Tell me about counterweight plugs

[Dot Heton]

I finally pulled the 390 out of my truck. It had zero oil pressure when warm.  There are no counterweight plugs in the crank. Was this the problem?

[Dot Heton]

An internet search confirmed my suspicions. Everything is new in the engine, pistons are .004 down in the hole. It ran like a top but I had to tear it down because of the oil pressure issue. They forgot to put the plugs back in after cleaning out the oil galleries.


I'm talking about these plugs, I didn't take pics of my actual crank.

[jayb]

Yikes!  Nothing like an internal oil leak...

[Barry_R]

Those plugs are only found in factory forged steel 391 or 427 cranks.
Is that what you have?

[Dot Heton]

No it's just a standard 2U 390 crank. Why wouldn't they be needed in all cranks?

[Dot Heton]

All I know is there are no plugs at all in my crank.

[thatdarncat]

Your 2U crank is a cast iron crank. The picture you have is a forged ( steel ) crank. Like Barry R. said, forged steel cranks ( like were used on some 427's and 391 FT heavy truck engines ) use the plugs. Cast iron cranks do not use plugs. The hole you are looking at doesn't go anywhere, shine a light into it and you will see. Unless the crank is cracked it won't leak oil there.

[Dot Heton]

Ahhh..... you learn something new every day.

[cjshaker]

The plugs are only needed on the steel cranks because they are cross drilled and the passages enter into that crank pin cavity, so it gets filled with oil. Cast cranks are not made that way.
First, I assume by the way you talked, that you have some pressure as the RPMs come up? Second, you said everything was new, so is this a new build? If it is, you either have some bad clearance issues someplace (maybe rockers and shafts), or possibly the pump relief valve is stuck (or the pump is just junk), or maybe they forgot to replace the plug down in the distributor hole. That last one will cause the issue you described and is an easy mistake for guys that don't know the FE engines. If you pull your distributor out and prime the engine, you will see oil gushing out the hole about half way down, if that plug is missing. That hole is supposed to be plugged as it feeds the lifter valleys. If it's missing, it will require tearing the front of the engine down and pulling the timing cover off to put a plug in.

[Dot Heton]

This engine came in the truck when I bought it, I've run maybe six tanks of gas through it in the two years I've had it. It has twenty some pounds of pressure when stone cold and none when warm. The pistons look new and there's  no ridge in the bore. It doesn't matter though since my new engine will be out of the shop in two weeks. I'm just trying to figure out why it's so bad. The rockers and shafts are badly worn and there's a scuff on the last crank weight from too much thrust. I'm just having fun poking around in the old engine.

[ChiefDanGeorge]

COuld try one of those rods you can drop in distributor hole to spin the oil pump. Although if the issue is in the bottom end it's not going to be visible.

[ericwevans]

COuld try one of those rods you can drop in distributor hole to spin the oil pump. Although if the issue is in the bottom end it's not going to be visible.

I use a thin wall 1/4 six point socket and a speeder handle to get the job done. Just use care when inserting and removing that you don't drop the socket off the end of the handle/extension.

[e philpott]

COuld try one of those rods you can drop in distributor hole to spin the oil pump. Although if the issue is in the bottom end it's not going to be visible.

I use a thin wall 1/4 six point socket and a speeder handle to get the job done. Just use care when inserting and removing that you don't drop the socket off the end of the handle/extension.

and duct tape the socket onto the extension for a little more insurance