For the last 600 hours (SMOH) the indicated oil pressure on my C-145 has been 25-30 psi at idle and 50-55 psi during normal operations at around 2400 rpm. I have always been able to get an indicated oil pressure of 20 psi by hand propping. All of this time I have used Aeroshell 15w50.
I just top overhauled. Immediately after the overhaul, using the starter (no plugs installed) I got 30 psi indicated. I flew for 2 hours with normal oil pressure readings during cruise - I don' recall the oil pressure readings duirng taxi and prior to shutdown. Now after two weeks of sitting, hand propping gets me about 5 psi indicated, idle at 800 rpm gets me 10 psi, and 1800 rpm is required for a 30 psi indication. At that point I decided to do some research before flying. All of this is being done with Aeroshell 40w mineral oil.
The continental manual states 5 psi min at idle and 30-45 psi during normal operation which I take to mean about 2400 rpm. The current oil pressure indications are in line with the manual. Based on this I should just go fly. But because the indications are so different from those before the top overhaul, I did not feel comfortable enough to fly.
Any thoughts on this? How does your oil pressure behave? Maybe my oil pressure relief valve has some overhaul debris in it. I hope to check that out next weekend.
-Allen
oil pressure readings
Moderators: GAHorn, Karl Towle, Bruce Fenstermacher
I don't believe the "hand -propping' reading means a thing. I'd disregard it completely. Firstly, there's no standard for that, and secondly the engine has undergone heavy maintenance since the ad hoc "standard" of 20 psi you recall. Things can change after heavy maintenance. (How do you know you didn't have debris in the gauge line prior to the mx which acted like a check-valve allowing pressure to build and give erroneous readings?)
You don't give the oil temp readings during your measurements but>...
Cleaning the relief valve and seat is a good idea. Hot oil will likely read lower psi (all other things being equal) than cold oil, but most healthy engines will show 30 psi at idle with cold oil.
In any case, unless you have a clean, reliable relief valve, a clear oil pressure line, and an accurate gauge (still not confirmed, by the way) then it's all merely a guess. You don't have to worry about any engine damage with current readings, but you'l likely want to pursue the dicrepancy in the readings.
You don't give the oil temp readings during your measurements but>...
Cleaning the relief valve and seat is a good idea. Hot oil will likely read lower psi (all other things being equal) than cold oil, but most healthy engines will show 30 psi at idle with cold oil.
In any case, unless you have a clean, reliable relief valve, a clear oil pressure line, and an accurate gauge (still not confirmed, by the way) then it's all merely a guess. You don't have to worry about any engine damage with current readings, but you'l likely want to pursue the dicrepancy in the readings.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
I'd make sure you're getting an accurate reading 1st. Best is to disconnect the line at the case and install a known good gage on a flex line and ground run it.
if the test gage shows all's ok blow the line out and fill it as best you can w/ a light oil like kerosene or diesel. That's the usual problem. And if that doesn't fix it you know it's the gage.
if the test gage doesn't show good pressure and the case fitting itself isn't clogged *then* pull & clean the relief valve and rewasher if necessary.
if the test gage shows all's ok blow the line out and fill it as best you can w/ a light oil like kerosene or diesel. That's the usual problem. And if that doesn't fix it you know it's the gage.
if the test gage doesn't show good pressure and the case fitting itself isn't clogged *then* pull & clean the relief valve and rewasher if necessary.
George you just HAVE to ease off!!! I don't know how long they;ve been goosing oil pressure up by putting washers under the relief valve spring, but they taught ME that when Lockheed Aircraft sent me to aircraft engine school at Grand Central Air Terminal in Glendale, CA, in 1941. Every mechanic I've ever known does it.
There may not be any "official" authorization for the practice, but common usage for over half a century must count for something.
In all the years I've been involved with these engines, you are the first person I've ever heard condemn the practice.
Tell us truly,George, do you have a vested interest in manufacturer of these relief valve springs?
There may not be any "official" authorization for the practice, but common usage for over half a century must count for something.
In all the years I've been involved with these engines, you are the first person I've ever heard condemn the practice.
Tell us truly,George, do you have a vested interest in manufacturer of these relief valve springs?
BL
My comments regarding "approval basis" (such as this one) should not be universally taken to be a condemnation. They are only intended to provide a comparison or reference-point to the methods that are less intrusive and/or most likely to be approved by the mfr and the certifying authorities. In virtually all cases if the approved method is not satisfactory then another, perhaps not so obvious, problem may exist which may be masked by the ad hoc fix.
I've known lots of good mechanics who have used that practice of adding washers to a relief spring in order to boost pressure. (Some types of oil pressure relief/regulator valves even have screw-type tensioners to arbitrarily adjust pressure to a desired level....for example on the IO-470/520 series engines.)
I'm only offering the comment to provide a reference. If the spring is the correct tension, and if the plunger and seat is in good condition and not eroded....then washers should not be necessary. If the spring and seat are good and still insufficient pressure exists....then the best fix may not be to simply shim with washers.....it might be to look elsewhere for the problem.
(The problem could be anything from bad gauge to worn bearings to cracked crankcase. Forcing the pressure up with washers isn't a fix I'd recommend as an automatic/arbitrary action.)
I have had two engine failures due to loss of pressure following the re-adjustment of oil pressure relief springs by mechanics who mindlessly boosted the pressure...rather than find and fix the problem. One failure occured as I taxied in to the ramp...but the other was immediately after takeoff. That engine seized at about 1,000' AGL ...but fortunately I was on a downwind departure and merely had to turn left and land back on the runway. The cause turned out to be a spun/split bearing which was dumping oil pressure back into the sump. Boosting the pressure merely masked the problem, and could have been much more serious had the final failure occurred elsewhere.
I've known lots of good mechanics who have used that practice of adding washers to a relief spring in order to boost pressure. (Some types of oil pressure relief/regulator valves even have screw-type tensioners to arbitrarily adjust pressure to a desired level....for example on the IO-470/520 series engines.)
I'm only offering the comment to provide a reference. If the spring is the correct tension, and if the plunger and seat is in good condition and not eroded....then washers should not be necessary. If the spring and seat are good and still insufficient pressure exists....then the best fix may not be to simply shim with washers.....it might be to look elsewhere for the problem.
(The problem could be anything from bad gauge to worn bearings to cracked crankcase. Forcing the pressure up with washers isn't a fix I'd recommend as an automatic/arbitrary action.)
I have had two engine failures due to loss of pressure following the re-adjustment of oil pressure relief springs by mechanics who mindlessly boosted the pressure...rather than find and fix the problem. One failure occured as I taxied in to the ramp...but the other was immediately after takeoff. That engine seized at about 1,000' AGL ...but fortunately I was on a downwind departure and merely had to turn left and land back on the runway. The cause turned out to be a spun/split bearing which was dumping oil pressure back into the sump. Boosting the pressure merely masked the problem, and could have been much more serious had the final failure occurred elsewhere.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
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zero.one.victor
- Posts: 2271
- Joined: Tue Apr 23, 2002 12:11 am
Thinking about this.....pre-loading the relief valve spring with washers doesn't really "force" or "boost" the oil pressure, it merely increases the set-point (for lack of a better word) of the pressure relief valve. If the low oil pressure reading is caused by the relief valve opening at too low a pressure, this will remedy the situation. You then know that the spring is too weak & needs replacement (or pre-loading!).
If something else is causing the low readings-- like a cracked case or faulty bearing-- raising the relief set-point should not affect the gauge reading. You would then know to keep looking.
I've seen this washer trick done many times-- it was even suggested by a TCM factory rep I know, George's friend Cory.
Eric
If something else is causing the low readings-- like a cracked case or faulty bearing-- raising the relief set-point should not affect the gauge reading. You would then know to keep looking.
I've seen this washer trick done many times-- it was even suggested by a TCM factory rep I know, George's friend Cory.
Eric
oil pressure readings
I kept wondering why George was hung up on the "new spring". I guess after you have been shot at with rock salt, you learn to quit stealing watermellons. 
Some where, I think it was from a Lycoming publication, there is a statement to the fact that three washers was the maximum permissable.
I am going by memory and do not intend to spend time looking for the reference.
Common sence should prevail, there is nothing better than new parts. That being said, new parts are not always available to use in testing or trouble shooting. I have torn down more than one runout engine (not a failure) that had washers on top of the spring.
I now understand where George is coming from on the new spring. A bad experience can make a fellow gun shy.
Some where, I think it was from a Lycoming publication, there is a statement to the fact that three washers was the maximum permissable.
I am going by memory and do not intend to spend time looking for the reference.
Common sence should prevail, there is nothing better than new parts. That being said, new parts are not always available to use in testing or trouble shooting. I have torn down more than one runout engine (not a failure) that had washers on top of the spring.
I now understand where George is coming from on the new spring. A bad experience can make a fellow gun shy.
In the case of in-flight failure, the increased spring tension did indeed bring the pressure back up to the normal readings, and the airplane was flown almost a week before it siezed. The TCM rep at the time (Mobile) blamed the increased relief spring pressure for masking the problem.
Increasing the spring pressure does indeed "boost" the apparent/realized oil pressure throughout the engine. (After all, that's why we do it.) It's sort of like a safety valve....it relieves excess pressure the pump in a healthy engine is capable of producing to prevent overpressure....and dumps the excess back to the sump. (Sort of like a controlled oil-leak back to the sump.) In our engine it's at the end of the line, so to speak. (In some designs it's at the early portion of the lubrication circuit.) This means that in our engines...if the pressure is boosted with washers placed (without full consideration of the problem) under the spring....then excess pressure can be realized in the engine. This would most likely occur as the result of a faulty gauge (reading low.) But it can also occur becuase pressure actually IS low...due to a crack, failed bearing, etc., somewhere along the line prior to the relief valve. Adding washers to a weak spring can mask the other failure. (In other words, just because the pressure increased due to washers....doesn't mean there isn't an incipient failure still hiding in there.)
The reason most washer-fixes work is because the most common problem is loss of spring tension or erosion of plunger seat. With spring tension loss it's a cheap fix. (So is buying a new spring, which I feel is the better solution.) With erosion, there's an increase in the "controlled leak" and when the plunger begins to lift excess oil is dumped back to the sump. While increasing spring tension may help the situation, it doesn't correct the seat erosion and the problem will eventually return. Replacing or re-facing the plunger is also cheap.
The only reason I frequently offer advice regarding "approved methods" is in order to provide a guideline to make a decision by. It's not to criticize an owner's actions.
Increasing the spring pressure does indeed "boost" the apparent/realized oil pressure throughout the engine. (After all, that's why we do it.) It's sort of like a safety valve....it relieves excess pressure the pump in a healthy engine is capable of producing to prevent overpressure....and dumps the excess back to the sump. (Sort of like a controlled oil-leak back to the sump.) In our engine it's at the end of the line, so to speak. (In some designs it's at the early portion of the lubrication circuit.) This means that in our engines...if the pressure is boosted with washers placed (without full consideration of the problem) under the spring....then excess pressure can be realized in the engine. This would most likely occur as the result of a faulty gauge (reading low.) But it can also occur becuase pressure actually IS low...due to a crack, failed bearing, etc., somewhere along the line prior to the relief valve. Adding washers to a weak spring can mask the other failure. (In other words, just because the pressure increased due to washers....doesn't mean there isn't an incipient failure still hiding in there.)
The reason most washer-fixes work is because the most common problem is loss of spring tension or erosion of plunger seat. With spring tension loss it's a cheap fix. (So is buying a new spring, which I feel is the better solution.) With erosion, there's an increase in the "controlled leak" and when the plunger begins to lift excess oil is dumped back to the sump. While increasing spring tension may help the situation, it doesn't correct the seat erosion and the problem will eventually return. Replacing or re-facing the plunger is also cheap.
The only reason I frequently offer advice regarding "approved methods" is in order to provide a guideline to make a decision by. It's not to criticize an owner's actions.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
Update on the original post:
I pulled the relief valve and saw no obvious debris. I pushed some oil through the port by hand propping and reassembled. I now have returned to the same readings as before the TOH. I am definitely more comfortable with these familiar readings that got me through the first 600 hours on the engine. Granted these may not be calibrated readings, but my engine likes them.
-Allen
I pulled the relief valve and saw no obvious debris. I pushed some oil through the port by hand propping and reassembled. I now have returned to the same readings as before the TOH. I am definitely more comfortable with these familiar readings that got me through the first 600 hours on the engine. Granted these may not be calibrated readings, but my engine likes them.
-Allen
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Steve Pierce
- Posts: 20
- Joined: Mon Feb 27, 2006 1:52 pm
George, When you had low oil pressure due to a spun bearing did the mechanic find anything in the oil screen prior to boosting the pressure? I have an O-300 which seems a little low on the oil pressure. Washered the relief valve but didn't really help. Screen looked normal, just some carbon. The airplane and engine are new to me. Had a TSIO360 with spuratic oil pressure. Pulled the screen and found bearing material. Dropped the oil pan and found a chunk broken out of the case and a spun main bearing.
Steve Pierce
Nothing was found at the time he increased the pressure other than the usual carbon particles. Found plenty after the bearing spun.Steve Pierce wrote:George, When you had low oil pressure due to a spun bearing did the mechanic find anything in the oil screen prior to boosting the pressure? I have an O-300 which seems a little low on the oil pressure. Washered the relief valve but didn't really help. Screen looked normal, just some carbon. The airplane and engine are new to me. Had a TSIO360 with spuratic oil pressure. Pulled the screen and found bearing material. Dropped the oil pan and found a chunk broken out of the case and a spun main bearing.
Worn engines can spin a bearing simply because there's excessive clearance due to wear. Another common cause of a spun bearing is following a cylinder change. When the defective cylinder is removed, ...the through bolts which help secure that cylinder to the case are loosened, of course. When the new/repaired cylinder is re-installed, the proper torque is not re-established...and the bearing spins... or excessive torque is established and the bearing is crushed and seizes. It's important when DIS-assembling engines to use a torque wrench and establish the approximate torque range the engine has operated within historically, according to some mechanics I trust. I should be within the specified torque range, of course... but re-assembly should also and should be nearly identical as the DIS-assembly torque.... has been their advice. (Lacking a good Disassembly torque reading,... the engine should be reassembled using the maximum specified torque-range, is what I was taught. I.E.-if the range is 600-900 in.lbs....then use 900 when reassembling with used/reconditioned or part-life components.)
I'm certain I'm not the most experienced engine mechanic present, and others might have further/different comment to offer, but the technique has been 100% successful for me so far.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
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cessna170bdriver
- Posts: 4063
- Joined: Mon Apr 22, 2002 5:13 pm
On torquing cylinders, Continental makes it a point in SB96-7C titled "Torque Limits" to say that through bolts must be torqued on BOTH sides, even if only one cylinder is being installed. There is a big bold warning: Failure to torque through bolt nuts on both sides of the engine can result in a loss of main bearing crush with main bearing shift and subsequent engine failure.
Miles
Miles
Miles
“I envy no man that knows more than myself, but pity them that know less.”
— Thomas Browne
“I envy no man that knows more than myself, but pity them that know less.”
— Thomas Browne