Compression Prob!!!
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Fleet Mechanic
Joined: Jun 2011
Posts: 1,804
Likes: 5
From: Southern California
Compression Prob!!!
Ok guys i have a 1974 F250 with a 390. To my knowledge it has a shift kit, high performance or off road cam, and a Holley Double Pumper....
Now, # 2 has no compression. I took the cover off and discovered a bent pushrod. So i replaced all the lifters and pushrods. B4 replacing pushrods, i had the rocker off and the lifter etc. out, and it had compression in #2. Put the new lifters and rods in and put the rocker back on, #2 still has no compression. My best guess is the timing chain jumped due to the double pumper. I believe its a stock chain and not a high performance double.
Any other ideas?
Now, # 2 has no compression. I took the cover off and discovered a bent pushrod. So i replaced all the lifters and pushrods. B4 replacing pushrods, i had the rocker off and the lifter etc. out, and it had compression in #2. Put the new lifters and rods in and put the rocker back on, #2 still has no compression. My best guess is the timing chain jumped due to the double pumper. I believe its a stock chain and not a high performance double.
Any other ideas?
Fleet Mechanic
Joined: Jun 2007
Posts: 1,931
Likes: 2
From: Ohio
you're saying it has no compression now that you've changed the pushrod? Are you sure everything was put back together correctly? I'd take the valve cover off and turn the crank with a breaker bar and watch the rocker you changed the pushrod for on the #2 cylinder to make sure it is moving correctly. If not that would cause it to not have compression.
Fleet Mechanic
Joined: Nov 2010
Posts: 1,501
Likes: 1
From: Axtell, TX
FE's that Bend Pushrods
Maybe a bent rocker shaft? They are easy to bend if you don't install/remove them very evenly to keep them from flexing. I only go 1/2-1 turn per bolt at a time. I agree with NW. Turn it over and see what the rockers are doing (valves opening and closing as normal).
Maybe a bent rocker shaft? They are easy to bend if you don't install/remove them very evenly to keep them from flexing. I only go 1/2-1 turn per bolt at a time. I agree with NW. Turn it over and see what the rockers are doing (valves opening and closing as normal).
Hotshot
Joined: Apr 2009
Posts: 14,333
Likes: 247
From: Stanley, VA
Also, there are three different length pushrods for the FE's. Too long will keep the valves from closing.
Bring #2 piston to TDC on compression and check that both valves are shut and not being held open.
Another possibility is one of the valves has sunk and is now being held open even though everything else is okay.
Also make sure the pushrods are actually seated in the lifter.
Bring #2 piston to TDC on compression and check that both valves are shut and not being held open.
Another possibility is one of the valves has sunk and is now being held open even though everything else is okay.
Also make sure the pushrods are actually seated in the lifter.
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Lead Driver
Joined: Mar 2004
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Loosen up the rocker shaft till the rockers are not touching the valve tips. Take the spark plug out and put some compressed air in the cylinder. Listen to hear just where it's going and get back to us.
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First of all, how are you testing for compression on a cylinder that has inoperable valves if the pushrods were removed?
Second, you need to verify the valves are opening the correct amount, as it stands right now, I would put money on a wiped cam lobe. Which would mean low compression if it were an intake lobe.
And third, it isn't a good idea these days to install new lifters on old camshafts. 7 times out of 10 it ends up taking out the cam anyways.
4th, a Holley double pumper has nothing to do with a jumped timing chain.
Josh
Second, you need to verify the valves are opening the correct amount, as it stands right now, I would put money on a wiped cam lobe. Which would mean low compression if it were an intake lobe.
And third, it isn't a good idea these days to install new lifters on old camshafts. 7 times out of 10 it ends up taking out the cam anyways.
4th, a Holley double pumper has nothing to do with a jumped timing chain.
Josh
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Joined: Feb 2010
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From: CASA GRANDE AZ
First of all, how are you testing for compression on a cylinder that has inoperable valves if the pushrods were removed?
Second, you need to verify the valves are opening the correct amount, as it stands right now, I would put money on a wiped cam lobe. Which would mean low compression if it were an intake lobe.
And third, it isn't a good idea these days to install new lifters on old camshafts. 7 times out of 10 it ends up taking out the cam anyways.
4th, a Holley double pumper has nothing to do with a jumped timing chain.
Josh
Second, you need to verify the valves are opening the correct amount, as it stands right now, I would put money on a wiped cam lobe. Which would mean low compression if it were an intake lobe.
And third, it isn't a good idea these days to install new lifters on old camshafts. 7 times out of 10 it ends up taking out the cam anyways.
4th, a Holley double pumper has nothing to do with a jumped timing chain.
Josh
AGREED , the cam lobe would be gone witch made room for the pushrod to jump off and get bent !
what caused the problem in that 1 cylinder ? and not the rest of the cylinders ?
Timing chain will affect every cylinder
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Fleet Mechanic
Joined: Jun 2011
Posts: 1,804
Likes: 5
From: Southern California
[SIZE=3][FONT=Calibri]
I’m so annoyed right now. So we found the problem at last. On the 3rd time i took apart the engine. Sooooo here we go.
<o
></o>
<o></o>
1) Timing chain jumped one tooth<o></o>
<o></o>
2) Bent pushrod<o></o>
<o></o>
3) Bad lifter<o></o>
<o></o>
4) Broken spring in head<o></o>
<o></o>
5) Cracked valve seat I believe<o></o>
<o></o>
IT’S A MESS!
Also found out that whatever moron rebuilt the engine used the wrong length pushrods, completely screwed up both heads. My guy who is currently completely redoing the heads says that everything was wrong. Between wrong parts and stuff being grinded down to much he was surprised the previous owner didn’t have these problems. (I am the 3rd owner, 1st owner rebuilt before selling to the 2nd). So, im not happy with this right now. My truck has been sitting in my driveway for a month now. I want to drive it! So 2moro my heads are going to be done so Tuesday I should have it going again
<o></o>
I’m so annoyed right now. So we found the problem at last. On the 3rd time i took apart the engine. Sooooo here we go. <o
></o><o
></o>1) Timing chain jumped one tooth<o
></o><o
></o>2) Bent pushrod<o
></o><o
></o>3) Bad lifter<o
></o><o
></o>4) Broken spring in head<o
></o><o
></o>5) Cracked valve seat I believe<o
></o><o
></o>IT’S A MESS!
Also found out that whatever moron rebuilt the engine used the wrong length pushrods, completely screwed up both heads. My guy who is currently completely redoing the heads says that everything was wrong. Between wrong parts and stuff being grinded down to much he was surprised the previous owner didn’t have these problems. (I am the 3rd owner, 1st owner rebuilt before selling to the 2nd). So, im not happy with this right now. My truck has been sitting in my driveway for a month now. I want to drive it! So 2moro my heads are going to be done so Tuesday I should have it going again
<o></o>
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Fleet Mechanic
Joined: Jun 2011
Posts: 1,804
Likes: 5
From: Southern California
BOOOOOOM! Im on the road again
Got the heads back and the engine repainted as i installed everything again. Started right up and there is a huge difference! I had no idea that i was running on 7 cylinders since i bought the truck. It is so smooth right now. 2moro AM i will be adjusting the distributer. I still think its a tooth off. Other than that it purrs. Its great! I also have a new performance distributer coming (a friend ordered it so i have no idea who makes it or anything, it was 300-350$ tho)
I will post pics of everything soon. I think ill start a thread on just mods ive done since i bought it. I have plenty of pics to share haha
Got the heads back and the engine repainted as i installed everything again. Started right up and there is a huge difference! I had no idea that i was running on 7 cylinders since i bought the truck. It is so smooth right now. 2moro AM i will be adjusting the distributer. I still think its a tooth off. Other than that it purrs. Its great! I also have a new performance distributer coming (a friend ordered it so i have no idea who makes it or anything, it was 300-350$ tho)
I will post pics of everything soon. I think ill start a thread on just mods ive done since i bought it. I have plenty of pics to share haha
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