Editing Determining top dead center (section)
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===Procedure without removing valve cover=== If checking an assembled/long block engine, you will install a piston stop tool into #1 spark plug hole ([http://www.offroaders.com/tech/V8-engine-firing-order.htm domestic V8 firing orders]). Screw the top dead center housing into the spark plug hole and snug it down. Insert the probe of the tool into the tool housing and screw it in until you feel resistance of the tool probe against the piston crown. Snug it down slightly against the piston crown and start from there. Attach a degree wheel or affix a 4 to 5 inch length of masking tape to the damper ring with the left end of the masking tape about 1 inch to the left of the timing pointer on the timing cover, positioning the masking tape toward the block-side edge of the damper ring, leaving room at the front edge of the ring to affix your timing tape later. With a ball-point pen, make a thin mark front to rear on the masking tape right at the point of the timing pointer. Rotate the crankshaft clockwise (here's where you'll be glad you purchased a piston stop tool with a hole drilled through the center of the tool probe) until the piston comes up against the piston stop tool probe again. Easy does it here, you don't want to bring the piston up against the tool so hard that it will dent the piston crown. Make another mark on the masking tape with your ball-point pen to coincide with the tip of the timing pointer. With your 6 inch caliper, measure the distance between the two marks you made with the pen. Divide this distance in half. Move the jaws of the caliper to show this half distance. With one caliper jaw on one of the marks you made with the pen, the other jaw of the caliper will be at true top dead center. Make another mark on the masking tape at the caliper jaw to show this center (or middle) position on the masking tape and affix your degree tape onto the ring, aligning TDC on the timing tape with the center mark you made on the masking tape. If the timing tab and damper line agree with this, they're accurate. If not, the tab can be readjusted or another line made on the damper to coincide with '''true''' TDC. Remove the piston stop tool probe and housing. If the rocker arms were loosened previously, tighten the rocker arms back the same number of turns you used when you loosened them. With your buddy holding his thumb over the #1 spark plug hole, rotate the crankshaft until he feels compression against his thumb. Continue to rotate the crank slowly until the timing pointer aligns with about 10 degrees before top dead center on the timing tape. STOP. DO NOT ROTATE THE CRANKSHAFT ANY MORE. Replace the spark plugs and wires. Remove the masking tape, reinstall water pump, pulley, fan, shroud and belts if they were removed previously. Replace any coolant/water you may have lost in the operation. Remove the cap from the distributor and align the rotor with the cap terminal that coincides with #1 plug by rotating the distributor housing. Looking down on the motor from a birds-eye view, the rotor needs to be pointing toward 5:30 on an analog clock face (pointed toward #1 cylinder). The gears that drive the distributor off the camshaft are helical, so you need to drop the distributor into place so that it can spiral down and be in the correct position when the distributor housing is seated on the intake manifold. On a Chevy, clockwise rotation of the housing retards the ignition timing, counter-clockwise advances it. On a Chevy V8, because of the pitch of the helical gears on the cam and distributor, the rotor will turn about 2 inches CW as the distributor is lowered into position. That means the rotor needs to start out about 2 inches CCW from where it needs to end up with the distributor fully seated. From #1 plug position on the cap, the wires will be attached clockwise around the cap following the [http://www.crankshaftcoalition.com/wiki/Category:Firing_orders firing order] (Chevy V8: 1-8-4-3-6-5-7-2). As was stated in the last paragraph, the rotor should be pointed to the 5:30 o'clock position to fire #1 plug. This will give maximum clearance between the vacuum canister and the runners of the intake manifold and firewall so that you have room to twist the distributor to fine tune the ignition timing when you get the engine running. If the valve cover was removed earlier, set the valve cover on the head to keep oil from flying everywhere and start the engine and allow it to warm up. Do the final adjustment on the #1 cylinder rockers. *Chevy: back off the rocker until it audibly clatters, then tighten it down 1/2 to 3/4 turn past where it quiets down. If you want to adjust the valves on the rest of that side of the block, now would be a good time. Replace the valve cover.
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