Well, my ignorance of how engines operate seem to have no bounds. With a pulley marked “OT”. Short for : Oben/Top (oben translates to “above”, “up” or “at the top” in german), and a mark on the case for alignment, surely this must be when the engine is at Top Dead Center.
I would be right, but only half the time. This being a four-stroke engine, it requires two revolutions of the pulley / crankshaft to complete a full cycle. This true whether you engine has four cylinders or twelve. This image from Haynes sums it up as well as anything I can find.
So that timing mark is going to line up at the top of both the compression stroke and the exhaust stroke. Since Top Dead Center (TDC) is defined as not just when the #1 cylinder as at the top of its travels (i.e. closest to the head), but specifically on the compression stroke and both valves are closed, you can’t be sure just by looking at the timing marks.
The significance of TDC comes into play not only when adjusting your valves, but also proper insertion of the distributor drive gear.
In any case, the position of the piston, never mind valve state, is not exactly staring you in the face when you have an assembled engine. That said, there is more than one way, and you can choose your own adventures so to speak.
As you might expect, you will need to rotate the engine to get there. I strongly advise you only ever rotate clockwise. Clockwise is from the perspective of standing at the back of the car, looking at the crank pulley. If you’re staring at the flywheel, you should be turning counter-clockwise. Otherwise, be prepared to take of the third piece of the case and replace your brass gear. Embarrassing and not fun. Don’t ask me how I know.
Check The Pressure at Spark Plug
If both valves are close, a significant amount of pressure (even if just air) should be built up in the cylinder. By removing the spark plug you can feel this if able to keep a finger over the plug hole while rotating the engine. If you are a solo act, then you also can DIY ways to see or tools that enable you to hear the displacement of that air.
Watch the Lifters
The late great Harry Pellow long ago wrote instructions for the 356 Registry. I don’t always find his references to direction as clear as I’d like. Example: “the “Front” Middle of the 4″ requires a few reads for me to get it’s the third from the pulley. I will restate his guidance in terms that are more obvious to me:
- Remove the right hand valve cover.
- Turn the crank pulley CLOCKWISE
- Watch the #1 cylinder intake valve open / go down (i.e. visible tip of valve at rocker going down indicates the valve is extending into the cylinder, thus “open”).
- Watch the same #1 cylinder intake valve close / raise up.
- Stop turning, and your OT mark should be about 7 – 8 O’clock
- Continue turning until the OT mark on the pulley lines up with the timing line on the third piece of the case (near generator stand)
You should be at TDC.
