I have an 86 with only 71K original on it. 302 V-8. Driving along with a fairly good load I lost power and the truck began to run AWFUL. Barely made it to the next town, truck died completely. Initial checking shows that there is little or no compression in cylinders 3,6,7. The speculation is that the timing chain jumped. If the timing chain jumped, would the valves have hit the pistons? Any other ideas of what could have happened????

 

dude do a search this subject is way over discussed so save everyone some hastle and search for ur answer

 

I don't think its a timing chain issue if you heard no backfiring, that would be a lost of timing ability, thus out of time bad....have you done a check of the codes? Possible...mebie a bad cam (broken for what ever reason) perhaps? Have you used a code reader to check the engine? Will it start and run? There are more questions than you gave answers to...did you do a proper compression check or someone else said they did? It doesn't make sense to me.. that all three cylinders would go compressless and of different cylinders spaced out as the numbers you gave....And another thought is that if its a broken tooth on the cam, (or a slip chain)you wouldn't had made it to another town...

 

6 and 7 are side by side, there is a possibility of head gasket failure. You can have head gaskets fail and only affect one cylinder as well. Was it running hot? I doubt it would be timing chain, if it got far enough out of position to hit any valves, it generally hits them in all cylinders.

 

The way it started acting before it stopped sounds like the Distributer cap and roter button worn out. I have had this happen and had to limp home.
The compression Maybe warped valves, or any number of things.

 

An interference motor is one that, should the valve timing go out of whack, or break leaving the valves open when the piston returns to the top of it's bore, it will bend the valve (or valves). It will not bend all of them, just the ones left open.
The older Ford motors are not interference motors! (I'm not sure about the new ones).
Your timing chain can skip a tooth (jump a tooth). It will run very sluggish. It will not have good compression because the valves are not opening and closing at their proper times. It will not necessarily backfire.
Find your #1 cylinder tower on your distributor cap. From the center tower on the cap take a yardstick and center it across the #1 terminal. Where ever the stick points, make a mark on the truck (tape, marker, etc.)
Remove the distributor cap and turn the motor over until the timing mark reads TDC (top dead center) If the rotor is 180 degrees off, turn the motor one more revolution.
If your timing chain HAS NOT jumped, your rotor will end up aiming within 10 degrees of the mark you put on the truck.
If it has jumped, it will be off 30 plus degrees.
To check timing chain wear, use a breaker bar and a socket on the crank pulley nut.
With the distributor cap off, turn the crank in one direction till the distributor turns. Now turn back the other way and note how far you turned the crank before the distributor starts to turn. This is timing chain play. With a good chain there should be little to none.
Good luck!
Steve G.

 

you can have a chain jump and still run then die completly
down the road
if the chain and plastic gears fail completly as in my
96 300 did then no comp. on cyl. with valves open and
not closing due to the cam not moving and comp. on cyl. with the valves closed

 

If the timing chain is broken and the cam is not opening and closing the valves, how will you have compression on cylinders with the valves closed?
The intake valve must open for the intake stroke to draw air into the cylinder to compress with the valve closing at the bottom.
4 cycle motor;
INTAKE; the intake opens and the piston travels to the bottom of it's bore, drawing in fuel/ air mixture.
COMPRESSION; the intake valve closes and the piston travels to the top of the bore, compressing the mixture.
POWER; the spark plug ignites the compressed mixture, the explosion forces the piston down the bore.
EXHAUST; the exhaust valve opens at the end of the power stroke and the rising of the piston forces the spent exhaust gasses out the exhaust valve.
If the timing chain is broken, the cam does not move, nor does the distributor, nor the oil pump, nor the valves.
Steve G.

 

cant explain physics but it works
try it sometime and you will see it happen

 

I can understand how the negative pressure created on the piston's downstroke (with both intake and exhaust valves closed) would draw some air passed the rings (reverse blow-by) into the cylinder to be compressed, however I could not imagine seeing normal compression pressures.
Unless the test started with the piston at the bottom with cylinder and crankcase pressures equalized, then it would have one, and only one shot at the highest pressure when the piston reaches the top of it's stroke.
When you do a compression test you crank the motor over until the gauge's needle ceases to rise. This takes usually about 10 revolutions of the motor.
Food for thought, thanks MHG.
Next time the opportunity arises I will try it!
Steve G.