So... this was in my oil drain pan...

[Dynomite]

I say remove the oil pan and check the windage tray to see if there is any place a 1/4 NPT plug can fall through.

If no.......then that plug has been in oil pan for a long time or in your oil drain pan for a long time and nothing to do with your perceived small drop in oil pressure (which you just noticed recently).

If that 1/4 NPT plug can drop through the windage tray........then check that bottom crankshaft plugs are intact. If they are intact......The Cams each have a rear plug about 3/8" OD, 1/8 NPT (.405" O.D.) unlike your 1/4 NPT Plug (.540" O.D).

And.......when you say idle pressure is 25psi-30psi (Hot)....what is your idle rpm?
Makes a difference in oil volume output. And.....what is your oil weight?? (Maybe you are using light weight oil for winter).

[A26B]

Originally Posted by Locobob

It does match those dimensions and it is NPT, it screwed right into the back of one of my air tools... although its path into the bottom of the oil pan remains a head scratcher. If it is a camshaft oil plug how big a deal is this? Oil pressure is still within minimum spec, am I looking at a rapid wear issue?

I should go check this before I start talking about it, but its late & too cold to go down to the shop to verify tonight.

There are 4 oil drain conduits from the cylinder heads, down through the cylinder block and into the oll pan exiting UNDER the baffle. If you will note, one of the 4 conduits is in the far rear corner of the cylinder head, right by the camshaft. The conduit is sealed with the head gasket and the oil pan gasket all the way down to within an inch or so of the very bottom of the oil pan, where an errant cam plug could exit underneath of the baffle tray.

Head gasket


Pan Gasket


and, the Oil Pan (note the exit from the drain back conduit at the bottom of the pan

[A26B]

Are your cams stock? If not stock, where did they come from?

[Dynomite]

Originally Posted by A26B

I should go check this before I start talking about it, but its late & too cold to go down to the shop to verify tonight.

There are 4 oil drain conduits from the cylinder heads, down through the cylinder block and into the oll pan exiting UNDER the baffle. If you will note, one of the 4 conduits is in the far rear corner of the cylinder head, right by the camshaft. The conduit is sealed with the head gasket and the oil pan gasket all the way down to within an inch or so of the very bottom of the oil pan, where an errant cam plug could exit underneath of the baffle tray.

That errant cam plug is most likely a 1/8 NPT (.405" diameter).......unlike the 1/4 NPT (.540" diameter) plug found in oil pan.

[Locobob]

Originally Posted by A26B

I should go check this before I start talking about it, but its late & too cold to go down to the shop to verify tonight.

There are 4 oil drain conduits from the cylinder heads, down through the cylinder block and into the oll pan exiting UNDER the baffle. If you will note, one of the 4 conduits is in the far rear corner of the cylinder head, right by the camshaft. The conduit is sealed with the head gasket and the oil pan gasket all the way down to within an inch or so of the very bottom of the oil pan, where an errant cam plug could exit underneath of the baffle tray.

Head gasket


Pan Gasket


and, the Oil Pan (note the exit from the drain back conduit at the bottom of the pan

Thanks Jerry! This is sounding like a very feasible scenario. The cams are stock. Sounds like there are differing opinions on the size of the plugs though? Can we get a consensus on the size of the plugs? Anybody have one they can actually put a caliper to? or any other plug in that area that could conceivably make its way down one of those 4 passages from the cylinder head? Judging by the pics of the windage tray and Marks input regarding clearances as well as the fact that the crank plug I bought doesn't match the plug I found I think we can discount the idea that it came from the crank.

[Dynomite]

Originally Posted by Locobob

Thanks Jerry! This is sounding like a very feasible scenario. The cams are stock. Sounds like there are differing opinions on the size of the plugs though? Can we get a consensus on the size of the plugs? Anybody have one they can actually put a caliper to? or any other plug in that area that could conceivably make its way down one of those 4 passages from the cylinder head? Judging by the pics of the windage tray and Marks input regarding clearances as well as the fact that the crank plug I bought doesn't match the plug I found I think we can discount the idea that it came from the crank.

I measured diameter of plug across end of cam.
I also found one more source of the Camshaft Plug Diameter in "Solutions".

See Post #26.........Camshaft plugs




Sent from my iPhone using ZR-1 Net Registry

[Locobob]

Originally Posted by Dynomite

I measured diameter of plug across end of cam.
I also found one more source of the Camshaft Plug Diameter in "Solutions".

See Post #26.........Camshaft plugs




Sent from my iPhone using ZR-1 Net Registry

Ah thanks Cliff, so the cam plugs are 1/8 NPT... are we sure that applies to all years? Mine is a 91. If its not a cam plug then perhaps one of those head plugs up by the cam chains? Something else on the cylinder head?

[Locobob]

Originally Posted by Dynomite

I say remove the oil pan and check the windage tray to see if there is any place a 1/4 NPT plug can fall through.

If no.......then that plug has been in oil pan for a long time or in your oil drain pan for a long time and nothing to do with your perceived small drop in oil pressure (which you just noticed recently).

If that 1/4 NPT plug can drop through the windage tray........then check that bottom crankshaft plugs are intact. If they are intact......The Cams each have a rear plug about 3/8" OD, 1/8 NPT (.405" O.D.) unlike your 1/4 NPT Plug (.540" O.D).

And.......when you say idle pressure is 25psi-30psi (Hot)....what is your idle rpm?
Makes a difference in oil volume output. And.....what is your oil weight?? (Maybe you are using light weight oil for winter).

I was just talking to Petey and he also says the cam plugs are 1/8 NPT

Mark told me he removed the windage tray and cleaned the pan so it wasn't sitting in there.

There doesn't seem to be a path from the plugs that are in the heads up by the cam chains into the bottom of the oil pan that I can see.

Assuming the plug is unrelated and was either overlooked laying in the drain pan or fell off the engine from somewhere other than the oil drain hole... oil weight could be a factor. I usually run about a half and half mix of Mobil 10-30 and Mobil 10-40. I ran out of the 10-40 a while back and have been topping off with 10-30 so maybe... but it seemed like kind of a sudden change to me... to the point where it immediately stood out to me as abnormal. IDK maybe its just 2020 stress and I'm losing it lol
Idle seems about where its always been.

[XfireZ51]

And Bob, your not seeing any oil leaks anywhere?

[wfot]

I suggested the rear cam plug a while back, it does appear to be too small, it is 3/8 roughly across the threads. picture is of the early cams '90 - '92

Also I agree with marc, that tray is pretty tightly spaced, I do not think a .525 plug will make it passed the tray

Also I agree with Jerry that the cam plug can sneak down an oil port

I just do not see another spot where a .525 plug can come from based on looking at my bare heads and block.

Is it possible that some cams have a rear .525 plug?? or are they all identical.

I fear that it is an actual drop in oil pressure and idling and light driving will not pose a problem, but if you lean on it, the lack of pressure will show up as a cam or bearing problem..

John