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Low compression on bank 1

 
  #1  
Old 03-17-2019, 02:56 PM
1Truck
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Low compression on bank 1

Welcome fellow ford truck enthusiasts,
I have an '01 F250 5.4L. I checked the compression today and bank 2 seems fine @150 psi with one cyl @155psi. Bank 1 is around 120. Sorry I didn't look to see exactly what the psi was, I seen cyl 1 stop at 120 psi and kind of panicked. I quickly rechecked cyl 5 to make sure a weak battery wasn't giving false reading. Nope still 150 psi. So I went back to checking bank 1. All of them looked to be between 110 or 115 and 125 psi.
The coil boots were not easy to remove from the plugs on bank 1 during compression check.
I've also got roughly 25% ltft bank 2 and -25% ltft on bank 1.
It's been rebuilt. It's got oversized pistons and rings. I'm not sure what the possible causes of this are. I am ready to take it to the stealership if needed. But I'm wondering if timing could be a cause? This was my first time doing a timing job. My camshaft position sensor is located on bank 2. There is nothing I can see to tell the pcm that timing is off on bank 1. I am about to head out the door to have my battery recharged and to pick up a leak down tester.
Does anyone know what the actual compression should be? Btw, this was done on a cold engine. Only ran it for about 3 mins before starting procedure. Just enough to warm the spark plugs.
I rebuilt the engine just before hurricane Michael hit us. I drove the truck from Florida to Tennessee to south Carolina to kansas in a week fully loaded and ran like a champ other than an oil leak from the timing cover and lack of power. Tops out at 100mph lol. Going thru Tennessee I had to find out. There everyone does 90+ at night on the interstate.
Thanks in advance for everyone's help!
 
  #2  
Old 03-17-2019, 06:09 PM
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first.. did you have the throttle wide open for the compression test,,. a must.

second test every cylinder..... record each one..

on the lower ones.. retest after putting a few drops of oil into spark plug hole and rerun that cylinder for compression... to figure out if its rings, valves or head gasket.. if oil increases the pressure... its rings..

also camshaft timing can alter compression... if off by a few teeth...
 
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Old 03-17-2019, 06:24 PM
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I added a little bit of oil to cyl 1 using a long funnel and retested with no change. I thought about head gasket and valves but am skeptical being that the heads were done by a reputable shop recommended by a few different people. The block however was done by napa, which had decent reviews and also recommended that I take my heads to the other shop as he does a better job. So their honesty has me feeling pretty comfortable that either I messed up somewhere or cam timing. My other thought was that side was bored larger than they meant and the piston and rings just dont seat tight enough. I will be taking it to a shop to have a cylinder leak down test done sometime this week.
 
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Old 03-17-2019, 06:31 PM
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And as far as timing, I placed all the marks where instructed and colored links lined up. I'm pretty sure I had cyl 1 tdc.
 
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Old 03-17-2019, 06:34 PM
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Is the low bank off timing?
 
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Old 03-17-2019, 06:47 PM
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Originally Posted by 1Truck View Post
I added a little bit of oil to cyl 1 using a long funnel and retested with no change. I thought about head gasket and valves but am skeptical being that the heads were done by a reputable shop recommended by a few different people. The block however was done by napa, which had decent reviews and also recommended that I take my heads to the other shop as he does a better job. So their honesty has me feeling pretty comfortable that either I messed up somewhere or cam timing. My other thought was that side was bored larger than they meant and the piston and rings just dont seat tight enough. I will be taking it to a shop to have a cylinder leak down test done sometime this week.
did you install the pistons and rings??? did you not measure the ring gap ??? for every cylinder and every ring ?
I always measure the cylinder bore. and bearing sizing.. before starting an assembly..
 
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Old 03-17-2019, 07:03 PM
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Originally Posted by Chuck's First Ford View Post
did you install the pistons and rings??? did you not measure the ring gap ??? for every cylinder and every ring ?
I always measure the cylinder bore. and bearing sizing.. before starting an assembly..
I did check ring gap on every cylinder but not with each ring. I do not have the tool to check the bore. Using a mic i check the the bore at each lip and everyone was the same. Rotating mic I check for any ovaling and didn't see any. I put all the rings together and verified all same size, then used one ring to check gap on all the cylinders. I checked the gap with the rings closer to the top of the cylinder where compression would be highest. They were within specs. This was my first rebuild. First time taking a timing cover off period. I learned a lot and did hours and hours of research and drove the shops nuts with questions. I wish I'd have known about this forum back then.
 
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Old 03-17-2019, 07:11 PM
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Originally Posted by Evan_P View Post
Is the low bank off timing?
I'm not sure what you are asking. If you are asking if the low bank timing is off, as far as I know, which isn't a whole lot, the timing should be spot on. Maybe cam sprocket was set wrong or has moved?
is it possible for all the timing marks to be in the right place but the timing still be off. For example is there an intake stroke and an exhaust stroke on the piston? Could I have set the timing to where cyl 1 was on exhaust vs intake? Or?
 
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Old 03-17-2019, 07:17 PM
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Old 03-17-2019, 11:39 PM
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Man this was a lot of help. This is something I've not heard of. I did more research into cam timing and found a 45 min video that shows how to do this on a 4.6 2v SOHC ford engine. Cam timing spec for it was 110 atdc.
I looked in my Haynes manual and online. I cannot find what my cam timing should be. Do you know where I can find this information?
I will be checking my cam timing asap.
thanks again.
 
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Old 03-18-2019, 01:08 AM
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Upon further research I came across an article that talks about engines being overcammed.

"So back to those two identical engines with different cams; if you did a compression test on either of these two 9:1 static compression engines, the engine with no overlap (or even negative overlap) would probably have about 140 -150psi or so in the cylinders. The engine with more overlap may only have 110 - 120 psi or so, depending on how much overlap the cam has, how narrow the lobe separation angle is, and most importantly... what the intake valve timing is."

Does this apply to me? If so, how do I check this without taking the heads off and visually checking the valves? If I place the cam so that both valves are closed for the selected cylinder and connect an air compressor to the cylinder, correct me if I'm wrong, I should not lose compression unless there is valve overlap. I've read that there should be overlap and that there shouldn't be. Both make sense but my educated guess says ones for performance engines and ones for typical people like me. I'm assuming I should not have any overlap.
overlap makes sense as to why my compression is low on that one side. If the valves are open at bdc, it allows air to escape preventing proper compression.
cam timing imo also makes sense for low compression. If the cam is not closing the exhaust port in time, it also allows air to escape preventing proper compression.
so my first step is to check cam timing. I believe I can do this without removing the timing cover, removing only the valve covers and connecting the degree wheel to the crank pulley using a longer bolt and spacer. After finding true tdc I then use my dial indicator to find true lift on cyl 1 for bank 1 and cyl 6? for bank 2. And compare the results for both sides for difference in timing. Yes there is more to it than this. Just didn't feel like typing it all out. Just trying to make sure I'm on the right track.
 
  #12  
Old 03-18-2019, 07:18 AM
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Sorry .. I am NOT a teacher....

but I have rebuilt engines over 50 years...

your questions are not easy to explain... even in person...
a keyboard.. the typer must be a book writer.. I am not.

my advice.. to learn.. go to public library.. and start reading...
I learned engine building in Tech School... 1967..... retired a couple of years ago.
if it was EASY,, everyone could do it..

before computers... if you assembled an engine wrong.. . . even 180 out of order......it would run. just not well..
or you bent valves... or cracked pistons..

the camshaft is the "Timing" of every moving part in an engine.. 100 percent right.. or 100 percent wrong..
under and over timing is a different animal.. and you better know what you are doing with this.
 
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Old 03-18-2019, 10:11 AM
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Originally Posted by Chuck's First Ford View Post
Sorry .. I am NOT a teacher....

but I have rebuilt engines over 50 years...

your questions are not easy to explain... even in person...
a keyboard.. the typer must be a book writer.. I am not.

my advice.. to learn.. go to public library.. and start reading...
I learned engine building in Tech School... 1967..... retired a couple of years ago.
if it was EASY,, everyone could do it..

before computers... if you assembled an engine wrong.. . . even 180 out of order......it would run. just not well..
or you bent valves... or cracked pistons..

the camshaft is the "Timing" of every moving part in an engine.. 100 percent right.. or 100 percent wrong..
under and over timing is a different animal.. and you better know what you are doing with this.
yea I cant say that I know what I'm doing. But I'm mechanically inclined and fairly intelligent enough I have faith. I do tons and tons of research. It took me 4 hrs to get thru that 45 min video last night, just because I took my time watching it, going back and forth, rewatching, and I will watch the video again at least twice before even checking cam timing.
I really appreciate your help man. Your lead with that video saved me hours of work and who knows how much money. I really cant thank you enough.
 
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Old 03-18-2019, 12:37 PM
Chuck's First Ford
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I hope you find the problem and get your "Girl" up and running again...

I can wrench.. but passing knowledge, I am poor at...

I have no idea how teachers can teach.. its Magic.. ..
 
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Old 03-18-2019, 03:55 PM
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Camshaft overlap has no affect on reading compression since the reading is taken on the compression stroke. Overlap usually occurs on the exhaust stroke, when intake valve opens early, especially with narrow lobe centers of 104-107 degrees.

If you are using the stock camshafts you have no reason to concern yourself with overlap, anyway.

The one bank of cylinders were over-bored and the other were not? Is this true or a typo? If so, you are saying that you have different pistons on one bank than the other. I know of no credible machine shop that would be associated with this, as the balance of the rotating assembly would be off by a huge amount.

Sadly you have a big mess on your hands.

Dave

 

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