Timing belt tensioner

[minesapint]

1986 325i Cab

I’m replacing my timing belt, new belt tensioner, spring & pin. Plus other bits & bats.

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The method is to compress the tensioner spring & lock it with the top tensioner bolt, fit the belt, then slacken the top tensioner bolt & the spring expands & tensions the belt, the WiKi then says to tighten the top & bottom bolts to 16 ft-lbs, ie tightish.
Now to my question…….when the tensioner bolts are tightened & the belt slackens over time, the tensioner cannot do its job as it is locked. If the bolts were left a little slack the tensioner would do its job & take up that slack, But ….. would those slack bolts vibrate loose over time & potentially caused havoc within the timing belt covers.
Do you get my logic here, what’s the point of the tensioner when it cannot continually tension the timing belt.
Would appreciate your comments.
Cheers

[flybynite]

Do you get my logic here, what’s the point of the tensioner when it cannot continually tension the timing belt.

Yes I get the logic, but simply it is not designed to do that. There are spring tensioners on newer engines but they are a different design with stronger springs.

If you left it loose, when you rev the engine the forces on the belt would simply compress the spring and the belt would jump. It took a while to design systems that can cover both static and dynamic loads, some tensioners vary tension with oil pressure to help do this.

Unfortunately the M20 comes from a time when cars were built by engineers to be maintained by mechanics but generally once set the belt stays good, only generally needing a tweak after it settles down. OEM or Conti belts don't stretch much and generally the only thing that causes slack in the system is a failed or loose tensioner.

Nice to see you uses an OEM belt