Engine locking up

Ref: 1998 5.4 2V engine issue. Engine totally rebuilt. Cranked up fine and seemed ok. After running some time engine starting missing. Checked compression and all 8 cylinders ok. Ran scope into cylinders and saw antifreeze. Ford installed a cross fitting into the throttle body that ran antifreeze thru it to heat air coming from the valve cover to the throttle body. Inspection revealed that the tube running thru this fitting had rusted thru and was sucking antifreeze into the throttle body. Pulled intake and had a lot of antifreeze in it. Cleaned everything up and reinstalled intake. Compression test showed all cylinders the same. Engine cranked up ok and was driven about 20 miles before it had a little miss in cylinder 8. Plug pulled and again checked compression, all ok.
Checked fuel pressure and ok. Figured #8 coil pack wire had come loose. All coil pack wiring was checked but on the last one the engine locked up. I mean solid. Pulled starter to confirm it not was the issue and it was not. Now the good part. If the crank is rotated CCW about 10 degrees it frees up. Then the crank can be turned exactly 3 turns ,CW, before it locks again. I mean it locks up at the same spot. This process had been done many times and same results.
I am not experienced in the 5.4 but can anyone share their thoughts on where the problem could be located. Have not pulled the engine but if the issue is in the timing area that can be accessed without pulling the engine. Any help will be appreciated.

Does your oil show antifreeze contamination? Is it milky? If so I would remove the engine for a complete tear down and inspection. There are many small parts inside that do not like antifreeze instead of oil. Lifters may pump up and valves may contact pistons. Cams can seize in the heads.

Anti- freeze will wipe a bearing in no time. If you have a bunch in it and have run it for 20 minutes, doesn't sound good. I'm afraid you have a bunch of work ahead of you.

Oil and filter was changed when antifreeze was first observed in the cylinders. Oil looks great now. Remember it was run at least 20 miles before the issue occurred. I am going to let it set for a few days and try turning it. If it turns it could be a lifter that pumped up too much and a piston is hitting a valve. The interesting thing is why does it lock up at the same spot after exactly 3 turns of the crank. Will advise in a few days.

Highway Man said:

Oil and filter was changed when antifreeze was first observed in the cylinders. Oil looks great now. Remember it was run at least 20 miles before the issue occurred. I am going to let it set for a few days and try turning it. If it turns it could be a lifter that pumped up too much and a piston is hitting a valve. The interesting thing is why does it lock up at the same spot after exactly 3 turns of the crank. Will advise in a few days.

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Let engine set for two days and still locked up. Turned crank CCW for about one inch on OD of crank pulley. It became free and then turned the crank four times without a lockup. Engine turned very free, no hard spots. At this point I am assuming that if it was a crank issue it would lockup every turn of the crank which it does not. I have researched looking for a 3 to 1 relationship but could find none. At this point the issue has to be in the area of timing chains/ cams. Maybe new chain guides have broken or some other failure in this area. Next step is to pull the timing cover and look for the problem. As this is a weird issue I will reply as to what we find.
PS- I like my 429's better!

Highway Man said:

Let engine set for two days and still locked up. Turned crank CCW for about one inch on OD of crank pulley. It became free and then turned the crank four times without a lockup. Engine turned very free, no hard spots. At this point I am assuming that if it was a crank issue it would lockup every turn of the crank which it does not. I have researched looking for a 3 to 1 relationship but could find none. At this point the issue has to be in the area of timing chains/ cams. Maybe new chain guides have broken or some other failure in this area. Next step is to pull the timing cover and look for the problem. As this is a weird issue I will reply as to what we find.
PS- I like my 429's better!

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In reading this with it first running OK after repair and then hard locking, with only way to unlock is to reverse rotate, I'm thinking it jumped time.