ability to climb to Flight levels, the reason one owns this type of plane.

[FlyDave]

I have a 1989 Bravo, original engine w/1600 hrs with Bravo conversion 600 hours ago.

My OP is usually around 60 PSI all the way up to FL210. I'm just offering a reference point.

[BuzzProc]

The engine was an overhaul, to "zero time" standards.

Roger on where the bottom of the green arc is, part of the conversation with Lycoming.

I don't have the records handy but it was done around 3 years ago.

[tls pilot]

question to BuzzProc, was it an overhaul from the Lycoming factory ?? or done at an outside the factory engine shop???

if at an outside the factory shop, were brand new Lycoming cylinder kits used?

and if you can find out what tappets and camshaft were used ie flat tappets or new style parabolic tappets???

The above points are seem to be extremely relevant to this issue and if you can research, the info would greatly assist us.

[MB65E]

There is an updated oil pressure spring. I bought it for the Bravo I used to maintain. The spring rate is different. I purchased it thru TopGun CA as they led me to the Fix.

-Matt

[tls pilot]

as noted in first post

the oil bypass spring was changed to the heaviest lycoming spring made

[Awful_Charlie]

Interesting problem, and not one I've noticed at all - my oil pressure remains pretty constant at about 80psi all the way to FL250. I do see your oil temp appears quite high though, mine is normally about 190 in the climb and 175 in the cruise, and hotter oil will normally cause a reduction in oil pressure.

 

I don't mean to teach you to suck eggs, but are you sure the pressure is related to the altitude, and not to the attitude? If nose up is causing the drop, then we should be looking at oil levels and maybe the cylinder drains.  What oil are you using (and are you adding anything to it?), and what level are you filling to? I normally fill to 8 and then add a litre when it drops to 7

[BuzzProc]

Good evening Newmember 1993 Bravo

I am in travel mode away from my hanger so I will be able to only answer some of your questions.

The engine is not a Lycoming overhaul. I will find out next week if it has the new Tappets. I suspect it does.

I did get a reply from the Lycoming tech of which I will paraphrase here.

First the Bravo engine is the only one to have exhaust valve oil cooling so it "makes this engine more susceptible to lower oil pressure". Not much new here.

He also said that the new tappets are designed to warbble more which causes, slightly lower OP than our old tappets...nearly a quote.

So starting to guess the combination are much of the issue.

He gave some suggestions as to where to set the OP at full throttle

Please excuse as I will try to insert his whole text tomorrow.

Ref another question, I always fly w 8 Qts...understandable question though.

Vr

buzz

[tls pilot]

Thanks BuzzProc

More than likely if the engine OH occurred in the last three or so years it has the new style tappets IF they used Lycoming parts.

But please verify.

If those are on your engine, was your case reworked prior to OH assembly and where?

This is truly the only variable on recently reworked Bravo engines.

All previous engines installed on our aircraft made proper oil pressure even at FL210.

As to other questions, running 8qts is the correct quantity.

[tls pilot]

Buzz

Additionally, DOES your oil pressure decrease as you climb ??

[BuzzProc]

Greetings All,

Yes, OP goes down as I climb.

Going from memory as my notes are 400 miles away,

On Engine start the OP is the very top of the yellow...Lycoming says they allow up to 115 on start at idle.

Then 5 min later, high 90s,

Then 8 min later, around 70s

 

Take off is MP 36.5 and 60 or 70 OP.

 

OP slowly decreases up to 10.5 and then it is down to 56.  OT is just under 200 and oil is kept at 8 QT and AeroShell 100.

 

At 14000 the MP is 27, TIT is say 1580, MP is 54, OT is 190s.

 

I have tried to cut and paste the Lycoming answer, but can't, due to the computer the note came in on is an Army computer and security limits imposed prevent the cut and paste.

 

In essence the Lycoming engineer says, the Bravo engine is more likely to have lower OP due the exhaust valve cooling.  He also said with the new style tappet the engine will lose "slightly more OP".

 

This new tappet, which started around 3 years ago, is seemingly the difference between older Bravo engines and new OH ones.  I am nearly certain my engine has these new tappets. 

 

I have turned up the Oil Pump out put so that I am about as high as allowed for engine start OP.  The Lycoming engineer suggested to set TO power OP for 90, but that will certainly bust the engine start OP limit.

 

Interesting.

Think I have added about all I can from memory.  Always appreciate the information. 

V/R

Buzz

[Piloto]

Buzz

 

Have you noticed an increase or decrease in OP over time with the new tappets?

 

José

[BuzzProc]

Only owned the plane since 3 Sept, however the previous owner said it ran low OP (in green).

He never flew above 10k.

Buzz

[tls pilot]

Buzz

Perhaps we should speak offline?

Not certain how to do that??

In any event the whole issue here is low oil pressure vs declining oil pressure with altitude and eventually NOT having oil

press in the green at FLight levels.

It appears Lycoming changed to parabolic tappets a few years back due to poor metal issues with the old style tappets- premature spalling issues.

Superior does make the old style tappets also and there are no reports of metal issues with them?

It does seem that the new parabolic tappets especially on this engine cause a lower oil pressure BUT it is still in the green AND

it is NOT a declining oil pressure with climb and then increase oil pressure with descent.

Two different issues- that are easy to confuse in conversations.

The issue of declining oil pressure may very well be related to the case and specs/tolerances. It appears the Lycoming factory

has no issue with declining oil pressure as you climb, THEY HAVE noticed a lower oil pressure, but NOT declining oil pressure as you can altitude.

It appears the issue is how the factory goes over the cases vs a field OH shop or case shop.

Somehow the Lycoming factory gets specs right on or on the top end in every area. Whereas the spread by a field OH engine shop varies (still within parameters) but just enough to cause this issue.

[carusoam]

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Best regards,

-a-

[N601RX]

Has the oil pressure ball and seat been inspected? You mentioned having the heavier spring above, but if the ball is not seating correctly in the seat or the seat has imperfections in it the oil pressure is going to be low.  I remember a couple of service bulletins about this.

[Piloto]

If the case is the problem what part of it would be the cause of the oil pressure drop. Since the oil pump is a suction pump type I would look into the oil pump housing on the back of the engine. Any leaks into the suction side of the pump will reduce it performance at altitude but would not show as an oil leak outside the case. I would try first putting sealant around the oil pump housing interface before splitting the engine case.

 

José 

[FoxMike]

Here is a wild guess.  The vernatherm seat may not be sealing completely.  Lycoming used to loan a tool out to true up the seat.  Again just a guess.  You might take the vernatherm home and put it in the oven make sure it meets specs. when hot.  Good luck.

[Piloto]

Here is a wild guess.  The vernatherm seat may not be sealing completely.  Lycoming used to loan a tool out to true up the seat.  Again just a guess.  You might take the vernatherm home and put it in the oven make sure it meets specs. when hot.  Good luck.

More accurate testing in a cooking pan on the stove in hot engine oil with a cooking digital thermometer.

 

José