4.6 Thor compression values??

Just about to check the compression on the cylinders as suspect head gasket failure but dont have my copy of RAVE handy, can someone please tell me what sort of pressures I should be expecting as the norm.


Thanks

CHris

Post MY99 HC Engines are 9.37:1 and LC Engines are 8.37:1 so I would expect...

HC to be around 138 psi when new
LC to be around 123 psi when new

EDIT:

Just been reading and it looks like CR is not as simple as multiplying the Compression ratio by atmospheric pressure (I think - I don't know my specialism is in Gas Turbines)

All cylinders should be within 10 PSI of each other. Do it dry and wet, any increase wet (squirt of oil in cylinder) would indicate piston rings worn. Two adjacent cylinders with the same low reading would indicate a cross blow. No increase wet would indicate valves leaking.

wammers said:

All cylinders should be within 10 PSI of each other. Do it dry and wet, any increase wet (squirt of oil in cylinder) would indicate piston rings worn. Two adjacent cylinders with the same low reading would indicate a cross blow. No increase wet would indicate valves leaking.

Click to expand...

So what should happen between dry and wet to indicate all is fine?

Wet test will increase the result a little in a normal test.....if it rises substantially piston rings are worn

TCubed said:

So what should happen between dry and wet to indicate all is fine?

Click to expand...

Wet test will always increase readings on a good cylinder. If you have a single low cylinder. And you do the wet test and there is no change, valves are leaking.