F250 compression #s

[boscoe99]

he started this thread to find out if it was normal for one bank to be lower compression.

Well now he is trying to compare a compression test to a differential pressure test. The apples to oranges thing again.

Either test can have it idiosyncrasies. Either one is not the be all end all. Despite Mr. Rodnuts opinions to the contrary.

Think about where the piston rings are when the differential test is being done. At the top of the cylinder. Where the wear will generally be the least. It is possible for there to be nil wear at the top of the cylinder and considerable wear lower down in the cylinder where the piston ring speed is the fastest.

It is possible to have 0% loss of air during a differential pressure test but for the engine to have considerable piston ring/cylinder wear that will affect the outcome of a compression test and the performance of the motor.

Now why two separate motors would have less compression on the same side and at the same values is the mystery. I don't see a cylinder head as causing the problem. Piston ring and cylinder wear, possibly. But still strange for both to have the exact same situation.

[formula29]

I don't see where I was comparing any tests? as stated from the beginning I am trying to figure out why one bank has 25 psi more compression than the other, for two engines to have the same values does not make sense to me, I did the leak down test as advised to eliminate valves not seating or blow by, so what is left boscoe? you are saying cylinder wear in the middle or bottom of the bore? just on one side of the motor? I guess if one side of the motor runs quite a bit hotter than the other it would be plausible, from what I know anything more than 15% between cylinders in not really acceptable,

[exeter27]

Are you aware that the Harbor Freight is initially built to work at 15 psi? That might be why your secondary gauge failed. In theory it's built to accept a full 100 p.s.i at the inlet - and with your new gauge in theory you could now read secondary pressure up to 100 p.s.i. But, that's a lot of 'theory' in a single sentence. I find nothing worse than diagnosing problem with my diagnostic gear - because they have led my on wild goose chases.

I like Harbor Freight for certain (i.e. non-precise) types of tools. I'd suggest purchase of a good leakdown tester. Better yet, build one very easily. At 100 psi, your ears have a much better chance of hearing a leak if there is one.

Speaking of that, I've not done a leakdown where I haven't seen some leakage. Good engines seal very well, but they still leak minimally. I'm suspect of your leakdown tester.

Keep at it - you will figure it out. And you should figure it out - as the guys said, if it's off by that much in compression tests - the engine(s) will fail at some point.

p.s. one thought. Is it possible that both engines were disassembled at the same time? If so, perhaps one bank of heads were swapped between engines (see 99yam40s post - with a twist!). That leads to two engines - each with a thick and a thin head - with similar oddities with compression values . But, this theory is a bit of a reach!

[99yam40]

But that should have lead to the different banks on the motors being different not the same side on both motors

At least he has been able to eliminate some things as the cause.

it would be nice to find markings on the heads that would lead to what has happened

[formula29]

The leak down gauge is nothing more than a manifold with a regulator, as long as you have 2 functioning meters on it that's all you need, I have about beat this horse to death here, if its not a matter of a head gasket or wrong head I just don't know, time to take it back to where I bought them.

[TownsendsFJR1300]

Correct, I connect the gauge with 0 psi, increase pressure up to 100 psi and both needles rise together and hold at 100 psi, I have also checked the gauge without it connected to the engine without andy backpressure and the secondary only reads about 70 psi

With the line not connected to the engine, there shouldn't be ANY PSI to peak of, much less 70.

Here's my unit, NOT hooked to an engine, free flowing air. 90 PSI set at the gauge, 10 psi showing (I'm assuming it slight back pressure in the hose, etc). There's something not correct with your gauges..

[99yam40]

The leak down gauge is nothing more than a manifold with a regulator, as long as you have 2 functioning meters on it that's all you need, I have about beat this horse to death here, if its not a matter of a head gasket or wrong head I just don't know, time to take it back to where I bought them.

I agree if the valves and rings (cylinders) are all sealing then the only thing that could cause the different compression #s is size/volume of the combustion chamber.
head ,head gasket thickness, or piston.

I have read that some motors have different compression on different cylinders designed into the motors, but never heard of a whole bank designed that way.
We need someone else with F250s to run compression tests on their motors to see what they get to compare to.

Edit: just had a thought, what if you have over sized pistons on one side of both motors?

and I too though that reading 70psi without it hooked to anything is strange.
That should be 100% leakage

[formula29]

The air still has to pass through an 1/8" hole exiting the gauge, so that is a restriction that will build pressure, I'm done, I just reassembled everything and it still starts and runs, so at least I didn't break anything else, again thanks to everyone that commented on the thread, you guys are providing help and knowledge to people that need it, I know it can be frustrating trying to explain things to people but for me I would rather help guys out on the net than sit in front of the tv, I will post the outcome if the dealer finds the problem

[99yam40]

maybe if that HF unit was not designed to run at 100 psi the volume of air is too great ,so the outlet pressure reads that high without it hooked up to anything.

Yes please do post what caused this if you find out.
and maybe someone will test another F250 and report what they get also

[boscoe99]

I don't see where I was comparing any tests? as stated from the beginning I am trying to figure out why one bank has 25 psi more compression than the other, for two engines to have the same values does not make sense to me, I did the leak down test as advised to eliminate valves not seating or blow by, so what is left boscoe? you are saying cylinder wear in the middle or bottom of the bore? just on one side of the motor? I guess if one side of the motor runs quite a bit hotter than the other it would be plausible, from what I know anything more than 15% between cylinders in not really acceptable,

I am not saying anything.

My comment regarding comparing tests was to 99yam. Not to you.

If the motor starts well, idles well, runs well, and appears to make rated power I don't see a problem. It was you that came here thinking that there was one. At least that is the reason that I think that you came here.

[99yam40]

Bosco99 have you ever heard of or seen yourself one or more of these motors having more compression on one bank?

[boscoe99]

Bosco99 have you ever heard of or seen yourself one or more of these motors having more compression on one bank?

No.

Have also never seen a motor that has 0 loss of air either.

[99yam40]

OK do you know anyone with a F250 that would be willing to do a compression test on the motor to see what they get?

which one is off the 195 or the 170?

I did ask if he listened for air leaking, no matter what the tester said
with 100psi on the cylinders you should be able to hear something some where even if it was very slight

[scofflaw]

He probably didn't remove the Schrader valve

[99yam40]

He probably didn't remove the Schroeder valve

I do not own a leak down tester, so I do not know if they have Schrader valves like the compression testers, but I would not think so