O-200 Loses Oil Prime

[cessna150pilot]

edited

 

[Kiddo's Driver]

I've never heard of this before. My GoogleFu brought this up:
http://www.bowersflybaby.com/tech/fenton.htm#a65_oil_prime

It talks about an A65 losing oil prime. It probably applies to your O-200.
(Edit: I changed O-300 to O-200. I was thinking about the 200 since it is similar and is often used on Flybabies also, but had O-300 stuck in my head from Bryan's 172 thread...)
Jim

 

[Dan Thomas]

The OP has an O-200, and it has a similar pump location to the A-65/75/85/90 series, which all have this issue. The O-300's pump is low in the accessory case, close to the oil level.

The pump's cover seeps oil over time, and once it's dry it can't suck the oil up out of the sump unless the pump is really tight--meaning within serviceable specs. I'd bet that the shop didn't replace the worn stuff, especially accessory case, where the pump bore is machined directly into the aluminum casting. It gets scored up, the gears get worn, and it won't suck oil if it's dry because it can't move the air along.

I have an A-65 that did this all the time. It resulted in crankshaft rod journal wear due to no oil pressure after start. I got tired of priming the pump and built a manual preoiler to shove oil into the galleries, which pushed oil into the pump cavity and primed it. This is on a homebuilt, of course.

Sealing the pump's cover plate doesn't work. There's very little mating surface area, and the plate flexes under pressure and breaks the seal anyway.

 

[Let'sgoflying!]

I have an O-200 that did this after someone overhauled it.
I think what happens is the overhauler says 'it was pumping just fine' before the o/h, Plus; gear or acc case or pump housing replacement is not spelled out as required, Plus; they are not cheap parts.....so it doesn't get done and in many cases this is no big deal until it quits holding the prime.
I played some with pre-oiling and starting every week, tried heavier grade oil, new gears, lapping the pump cover to reduce the clearance....then I used the new gears on a new acc. case and pump cover and it was immediately better.
I am surprised you can bush the acc case; as I recall from when I had the problem no one would do it; can't recall if it was thought to be illegal or technically difficult. And some of my wear was the magnesium accessory case, and there is (was apparently) no way to build that up and resurface it.
There have also been cases of cracked pickup tubes and bad seal between that and the case causing it to suck air.

 

[nrpetersen]

I have a C-85 that does this on occasion. I tore the accessory case down and found that the pump cover was poorly aligned to the accessory case as there is no alignment pin system. This caused a tapered axial clearance on the two gear faces giving a somewhat greater potential for leakage and drain back. (a hydraulic trick as leakage goes as the cube of the clearance)

I also have a full flow oil filter which the inlet check valve pretty much prevents engine oil from getting back to the pump gears via the galleries or even the oil pressure gage port. Some people remove the oil temp sensor and insert priming oil there. This eventually can fatigue the oil temp bulb's line and doing this enough times with a pliers wrecks the temp sensor (which can be rebuilt).

The filter inlet check valve, the pump gear clearances, and a low oil level are all related to the problem. If oil is pumped via an oil can into the kidney (not the center) of the filter adapter that oil can dribble to the pump gears for priming. At prestart if it has been sitting for a long time, I routinely raise the tail high momentarily on my (1941) J4A as that also dribbles oil into the gears.

You can't do that on your 150.....

 

[Dan Thomas]

I am surprised you can bush the acc case; as I recall from when I had the problem no one would do it; can't recall if it was thought to be illegal or technically difficult. And some of my wear was the magnesium accessory case, and there is (was apparently) no way to build that up and resurface it.

I don't think bushing that cavity is possible. First, it's a figure 8-shaped thing, so no bushings are going to press-fit into it. Second, the walls of the pump cavity are thin, and they would have to be machined out to make room for the bushing.

Some info here:

http://www.ercoupe.info/?n=Main.OilPump

Couple of pictures from that page:

Think you could bush that bore?

 

[Henning]

By 'losing prime' do you mean to say that the engine will not pick oil back up and have pressure on the gauge within 4-5 seconds?

 

[Tom-D]

Hello, I fly a cessna 150 with a continental O-200 that was overhauled about 2 years ago. A year ago the plane lost oil prime after sitting for a few weeks. The engine shop reinspected the engine, and brought the whole oil pump up to continental standards and seemed to have fixed the problem. Now a year later I have had it lose oil prime again, after sitting for about 2-3 weeks no running. The engine shop is refusing to help me at this time so now I am trying to figure out the best way to re-oil the engine.

what weight oil are you using?
And what is the total time on the engine ?

The real fix for this is a new accessory case and new gears.

Stuff wears out,

that case is a mag casting and can not be welded and remachined. once worn it is gone to the junk pile.

Call the TCM parts line and price out the parts.

 

[Henning]

Yes losing prime I mean no oil pressure on startup. I'm surprised no one has used the pressure pot to fill the oil pump. The mechanic suggests that it attaches to the front oil gallery. The business that did the work is well respected, do other mechanics here suggest that it's not possible to have bushed this cavity? What do you all recommend

How long do you let it try to pick up oil? Seriously, I've never seen this happen in an O-200/O-300. Is there a check valve in the system that isn't holding? Even so, if they just went through this pump, I've not seen these pumps not be able to pick up a prime if in good condition. It's kinda weird and makes me wonder if you don't have a crack in an oil gallery.

 

[Henning]

I ran it about 25-30 secs before cutting it. Usually it gets oil pressure in a few seconds. It has been colder her than usual and the plane wasn't run for a few weeks.

Yeah, that's definitely too long. The question is why is it draining back and going dry? What oil are you using?

 

[iflyvfr]

You might consider joining the Cessna 150 152 type club and posting there. There are some knowledgeable A&P owner pilots over there.

 

[Henning]

Aeroshell 100w. Normal temps around here range 46 low 65 f high this time of year

You have a problem somewhere inside the engine. It's too new to be doing something like that. It needs to come off and open in order to properly investigate.

 

[Tom-D]

How long do you let it try to pick up oil? Seriously, I've never seen this happen in an O-200/O-300. Is there a check valve in the system that isn't holding?

No there is not/B]



Even so, if they just went through this pump, I've not seen these pumps not be able to pick up a prime if in good condition. It's kinda weird and makes me wonder if you don't have a crack in an oil gallery.

Once again you make statements that prove you know nothing about the subject.

 

[Tom-D]

You might consider joining the Cessna 150 152 type club and posting there. There are some knowledgeable A&P owner pilots over there.

Because he knows I overhaul these almost daily.

 

[Tom-D]

Aeroshell 100w. Normal temps around here range 46 low 65 f high this time of year

What is your normal oil pressure while in cruise ?

 

[Tom-D]

do other mechanics here suggest that it's not possible to have bushed this cavity? What do you all recommend

Not no, but hell no, that is a major modification to the engine. by the time you gain authorization the money will buy you a new engine.

 

[Sleepingsquirrel]

I've read somewhere that the filler neck of the oil sump is above the oil pump. It may be primed by filling the oil up into the filler neck,turn the prop (mags off) by hand then drain excess oil. This may be worth checking out.

 

[Dan Thomas]

I've read somewhere that the filler neck of the oil sump is above the oil pump. It may be primed by filling the oil up into the filler neck,turn the prop (mags off) by hand then drain excess oil. This may be worth checking out.

Way more work than just priming it. And that neck is often not nearly tall enough anyway. You'd have to fill the lower half of the crankcase with oil for it to work, because the pump is directly driven off the camshaft. What would that be? 20 quarts?!!

Best thing is to spend the money to fix it right.

 

[Tom-D]

I've read somewhere that the filler neck of the oil sump is above the oil pump. It may be primed by filling the oil up into the filler neck,turn the prop (mags off) by hand then drain excess oil. This may be worth checking out.

Nope, sorry that won't work.

 

[Dan Thomas]

Out of curiosity, how long can an o-200 normally sit before it will lose oil prime, would it take months ?

Depends how bad the leak is and how worn the pump parts are. It can lose its prime in 24 hours or three months or anywhere in between. It can lose its prime and go right back to work if the parts are in good condition.

Welcome to the world of old airplanes. I have discovered that there is no such thing as a cheap old airplane.

 

[Tom-D]

Pre-heat, get it good and warm, start it, let it run, if it hasn't gain oil pressure by 3 minutes it isn't going to. it needs over haul of the accessory case and oil pump.

If it gains oil pressure, change oil, and use this as a refill.

http://www.skysupplyusa.com/phillip...roductsearch&gclid=CKvNto35u8kCFcVffgod2QoJnw

But then NEVER start with out a pre-heat. this stuff is radial engine oil, and meant for old loose oil pumps.

or simply sell the 150

 

[Tom-D]

I'm not about to run it for 3 minutes without oil pressure, does this not cause damage ?

We are not talking full power, idle it should not, but run it as long as you dare.

And next time don't allow it to set this long.

Do you have a filter on it ?

 

[Let'sgoflying!]

....then I used the new gears on a new acc. case and pump cover and it was immediately better. =

do yourself a favor; quickest, happiest solution immediately above^^^

 

[bnt83]

I ended up with a new accessory case, oil pump gears and oil pump cover when we overhauled my Cessna 150's O-200. Old case had about 4,000 hours on IIRC.

I never noticed it losing prime before or after overhaul though. Even when flying it in -20F weather in Watertown South Dakota. (Did have an oil tank heating pad) We ran 20w-50 X-County in it.


Is the suction tube loose chipped or cracked in the oil tank? Sucking air from somewhere?

 

[Dan Thomas]

I'm not about to run it for 3 minutes without oil pressure, does this not cause damage ?

It will. I had to regrind my crankshaft after several dry starts, and it only ran for maybe 15 seconds before I shut it down. The front journal suffered the most, since it's the farthest from the pump and the last to get any oil. This damage occurred within 150 hours of the last time I'd opened the engine. It didn't help that the A-65's crankshafts aren't nitrided like your O-200's will be.

The bearings need oil, and lots of it, to keep the metal surfaces apart. They need even more when they're worn. The pistons and rings can survive with very little oil, since the pressures on them are far smaller per unit area.

 

[tawood]

This post has me scratching my head...


I've had two Cessna 150's with O-200's and I have NEVER, EVER seen them develop oil pressure within 30 seconds...my current 150 has 100 hours since overhaul and usually take 45 seconds or so, at idle, to show oil pressure whether warm, cold, etc, which is exactly what my last 150 did as well.


Now, I had a Taylorcraft with an A65 that would loose prime regularly if I used synthetic oil, and after 30 seconds I would shut it down...but my O200? I would be shocked to see oil pressure within 30 seconds!!!

 

[Tom-D]

Way too many 0-200 will have air in the gauge line, which is a #2 copper tube. So during these cold temps the oil in that line is very cold and thick, and requires a few minutes to move oil up the line and compress the air in the line to show a reading on the gauge.

We all preheat the oil sump/tank/what ever, but seldom do we heat the line.

 

[Tom-D]

This post has me scratching my head...

Welcome to the club,, but remember the accessory case and oil pump has been messed with.

 

[Tom-D]

Do this prior to posting again..

go to NAPA and buy a 0-100 pound gauge, buy a pipe / to/ AN#2 adaptor have the NAPA dealer manufacturer a short #2 copper line with AN flares at each end.
attach that line to the oil pressure port on the engine and the other end to the gauge, Pre-heat the engine, and start have some one watch the gauge see if you have oil pressure at he direct reading gauge.

You can order these parts at Aircraft Spruce

 

[Tom-D]

I have a C-85 that does this on occasion. I tore the accessory case down and found that the pump cover was poorly aligned to the accessory case as there is no alignment pin system.

I am wondering how you got the case down over the two big studs, and all the bolts in place with out the accessory case aligned well enough to position the oil pump over the cam drive?

 

[nrpetersen]

I am wondering how you got the case down over the two big studs, and all the bolts in place with out the accessory case aligned well enough to position the oil pump over the cam drive?

I was referring to the oil pump cover piece on a C-85 that is held on with two (no, it is four!) carefully torqued 1/4-20 bolts that screw directly into the accessory case. There is some clearance for the bolts in the o.p. cover that if it is assembled wrong, makes the two gears run on a slightly off axis. The internal wear marks suggested the gears were each contacting on one side only. This makes the face gaps to be tapered.

The alignment of the OP cover to the accessory case should be done with a mandrel setup, except you'd have to remove the cover again to get the mandrel out.....

It sure is an opportunity for someone to make a run of very slightly oversize gears. I was amazed at the gear widths (which are ground), are as varied as they were - right at the high and low service limit respectively even though they were not worn. Sloppy manufacturing, but I suppose it was state of the art then.

 

[Henning]

I'm not about to run it for 3 minutes without oil pressure, does this not cause damage ?

Not really, not so long as you aren't making significant power/heat. The bearings self lubricate against polished steel as long as the temperature stays below the critical temp for the bearings and they start to smear. The main purpose of oil is carry away heat. At idle power-900rpm, there really isn't that much heat being produced and your risk of getting a good bearing to go bad are pretty minimal.

 

[Tom-D]

I was referring to the oil pump cover piece on a C-85 that is held on with two carefully torqued 1/4-20 bolts that screw directly into the accessory case.

that oil pump cover is a flat cover, how can it be misaligned ?

the pumping gears always leave a run mark on the case or cover. no biggie.

 

[nrpetersen]

that oil pump cover is a flat cover, how can it be misaligned ?

It can be radially displaced by an amount equal to the cover bolt hole diameters minus the bolt(s) body diameter.

the pumping gears always leave a run mark on the case or cover. no biggie.

Yes but I expected them to be all the way around, not worn on one quadrant only.

 

[nrpetersen]

Although the step doesn't look very large, the wear difference in the face is over .001 inch

Trying to host a picture at my website.

Well that didn't work worth a darn.............

 

[Dan Thomas]

It can be radially displaced by an amount equal to the cover bolt hole diameters minus the bolt(s) body diameter.

Yes but I expected them to be all the way around, not worn on one quadrant only.

If the gear-to-cover clearance is what it should be you'd have a really hard time getting the gears off-axis. Those gears should fit into the cavity with less than something like .001" clearance, and so no cocking would be possible without deforming the cover. If they're still slopping around, the bearing bores in the accessory case are worn out.

 

[Dan Thomas]

Way too many 0-200 will have air in the gauge line, which is a #2 copper tube. So during these cold temps the oil in that line is very cold and thick, and requires a few minutes to move oil up the line and compress the air in the line to show a reading on the gauge.

We all preheat the oil sump/tank/what ever, but seldom do we heat the line.

Add to that the restrictor oil pressure fitting in the case. A really tiny hole in it, and it will restrict the flow of cold oil. If there's air in the line it will take forever to get an indication. I have put 5606 in the line, like some guys way up north, to get a near-instant reading.

 

[bnt83]

Wait wait wait here a second. Your engine was just overhauled recently and the oil pressure gauge doesn't show pressure at all sometimes or?

Is there some junk plugging the pressure sense fitting on the case? Verified the gauge isn't sticking? I remember a guy that bought cessna 172 serial #1 a few years ago and made an emergency landing at the nearest airport after oil pressure dropped. They found crap in the fitting screwed into the engine. Cleaned out the lines to the gauge & fitting and all was well.

How is the digital oil pressure gauge plumbed in? How big is the hole in that sensor? Got a new one to test with?