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Timing belt tension - FSM vs. Haynes

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  • Timing belt tension - FSM vs. Haynes

    I've got my new timing belt on and was ready to set tension when I realized the FSM and Haynes procedures are different. Came back to consult Z31P and found good info... but still wanted to post this up as a way of confirming my thinking... yeah, I'm a bit anal about getting it right. I've seen the pictures on Xenon's website and I don't want my engine to look like that...

    I've got the rocker covers off because I also replaced valve stem seals. I reinstalled the lifters and have tightened rockers to check for interference. Everything seems good, but based on FSM, I need to loosen them again to set belt tension without valve spring tension applied to it. I've read a thread that went into detail about how wrong Haynes is, so I just intend to stick to FSM. I suppose if I had understood the tensioning procedure better, I would've just set it before testing for interference... oh well, that's 24 bolts I get to loosen and retighten. Won't be the last time...

    Just a couple of thoughts and/or questions...

    Assume I don't need to go back to TDC before loosening the rockers. It's not that difficult to do, but I see nothing special about that position as long as the timing belt stays on (which is pretty much required if I'm going to set tension.... lulz).

    The Haynes procedure has you rotate the crankshaft by hand and set tension with the rockers tightened and the spark plugs installed, which were both red flags to me. Haynes also states a specification for belt tension which I find no where in the FSM.

    The FSM actually duplicates the belt tensioning procedure - it's in both the MA section and the EM section. Both are consistent (whew!).

    Not trying to draw out the "pro-Haynes vs. anti-Haynes" debate, just wanted to put this out for clarification and future reference to others newbs who, like me, want to get it right the first time.

    Any pros out there who want to add to what I've said?
    '86 NA - original owner (1986-93) and final owner (2005-present)

    My build thread: http://z31performance.com/showthread...-Got-mine-back


  • #2
    I think the deflection is half an inch. I cheated. I got everything to TDC and counted 40-43. THen I put pressure on the belt and rotated it until I got slack at the tensioner. ONce I got slack I put tension on it and rotated the engine. I then made sure I had half an inch deflection and I could barley turn 90 degrees.

    They say take out the spark plugs so you don't feel the compression, etc.
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    • #3
      Just curious what resource you used for that procedure... did you do that with or without the rockers tight? Don't quite understand the "put pressure on the belt and rotated it" part. What you describe seems like a practical "that's about right" approach from having a lot of experience, rather than anything systematic that a newb could do.

      As to having the spark plugs out, I understand and that's why I said it was a red flag for the Haynes procedure. Makes it very hard to rotate the engine by hand, much less feel any sort of interference between piston and valve from an improperly set timing belt.
      '86 NA - original owner (1986-93) and final owner (2005-present)

      My build thread: http://z31performance.com/showthread...-Got-mine-back

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      • #4
        The FSM route is the best one to follow. You put it back to TDC before you fuck with anything on the belt, on the assumption that something will go wrong. Mechanically, there's nothing that makes TDC #1 a sweet spot, quite the opposite actually if you don't loosen up the rockers. It's a good habit to set it to TDC cyl 1 whenever fucking with the belt.
        Feedback- viewtopic.php?f=18&t=19840

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        • #5
          I was reading on here, and some don't loosen the rockers and some do.

          I just did it without, and what I mean by putting pressure on the belt was that the belt had no tension and I was trying to get the slack by the tensioner. So he put pressure on the belt inbetween the cams as I rotated the engine by hand. Once we got a decent tension, we (mind you this was after we counted teeth) got it back to TDC and made sure everything lined up as well as count the teeth and checked the deflection.

          This is just how I did it. If your not comfortable, then don't do it this way. =)
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