Engine Compression Specs?

[FOMOCOTOSHO]

Does anyone know what the specs should be for compression on a Gen 2 motor? I know the ratio but I'm trying to find out what the individual psi spec should be. Someone told me 250psi on each cylinder but that seems really high. 5 of my 6 make about 200, but the #1 cylinder is low around 160:laugh_ti:. I've checked with Ford and several other sites (Mitchell, AllData, Identifix, Motorcraft Technical Site) and no one has what the spec should be.

Anyone know what this should be? I really need to know ASAP> I just tore down my motor & sending out the heads to be checked & resurfaced; I need to decide if I need to do bearings and piston rings also or am I ok for now?

I know some will tell me to do them now anyway and I agree with you, but that's not what I need to know right now. Please help!!

 

[tompumped]

Before you tore the motor down you should've done a leakdown test to see where the problem lied. It would only be a guess to say you need rings without a leakdown test.
From what i've read on here, these motors can go for a while without needing a complete rebuild.

 

[tompumped]

I also wouldn't recommend just doing rings and bearings without having the block gone through by a machine shop if you don't have the tools/knowledge. Maybe the machine shop will find that there was a valve problem on that cylinder so at least you'd know. I've also seen visual problems with head gaskets that were bad, but they were real bad. Take a good look at the gasket.

 

[rubydist]

The difference between 200 and 160 is larger than you would want at around 20% (you would like 10% or so as the max variation).

These engines have a tendency to have rings stick, especially if the oil isn't changed on time, since they have low-tension rings. Others have reported that simply removing the pistons, cleaning up the rings & grooves, and then reassembling with the 'old' rings has resulted in fixing the compression, improving power and reducing oil consumption. Typically, the cylinder wall will still show the factory cross-hatching, so there is no need to bore or even re-hone the cylinders.

 

[sho_sc]

Does anyone know what the specs should be for compression on a Gen 2 motor? I know the ratio but I'm trying to find out what the individual psi spec should be. Someone told me 250psi on each cylinder but that seems really high. 5 of my 6 make about 200, but the #1 cylinder is low around 160:laugh_ti:. I've checked with Ford and several other sites (Mitchell, AllData, Identifix, Motorcraft Technical Site) and no one has what the spec should be.

Anyone know what this should be? I really need to know ASAP> I just tore down my motor & sending out the heads to be checked & resurfaced; I need to decide if I need to do bearings and piston rings also or am I ok for now?

I know some will tell me to do them now anyway and I agree with you, but that's not what I need to know right now. Please help!!

~210-215 psi on stock pistons and cams.

What proceedure did you use to check them? Warm Engine?? Throttle to the floor (or my favorite cross-over tube removed). Battery charged?? If they come back with #1 low again, try squriting a couple of drops of oil in that cyl. ...

 

[SHOZ123]

Time for Auto-RX!!

 

[FOMOCOTOSHO]

~210-215 psi on stock pistons and cams.

What proceedure did you use to check them? Warm Engine?? Throttle to the floor (or my favorite cross-over tube removed). Battery charged?? If they come back with #1 low again, try squriting a couple of drops of oil in that cyl. ...

My friend who is a technician at my shop (used to work @ Ford dealer) did compression test for me. He used a manual gauge on each cylinder but the first one we tested (#1 cylinder that was low) we tested with the battery cables hooked up to a jump pack. I thought it seemed like it was cranking slow so we hooked up the battery from then on, then the cranking speed was much faster. Is it possible just the slow cranking speed could result in the lower #'s?
He did try and squirt some oil down the cylinder & retest but the oil shot back up his pressure gauge & ruined his gauge (d'oh!) so not sure if it made any difference or not.

What are people's thoughts if I should tear it down to the bones or let it ride?
Nevertheless the heads are getting sent out to be checked, refinished, & cleaned. They will also replace the valve stem seals. When I get them back I will set the valve adjustment with the shim kit I rented from Sho Source.

 

[projectSHO89]

Is it possible just the slow cranking speed could result in the lower #'s?

Yes. Not using the same testing procedure effectively invalidates the test results.

Rings rarely nned to be done on these engines, however, do not pass up an easy chance to replace the rod bearings since they are a definite wear item.

Steve