Where is the timing mark on crankshaft?

A timing mark is an indicator used for setting the timing of the ignition system of an engine, typically found on the crankshaft pulley (as pictured) or the flywheel, being the largest radius rotating at crankshaft speed and therefore the place where marks at one degree intervals will be farthest apart.

Which is TDC when the crank is 180 degrees off?

If the cam is 180 degrees off (360 deg for the crank) it should not make a difference. because each 360 the crank does the cam does 180 meaning piston 1 will be tdc when the cam lobes are pointing up and again when they are down. but you still need to make sure your cams are at exactly their 180 degree spot relative to the cranks 360 degree spot.

When is the bottom end of a piston at TDC?

There is no concept of a compression stroke if you remove the cam from the equation. The bottom end simply goes up and down. When piston number 1 is at the top of it’s travel, your bottom end is at TDC.

How to determine TDC after bottom end rebuild?

2) look through the spark plug hole and eyeball it till the proper piston is nearly tdc (you may be off a few degrees but at this point some marking on the crank should be pointing up, typically a dot on the timing cog)

Where does the TDC occur in an engine?

To answer that, it would be vital to know the specific engine you are working on because they are all designed differently. All TDC’s are not equal. TDC occurs at the end of compression stroke and end of the exhaust stroke.

There is no concept of a compression stroke if you remove the cam from the equation. The bottom end simply goes up and down. When piston number 1 is at the top of it’s travel, your bottom end is at TDC.

If the cam is 180 degrees off (360 deg for the crank) it should not make a difference. because each 360 the crank does the cam does 180 meaning piston 1 will be tdc when the cam lobes are pointing up and again when they are down. but you still need to make sure your cams are at exactly their 180 degree spot relative to the cranks 360 degree spot.

2) look through the spark plug hole and eyeball it till the proper piston is nearly tdc (you may be off a few degrees but at this point some marking on the crank should be pointing up, typically a dot on the timing cog)

To answer that, it would be vital to know the specific engine you are working on because they are all designed differently. All TDC’s are not equal. TDC occurs at the end of compression stroke and end of the exhaust stroke.