But Patrick---Pretty close to tdc is not the result we're looking for---When we degree an engine, whether its to check cam or set the timing pointer, we usually will use a positive stop piston stop that will contact the piston aprox 3/8 to 1/2 inch before tdc----mark the degree wheel--rotate the cranshaft in the reverse direction til the piston contacts the stop, mark the degree wheel---tdc will be EXACTLY 1/2 the number of degrees between these two marks---remove the positive piston stop and turn the crank until the newly arrived at tdc is lined up at the degree wheel pointer--at this point we'll do all the camshaft spec checking and adjust timing as necessary.and we'll then leave the crank/piston at tdc per our set up degree wheel, install the front cover and harmonic balancer, checking the degree marks are lined up and if not correcting them.
If the engine is assembled, and it is necessary to verify tdc, we will install a positive stop as has been described by others(not a thumb) and rotate the engine til it contacts the piston, mark the dampner, rotate crank the other way until contact, mark the dampner, splict the differance for tdc, and then will place marks at 90,180,270 for adjusting the valves, doing leak down checks, etc.
If doing a leakdown check, turn to tdc 0*, insert leakdown ---if it is 100 % your on wrong cylinder by one crank revolution and can either go to that cylinder of the firing order or preferably turn one rev til on #1 and start again, then turn to 090 and do 2nd cyl, 180 3rd cyl,270 4th cyl etc thru 2 complete revolutions of the crank/ I will also check the adjustment of the valve clearances as I work thru the order plus check spring pressures if at a race.
At the end of the firing order of checks/adjustments we will be coming up on the timing marks for the ignition and we'll check for anything gone array or change timing at this time. Valve covers back on, spark plugs indexed and now its time to make jetting changes if spark plug check/ air/weather data shows a need for rich or leaner jets.
Fill fuel cell,
oil level, pack parachutes, adjust tire pressure---add/remove weight, gear ratio change then pretty much ready for interviews and signing autographs
The
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