Thread: 350 issues

Tweet

Jon, since Bob and Glenn are covering the carb, I'll move on to some other areas.

You said you pulled the top end down. Did you retain the intake gaskets? If so, examine them closely for being compressed (pinched) all the way around each and every intake port. You could have an internal vacuum leak that you would never find by spraying a flammable material on the outside of the motor in an attempt to find a vacuum leak. Here's a tutorial I wrote for the wiki on another forum.....
http://www.crankshaftcoalition.com/w...ad%2C_internal

The other thing that comes to mind is the valve adjustment. Valves could be too tight, particularly if you used the "twist the pushrod" method of adjusting. Follow this procedure and see if it helps.....
Bring the #1 piston to TDC on the compression/firing stroke. Do this by removing #1 spark plug and rotating the crankshaft clockwise by hand while holding your thumb (or your buddy's thumb) over the spark plug hole until you/he feels compression as a result of the piston coming up the bore with both valves closed. Continue rotating the crank while watching the harmonic damper. When the TDC notch on the damper aligns with the timing tab on the front cover, indicating TDC, stop. Back off the nuts on the intake and exhaust valves on #1. Move the pushrod around a little to make sure it is seated in the pushrod cup of the lifter plunger and not up on the face of the plunger. While holding the rocker arm tip down against the valve stem tip, jiggle each pushrod up and down while you tighten the nut down to zero lash. Give the nut another 1/2 to 3/4 of a turn. Adjust both intake and exhaust.

On the front face of the harmonic damper or on the face of the crank pulley, use WhiteOut to make four marks. One at 12 O'Clock, one at 3 O'Clock, one at 6 O'Clock and one at 9 O'Clock. This stuff ain't rocket science, so the marks don't have to close to the nearest thousandth or anything. Just eyeball them like you would a clock face and get them close.

Turn the crank 90 degrees clockwise (1/4 turn) so that the mark you made at 9 O'Clock comes up to 12 O'Clock. Adjust both valves on the next cylinder in the firing order (#8). Turn the crank 1/4 turn so that the mark you made at 6 O'Clock comes up to 12 O'Clock and adjust both valves on #4 cylinder. Continue doing the rest of the valves in the firing order (1-8-4-3-6-5-7-2). To adjust all the valves, you will make 1 3/4 revolutions of the crankshaft from your starting point at #1, rotating the crank 1/4 turn (90 degrees) clockwise each time between adjustments.

For those wondering about adjusting both valves on one cylinder at the same time.......
There are 720 crankshaft degrees of rotation (2 complete turns) to go through a complete firing of all 8 cylinders.
With the piston at TDC firing, the intake valve closed about 140 degrees ago and won't open for another 330 degrees, so the intake lobe is on the base circle. The exhaust valve closed about 340 degrees ago and won't open for another 120 degrees, so the exhaust lobe is also on the base circle.

Now, all this valve adjustment business assumes that the harmonic damper inertia ring hasn't slipped on the hub and still is valid for TDC as relates to the hub (crankshaft key). It also assumes that you are using the correct timing tab on the front cover for the harmonic damper used. There are 3 different timing locations used on a small block Chevy, 12 O'Clock, 2 O'Clock and 2:30 O'Clock. So, if you had a 12 O'Clock damper and a 2:30 O'Clock timing tab on the cover and/or the inertia ring has slipped, it is possible that you could be off the base circle when trying to adjust the valves. Of course, if that were the case, the valves would be too loose and thus noisy like solids. Here's another tutorial I wrote to validate the damper inertia ring as it relates to piston TDC.....
http://www.crankshaftcoalition.com/w...op_dead_center