I believe the pin you are talking about is the #1 cylinder TDC locating pin. On the 12-vavlve engines, it was located on the back of the timing gear housing, under the injection pump. When cylinder #1 was at TDC, the pin would fit into a hole in the camshaft gear.
So now some of you may ask, "what's it for?"
Well, two things...
First, it is used for aligning the engine to do a fuel injection pump timing check/adjustement. Second, it can be used as the starting point to do a valve adjustement. Both of thse things require you to have cylinder #1 at TDC. If you ask me, using this little pin to find TDC is fairly difficult. I prefer to do it other ways, such as using a TDC locator when doing timing check/adjustment.
If after doing one of the above tasks the timing pin is NOT pulled back out, it will break off once the engine is started. The part that breaks off
could get itself jammed in the timing geartrain, casuing extensive damage. Or it
could just fall to the bottom of the timing gear cover and not cause any problem. I for one, would reomve the gear cover and get the piece out to avoid any problems down the line.
So to answer your question... The 24-valve does not have a timing pin. The 24-valve uses a stamped mark on the front of the timing cover to locate TDC. Just pull off the crankcase breather filter assembly, and align the keyway on the injection pump shaft with the TDC mark on the cover. Simple as that.
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Hope this answers your question.
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