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Valve Adjustment/Knock question
I was reading on PG.35 on this for specs and I just had to questions I wasn't sure of that I could not find on any other threads from the past.
http://www.ncttora.com/fsm/1993/engine/7cylinder.pdf 1) After all valves are adjusted should they all be tight? 2) What is the purpose of the spring next to the rockers? The problem I am having with a truck is that the top end is REAL noisy and at TDC the cylinder 1 rockers are very loose which seem to be far out of spec and the number 4 are tight but some of them you can move side to side. Is that normal? I just don't understand the side to side play. Something is def up with the top end, there is a lot of fine metal shavings up top but the pan is dropped and bearings all check out fine to the eye and its not a piston slap I disabled 1 cylinder at a time when running to see if the knock would go away. I'm going to hook up a oil pres gauge and compression test it next, but I'm almost positive they will check out. Previous owner did timing chain and guides which was obvious for me since half of the worn out old guides were in the pan. Any ideas? And I did find the specs you guys were talking about for cold .007/.011 |
You need to adjust the valves in 2 stages. At #1TDC, the intake and exhaust on#1 should be adjusted and I THINK the intake on 2, and exhaust on 3. Then you turn the crank 360* (rotating the cam 180*), and do the others. If your rockers ar "very loose", they need adjusting. There should be just a tiny amount of movement in them.
I believe the purpose of the spring is to keep a little tension on the rockers to keep them from bouncong around a lot, but I could be wrong. While you have the valve cover off, check the tension on the timing chain. A loose chain will make a ton of noise too. |
They do have to be adjusted in sequence. A regular Haynes manual lists the sequence and the specs. The rockers will be loose even after adjustment. I'm wondering though if the noise you hear is a timing issue and not rockers. Rockers that make noise are 'falling off' loose, but incorrect ignition timing will make it rattle alot.
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How do you know which one is the number 1 piston. Does it go from front to back?
I forgot how to tell or maybe im getting confused with firing order piston 1 2 3 4 ?????? |
yep, the one closest to the rad is num one. Could be wrong but I thought as long as the valve was set while on the back side of the lobe it is ok? the loose spot.
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Originally Posted by Myron
(Post 51275206)
How do you know which one is the number 1 piston. Does it go from front to back?
I forgot how to tell or maybe im getting confused with firing order piston 1 2 3 4 ?????? |
Originally Posted by peapicker
(Post 51275210)
...
Could be wrong but I thought as long as the valve was set while on the back side of the lobe it is ok? the loose spot. |
1) Valves should only be tight if the cam is applying pressure to the rocker, i.e.: the valve is being opened or is closing. At any particular time, some of the valves will be loose and others will be tight.
2) The primary purpose of the spring is to hold the valve closed. On our engines it also provides the force to close the valve as the cam rotates past full lift (opening) of the valve. There should be some ability to 'slide' the rocker arms along the rocker shafts but if the rocker arms can be 'twisted' on the shafts (turned so the rocker arm is not 90 degrees / perpindicular to the shaft), there's a good chance the rocker shafts and/or rocker arms are worn. This will cause a tapping-like sound that won't go away no matter how many times you adjust the valves to spec. Debris in the valve galley area suggests this is what's going on. Repair consists of replacing the rocker shafts and rocker arms which also may require a headgasket if a lot of caution and careful work isn't done while removing the head bolts and rocker shafts.
Originally Posted by Booosted Supra
(Post 51274297)
I was reading on PG.35 on this for specs and I just had to questions I wasn't sure of that I could not find on any other threads from the past.
http://www.ncttora.com/fsm/1993/engine/7cylinder.pdf 1) After all valves are adjusted should they all be tight? 2) What is the purpose of the spring next to the rockers? The problem I am having with a truck is that the top end is REAL noisy and at TDC the cylinder 1 rockers are very loose which seem to be far out of spec and the number 4 are tight but some of them you can move side to side. Is that normal? I just don't understand the side to side play. Something is def up with the top end, there is a lot of fine metal shavings up top but the pan is dropped and bearings all check out fine to the eye and its not a piston slap I disabled 1 cylinder at a time when running to see if the knock would go away. I'm going to hook up a oil pres gauge and compression test it next, but I'm almost positive they will check out. Previous owner did timing chain and guides which was obvious for me since half of the worn out old guides were in the pan. Any ideas? And I did find the specs you guys were talking about for cold .007/.011 |
Originally Posted by abecedarian
(Post 51275288)
1) Valves should only be tight if the cam is applying pressure to the rocker, i.e.: the valve is being opened or is closing. At any particular time, some of the valves will be loose and others will be tight.
2) The primary purpose of the spring is to hold the valve closed. On our engines it also provides the force to close the valve as the cam rotates past full lift (opening) of the valve. There should be some ability to 'slide' the rocker arms along the rocker shafts but if the rocker arms can be 'twisted' on the shafts (turned so the rocker arm is not 90 degrees / perpindicular to the shaft), there's a good chance the rocker shafts and/or rocker arms are worn. This will cause a tapping-like sound that won't go away no matter how many times you adjust the valves to spec. Debris in the valve galley area suggests this is what's going on. Repair consists of replacing the rocker shafts and rocker arms which also may require a headgasket if a lot of caution and careful work isn't done while removing the head bolts and rocker shafts. |
the springs on the rocker shafts are there to help keep the rocker arms located over the cam and valves. they allow some left/right without letting the rocker arms slide too far.
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