history of the motor
it in a f-series 750 truck use to be a propane truck
compression
#1 30 #2 120
#3 90 #4 40
#5 120 #6 120
#7 30 #8 90

when we got the truck they told us it drop a valve , remove valve covers all valve are still there , check the compression that what i got , my question if it has jumped timing can it cause this , check no.1 tdc the dist. was off about inch and half . please help

 

Jumped timing throws off the cam to crank relationship, and usually you end up with the same compression numbers across the cylinders, just much lower.

Did the pressure gauge jump to those numbers right away, or did they pump up? Pumping off can indicate a weak hydraulic lifter, or the cam being out of time but usually all cylinders would exibit the same behavior if its the cam.

Is their oil in the coolant, or coolant in the oil? Might even be a blown head gasket.

Also, not all valve leaks are obvious to the naked eye. SOmetimes valves do hang down or don't close all the way to the point where you can see it sticking, but sometimes the seat is worn enough that air can get by the seal, even though the valve is closed all the way.

If you have the valve covers off, measure the valve stem height, then turn the engine by hand using a breaker bar (with the plugs out, key off, serpentine belt off) and measure all the valves intake and exhaust, as far as travel. Radical differences might indicate a destroyed seat (allowing the valves in too far), or a bad lifter (valve doesn't move much). etc.

Or, pull the head off and measure it that way.

 

it pumped up on some cylinders, there is no coolant in the oil . thanks for the repley
is the cylinder order on a 460 is it the same as chevy 350