Big Bart
Tow&Slow
As you mention you need a diesel compression tester. If your glow plug compression tester fitting is the same as the leak down tester you can use that on your glow plug fitting. Harbor Freight has a cheapy (Have to cut off the bottom part of the glow plug adapter as I recall.) Or buy a OTC one for something that will last. Or find a used Snap On off CL, Offer Up, or Ebay.
Ford did not document what proper compression limits should be, they just stated no two cylinders should be more than 20% differnent. I was teasing another member the other day that even though he had zero compression across the board, according to Ford he was good to go!
But for your reference many of us get 400-430psi on compression stroke 5 or 6 with a lower miliage engine. (Under 200K) Some are in the 300's doing the same test but their trucks run good. But if you are in the 200's you should be thinking rebuild VS just heads. Unless your heads are the issue.
The leak down test is basically sending compressed air down each cylinder while it is at TDC in the compression stroke. (That means both valves are closed.) The tester will show how much difference between the air pressure you sending out and what the cylinder holds. In your case you will take off the oil fill cap and listen. You may hear a little air and that is ok. (Some air is likely to get past the rings.) But if you compression test said 225psi on cylinder 5, you can hear and feel air pouring out the oil cap. Well you know your rings or piston are shot and need to be addressed. (No use doing heads, to have to pull the motor in 5,000-15,000miles for rings.
In a normal leak down test you would also listen at the intake manifold opening and tail pipe to determine if either valve is leaking. In your case you are doing a valve job so not needed in this example.
Also you will need to hold the engine at TDC for each piston. (The air is going to push the piston down.) So use a wrench or socket on the damper nut. Also start at say 50psi and go up to 100 PSI if your system will allow VS starting at 100psi and the crank trying to turn. If you are losing more than 25% of the PSI going in and you hear and feel a lot of blow by coming out of the oil fill port, then you should think about doing rings and bearings at a minimum.
Also its probably 50/50 if the valves and piston collided you will need to replace the piston. (Send pics, collectively we can tell you what is the best course of action.) If pulling one piston you would simply replace all the pistons, rings, and bearings. Probably at least have the cylinders honed or bored, cam bearings replaced, if needed decked, and crank checked.
But then you have a long term runner!
Ford did not document what proper compression limits should be, they just stated no two cylinders should be more than 20% differnent. I was teasing another member the other day that even though he had zero compression across the board, according to Ford he was good to go!
But for your reference many of us get 400-430psi on compression stroke 5 or 6 with a lower miliage engine. (Under 200K) Some are in the 300's doing the same test but their trucks run good. But if you are in the 200's you should be thinking rebuild VS just heads. Unless your heads are the issue.
The leak down test is basically sending compressed air down each cylinder while it is at TDC in the compression stroke. (That means both valves are closed.) The tester will show how much difference between the air pressure you sending out and what the cylinder holds. In your case you will take off the oil fill cap and listen. You may hear a little air and that is ok. (Some air is likely to get past the rings.) But if you compression test said 225psi on cylinder 5, you can hear and feel air pouring out the oil cap. Well you know your rings or piston are shot and need to be addressed. (No use doing heads, to have to pull the motor in 5,000-15,000miles for rings.
In a normal leak down test you would also listen at the intake manifold opening and tail pipe to determine if either valve is leaking. In your case you are doing a valve job so not needed in this example.
Also you will need to hold the engine at TDC for each piston. (The air is going to push the piston down.) So use a wrench or socket on the damper nut. Also start at say 50psi and go up to 100 PSI if your system will allow VS starting at 100psi and the crank trying to turn. If you are losing more than 25% of the PSI going in and you hear and feel a lot of blow by coming out of the oil fill port, then you should think about doing rings and bearings at a minimum.
Also its probably 50/50 if the valves and piston collided you will need to replace the piston. (Send pics, collectively we can tell you what is the best course of action.) If pulling one piston you would simply replace all the pistons, rings, and bearings. Probably at least have the cylinders honed or bored, cam bearings replaced, if needed decked, and crank checked.
But then you have a long term runner!