F250 compression #s

[formula29]

I need a little help from a Yamaha tech, but I'm afraid I know the answer. I just bought a used set of 2007 f250's aprox 900 hrs, they run fine mostly but the strange part is both motors have low compression on all 3 starboard cylinders, both engines have 195 psi on the port banks, and 170 psi on the starboard banks? test was done with throttle open, this cant be normal for these engines is it? I am aware that a leak down test will pin point where the problem is I just want to hear if this is common or not, I bought them from a reputable dealer and they told me they would take them back but if its normal so be it, its just weird to me that both engines are identical. thank you for any replies.

[rodbolt17]

compression test on that motor is as much value as a teat on a steer.

do a leakdown.
do a good treatment with the YIES treatment, NOT combustion chamber cleaner or ring free.
re run the leak down.
takes maybe an hour.

[formula29]

Thanks rodbolt, I will do the leak down next, if it needs a valve job its not the end of the world but if its the rings I would be inclined to return the motors, I am still wondering why both engines have the same unequal numbers between left and right bank? that part doesn't make sense to me.

[rodbolt17]

could be a lot of things,cam timing,cranking speed.
that's why I don't do compression tests.
I do leakdown tests.

did one on a master craft yesterday with an Ilmor 5.7.

compression test "said " all was good.

I followed with a leakdown test.
engine FAILED.
1 80%
2 20%
3 85%
4 85%
5 85%
6 40%
7 85%
8 40%
#1 had 180 PSI on the pukey test.
the leakdown showed it was not only incapeable of sealing it was leaking past the intake valve.
and that is why I don't normally compression test a 4 stroke.
the compression tested good, the engine is very sick.

[formula29]

I just came in from verifying the camshaft timing marks lined up to rule that out. I was kind of leaning toward that maybe the cam timing being off either because of the vvt or possibly a tech missed one tooth on the install of the belt, I tend to over think things, if the numbers were all other the place it would make sense that it was carbon or valve issue or worn rings, it is just strange to me that one whole bank is evenly 25 pounds lower that the other on both engines? I do thank you for your time to respond to my questions rodbolt, I value an experts advise,

[formula29]

I just ran the motors while watching the yds, it showed port cam intake timing at +12 degrees and the starboard was showing -2 degrees does this look right rodbolt?

[rodbolt17]

no, something is not right.
they should run within a few degrees of each other.
do the leakdown test.

[zenoahphobic]

I just ran the motors while watching the yds, it showed port cam intake timing at +12 degrees and the starboard was showing -2 degrees does this look right rodbolt?

Now that is telling.
Previously as you were not given an answer, I would have said as both appear the same in compression tests that both suffer maybe something like carbon build up on the starboard(?) valves due to the way they have been used.

But it is also logical to assume that all maintenance (adjustments, replacements) would have been done at the same time and by the same person. Human error maybe, or far more remotely, a faulty batch of parts.

Or maybe simply the engines have been neglected and have developed there own individual problems (return to supplier).

[boscoe99]

Yes. Do the leak down test. More correctly known as a differential pressure test.

Might want to do it three times just to be sure and average the readings. If each and every cylinder is not perfectly aligned with every other cylinder, great harm may come to the motor. Each cylinder ideally will have no more than one psi loss of pressure. Hard to get those pesky rings to make a perfect seal. If not within the one psi tolerance, at best it won't run as well as it should.

It will magically cure the motor of any and all ills.

Yamaha thinks so highly of the differential pressure test that they make no mention of it at all in their service manuals. I guess they assume that all will know that it has to be done (every six months would be a good schedule) as it will go a long way to ensure great engine life.

If the aluminum does not corrode away first.

[rodbolt17]

Boscoe
just cause I guess you don't like nor use the leakdown test its ok to make fun of it.
in the above example the engine had been passed by another tech.

all his compression numbers ran from a high of 185 to a low of 165.
well within the industry standards of 20% higest to lowest.
however I was tasked to do an engine survey for a customer prior to his purchase of the above motor.

I read the other shops numbers, they looked ok.

however 4 had intake valves leaking and 3 had excessive blowby past the rings.

this was found with the leakdown test.
I am 55 and have been doing leakdown tests since I was 15.

Yamaha DOES ask for the leakdown test results on blown or suspected blown 4 strokes.

the above customer tipped me well and backed out of the purchase.

I saved him a ton of money in a 15 min test of 8 cylinders.

I can do a leakdown test in about 1/2 the time of a compression test and it way more accurate.

the owner of the above engine says it runs great and he is going to run it.
I said arrriighht.

in the posters 250 most likely he is going to find one bank that all the intake valves are leaking slightly due to a mispositioned intake cam.

however the industry standard of 20% highest to lowest would make the posters F250 a pass yet the above poster is most likely going to find mechanical issues.

either a cam is out of position or the mechanism is stuck or the OCV is stuck or the filter clogged.

[99yam40]

in the posters 250 most likely he is going to find one bank that all the intake valves are leaking slightly due to a mispositioned intake cam.

however the industry standard of 20% highest to lowest would make the posters F250 a pass yet the above poster is most likely going to find mechanical issues.

either a cam is out of position or the mechanism is stuck or the OCV is stuck or the filter clogged.

I am sure this is the stuff the OP was looking for

[rodbolt17]

the intake cams at idle typically bounce between about -2* and 2 *.
if one is at -2* and the other is at 12* that indicates a problem.

[99yam40]

would the filter be the most likely

[formula29]

Guys I welcome all of the feedback at this point, after running this morning I did the static test on the oil con*****ers and they did the clicking thing, then I went out and bought a leak down tester, unfortunately I bought a harbor freight and it is a pos and does not work, with #1 on top dead center all the cam pointers were lined up and when I put air to the #1 cylinder I could hear it leaking through the exhaust, I rotated the crank another couple of degrees and the exhaust valves sealed, when I was looking at the intake valve timing earlier on the yds the port being advanced 12 and the starboard being retarded 2 degrees I ran the engine rpms up to see if they changed at all, they evened out both sides at I think +14 degrees at 2500 rpms. I think something is out of wack with the intake cam timing personally, I may pull the flywheel and try a new timing belt on one motor but will also buy a good leak down gauge to get a proper test, I have read the manual regarding the vct and how it works with some kind of pin holding it in place until oil pressure takes over? these powerheads were replaced several years ago, I wonder if the tech could have assembled something wrong back then and nobody ever checked compression? I had enough for today, back at it in the morning and thanks again for all the information.

[TownsendsFJR1300]

IMO, you may consider bringing them back and let them deal with it (then double check their work if its repaired). Seems like a headache that the dealer should have found and repaired before selling them....


But, if not, here's a good leak down tester I've been using for years. It seems very accurate and won't cost an arm and a leg.

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https://www.otctools.com/products/cy...age-tester-kit

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