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I'm changing the timing belt on my 1996 Ford Ranger 2.3L. It's my first time doing a timing belt.

These are the directions that came with the new belt:

1995-1997 Ford Ranger 2.3L Timing Belt Replacement Instructions

I have all the pulleys aligned and the belt is on and tight. Step 6 of the Installation instructions says to then

Turn crankshaft clockwise two turns until No. 1 cylinder at TDC of compression stroke with timing marks 4, 6, & 7 aligned.

Is this step necessary or is it just to double check the timing? If it is necessary for another reason, why?

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Yes, it's absolutely necessary. As you state, the primary purpose is to check the timing. It is far better to do this by hand and ensure the timing is right rather than to start the engine without it being in time and it trashes your entire valvetrain. When turning the crankshaft by hand, you can feel if there is any binding, which will allow you to double check things if needed. Also, just because you think you've gotten everything right doesn't mean it is. You can easily have one tooth off and it appear good at first. By the time you have turned it two full crank revolutions, everything will be as it is going to be with alignment. If something is off, it will show itself when you've completed this step. Belt tension in the wrong place us usually the culprit and can throw things off. Turning the crank two turns is a VERY valuable step in ensuring everything is right, so don't skip it.

Also, in reading the step after the step you've stated, part of the reason for turning the crankshaft over two turns is to ensure the tensioner is pre-tensioned correctly, then you torque it in place. This ensures your belt will stay in place as well as not get worn out too soon.

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    yep, you basically put your new alignment for timing to the test to verify everything is in fact in alignment to keep time as the engine would expect. If you hit an obstacle along the way like a valve interfering with a piston then much better to feel that out manually with a low force hand turning than blasted by an engine in motion swinging by high power combustion.
    – jxramos
    Commented Nov 26, 2020 at 5:39
  • This makes perfect sense. However, every other source (including my friend's Ranger's broken timing belt) says that this vehicle has a non-interference engine. The instructions erroneously label it as an interference engine. So the step might not help check the valves on this particular vehicle (but still helps to check the tension).
    – ki9
    Commented Nov 26, 2020 at 23:40
  • @Keith - Did you read the second paragraph.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Nov 27, 2020 at 0:38
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    @Keith - Yes :o) When you first put the belt onto the tensioner, it is pulled back too far. When you rotate the engine (in the correct direction), it takes all the slack from everywhere else in the belt path and gives it to the tensioner. Once that is done, then you lock it in and it's good.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Nov 27, 2020 at 13:51
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    @Keith Just because the valves won't get broken, it doesn't mean you're good to go. The valves do still have to open and close at the right time relative to the piston movement. One of the ironies of engines is that they'll actually run even if they're ridiculously badly set up, but of course performance and emissions will suck. Trust me, it's way easier to check this whilst the engine is still apart, instead of finding out when everything is back together and having to unbolt stuff again to fix the problem.
    – Graham
    Commented Nov 27, 2020 at 15:32

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