Accessory Case gasket mismatch

[T. C. Downey]

Tom, You've a lot more experience than I do. Help me figure this out. Doesn't the oil go out of the accessory case, up the left galley of the crankcase, across the front of the crankcase to the galley on the right side of the crankcase, past the oil pressure gauge port at the back end of the right galley (but still on the crankcase), past the crankcase/accessory case split pictured above then finally to the pressure relief valve? If that is correct and the gasket pictured restricted the hole (and did not allow oil to leak out) then I would think one would see a higher than normal oil pressure as the gasket is downstream of the oil pressure gauge port.

Acc. Case.jpg

Left oil galley.jpg

Front View.jpg

Pressure is caused by a resistance to flow, a pump causes flow, it does not cause pressure. A restriction at the junction we are talking about, will cause a higher pressure between the pump and this restriction, but after that the flow will be lessened and a drop in pressure will be noted on the pressure gauge which is at the end of the oil passages.

[T. C. Downey]

I

photo 3.JPG

As noted in this photo, the crush gasket shown is fully crushed all the way around. and the passageway is nearly open. I don't believe that was leaking or causing a restriction.

[n2582d]

Pressure is caused by a resistance to flow, a pump causes flow, it does not cause pressure. A restriction at the junction we are talking about, will cause a higher pressure between the pump and this restriction, but after that the flow will be lessened and a drop in pressure will be noted on the pressure gauge which is at the end of the oil passages.

Tom, It sounds like we are on the same page but just disagree about the location of the of the oil pressure gauge line tap-in point. Isn't this the oil pressure line here on the crankcase?

Oil pressure gauge port.jpg (43 KiB) Viewed 5721 times

As noted in this photo, the crush gasket shown is fully crushed all the way around. and the passageway is nearly open. I don't believe that was leaking or causing a restriction.

I'd agree except that Tim said it leaked. See the darker "stain" around the passageway? (It's more evident when enlarging an earlier picture.) It gives me the impression that at some point the hole aligned perfectly with the accessory case or a previous gasket. Or is that some sort of bushing in there?

[johneeb]

Tim,
Can you borrow a Acc. Case gasket number 530909 and hold it up to your Crankcase and see if it lines up better.

The Cont. O-300 parts manual lists two different Acc. Case numbers 530007A1 for ABCDE and 627881A1 for Cs (like yours) and Ds.

The parts manual also lists two Acc. Case gaskets, one for all but the 6725 Cover (which I cannot figure out where it is used) and the other for all the rest.

Perhaps you have a parts mismatch going on here.

[T. C. Downey]

Tim,
Can you borrow a Acc. Case gasket number 530909 and hold it up to your Crankcase and see if it lines up better.

The Cont. O-300 parts manual lists two different Acc. Case numbers 530007A1 for ABCDE and 627881A1 for Cs (like yours) and Ds.

The parts manual also lists two Acc. Case gaskets, one for all but the 6725 Cover (which I cannot figure out where it is used) and the other for all the rest.

Perhaps you have a parts mismatch going on here.

There are 3 & 5 bolts Accessory and sump set ups.

[T. C. Downey]

Tom, It sounds like we are on the same page but just disagree about the location of the of the oil pressure gauge line tap-in point. Isn't this the oil pressure line here on the crankcase?

Oil pressure gauge port.jpg

The oil pressure tap, is less than an inch away from the oil pressure relief valve, pressure wise they are in the same place. and last to get oil from the pump.

[T. C. Downey]

I'd agree except that Tim said it leaked. It gives me the impression that at some point the hole aligned perfectly with the accessory case or a previous gasket.

Or is that some sort of bushing in there?

Did Tim actually pull the left mag and crank the engine to see if it was leaking?

The copper ring is a crush gasket similar to a AN1900- crush gasket. If it is crushed 360 degrees, it was sandwiched between two hard surfaces.
None of the case to accessory case fit perfectly, after all they are just a casting hole, not a machine drilled passageway.

I'm hoping we do not have a change in gasket fit, because both engine I know of that have low oil pressure, are resent tear downs, and new gaskets.

[Flyfshr]

Update after talking things over with my A&P. The leak I'm actually not so concerned anymore with and am actually glad that it happened because it pointed out the mismatch. I'm confident the leak can be solved.

Right now I want to put to bed any potential for having problems down the road. TCM so far hasn't come up with any history on this on whether they've seen it before but we're still trying.

The copper ring looks like it is solid copper, smooth on both sides, and similar to one you would put on a motorcycle drain plug or something like that.

The shop actually did have the other style gasket in inventory and I lined it up with the back of the crank case with the same result.

[Flyfshr]

Tom I'll see if TCM can tell me if they changed the gasket design and when. I'll let you know.

I'd agree except that Tim said it leaked. It gives me the impression that at some point the hole aligned perfectly with the accessory case or a previous gasket.

Or is that some sort of bushing in there?

Did Tim actually pull the left mag and crank the engine to see if it was leaking?

The copper ring is a crush gasket similar to a AN1900- crush gasket. If it is crushed 360 degrees, it was sandwiched between two hard surfaces.
None of the case to accessory case fit perfectly, after all they are just a casting hole, not a machine drilled passageway.

I'm hoping we do not have a change in gasket fit, because both engine I know of that have low oil pressure, are resent tear downs, and new gaskets.

[johneeb]

I think Superior sells Acc. Case gaskets, maybe theirs would fit better however that won't solve the miss-match problem.

[Flyfshr]

Thanks for the photo Aryana, it makes it look like whoever built the right side of my crank case just eyeballed it with a hand drill.

As for the gasket... I was unable to get any pertinent history of changes to its design or any other reports of issues with it.

Here is a picture of the aft end of the case of the engine I bought from BL and disassembled.

image.jpg

[hilltop170]

It looks like they oversized the copper crush washer ring in order to accomodate manufacturing tolerances in the location of the cast oil passage hole. Sometimes the tolerances add up and are right at the limit for fit.

Obviously, the gasket did fit at one point in time, say 60 years ago or it would not have made it this far. It might be necessary to cut and fit the copper crush washer into the proper location and hold it with gasket cement until assembly is completed. Once all bolted up, it will not move.