zero pressure at compression #5?

the motor threw a rod on 95 windstar (looks like shotgun blast on oil pan from the inside) so I replaced the motor. Since all 1995 Windstar 3.8 is the only year that is not interchangable with any other years and junkyard asking too much for it so I turned to 91-94 Taurus 3.8 and found cheaper one. (Only thing needs to be switched is the teeth gear behind crankshaft harmonic balancer for crankshaft position sensor and also the water pump COVER because windstar one has the bolt holes to hold the crankshaft position SENSOR.

Anyways... as I unassembly Taurus 3.8 motor to replace the head gaskets and valve seals and somehow broke one bolt that holds rocker arm on one of the head (suprised the heck out of me) so i took the head off old windstar motor and put it on taurus (its compatible).

Put the motor back together and got it running but its making lot of popping noises.. so I went and did compression test on each cyclinder (at this point, i really really truly got sick of working behind the motor way under the dash i practically had to climb in)

Compression #1,2,3,4, and 6 I got ~150-175psi but ZERO on #5.
I just realized that the head i swapped off windstar motor was on the same side where the rod blew and it was #5 piston. I am going to take off the head of the block and see if the valves or head are bad (I HOPE)
and im not truly expert with heads... what do i look for? the valves and pushrod moves normally as i turn the motor over with valve cover removed. maybe chipped valve? do i need to take the head to the shop to see if its bad or can i find it myself?

any input would be appreciated... not too eager about taking the block out if it turns out to be bad rings (i replaced oil pan on taurus motor and there was no pieces from rings or anything)

Later!

1. Are you sure the valves on that cylinder are lifting... and lifting what looks like the right amount?
2. Is the piston actually moving as it should? Pull all the plugs and turn the engine by hand (only in the right direction). If you can get the right eye angle, look into the plug hole to watch the piston. If you can't see into the cylinder, you may have to "feel" the piston movement using a long slender rod of some sort... I have a very long phillips screwdriver that I use for this task. Does the piston come to TDC when the valves are closed on compression stroke?

It would take a very large chip off of a valve to give you zero pressure. With the plugs out, dump some(1 - 2oz.) engine oil into the combustion chamber... have someone crank the engine while you watch to see if the oil gets "wheezed" out of the cylinder. (Stand to one side for this observation...don't want to mess up that blazer!).

i took off the head and crank the motor (clockwise) and the piston seems to move normal and i check the wall and seems good shape and no stratches or anything and top of cyclinder looks good.

now as for the head... it seems normal from top and bottom however there is SMALL bend in head's combustion chamber (the big hole, not the valve holes) at one area and i think that might be reason i didnt get any compression reading. but its hard to believe that tiny bent could give zero reading instead of low reading.

perhaps the valve is bent? I will need to take the head apart to inspect the valve. while the head was still on the motor, i watched the lifters going up and down while a friend crank the motor and it appears normal movement and height. am i missing something here???

I am not sure what you mean by a bend in the combustion chamber but if your piston seems to be in good shape then you must have a valve not closing or a crack in the head or a leak somewhere else. How are you measuring compression? A small leak would lose compression but it would show some compression initially. It sounds like a valve is open when it should not be. Not to oversimplifiy but there has to be a big gapping area for the leak I would think. Consequently is it possible that when the piston moves down it creates negative pressure (from a valve not opening) and shows normal pressure when it "compresses"?

Just throwing ideas.

Yes, you may have a bent valve stem that would keep the valve from seating.
I not sure I visualize the "bent" in the head that you mentioned. Are you saying the head does not have a flat sealing surface?
Years ago I did my own head repair, but there are now many good shops in my area that specialized in cyl head check-out and repair. Life is easier... just to give them the heads for a check-up.

best way to put it this way with the small bents in the head... imagine somehow the rod bearing got loose and the piston travels tad bit farther thus hitting the head and the line where head and combustion chamber meets are pushed inside the chamber. there is two bents on bottom right and bottom left of the circle. the man at the machine shop said i could replace the valves and put new ones in and reuse the head.

while i was at the shop, they took out the valves and yes, exhaust valve were bent around 10 degrees... that explains why i recieved zero reading on compression test.

I already picked up a used head off windstar with blown engine from junkyard and the rocker arms and pushrods are pretty rusted out and the rest looks fine. the block looks fine on the side close to radiator on blown engine.

Now, I am not too sure if I just swap the valves (intake and exhaust) on #5 and reuse the head like guy suggested or clean up the head i got today and (also replace the valve seals) put it on the motor??? remember this head comes off the blown motor and i hadnt the chance to turn the motor over to see pistons clearance.

Im gonna put on either head tonight so quick responses would be appreciated!!! Thanks ya'll for the helps!!!

I would be inclined just to let the machine shop do the repair on the head that you have already given them. They will replace valves that are bent with new ones and reface the others. They should check for head cracks ... which they can reweld/refinish.

I'd definately send whichever head off to a machine shop for rework... I'd be knda leery of any "bends" in the head itself, personally.

ok... the valves has been replaced and put back on the motor and it starts right up without any popping noises... but now the temperature shot up to high on the gauage and i turned the motor off.

now i am getting really frustrated... what would cause the temperature to go up real high after running for like 5-10 minutes? i filled the radiator with all water and plan on flushing it and fill with antifreeze after i am done working on the engine.

could it either be waterpump or thermosat?? im too tired, cold, and hngry to think right now...

On earlier Windstars, and any other "older" unit with the radiator cap, it is impossible to get a good fill on the cooling system in one filling. Air gets captured in the engine and can be the dickens to get out.
Normally it just takes slowing adding coolant and replenishing the radiator as the water pump is turning and working the air out. It helps to detach some coolant hose while the engine idles.
The above is especially true when we're talking about a minivan with hoses going back to a rear heater.
If the thermostat gets plugged ... the air purging process cannot not happen as air can't get out of the top of engine. Some folks remove the thermostat for the initial fill and start-up after engine repairs.
Newer cooling systems, with remote high pressure expansion reservoirs, are more "self-purging" and no problem to fill.

Be careful about using only water (no rust preventative) as a coolant. Ferrous metal can rust up very fast...especially hot metal. I always fill with the anti-freeze going in first.

The cooling system is designed to run at around 16psi, so you can't just run it without the cap on.

I used the "rad cap" as an indicator of the older systems with overflow reservoir bottles that were not under pressure and operated at atmospheric pressure.

About '99, or so, the Windstar became radiator cap-less. In this design the overflow reservoir is part of the pressurized volume...same as the radiator. Much simpler. Easier to fill and purge.

I believe the offical ford thermostat has a small ball valve, at any rate,
I suggest the drilling of a 1/16 hole in any thermostat in any vehicle.
It won't slow warmup of engine too much, helps trapped air get out
of system. I also have a theory this prevents thermal shock to the
heads that comes from a closed thermostate going open, and the really
cold water from radiator starts flowing into hot engine.