F250 compression #s

[rodbolt17]

if I tested 6 cyl's 4 were 5% or less and two indicated 0 then I would figure the leakage is to small for my equipment to measure and all is good in the hood and continue on.
this stuff aint hard if you don't over think it.
don't get hung up on stupid stuff.
remember that motor is actually 6 little motors that share a common crank and a common air intake.
if the compression test shows 195 on one bank and 170 on the other its FREAKING trying to tell ya sumptin ya think?

the next clue, the freaking cam timing IS NOT where it should be.
the cams should pretty much stay within a few degrees of each other at all times.

intake cam timing WILL affect compression.
it is NOT designed to have unequal compression unlike some 2 strokes of years past.

the compression test indicated a POTENTIAL [problem.
that needs to be looked at via a LEAKDOWN test.

now if it was your 100 bucks an hour,and its faster to do a leakage vs compression, would you like to pay for BOTH tests or just the more accurate of the two?

so that leaves did someone use the wrong parts that physically fit?
did someone reinstall a cam incorrectly?
did someone improperly shim the intake cam during a repair?

but something is wrong and its time to follow a logical rabbit trail.

not all throttles will open at just key on.
then you have to disable BOTH spark AND fuel.

[zenoahphobic]

Sorry to bring up leakdown tester again. Reference to it continued in regard to 0%. It is important to know our test equipment because we rely on them to not make wrong decisions that can lead to unnecessary costly maintenance.

Simply, when one sees the second gauge reading 100 psi the leak is not necessarily zero, it is more likely that there is a leak that is equal in area to the orifice between the gauges. We conveniently set the pressure to 100 so that we convince ourselves (not me though) that a lesser reading on the second gauge is a percentage loss. This is BS of course.

If I were a master mechanic, not only would I not use analogue dial gauges but transducers, but have an adjustable (graduated) orifice (sorry I don't wish to appear to have an obsession with these). I would not then question a "zero percentage", and make a statement that I would question my test equipment only if all readings are "zero percentage".

You can do 3 things:
1. ignore, no problem here,
2. turn off your compressor and shut off valve and watch the pressure drop which will tell you something. Just like a compression gauge(s) with the one way valve removed, or
3. use your tester correctly and screw the orifice down until the second gauge actually begins to drop! indicating the actual leak.

[zenoahphobic]

yes, both sprockets are the same on the parts diagram, one of mine is wrong, I compared the cam dowel inside it and they look to be about 1/16 farther apart

Well there you have it. Cam sprocket but which one?
Has it been agreed that the correct compression is 195psi?

[formula29]

I wonder if the cam timing Degrees on YDS changed also?

Are the sprockets suppose to be the same on both sides in the parts breakdown?

yes, both sprockets are the same on the parts diagram, one of mine is wrong, I compared the cam dowel inside it and they look to be about 1/16 farther apart

[formula29]

Rodbolt is answer to holding the throttle open, you simply push in the neutral detent in the shifter and open the throttle, I verified the plate opened fully. prior to this I tested with throttle closed and got the same numbers believe it or not, I my first attempt I didn't know if you could open the throttle plate manually and I didn't want to damage it so I ran the test with it closed, I came up with the funky numbers so I was going to pull the throttle body and re test, after I removed the upper housing I figured I would see if the throttle would open up with the engine not running but key on and wide open throttle and it does.

[99yam40]

I wonder if the cam timing Degrees on YDS changed also?

Are the sprockets suppose to be the same on both sides in the parts breakdown?

edit
not sure if I looked at the correct f250 breakdown but the driven gear and the pully lists 2 each, so they should be the same is my thoughts

[formula29]

mystery partially solved, I just swapped vct gears from port to starboard, now I have 195 psi starboard and 170 psi port

[99yam40]

if at idle one cam is showing about -2 and the other is showing +12.
either the cam was installed incorrectly,the VCT assy is sticking or the VCT filter is severly clogged and wont allow oil to return.
cam timing will affect compression reading.

and I gotta know, how did you hold the throttle valve OPEN when doing the compression test?

the cam angle on YDS should show both banks within about 4* all the time.

the ECU is not designed to move one due to any issues.

it is designed to move both based on RPM and throttle angle.

just some thoughts this morning

Is it possible that there is a special way to hold the throttle plates open during a compression test?
seems like the compression difference is possible a result of cam timing being different.

the cam timing is different because the VCT is not retarding the cam on both motors on the port side
"+14 degrees at 2500 rpms" the cams even out with RPM so does that mean they are not stuck?
or is it that only the one filter on both motors is plugged up and not letting the oil return to pan.

kind of looks like the filters would be the thing to check on

and the proper alignment of cams

I have no clue how you would test to see if cams were stuck

[rodbolt17]

no
he did not check it correctly.
you have to line up the mark on the reluctor with the tab cast in the block THEN look at the cam sprocket marks.
the TDC marks on the flywheel are NOT used to set the cam sprockets.
it can be seen with the flywheel in place but its not easy.
the filters are under the OCV.
the plastic ones are about 70 bucks each.
the later paper style are like 8 bucks.
Yamaha recommends replaceing them about 400 hours.
the valve cleaarence is about 400 hours.
never ever gets actually done.

the maint actions are in the book.
the 10,50,100,200,400,500, and 1000 hour OR yearly, monthly specs are all in the maint guide.
10 100 hours services does NOT equal 1 1000 hr service.
is it my fault it takes 100 bucks woth of gaskets and 5 hours or so to check valve lash on an F350?
nope but it is recommended every 400 hours.

same as cam chain tensioner check on the F200/225 v6. no one ever does it till it fails.

[TownsendsFJR1300]

I would think with what you posted above, the most likely would be a dirty filter (wherever those are located).

Especially since you haven't mentioned any failures of those cams.

As noted earlier, they cannot be serviced, but have you seen any/ many fail?

We don't know the PO's maintenance to the engines. How temperamental is the internals are for the variable cams?

The Op did check alignment and everything appeared dead nuts on.


Seems its getting narrowed down in any case...

[rodbolt17]

if at idle one cam is showing about -2 and the other is showing +12.
either the cam was installed incorrectly,the VCT assy is sticking or the VCT filter is severly clogged and wont allow oil to return.
cam timing will affect compression reading.

and I gotta know, how did you hold the throttle valve OPEN when doing the compression test?

the cam angle on YDS should show both banks within about 4* all the time.

the ECU is not designed to move one due to any issues.

it is designed to move both based on RPM and throttle angle.

don't know how this got so crazy.
all you need to know is CAN it mechanically SEAL said cyl.
if it can your ****en there and just neeed to find out why the cams wont follow each other.
if it CANNOT then you need to find out WHAT is NOT sealing and fix that before proceding.
as for the 0%.
I was doing a leakdown on an F350, all were less than 7% and 2 showed 0%.
that I attributed to my gauge simply could not measure a very small leakage.

I have seen the 0% reading on a few others over the years. doesn't concern me as long as ALL do not read 0%, then I would suspect my test equipment.

kinda like testing a circuit with a standard digital meter yet the spec is in micro mo's.
standard meter wont see a resistance that small.

[zenoahphobic]

why are we still harping on the differential test? The intake cam being +12 degrees advanced seems to be a more likely problem unless we want to dwell on weather I had the YDS hooked up properly? while it has been pointed out the advance timing is not right I have not herd any insight as to why it could be advanced like it is?

Its all good what is being said, albeit repetitive or the same from different points of view and different world times in the order of posting.

The differential test points have been dealt with.

The 25psi remains a mystery.

And in all likelihood your VCT is stuffed, cannot be fixed, only replaced.

If replaced, then we can retest compression and wipe away that 25psi as being anything but an anomaly of the type of test, and has nothing to do with the cylinder compression ability in operation.

[boscoe99]

seems like most do not believe the test you did was a valid one

but if one cam is advanced farther than the other at cranking it seems like it could be seen with the eye

not sure how the oil pressure changes the timing of the cam.
I take it it pushes a device that advances or retards the cam.

someone want to enlighten us on that.

Consider yourself enlightened.

[boscoe99]

why are we still harping on the differential test? The intake cam being +12 degrees advanced seems to be a more likely problem unless we want to dwell on weather I had the YDS hooked up properly? while it has been pointed out the advance timing is not right I have not herd any insight as to why it could be advanced like it is?

Zeno and I are having a side discussion.

[99yam40]

why are we still harping on the differential test? The intake cam being +12 degrees advanced seems to be a more likely problem unless we want to dwell on weather I had the YDS hooked up properly? while it has been pointed out the advance timing is not right I have not herd any insight as to why it could be advanced like it is?

seems like most do not believe the test you did was a valid one

but if one cam is advanced farther than the other at cranking it seems like it could be seen with the eye

not sure how the oil pressure changes the timing of the cam.
I take it it pushes a device that advances or retards the cam.

someone want to enlighten us on that.