Another rocker arm question
Thread Starter
Melting Slicks
Joined: Jun 2002
Posts: 2,152
Likes: 243
From: Northern VA
Another rocker arm question
Ok, got serious about adjusting the pro mags. I followed instructions in the manual and got #1 cylinder to TDC and adjusted int. and exh as noted in the manual. I took Nathan Plemon's advice and adjusted the outer nut down finger tight until the pushrod was tight. Then I tightened the poly lock down, then I went back and tightened the outer nut about 1/4 turn. I then I cranked over the engine to #6 and did the same routine. The arms I previously adjusted were now just a little loose. Is this correct? I DO NOT want to do this again for a while!! Thanks
Melting Slicks
Joined: Sep 2000
Posts: 2,710
Likes: 1
From: Green Bay WI
Re: Another rocker arm question (jerkyboy)
When I adjusted mine, I moved the pushrod up and down until the very point where it didn't move upwards or downwards anymore. I then tightened the outer nut 1/4 turn and put the inner locking nut down as tight as it would go.
Then, I turned the outer nut a little more (it wouldn't go much more - not even an 1/8th of a turn).
I found it too hard to try and judge when I felt a "little or slightest" drag when spinning the pushrod between my fingers. IMHO, the method I used "felt" a lot more accurate... :)
Then, I turned the outer nut a little more (it wouldn't go much more - not even an 1/8th of a turn).
I found it too hard to try and judge when I felt a "little or slightest" drag when spinning the pushrod between my fingers. IMHO, the method I used "felt" a lot more accurate... :)
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Re: Another rocker arm question (cprgmr)
I noticed that there was only about 1/8 turn between "a little" drag and the point where I could hardly turn the pushrod.
So I set lash to zero + 5/8 turn which puts preload at 1/2-3/4 turn.
So I set lash to zero + 5/8 turn which puts preload at 1/2-3/4 turn.
Le Mans Master
Joined: Feb 2000
Posts: 9,715
Likes: 27
From: Kempner Texas
Re: Another rocker arm question (jerkyboy)
No, that's not correct.
It's not where the piston is, as you indicated that the #1 was at TDC, it's when the lifter is on the base circle of the camshaft lobe. Since you can't actually see the camshaft, you have to watch the rocker arms to tell when the lifter is on the base circle of the camshaft lobe.
That's the real "trick", to make sure the lifter is riding on the base circle of the camshaft lobe when you adjust the preload for THAT lifter.
When the piston is at TDC, the valve has already begun to open and the lifter will not be on the base circle of the camshaft. So the lifter will be on the cam's RAMP, not the base circle.
There are several different ways to adjust lifter preload, each has his favorite. I'm not going to fight over which method is "best".
I posted, in the TOOLS section on this Forum, the method I like best. A few of the cam companies, such as CompCams, recommend the same procedure; you bump the engine while watching, say, the EXHAUST rocker. When it just begins to move you set the INTAKE lifter preload for the same cylinder.
Now you bump the engine and watch the INTAKE rocker and when it goes fully open then about 2/3rd of the way toward being closed, you set the EXHAUST lifter for THAT cylinder.
You continue on until you've done the other 7.
Jake
It's not where the piston is, as you indicated that the #1 was at TDC, it's when the lifter is on the base circle of the camshaft lobe. Since you can't actually see the camshaft, you have to watch the rocker arms to tell when the lifter is on the base circle of the camshaft lobe.
That's the real "trick", to make sure the lifter is riding on the base circle of the camshaft lobe when you adjust the preload for THAT lifter.
When the piston is at TDC, the valve has already begun to open and the lifter will not be on the base circle of the camshaft. So the lifter will be on the cam's RAMP, not the base circle.
There are several different ways to adjust lifter preload, each has his favorite. I'm not going to fight over which method is "best".
I posted, in the TOOLS section on this Forum, the method I like best. A few of the cam companies, such as CompCams, recommend the same procedure; you bump the engine while watching, say, the EXHAUST rocker. When it just begins to move you set the INTAKE lifter preload for the same cylinder.
Now you bump the engine and watch the INTAKE rocker and when it goes fully open then about 2/3rd of the way toward being closed, you set the EXHAUST lifter for THAT cylinder.
You continue on until you've done the other 7.
Jake
Thread Starter
Melting Slicks
Joined: Jun 2002
Posts: 2,152
Likes: 243
From: Northern VA
Re: Another rocker arm question (JAKE)
You're right, I should not have said TDC. I turned the crank pulley until I saw the line on the damper match up to 0 on the tab while having my other hand on the #1 valves. They did not move so according to the manual, I think I was at the right place???
Le Mans Master
Joined: Feb 2000
Posts: 9,715
Likes: 27
From: Kempner Texas
Re: Another rocker arm question (jerkyboy)
As I said, there are lots of different views/recommended methods on this; depends on who you ask.
GM's Shop Manual, Chilton, HP books, and other books you buy at some of the auto parts stores all have a procedure that will work, but ONLY if you follow the instructions/directions exactly.
Using those procedures, though, has caused lots of guys to get all screwed up; it's just too darn easy to get confused and adjust the wrong valve. Some report that those procedures don't work well with aftermarket camshafts which have different lift and duration specs from stock.
Check the websites for CompCams and Crane and see if their recommended procedure is posted. I know both of their catalogs (which you can order for free) contain the step by step procedures.
Next time you're at the track, watch the procedure the "Big Boys" use when they adjust/check their valves between rounds. You can bet they use the most fool-proof/precise method.
Jake
GM's Shop Manual, Chilton, HP books, and other books you buy at some of the auto parts stores all have a procedure that will work, but ONLY if you follow the instructions/directions exactly.
Using those procedures, though, has caused lots of guys to get all screwed up; it's just too darn easy to get confused and adjust the wrong valve. Some report that those procedures don't work well with aftermarket camshafts which have different lift and duration specs from stock.
Check the websites for CompCams and Crane and see if their recommended procedure is posted. I know both of their catalogs (which you can order for free) contain the step by step procedures.
Next time you're at the track, watch the procedure the "Big Boys" use when they adjust/check their valves between rounds. You can bet they use the most fool-proof/precise method.
Jake
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Pro
Joined: Jan 2003
Posts: 669
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From: memphis tn
Re: Another rocker arm question (JAKE)
i always do it EXACTLY the way jake suggested. it has never failed me no matter what cam i used. EO,IC.
i also spin the pushrod and tighten down on the poly lock using my fingers until i feel resistence. tighten the outer nut 1/2 turn, tighten the center lock screw, break out the torque wrench and tighten the outer nut to 45lb.ft. this is usually less than 1/8 additional turn.
i also spin the pushrod and tighten down on the poly lock using my fingers until i feel resistence. tighten the outer nut 1/2 turn, tighten the center lock screw, break out the torque wrench and tighten the outer nut to 45lb.ft. this is usually less than 1/8 additional turn.