Rebuilt 300D loosing oil pressure

[dlginla]

Hi All,
I just had my Continental 300d rebuilt and installed. Running with Mineral oil till broke in.
Problem I am having is as the engine warms up, the oil pressure goes down. The pin and spring have been replace with new, and we noticed that there are some small scratches in the seat for the pin on the accessory case. Could this be causing the oil pressure to drop from 50 to 10 as the engine warms up?

Also, is there a tool to cut a new seat in the case. Probably only need about 1/32 cut. Where would I get one.

If you think this is not the problem what would you suggest? All plugs are good, no oil on them, no oil leaks, engine holds good pressure for about 15 minutes until hot.

Thanks in advance,
Dan

[bagarre]

Was the accessory case and pump gears verified to be in spec?

[Bruce Fenstermacher]

Very hard to judge with out more info . How many hours since overhaul? What did the oil pressure do in the first hour of operation? Do you have a filter or screen and have you found any metal in it?
What is the max pressure you see on startup when the engine is cold and what oil are you running. What is the OAT.

Here is the just of it. The relief valve is just that. It relieves high pressure. When at operating temperature the valve is closed.

If the valve is leaking you will have low pressure so you are right to look at it and the seat. The next stop is likely your main bearings. I don't know of a grinder for the seat. I have carefully lapped the seat and piston with valve grinding compound. At the least with a few spins you should be able to see if the valve is seating. Don't be in denial as I was and run your engine till you destroy your crank.

[dlginla]

This is first overhaul at 1500 hrs. First running of engine had low oil pressure, which it didn't have before overhaul. We changed out the relief spring, then oil pressure went up to 55 when cold and dropped down to 15 when hot. It was flown for about 20 minutes, then landed because of drop in pressure. The bearings are new and crank was yellow tagged. There has been no metal found in previous oil.

The Maximum pressure at cold startup is 55lbs. The oil is Shell mineral. I don't know what OAT stands for.

Could the bad seating of the relief pin allow enough oil to escape to drop the pressure down to 15 when it gets hot?

Thanks for the advice! I definitely will not be flying it until this issue is resolved, I have to much $$ in this engine.

[170C]

OAT = outside air temperature

[n3833v]

Yes, a bad seat when oil heats up can definately drop pressure. Check the seat as Bruce said to see how the seat is.

John

[GAHorn]

"I just had my Continental 300d rebuilt..."

" How many hours since overhaul? "

I'll bet it was neither. I'll bet it was a "repair".

The high pressure is at what indicated oil temp? The low pressure is at what indicated oil temp?

Was the crank machined? or was it merely measured and "yellow tagged" still "within limits"....?
Was the oil pump and gears recertified? or were they merely reinstalled ...?
Were the new main bearings properly sized for the actual measurements of the crank...?

This sounds like worn oil-pump and wrong or worn main bearings.

Who did this work? Are you certain it was properly repaired according to the TCM Overhaul Manual..? ....or was this simply a good ol' boy rattle-can "overhaul"...

[dlginla]

We are looking into where to send the accessory case to have the seat repaired.

Yes, a bad seat when oil heats up can definately drop pressure. Check the seat as Bruce said to see how the seat is. John

This is our belief also.

"I just had my Continental 300d rebuilt..."

" How many hours since overhaul? "

I'll bet it was neither. I'll bet it was a "repair".

The high pressure is at what indicated oil temp? The low pressure is at what indicated oil temp?

Was the crank machined? or was it merely measured and "yellow tagged" still "within limits"....?
Was the oil pump and gears recertified? or were they merely reinstalled ...?
Were the new main bearings properly sized for the actual measurements of the crank...?

This sounds like worn oil-pump and wrong or worn main bearings.

Who did this work? Are you certain it was properly repaired according to the TCM Overhaul Manual..? ....or was this simply a good ol' boy rattle-can "overhaul"...

This was done by the TCM Manual, all parts were replaced or inspected and certified to be within limits. I live in Los Angeles, the serviceable parts were sent out, machined, yellow tagged and sent back. This was an overhaul. All Cylinders, pistons, etc. are new.
Could I have gotten inadequate work done on what was sent out? Of course, and if we take off the accessory case we will go over the pump gears to make sure that is not the problem.
I do not have an exact oil temp gage, only the one in the plane. Outdoor air temp was about 75 while testing.

So our next step is to repair the relief pin seat.

[T. C. Downey]

Some body put the wrong gasket on the accessory case to case seam.

[GAHorn]

Advisory Circular 43-11 explains the differences between "overhaul", "rebuilt", and "remanufactured".

Most C145/O300 engines are no longer "overhauled"....they are "repaired"...and if properly repaired, they will meet new or serviceable limits in most major respects. However, in the majority of cases, for example, the accessories such as carburetor, magnetos, pumps, lifters, etc.are not given the required service to meet the definition, therefore the engine does not. Even tho' the cam or crank or lifters may be sent out and "yellow tagged"...the actual work performed on them often do not meet the standards required to meet the standard of overhaul. Most owners mistakenly use the terms "overhauled" and "rebuilt" erroneously because each and every operation specified in the TCM Overhaul manual is not followed to the letter, nor is the engine treated so as to qualify as "zero time" since rebuild.

AC 43-11_CHG1.pdf

Reciprocating Engine Overhaul Terminology and Standards

(71.77 KiB) Downloaded 281 times

dlginla, I was not attempting to denigrate your particular engine or the work performed upon it...I was just focusing on the oft-improper useage of the terms. I hope the problem is indeed so minor as to be the pressure relief valve. That valve has a specified spring also. (Relying upon memory, it has a Blue paint upon it for identification, and a specified strength at a specified length of compression, which I will attempt to retrieve and post in this thread. You can easily test the spring yourself by merely using a bench-vise to compress the spring to specified length, in-series with a weight-scale.)

PS: The oil pressure relief spring should be compressed to 1.56 inches and the pressure should be 6.06 to 6.31 lbs if new, and 5.75 lbs minimum if used.
Another method to check it is to cut a tube, rod or other piece of metal to 1.56", then place it upon a firm surface of an accurate scale (postal or bathroom, etc).... within the coils of the spring. Now, using a flat piece of metal on top of the standing-spring ...compress the spring while observing the scale reading. When the scale suddenly increases due to the rod having been contacted (the spring has compressed to the length of the rod)....you can make note of the maximum scale reading achieved prior to that increase, and compare it to the specification.

[Bruce Fenstermacher]

The madness behind my questions was to try to figure if I felt you had low oil pressure throughout the range of oil temperature. I spent about 50 flight hours studying this on my C-85 which is nearly the same engine minus 2 cylinders. Unfortunately by the time I eliminated all possibility of accessory case ie oil pump and relief spring problems, I cooked a $2500 crank because the problem I refused to believe was always the new bearings and the certified crank that didn't play well with the silica left in the case that wiped out the bearings and crank.

Since you've only run it 20 minutes I doubt you've wiped out the bearings and crank. I'd compare the old spring pressure to the new. Figure out why it was better with the new spring. How did the accessory case seat get damaged would be my question. Again I'd do a quick lapping test to see if in fact the piston is not seating then go from there. As Tom suggested make sure the correct gasket was used. We also recently had someone with low oil pressure find the gasket blown out as I recall releasing pressure like a stuck open relief valve.

I know disassembly of the engine is not what you want to hear and it is not what I'd do until I investigated the accessory case fully from all angles. Just don't get blinders as I did and refuse to see the obvious should you run out of ideas.

[dlginla]

Thank you guys for your insightful answers. Me, not being the mechanic of the plane, only the owner and pilot have learned a lot since starting this project with my A&P, who has 40 years exp. I wish I had all the right terminologies for you, but I don't have the knowledge. I do know that one place that some of the cases were taken to (accessory case included) did the worst work, and they pride themselves on rebuilding Continental engines. We have no idea how the pin seat was damaged. It would seem you would have to go out of your way to stick something in there to create a burr, and of course it wasn't thoroughly inspected before sending in and upon receiving it, you would think you could trust a business that only did continental engines and yellow tagged the case .

Thank you for the spring information, that is the first thing I did is get a new spring and pin and test the spring, we (my engine builder) even put a nut behind the spring to add more force to see the results and it still dropped in pressure. So before taking off the accessory case we will create a better seal against the pin (temporary) to see if the pressure drops, if not, then it is the damaged seat, if it does drop, than looks like the case comes off to check the oil pump and and the gaskets used. And thanks for the gasket info, we had not discussed that as a problem, but it might be.

I will keep you all posted!

[cessna170bdriver]

If you haven't yet found a place to send your accessory case, Nickson's Machine Shop up in Santa Maria, CA did good work for me in 2006 on all the case and rotating parts. Their website doesn't seem to be there any longer but they still have a yellow pages listing:

NIckson's Macine Shop
914 W Betteravia Rd
Santa Maria, CA 93455
(805) 925-2525

[dlginla]

If you haven't yet found a place to send your accessory case, Nickson's Machine Shop up in Santa Maria, CA did good work for me in 2006 on all the case and rotating parts. Their website doesn't seem to be there any longer but they still have a yellow pages listing:

NIckson's Macine Shop 914 W Betteravia Rd Santa Maria, CA 93455 (805) 925-2525

Thanks, someone else just gave me Nickson's number, along with Divco in tulsa OK

Tomorrow will take me to the next step!

[T. C. Downey]

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.