1998 F150 w/4.2L

1998 F150 w/4.2L V6 62,000 miles
Dads truck developed a knock. From talking to you guys and looking on the net I find this engine has a history of leaking radiator water past the intake gasket and bending a rod. Was going to have a new engine put in but decided to rebuild the original engine.
Finally get it towed the 60 miles to my house so I can work on it.

When it arrived I started it up to check it out.
Did not knock for the first split second but did not give it a second thought at the time.
Runs with a miss and has what sounds like a deep knock. If you drive it after warmed up it billows what looks to be steam out the tail pipe but the knock stops under a load.

The tail pipe steam and knocks leads me to believe it has the problem above but why does it only knock under NO load. So could it be a spun bearing instead of a bent rod. Does not fit the water lock theory but we will see.

So I pull it in the shop and start taking it apart. Just for kicks I run a compression test to see if I can find what cylinder is knocking.

I get...........
LF 0........ RF 182
181..........190
185..........175

Now this has me really stumped. Why would a cylinder that supposedly has a knock from a bent rod due to water locking have 0 compression. It could have blown out all the rings on that cylinder but that seems unlikely. Then I remember the knock did not start till about 1 or 2 seconds after start up. About the time it would take for a hydraulic lifter to fill with oil on a engine that has not been run for the past month or so.

I am really stumped now and about ready to go threw the trouble of pulling the head only to make sure this is not a valve problem. Recon I should pull the whole motor so I can get the pan off and at least check the lower end.

I guess time will tell as I get deeper into this motor but it sure has me guessing right now.

Your thoughts...............

Cylinder leakage test is a wonderfull thing . Back off rockers, hook up air to sparkplug hole ,,listen ,,,air out intake or exhaust ,,valve. Remove oil fill cap ,,air there,,,piston/ring problem

Hi John,
As mentioned these motors had a history of these problems. The issue at hand is your getting anti-freeze in the oiling system & at least one cylinder, and probrably have been for awhile. Anti frz. will break down oil very fast, so anything the oil lubes the anti frz. has also gotten too, i.e. rod & main bearings, rings, cam bearings,valve guides etc....You should stop looking for a possiable quick fix or the One problem...self assured if it was a intake or head gasket and you fix it...soon after you will find yourself having low end crank problems or oil pressure problems, along with the fact you will start burning a quart of oil every 200 miles ! Been there Done That. After being in the auto repair buss. for over 30yrs i have seen alot. Dont be fooled, just because these engines are made buy Big Car manufacture's that they were not all engineered perfect. On the contrary, As you will find out the big boys cut costs by putting some of the cheapest intake and head gaskets on their products, which in turn cause you ! all these problems. The gaskets you will buy from most private suppliers will be superior.
Your best bet is to replace the engine with a reputable reman. engine (mayby Jasper inc.). I have seen it so mant times, patching up motors spending $$$$$$$ only for the motor to throw a rod 2 months later. Get rid of the cancer (the motor) and replace it. It will have a good warranty and you will have peace of mind.
p.s. - You will need to replace all (4) o2 sensor's on the exhaust, anti freeze will kill them going thru the exahust. Be carefull of the Catalyic converters too !!
Good luck.