Rebuilt 300D loosing oil pressure

[dlginla]

Remove the left mag, and see if you have a mis placed gasket between the accessory case and the left case half. you can remove the spark plugs, crank the engine, use a mirror, and watch the junction of the oil pressure passage way to see if it is bleeding off the pressure there.

That is the only point in the oil system that, that much oil can be bled off.

You can also see if the oil pump cover is loose from the left mag opening.

If you are thinking about removing the accessory case these parts must come off anyway.

If your accessory case is warped enough to bleed off this much oil pressure, there will be an external leak.

I'm betting the case to accessory case gasket is on backwards left to right. and the reinforced oil passage way hole is on the right not on the left as it should be.

Thank you for this information, it will give us the next step in this puzzle.

[Bruce Fenstermacher]

FYI adding spring pressure with spacers or stiffer spring only raises the blow off pressure. It does not regulate the operating pressure. I'd think if the pin is being held off the seat and leaking, it will be held off the seat with even more pressure. I don't blame your mechanic for trying it, I did.

[dlginla]

Hi Everyone,

here is where I am at, unfortunately being a fireman, I can't get to the airport everyday to work on the plane. So Wed. found someone with a tool to clean the seat for the pin, so took care of that then put the pin back in with a nut behind the spring just to keep it closed. (if pressure would have gone to high I would have shut off engine). Started up the engine, pressure went up to 55ish, where it had before ran with the cold oil, then ran the engine between 1500 and 2000 rpms until it heated up, about 8 minutes. Then the oil pressure started to drop, when it got down to 20 (as I also lowered the throttle to prevent damage), I shut it off. So I figured one last thing to check before taking off the accessory case. The oil gauge and line, just to make sure. So took off the line, it had junk in it, so cleaned it out, hooked it to an external oil gauge, started engine and pressure stayed at about 20 psi. I took off the gauge, started engine and put the end of the line in plastic cup, it was barely squirting out. So although there is some pressure, nearly not enough, and that proved the gauge in the plane is good.
So Sunday morning while the engine is cold, I will take the oil pressure line off again, and flow it in the plastic (since I have to warm up oil to drain). It should have a decent stream at 55 psi, then all doubts will be gone. The case is coming off and the case and the oil gears will be inspected. Either way it has to come off to check the gaskets.

So far thank you all for all your help, I will be sending it to Nickson's on Monday to get started.

I will keep you posted as the progress goes, so this might be helpful for someone else.

[FredMa]

your oil pressure line is not supposed to have much flow. It only needs a small amount for your gauge to provide an accurate reading. It is restricted in case your pressure gauge or line fails. You don't want the cockpit flooded with oil or worse yet, your engine to fail due to a leak. Hopefully your problem ends up being something simple but there are more serious problems that could cause your pressure problem. There have been several cases where the crankshaft journals have allowed the bearings to crack the engine case as the case halves are bolted together, perhaps due to the bearings rotating before final torqueing of the case halves. Not trying to scare you but this is something you need to be aware of.

[T. C. Downey]

There have been several cases where the crankshaft journals have allowed the bearings to crack the engine case as the case halves are bolted together, perhaps due to the bearings rotating before final torqueing of the case halves. Not trying to scare you but this is something you need to be aware of.

This will seize the crank, and not cause oil pressure to drop over time as it heats up.

This engine has a large internal leak that is bleeding off all the oil that would normally be bypassed by the pressure regulator.

There are only two places this can occur, and not make a mess on the floor, first is the gasket between the case and the accessory case where the oil passageway travels across the seam where the gasket must be reinforced by a copper gasket. This gasket can be installed with the copper gasket on the right leaving the left oil passage way unprotected. this will blow out after about 30 minutes of flight when the oil gets warm and the cases swell.

The other is the oil pump itself when the 4 bolts that hold the cover on become loose, they are to be safetied but you know sh-- happens.

[HA]

or somebody didn't measure the new parts out of the box and there's an undersize bearing in there somewhere

[FredMa]

This problem most certainly can be caused by crankshaft bearings. The instance I witnessed firsthand was on a new engine that had been run too long without noticing that there was no oil pressure. the crank bearings were shot and even after the cause of the low oil pressure had been corrected the engine would would have normal oil pressure after start then low pressure as soon as the oil warmed up exactly as described here. That is when it was decided to tear the engine down and the cause was discovered.

[bigrenna]

delete

[T. C. Downey]

This problem most certainly can be caused by crankshaft bearings. The instance I witnessed firsthand was on a new engine that had been run too long without noticing that there was no oil pressure. the crank bearings were shot and even after the cause of the low oil pressure had been corrected the engine would would have normal oil pressure after start then low pressure as soon as the oil warmed up exactly as described here. That is when it was decided to tear the engine down and the cause was discovered.

This engine had good oil pressure for the first 30 minutes of flight, the wrong sized bearings would have had no/low oil pressure from the first minute.

If the bearings were the wrong size as in a -.oo2 bearing on a standard crank the engine would have been seized and the crank would not rotate. If you have a .002 under crank fitted with standard bearings it will knock like crazy. and would have thrown a rod by now. and shown no oil pressure from minute 1.

[dlginla]

Hello Everyone,

Here is an update: Sunday the 27th I took off the Accessory Case, gasket was correct (hard to put on wrong with the pilot pegs), the four bolts where wire tied to the oil pump. So I sent in the case to Nickson's on Monday morning the 28th, I will call tomorrow to see whats up. I left in the pin and spring and the oil gears, all to be checked. So I should find out this week if the Case is the cause. If not, then the engine will have to come apart for inspection.

Sorry for the delay info, I was out of town for a week. Nothing to do anyways, no airplane to fix and fly.

[T. C. Downey]

Hello Everyone,

Here is an update: Sunday the 27th I took off the Accessory Case, gasket was correct (hard to put on wrong with the pilot pegs), the four bolts where wire tied to the oil pump. So I sent in the case to Nickson's on Monday morning the 28th, I will call tomorrow to see whats up. I left in the pin and spring and the oil gears, all to be checked. So I should find out this week if the Case is the cause. If not, then the engine will have to come apart for inspection.

Sorry for the delay info, I was out of town for a week. Nothing to do anyways, no airplane to fix and fly.

Wow I woulda bet.

[FredMa]

Sorry to hear that your problem is not the gasket. That would have been the simplist and least expensive cause to fix. The pump I believe is considered a positive displacement pump. The clearance of the crank bearings create the resistance to flow that allow the pump to build up pressure until it reaches that pressure at with the regulator starts to relieve it. If there is an internal leak at any point in the internal passages leading to the crank bearings obviously there will be a loss of pressure. If the leak is large enough you will simply have a low pressure indicated. If the leak is less than what the regulator normally bypasses, you will not notice a problem. If the leak is somewhere in between you can have the indications you have described. A small crack somewhere along the internal oil passageways could start of as a small (unnoticed) leak that grows as the engine and oil heats up and expansion occurs. If you had continued to operate the engine It very well could have seized, but these engines are known to be pretty robust. I would do a very detailed exterior inspection of the case along where the internal passages are, see the pictures in the overhaul manual of where the passages run. I would also try doing internal inspections using a boroscope to look at the crank journals as best you can with minimal disassembly before a complete teardown.

[dlginla]

Update:
Called Nickson's about the Accessory Housing, they said the housing is good, relief pin and seat are good, but the oil gears look bad, so the housing and case are being sent back
and next week I will be able to inspect the gears and reorder new parts along with all new gaskets and put it back together. It is their belief that the gears and shaft are the problem.

I will keep you posted as the info come.

[c170b53]

Wonder what is "bad" about them? Hard to imagine the teeth would lose their hardened surfaces in a short run unless something went through the pump. Tom thought the oil pump plate had backed off; not far off the mark but If the gears have or have wobbled at all, likely the acc. case cavity is worn but for me it's a bit hard to understand how wear which normally takes time to occur would occur rapidly as in your case. Any metal in the screens?

[hilltop170]

Be sure to dimensionally inspect the case bearing journals where the oil pump gear shafts run. Mine were wobbled out to the point that bushings had to be machined and pressed into the case. The gears were bad also due to the loss of tolerances in the bearing journals. I'm not intimately familiar with the back side of the engine so what I have described might not be completely accurate but is what I understood from the engine builder.