What is the 1/4 pipe plug on the left side of the engine block used for?

On older engines that I am familiar with, the hole had a pet cock to drain the block and flush out rust and crud.

On this one there is no water, but only dirty oil residue, like you would find in a vent chamber.

Nothing shows up when running the engine.

The accelerator return spring hooks on this plug.

Help.

I think you are looking at the oil filter return plug or the oil input line connection. It is of no cercern, if you are not planning to install an oil filter.

If its in the center of the block its the oil filter line outlet connection port. If its way to the rear its the cooling system drain plug. The cooling system would be 1/4" and the oil is 1/8" pipe . When the cooling system plug is removed coolant should run out. If it dosen't probe around in the opening with a stiff wire. The passage is usually plugged with rust and sludge.

Thanks for the responses.

I said 1/4" plug but forgot to mention rear of block.

The engine does have an oil filter.

Just never have seen this port plugged up completely. Planing on changing the coolent, so I will try a little air pressure to dislodge the plug.

Thank again, will keep you posted.

25 Speedster, when you are done flushing you block exchange the plug with a petcock...Oscar

It also took more then air pressure to unplug my 61 235. I had to use a phillips screw driver and tap it with a hammer. When you start getting gunk out flush the block with a good acid flush until the water runs out in a steady stream. You will be supprised how much cooler you motor will run...Oscar

Thanks, Ray, Chevgene, Oscar.

Had a dry hole having scraped, gouged, and blew with air hose, still nothing. Fitted a push on 3/8" flex hose with 1/4" mail pipe thread end in order to force air into the passage. First few trys, nothing, than I heard gergling but no air bubbles. One more time, held it longer, looked into the open cap of the radiator when the gusher came. Seams like a gallon of antifreeze hit me in the face and covered my head and the rest of my clothes.

After showering again and dry clothes I finished flushing the crud out of the now open lower back port and installed my mechanical tempreture gage in that same port.

Interesting that it takes about 30 min. of driving to get the temprature up to 180 deg. Must be very little circulation in that area and the heat rises by association not circulation. No wonder the crud builds up in that area.

Thanks again for your collective help.

The plug is at the lowest point in the block. The crud tends to settle therre but believe me there is much more on the bottom of the water jackets.

I hope I am reading you wrong,

The temperature sending goes in the HEAD. Can't imagine what combination of fittings allowed you to install it in the block. That is why it takes so long to READ a temperature.

There should be a place on the left rear of the head for you connection.

Ray, don't get upset, I am only doing this on a temporary bases, always wanted to know the temperature low down and opposite of the discharge where all the heat leaves the engine.

The electrical gage on this set up is less than reliable. Had to install an extra resister in the gage circuit to get the indicator to read in the center and that after changing out the sending unit.

I have never had a temperature problem on this engine, just temperature indicator problems.