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Old 10-27-2010, 09:11 PM
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valve lash question

i just installed a new cam/lifters and im a little confused on setting the lash and breaking the cam in. the cam is a comp 292/.501 hydraulic lifters and roller rockers. ive been reading previous post and most say to follow the firing order get the #1 on the backside of the lobe find zero lash then 1/2 turn. now in a couple other post ive read to skip the 1/2 turn to relive stress from the cam during break-in. any suggestions? thanks

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Old 10-27-2010, 09:21 PM
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Setting valve lash & ignition timing, SBC/BBC....
Remove spark plugs.
Remove valve covers.
Remove distributor.
Standing at the front of the motor, at the water pump and looking toward the rear of the motor, #1 cylinder will be on your right, the first one, just behind the radiator. The next one to the rear will be #3, then #5, then #7 will be the last one on the driver's side, next to the firewall. Looking on the other side of the motor, the passenger side, the front cylinder will be #2, the next one to the rear will be #4, then #6, then #8 all the way to the rear against the firewall. Do whatever you have to do to get this all fixed in your mind. If you have to make a diagram on a large piece of paper and sit it against the carburetor, then do it. Knowing which cylinder is which cannot be over-stated.

Also, knowing which way the crankshaft turns and which way the distributor rotor turns cannot be over-stated. As you are standing at the water pump, the crankshaft turns clockwise, the same way the hands on an analog watch or clock turn.

If you were to climb up on top of the motor from the front and look directly down on the distributor with the cap off, you would see the rotor turning clockwise also. See this cute little animation.....
http://www.boxwrench.net/specs/chevy_sb.htm

With a socket and long bar with a ratchet attached to the bolt head that holds the harmonic damper onto the front of the crankshaft, turn the crank clockwise while a friend holds his thumb over the #1 spark plug hole. Using the starter for this operation WILL NOT WORK. When your friend feels air pressure beginning to build under his thumb, that means that both valves are closed and the piston is coming up on the compression stroke of #1 cylinder. Watch the harmonic damper and you will see the notch that is cut into the outer ring of the damper come up to the top. When that notch is at the top, STOP. You are now at approximately top dead center on #1 cylinder. It doesn't have to be EXACTLY at top dead center to adjust the valves.

Make a mark on the harmonic damper ring so that you can reference this TDC position again later. Either use a yellow crayon like they use at the tire store or a piece of tape placed at that position or whatever your mind can come up with. Make the mark at the top of the harmonic balancer inertia ring. We are going to refer to this position as NORTH, because if you got down on your knees and looked at the harmonic damper from straight on, like you were looking straight through the centerline of the crank, this would be the NORTH position.

Loosen both adjusting nuts on both rockers on #1 cylinder until the rockers are loose on the studs. Have your friend hold his finger on the tip of one of them so that he is pinching the rocker arm down onto the tip of the valve, holding it tightly. Now, you grasp the pushrod for the rocker he is holding down and jiggle the pushrod up and down while using a socket wrench to slowly tighten down the adjusting nut until all the slack is removed and you cannot move the pushrod up or down any longer. Be delicate here. This is not a strong-armed operation. You are simply taking all the slack out of the pushrod and getting the rocker adjusting nut very slightly tightened down against the trunnion of the rocker arm. Now, make 1/4 turn more on the adjusting nut.....1/4 turn.....90 degrees......OK, that valve is done. Now, move over to the other valve on #1 cylinder and repeat the operation.

You may have heard that you can rotate the pushrod with your thumb and forefinger until the pushrod gets tight and use that for adjusting the valves. While that may work for someone who builds motors day in and day out for a living, it WILL NOT WORK for someone like you who has no way of knowing how much resistance he should be feeling for. Jiggling the pushrod up and down is BULLETPROOF and can be done successfully by even a first-time builder.

Now, you have both valves adjusted on #1 cylinder. With the socket and ratchet on the harmonic damper retaining bolt head at the crank, turn the crankshaft 1/4 turn clockwise. That will mean that the mark you made on the damper ring will move clockwise from NORTH to EAST.....STOP. Make another mark on the damper ring at the straight-up position. Now, you will have a mark at EAST and a mark at NORTH.

You have moved the crank 90 degrees and into the next cylinder's firing range. There are 720 degrees in a full cycle to fire all 8 cylinders, so turning the crank 90 degrees at a time will allow us to adjust the valves on all 8 cylinders with just 2 full turns of the crank. If you knew that a small block Chevy's firing order is 1-8-4-3-6-5-7-2, then you would know that it is #8's turn to fire. Go to #8 and loosen both adjusting nuts, just like you did on #1. Have your buddy hold the rocker down against the valve stem while you jiggle the pushrod up and down to remove all play, all the while slowly turning the adjusting nut to remove the play. When all the play is removed, tighten the nut another 1/4 turn. Move on to the other valve on #8 and do the same.

Now, you have adjusted the valves on cylinders 1 and 8. Put the socket on the crank nut and turn the crank 1/4 turn to the right (clockwise, just like before). Place a mark at the top of the inertia ring like you did last time. This mark will be at NORTH. The mark you had at EAST will move to SOUTH and the one you had at NORTH will move to EAST. Following the firing order, we will now go to cylinder #4 and adjust both valves. Then we will move the crank 1/4 turn and make another mark and do cylinder #3. Then we will move another 1/4 turn (the crank has marks for each 1/4 turn now) and do cylinder #6. Then we will move the crank another 1/4 turn and do cylinder #5. Then we will move the crank another 1/4 turn and do cylinder #7. Then we will turn the crank another 1/4 turn and do cylinder #2. Then we will turn the crank another 1/4 turn and be back to firing on #1, where we will stab the distributor and install the retaining clamp and bolt. We will leave it a little loose so we can rotate the distributor housing. You may have to use a long screwdriver to line up the slot in the distributor driveshaft as you look down into the hole where the distributor goes.

As if we were standing on the motor and looking down on it, we will want to point the rotor tab at #1 cylinder, approximately 5:30 O'Clock if you look at a clock face. Position the distributor housing so that you can twist it both ways without the vacuum advance can hitting on the intake manifold. Replace valve covers. Replace spark plugs. Using your longest spark plug wire, plug it into the 5:30 position on the cap, co-inciding with the tab on the rotor at 5:30 and run the other end of the wire to #1 spark plug. The longest wires will be for #1 and #2. The next longest wires will be for #3 and #4. Next longest for #5 and #6. The shortest wires will be for #7 and #8. Going around the cap in a clockwise manner, the next hole in the cap will take the wire for #8 spark plug, then #4, then #3, then #6, then #5, then #7, then #2.

Now, depending on where the timing tab is on your motor (there were 3 different positions used), you might have to rotate the distributor housing a little one way or the other to get the motor to fire off, but unless I miss my guess, SHE WILL FIRE OFF THIS TIME. Have a timing light affixed to the #1 spark plug wire, adjust timing and lock the distributor down.

A little more info about the different timing positions. Like I said, there are 3 different ones. If you were to stand up over the motor and look down on the harmonic damper, there is a 12:00 Noon position, a 2:00 O'Clock position and a 2:30 O'Clock position. Through the years, the timing tabs and front covers get mixed up on these motors, so you really should find top dead center and use the proper mark on your harmonic damper to line up with the timing tab on your front cover. Here is the procedure for doing this with the motor assembled that I wrote for the Crankshaft Coalition Wiki....
http://www.crankshaftcoalition.com/...top_dead_center

Others will have different procedures for setting the lash, but the method outlined here has served me well for decades....
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Old 10-27-2010, 09:42 PM
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thanks techinspector1

you just made my mind up for me. appreciate your info
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