Determining top dead center

First off, the large round hub on the front of the crankshaft is called a harmonic damper by some and a harmonic balancer or simply "balancer" OR "damper" by others. If it is bolted to the crank of an engine that is internally balanced, then it serves only the function of being a harmonic damper, dampening vibrations set up in the crankshaft as a result of the rod journal springing back and forth from the forces applied to it during operation. If it is bolted to the crank of an engine that is externally balanced, then it serves the dual purpose of damper and balancer. Unless the engine has been unaltered and is "as built" by the manufacturer, you have no idea if the TDC notch on the ring matches the timing pointer attached to the block or front cover, even if the outer ring has not slipped at all.  

There are a multitude of different dampers and three different timing pointer locations on a Chevy. I don't know about other brands, but small block Chevies use 12:00 noon, 2:00 O'Clock and 2:30 O'Clock and if anyone has had the engine apart, you don't know if they used the original damper and timing pointer or other swap meet parts when they went back together with the engine. The whole reason for doing this operation in the first place is to be able to time the engine with a timing light and know- absolutely- that the timing is correct. The elastomeric material that connects the outer inertia ring of the harmonic damper/balancer to the inner hub of the damper/balancer which presses onto the snout of the crankshaft begins to break down over time due to ozone in the atmosphere and oil and fuel or other foreign materials which may find their way onto the material. When this happens, the outer ring may slip circumferentially in relation to the inner hub, rendering any attempt to time the engine with a timing light futile. Even though this operation you are about to do will bring the timing marks back to correct for the time being, there is no guarantee that the ring will not slip further after a while. You also have no idea if the timing pointer matched the inertia ring in the first place if the engine has been disassembled and reassembled by someone else in its lifetime. If you want to bulletproof the operation, then start with a new or rebuilt damper and use the correct timing pointer for that damper.

I use and recommend a rebuilt damper/balancer from Damper Doctor. They disassemble stock, OEM production dampers, clock the hub to the ring and reasssemble the unit with new elastomeric material pressed together under tremendous hydraulic pressure. An 8" damper for a 350 Chevy can be had for a mere $32.95, deal of the century!!!! The option is a used damper/balancer that may be clocked worse than the one you have or an aftermarket damper/balancer that will cost more money and may not have been correctly machined on the inner hub diameter. Some of these fosdick Chinese dampers being sold are either oversize or undersize for the production crank snout diameter. The damper/balancer MUST BE A SNUG PRESS-FIT on the crank in order to properly transfer harmonics from the crankshaft to the damper/balancer hub. On a street engine or a drag race engine down to 11.00 E.T. in the quarter mile, an OEM-type damper/balancer may be used legally. At 10.99 E.T., an aftermarket SFI-18.1 damper/balancer is required.   

If the engine is a short block on the stand, you can determine TDC with a strap bolted across two head bolt holes, with the strap drilled and threaded and using an adjustable bolt/nut arrangement. If the engine is assembled, use the method described here, using a piston stop tool.  

In this exercise, you will install a piston stop tool into #1 spark plug hole (driver's side front on a Chevy/Mopar, passenger's side front on a Ford). If you use the damper/balancer retaining bolt to turn the crank and turn the crank counter-clockwise, you risk loosening the bolt in the crank that retains the harmonic damper. Then you have to get your buddy to crawl under and hold a large flat-blade screwdriver into the flexplate/flywheel ring gear teeth and jam it against the bellhousing to keep the engine from turning while you tighten the bolt back (60 ft/lbs on a SBC, 85 ft/lbs on a BBC). Far better to just turn the crank clockwise only (keeping the bolt tight) and sidestep a problem before it occurs. Been there, done that. The following tool also solves this problem. Remove the crank pulley and bolt it onto the damper/balancer .............

You'll need to get everything out of the way so you can work on the harmonic damper ring. Remove the fan, belts, shroud and water pump pulley. You may have to remove the water pump to gain full access to the damper ring and do the measuring needed for this operation. This would be a good time to replace the pump anyway. Pumps and gaskets are not that pricey. Whether or not you replace it, remove the pump and check for impeller slip on the pump driveshaft. Hold the impeller with one hand and the drive hub of the pump in the other hand and twist in opposite directions. I have encountered overheating and found this problem....FINALLY....after much head-scratching. Even if the pump is good, you may at this point want to replace it with a good, high-flow unit. Flowkooler, Stewart and Edelbrock are names that come to mind, there may be others who produce a quality high-flow pump. A good high-flow pump is nearly MANDATORY on a 400 SBC or any other engine which uses siamezed cylinders.  

Anyway, back to the task at hand. First use solvent and then hot soapy water to thoroughly clean the harmonic damper and timing pointer. Remove the valve cover for #1 cylinder and back off the rocker arms for both valves for that cylinder. COUNTING THE NUMBER OF TURNS YOU LOOSEN THE ROCKER NUTS WILL MAKE IT A SNAP TO GET NEAR TO THE CORRECT LASH WHEN YOU TIGHTEN THEM BACK AFTER THIS OPERATION. Disabling the valves by backing off the rocker arms will prevent interference between the timing tool probe and the valves while turning the crank. Turning the engine over by hand will be easier if you remove ALL the spark plugs. With a socket on the damper retaining bolt or using the tool described and a long socket handle, rotate the crankshaft clockwise while your buddy uses a stong flashlight to look into the #1 spark plug hole. Bring the piston up to top dead center, then continue rotating the crank very slowly so that the piston comes down in the bore slightly. You want the piston slightly past top dead center down in the bore, but not so far down in the bore that the probe of the top dead center tool will not contact the piston crown. At this point, we are not concerned with where the crank/piston is in the total 720 cycle of operation. In other words, we have the valves disabled, so it doesn't matter whether you are on the exhaust cycle or the compression cycle as the piston comes up to TDC. All we are working with at this point is the 360 degrees of the damper, regardless of the cam and valves. 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.  

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. Remove the piston stop tool probe and housing. 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 spark plugs and wires. Remove the masking tape, reinstall water pump, pulley, fan, shroud and belts. 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. On a Chevy, clockwise rotation of the housing retards the ignition timing, counter-clockwise advances it.  From #1 plug position on the cap, the wires will be plugged in clockwise around the cap from there and will go in the firing order (Chevy 1,8,4,3,6,5,7,2). The rotor should be pointed to the 5:30 O'Clock position to fire #1 plug. This will give maximum clearance between the vacuum cannister and the runners of the intake manifold so that you have room to twist the distributor to fine-tune the ignition timing when you get the engine running.  

Hook up your timing light to #1. Remove the vacuum advance rubber hose from the vacuum canister at the distributor and plug the end of the hose with a golf tee or other suitable plug. Adjust initial timing at the crank to what you want by rotating the distributor housing. Some use the factory setting while others prefer to set it a little more advanced for good throttle response. If using a little more initial advance at the crank, make certain you don't have so much mechanical advance in the distributor that you exceed the total timing (initial and centrifugal) specified for the engine. Most small block chevies will run best with around 32-34 degrees (initial and centrifugal) with fast-burn heads and 35-36 with conventional heads. If using a camshaft with more duration, you may want to increase the ignition timing lead at the crank and limit the centrifugal advance in the distributor to achieve your total ignition timing. Ignition curve kits are available to customize the centrifugal advance curve in order to limit total advance when using more advance at the crank.