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[FlaL4]

I thought the oil pressure relief controlled Max pressure. It shouldn't have anything to do with min pressure unless it's stuck open a little, which would be fixed by a stronger spring. If the engine truly had low oil pressure due to some other reason, coil springs from a chevy wouldn't bring it up. Or am I mis guided again?

Rich

I thought so also until I read a lot of the stuff from Harry Fenton. Again here is what he says on the subject and it fixed my problem moving the idle pressure from 6 to 12 indicated after all other fixes were in place.



"Quote
Another popular fix, but one I really don’t like, is to slip some AN washers into the ID of the plunger to increase the spring tension and create a more positive push of the plunger against the case.  However, if the valve is leaking, no amount of spring tension will fix the problem.  If not (I can’t believe that I am suggesting this) install some washers under the spring to see if the idle pressure comes up.  Actually, I am not totally against this, so long as the major cruise oil pressure is ok.

Too often, the washers under the spring are used, incorrectly, as an attempt to improve running oil pressure, not idle pressure.

 If overall system pressure is low, the washers will improve idle pressure, but as soon as cruise rpm oil volume pushes the valve open, the overall oil pressure goes low.  However, if the overall system pressure is ok, then the idle pressure can be tweaked by increasing tension on the spring or by trying another spring.
 
Let me know if this works.  I think that this is your problem and I’d like some feedback to know if this solves the issue.  Or not.
 Harry
End Quote

[FlaL4]

I know in the Continental A-65/75 overhaul manual they list two different springs.
P/N 631706 is for the A-65 engines
P/N 21352 is for the A-75 engines

However it does not give specs on the size. So maybe you had the wrong size spring installed. I am also wondering if your Crankshaft has the right size bearings installed.....I don't mean to throw gas on the fire but you shouldn't need to add any washers to the plunger  (at least that's what the Continental engineers would say).
DC Krog

DC, the spring I installed is an old one and needed the one washer. As soon as I can find a new correct replacement I will change it out.  Here is a picture of the short blue spring we removed. Compare the length to an original you have.

The engine internals are good and will hold 37 pounds of OP at 180 degrees without any decline in flight. The engine was rebuilt by Frank Sabo and I asked him about the bearings early on. He verified the part numbers before installation and they are the correct parts.

Steve

[huston marlowe]

Hey all !  I have my little blue spring out today and it is exactly the length you show . Thanks for the photo !  When I installed it I don't remember it was very different than the one I removed. I'd like to know the correct part # and dims. of the one listed for a C-85 ..thanks (I have no parts book)

[FlaL4]

Hey all !  I have my little blue spring out today and it is exactly the length you show . Thanks for the photo !  When I installed it I don't remember it was very different than the one I removed. I'd like to know the correct part # and dims. of the one listed for a C-85 ..thanks (I have no parts book)

I think someone is selling this spring as a "one size fits all" Continental replacement spring. All I know is that the spring does not work in my A-65. My A&P who is also an expert on small Continentals immediately knew the spring was wrong for my engine. I also believe it was smaller in diameter than the original we installed.

Steve

[huston marlowe]

By observation, the area of the plunger available to the oil is about .126 sq in. So, at the 35 psi relief pressure the oil must exert 4.41 pounds to get it off the seat. The little blue spring measures to have about a 6.8 lb / in. rate. So, the installation should compress the blue spring .65 inches. I'll have to measure that when I put it back in.

[huston marlowe]

One last post from me. Earlier I reported measuring the rate of the "blue" spring as 6.8 lb/inch. Continental lists the 631706 spring as 6.01-6.31 lb when compressed 1.09"...or lets say 6.25 lb/inch. So we are in the ballpark with a compression rate of say 6.4 lb/inch for calculation. On installation in my engine the spring got compressed almost 1.25" by the cap. This is a developed force of 8 lbs.  I measured the exposed piston area of the plunger at about .4" diam ,or .126 sq inches. Doing the math this means the oil must reach about 60 psi to unseat the plunger/piston !  This explains how the gage can show these high pressures when oil is cold. As the oil warms it can slip out all the bearing clearances and lifters and push rods and register lower pressure. Continental lists 30-35 psi as normal at cruise rpm , probably with 180 F oil. The relief valve plunger is seated.  No pressure at idle could be a combination of bearing clearances, worn pump housing/gears, and/or a leaking pressure relief plunger.  At least this story makes sense to me.

[Alcyons]

Hi !

My very first time on this forum, and I see the problem I encountered yesterday is not unique. L4 with C65.

First two hour flight ok and the next flight, I noticed fairly low oil pressure at idle. Decided to stop the engine, stop flying and wait for the mechanics to check that next week. This was before discovering the forum !

Can anyone help to explain what is the washer and what is the plunger? Thanks !

Laurent,
Paris, France 

[FlaL4]

Hi !
My very first time on this forum, and I see the problem I encountered yesterday is not unique. L4 with C65.
First two hour flight ok and the next flight, I noticed fairly low oil pressure at idle. Decided to stop the engine, stop flying and wait for the mechanics to check that next week. This was before discovering the forum !
Can anyone help to explain what is the washer and what is the plunger? Thanks !
Laurent,
Paris, France  

Laurent,
There is a gold mine of information on small Continentals here:
http://www.bowersflybaby.com/tech/fenton.htm

The spring and plunger are located in the pressure relief valve housing at the ear of the accessory case. I was only getting 20 lbs at cruise until I changed the oil and replaced the spring. Now it is solid in the green at 180 degrees and after 1 1/2 hr in flight.

My gauge reads 6 to 8 lbs low at idle but now reads around 11 (actual pressure of 17 to 19). It was 95 degrees outside yesterday and my engine temp was running at 180 degrees, OP was around 35.

The very first thing you need to check is the accuracy of your OP gauge.

Steve

[Alcyons]

Laurent,
There is a gold mine of information on small Continentals here:
http://www.bowersflybaby.com/tech/fenton.htm

The spring and plunger are located in the pressure relief valve housing at the ear of the accessory case. I was only getting 20 lbs at cruise until I changed the oil and replaced the spring. Now it is solid in the green at 180 degrees and after 1 1/2 hr in flight.

My gauge reads 6 to 8 lbs low at idle but now reads around 11. It was 95 degrees outside yesterday and my engine temp was running at 180 degrees, OP was around 35.

The very first thing you need to check is the accuracy of your OP gauge.

Steve
[/quote]

Hi Steve,

Thanks for the message. I checked yesterday my data and got near 20 lbs at idle, with 165 °F, and about 35 lbs at 2100 RPM. Would you consider this value to be correct ?

Laurent

[FlaL4]

Laurent,

Those pressures look good for a A-65. 

Steve