Accessory Case gasket mismatch

[Flyfshr]

I'm in the process of replacing the the accessory case and went to install the new TCM gasket and discovered that the copper ring that surrounds the oil pressure relief valve port doesn't match the port on the engine case. But the gasket mates perfectly with the accessory case itself. You can see in the photo that the port isn't centered onto the case wall which I find strange.

I went back to look at my part numbers and model numbers and so far haven't been able to crack the nut. Has anyone run into this issue with their project?

Here are the details
The engine is an O300-C s/n 7974-D-3-2
The gasket is a new TCM gasket using part number: 530011
The Accessory Case is the "old style" on figure 9 in the parts book.

Thanks for the help.
-Tim

[johneeb]

Tim,
I have nothing constructive to add about your problem, just a curiosity about how the gasket lines up with the oil passage in the accessory case?

[hilltop170]

That looks like the old gasket which has been in place, was it leaking?

From a manufacturing standpoint, that could just be manufacturing error in the case. The boss is in the right position, the drilled hole looks out of position. But, I've never seen that end of these engines before so I don't know.

[c170b53]

I thought the pump output was on the L/h side....

[T. C. Downey]

I wonder if these mis fitting gaskets are the cause of the two engine with low oil pressure?

[n2582d]

I thought the pump output was on the L/h side....

I was a bit confused by the picture as well. Turning it right-side-up makes it easier to see that the holes which do not match up are on the right side, next to the relief valve.

If I understand correctly the gasket matches with the accessory case but not the engine case; i.e., the oil passage on the accessory case and the engine case don't line up. It looks to me like the gasket is designed with a large enough hole dia. there to accomodate some mismatch. Isn't there enough play around the adjacent stud so the copper gasket is outside the oil passage hole on the engine case and the accessory case? Continental Parts Interchangeability Catalogue has this chart in it but it seems to me that if the accessory case and gasket p/n 530011 seem to match, that combination should work with any engine case.

I wonder if these mis fitting gaskets are the cause of the two engine with low oil pressure?

Wouldn't a mis-match there, upstream of the pressure relief valve, increase the oil pressure rather than reduce it? The oil pressure is read from a point just before this gasket.

[T. C. Downey]

Wouldn't a mis-match there, upstream of the pressure relief valve, increase the oil pressure rather than reduce it? The oil pressure is read from a point just before this gasket.

No leak will increase pressure. it simply bleeds off pressure before it gets to the engine case, bearings and cam followers, and lastly the oil pressure relief valve.

[n2582d]

No leak will increase pressure. it simply bleeds off pressure before it gets to the engine case, bearings and cam followers, and lastly the oil pressure relief valve.

Agreed, but the gasket in the picture looks more like it would cause a restriction rather than a leak.

[T. C. Downey]

No leak will increase pressure. it simply bleeds off pressure before it gets to the engine case, bearings and cam followers, and lastly the oil pressure relief valve.

Agreed, but the gasket in the picture looks more like it would cause a restriction rather than a leak.

Even a restriction there would decrease pressure, the gauge port is the last thing in the system.
There simply wouldn't have enough flow thru the restriction to feed all the bearings and have enough pressure left to read on a gauge.

[Flyfshr]

Tim,
I have nothing constructive to add about your problem, just a curiosity about how the gasket lines up with the oil passage in the accessory case?

Yeah, the gasket does line up perfectly with the case which makes me wonder if deeper issues are going on here.

[Flyfshr]

That looks like the old gasket which has been in place, was it leaking?

From a manufacturing standpoint, that could just be manufacturing error in the case. The boss is in the right position, just not the drilled hole. I've never seen that end of these engines before so I don't know.

Long story short it is a new gasket but... full disclosure... I did try to install it and it did leak. I lined up the gasket with the accessory case but did not do the same with the crank case assuming they would be the same. I plan on ordering a new one once I figure out the root cause. I'll call it a tax for being stupid/hasty/not remembering what the word assume does.

[Flyfshr]

I thought the pump output was on the L/h side....

I believe that may be the way it is with the "new style" accessory case.

[Flyfshr]

It looks to me like the gasket is designed with a large enough hole dia. there to accomodate some mismatch. Isn't there enough play around the adjacent stud so the copper gasket is outside the oil passage hole on the engine case and the accessory case?

Thanks for looking into the part numbers. Confirmation is nice to have in this business.

The gasket is a very snug fit around the studs. I'm concerned that enlarging the holes around the studs and bending the gasket into place would lead to potential tears and leaks.

[n2582d]

I agree with Richard, the galley hole looks like it should have been drilled further inboard. I've got a crankcase I can take a picture of when I get home Sat. to compare with yours.

Even a restriction there would decrease pressure, the gauge port is the last thing in the system.
There simply wouldn't have enough flow thru the restriction to feed all the bearings and have enough pressure left to read on a gauge.

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.

Front View.jpg (59.33 KiB) Viewed 8894 times

[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.