F250 compression #s

[99yam40]

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.

I do not believe air leaking through the exhaust is a problem with the HF gauge.
Is that what you were getting at?

May need to check all of the cylinders with it.
I do not see where the gauge is a problem with just what you wrote.

I wonder since this VCT works off of oil pressure, what is the oil pressure at idle?

since you were reading +12 on one side and Rod said that is the one that is way off, it must be stuck maybe.
If a filter is plugged would / could it show up like this?

I have no clue about this problem, but this is interesting to me

[rodbolt17]

do not worry about any cam mark
what your looking for is #1 at TDC on compression stroke.
so line up the flywheel index mark with the pointer.
its either going to be TDC compression or ex.
if its on the ex stroke rotate the flywheel 360 and then try.
from there simply run the index marks through the fireing order.
once #1 TDC compression stroke is found every 120* for the next 720* of rotation is going to bring the next piston up.
fireing order for that motor is a complex 1,2,3,4,5 and 6.

your flywheel should have 3 index marks numbered 1-3.

DO not worry about the cam maarks at this point.
the flywheel marks are not used in any cam timing operations.

[formula29]

If I cant figure it out I will be taking it back to the dealer, problem being its a 3 hr trip or they would already be there, I am going to spend some more time on it today, things like this really help you get familiar with your motor anyway! try to stay positive !

[rodbolt17]

look on your flywheel.
do you see the 3 index marks, one is going to have a grid with a TDC mark and marks for BTDC and ATDC.
the other two will simply be labeled TDC.

the one with the grid is the #1 cyl.

remember that motor,unlike a two stroke, has to rotate 720* to complete all 6 fire cycles.
means each piston comes to TDC twice in 720*.
once on compression stroke(all valves closed) once on ex stroke,valves still open.

[formula29]

I'm working on it, the pointer for tdc has not been reinstalled when they did the powerhead I assume, so without pulling the flywheel I am guessing it is close both, motors!. the problem with the gauge I bought is the 2nd gauge does not read at all, it is defective,

[formula29]

I do not believe air leaking through the exhaust is a problem with the HF gauge.
Is that what you were getting at?

May need to check all of the cylinders with it.
I do not see where the gauge is a problem with just what you wrote.

I wonder since this VCT works off of oil pressure, what is the oil pressure at idle?

since you were reading +12 on one side and Rod said that is the one that is way off, it must be stuck maybe.
If a filter is plugged would / could it show up like this?

I have no clue about this problem, but this is interesting to me

Oil pressure was aprox 80psi ad idle, the problem with HF gauge was the second indicator gauge is broken, the needle doesn't move at all, I am more obsessed with figuring out where the problem lies than anything, things like this drive me nuts until I can figure it out, I actually enjoy repairing engines, just not when I pay for a good running engine.

[99yam40]

Just in case you do not know it yet,
Rodbolt is a Yamaha master tech

Pay attention to his posts
I am just someone that likes to read and learn from the posts on here

[boscoe99]

Oil pressure was aprox 80psi ad idle, the problem with HF gauge was the second indicator gauge is broken, the needle doesn't move at all, I am more obsessed with figuring out where the problem lies than anything, things like this drive me nuts until I can figure it out, I actually enjoy repairing engines, just not when I pay for a good running engine.

How do the motors run by the way? Good, bad or ugly? If badly running, what are the symptoms?

[rodbolt17]

dude.
this aint that hard.
the 4.2L and all the v8 motors have NO index marks.

simply bring #1 to TDC,you can use a slim screwdriver to find it.
does not have to be PERFECT like a two stroke.
you can miss a few degrees either side.

now simply make your own timing mark that lines up with the flywheel index mark.

you can fasten a bent paper clip or use a magic marker.

remember in a complete cycle(720*) #1 is going to be at TDC twice.

once you find TDC #1 compression stroke simply test it.
if the ex valves are open(ex stroke) you will hear air blowing past the ex into and out of the ex system.
simply rotate it 360,now you will be on compression.
now listen for air past the throttle plate and the ex system.
any air requires investigation as to why that valve is leaking.

if you have an engine with no flywheel index mark you simply find TDC of the easiest accesable cyl
divide the number of cylinders into 720(4 stroke) that will tell you how many degrees of flywheel rotation is needed to fire the next cyl in the fireing order.

in the case of a V8 you will have 4 marks at 90*,V6 3 marks at 120* inline 4 will be two marks at 180*.

its actually simple.

[boscoe99]

You don't need to do anything at all with respect to trying to get the crank shaft to line up with any marks.

Remove all spark plugs. Rotate the motor until the number one cylinder is coming up on the compression stroke. Put your finger over the spark plug hole (or over the tool that was inserted into the spark plug hole, to which the air hose will be attached) and you can feel the pressure being developed as the piston comes up to top dead center.

Then attach the air hose to the tool. Adjust the regulator so that there is about 20 psi being applied to the cylinder. Rotate the crank shaft so that the piston comes up to top dead center. You will feel top dead center when the resistance to the rotation of the crank shaft diminishes. Have someone hold a wrench on the crank shaft nut just in case air pressure tries to turn the crank shaft. Which it won't if the piston is on top dead center.

Helps to have the lower unit removed although not necessary.

Adjust the air pressure regulator so there is 80 psi being applied into the cylinder, as noted on the primary gauge. Note and record the air pressure on the secondary gauge. If you want to know where any leakages is coming from you will need to use your ears. Listen into the oil fill cap opening for crank case leakage. Listen to the exhaust for exhaust valve leakage. Listen into the intake manifold for an intake valve leak.

Repeat the process for each cylinder. Let us have the results. Oh, the motor needs to have been recently run so that it is hot when the differential pressure test is performed.

[rodbolt17]

the valves wont care if it is hot nor cold.
they seal regaurdless.
if I do a cold motor and note leakage past the rings I look for are all the same leakage?
in this case where I lost almost 30 PSI on the compression test on ONE bank, I would suspect someone or something is holding a valve open slightly or the wrong cyl head is installed.

run a motor much that cannot seal,valve open,head gasket leaking or the piston ring gaps lined up and failure is swift and sure.

in this case IF an intake valve were leaking,remember we no longer use intake vacuum to move fuel, with a 170PSI compression its can fire on the power stroke.
now this combustion pressure is not only going to push on the piston it will JET a HOT gas flame past that small leakage.
this leads to severe metal erosion on whatever is leaking.
valve faces burn off,seats melt lines get etched in blocks and heads,pistons get melted spots.
don't trust the air and pulling up to TDC much.
the above referenced 5.7 I posted 4 cylinders while injecting 100 PSI(standard for my tester) I could pulled each cyl right on by the compression stroke with one hand and a 1/2 drive ratchet on the crank bolt.

had that cyl been sealed I would have snapped off the crank bolt long before I pulled past it at 100 PSI.

you already know this F250 has an issue,now ya gotta find out what it is.

if nothing else bring each to TDC compression stroke,add about 100 PSI and simply use your ears.

if an intake is leaking(hot or cold) it will blow air back into the intake and past the throttle plate.
if an EX valve is leaking (hot or cold) it will blow air into the ex system.
if the rings are leaking(hot or cold) it blows air into the crankcase,this can be heard and felt by simply removing the crankcase vent line at the air box.

on a COLD engine I am not real concerned with 20-25% past the rings,anything more may mean an issue.
but valves seal hot or cold.

if it cannot seal cold it will not seal hot.

its how the doing vacuum tests on the intake and ex valves before and after refacing and seat cutting work.
we know it seals before it boxed and shipped back.

so even with your broken tester you can test for valve leakage.

[formula29]

How do the motors run by the way? Good, bad or ugly? If badly running, what are the symptoms?

The motors run good and strong, they fire right up and idle perfect, and run on up to 6000 without issue, if I didn't know the numbers were off you wouldn't know by the performance of them running.

[formula29]

By the way, both of you guys helped me big time a couple years ago when I bought a used f300xca and the thrust bearings went out, it was way out of warranty and one of you guys recommended asking for Yamaha goodwill which I would have never thought possible and they came through with a new crank case assembly, that was the only other 4 stroke I have owned and I actually assembled the motor myself and it ran great afterward, I have quite a bit of mechanical knowledge but some of these things are much easier to diagnose when you are familiar with the model and work on them everyday.

[TownsendsFJR1300]

The more information gathered, especially with both engines doing the same thing, sounds like when the engines were put together again, one cam is a tooth off (on both engines-same mechanic, same mistake).

[boscoe99]

I am going to stick my skinny neck out and guess it is a piston ring/cylinder leakage issue. Do the differential pressure test and find out for sure.

Now if you think the crank shaft is not phased correctly with the cam shafts then a quick visual inspection will let you know for sure. Rotate the crank shaft until the alignment mark on the drive gear aligns with the alignment mark on the cylinder block. Verify that the alignment marks on the driven gears for each intake cam shaft aligns with the corresponding alignment marks on the exhaust cam shaft. If at first they don't line up rotate the crank shaft another 360 degrees. See illustration below.

You can always remove the valve covers and verify there is clearance on both intake valves and both exhaust valves for each cylinder when the piston for that cylinder is at top dead center on the compression stroke.