Small Block Oil Plug for Filter

[Xcudame]

This comes up time to time and it was suggested to post a separate post on how to address this issue for future reference.

When disassembling and hot tanking a small block Mopar, engine builders love to knock out the plug that goes into the oil gallery located beneath the rear main cap. Then occasionally this plug gets forgotten about and not reinstalled. What this plug does is forces the oil from the oil pump into the oil filter. So you'd basically have unfiltered oil and pressure dynamics become erratic when the plug isn't there. See below for the location of the plug.

 

[Xcudame]

So, how to check and see if the plug is in there after the engine is built and running? It's actually not too difficult. By removing the oil pressure sending unit at the back of the block next to the distributor, a piece of wire can be inserted down the hole. If the plug is there, the wire will only go in about 7 1/2" from the surface of the block. More than 8" and the plug is definitely missing.

 

[Xcudame]

OK, you find out it is missing and you don't want to yank the engine to fix it. It's not fun, but it can be done from under the car. First the oil pan needs to be removed which means draining the oil, most like disconnecting the steering center link, and perhaps removing the through bolts on the motor mounts and lifting the engine. Once the pan is off, the oil pump and rear main cap need to be removed. Then a new plug can be driven into the hole on the passenger side covered by the rear main cap. See photos below. The one photo has the hole circled to install the plug into. The other photo gives you an idea of the depth (red line). Keep in mind the crankshaft is right there with an exposed bearing surface! Be careful not to nick, scrap or otherwise damage the crankshaft main journal! I suggest wiping any oil off the main journal and coving it with duct tape or similar to help prevent an accident. Like I said, not fun, but definitely doable in a few hours.

 

[Xcudame]

Hat tip: @WFHDANB426 and @Challenger RTA

The location photo:

 

[Xcudame]

Sorry for the rust block.