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My car is due for a timing belt change now. I have done everything, locked the camshaft pulleys and crankshaft sprocket and removed the old timing belt. Now, I want to install the new belt on the car but there are some procedures that I don't fully understand. In the following pictures, you will find the steps for tightening the belt tensioner after installing the new belt.

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In the manual, it is said that you have to tighten the belt tensioner, crank the engine, then loosen the tensioner, then again tighten it. I don't understand these parts. Why don't they tighten the belt tensioner in the first place after fitting the new belt and adjusting the index pointer?

I also found a video in Youtube in which a Russian mechanic explains the whole procedure.

https://www.youtube.com/watch?v=5b0lciKkEdQ

In the above video, first he tightens the belt tensioner bolt at 23:00, then he tightens it again at 24:52 and then again he tightens it at 29:25! And finally, he tightens it at 34:26 for the last time!

Why did he divide the tightening into 4 different phases?

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Initially any slackness in the belt will be spread between all of the pulleys. By tensioning it, then cranking by hand, you are moving all of the slack to the location of the tensioner. The tensioner can then be adjusted correctly.

Edit - You will appreciate that there is a lot of friction associated with each of the pulleys that the belt travels around. If you try to turn them by hand it is quite difficult.

There will be a very small amount of slackness in the belt between each pulley after first fitting the belt. If there were not slackness, you wouldn’t be able to get the belt on.

The initial adjustment of the tensioner will not add enough pressure to overcome the friction of the pulleys, so they won’t move and any slackness between them won’t be taken up. By rotating the engine by hand, you move the slack between each of the pulleys so that it is now at the location of the tensioner. You can then adjust the tensioner to take up the slack.

By repeated adjustment you are ensuring that any remaining slackness in the belt is taken up by the tensioner.

Another edit -

When you said in the video that he tightens it four times, I believe what you described as the first 2 times was just 1 attempt. He was just struggling to get it tightened. The very last time he was just making sure that the bolt was tight before he finished.

I do think that he didn’t do the initial tensioning correctly. He turned the Allen key anti-clockwise before locking the bolt. I believe he should have turned it clockwise to put the maximum tension on the tensioner as described in step 63, but please do not take my opinion as correct. Maybe someone else will back this up.

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    Added a bit more to my answer. – HandyHowie May 17 at 7:06
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    Yes, you turn the crank pulley, which pulls the belt tight going back to the cam shaft pulley. Therefore any slack will appear in front of the crank pulley. That is where the tensioner is located. – HandyHowie May 17 at 8:22
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    You should really wait before accepting this answer just in case someone else has more useful information to add. – HandyHowie May 17 at 8:23
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    No, as long as you turn the engine in the same direction that the engine usually runs, the tensioner will take up the slack as described in the instructions. You can rotate it a few times. If you rotate the engine in the opposite direction you will add slackness in the belt, so only rotate the engine in the specified direction. – HandyHowie May 17 at 11:47
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    If you follow the instructions exactly, you should have no problems. The process is just making sure that the belt it under tension all the way around and that you don’t have hidden slack between the pulleys, – HandyHowie May 17 at 11:54

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