Tension in TB

[duncan]

Advice, words of wisdom requested.
I’m in the middle of doing a major service.
TB replaced;
Cams pinned, old belt marked with dots against cam gears, teeth on belt counted and transferred to new TB. New TB fitted, cams un-pinned, crank rotated and TB tensioned against blue mark on pulley. All happy.

End covers on, engine remounted, re-check on valves, and rear cam cover on.
About to fit front cam cover and slack now apparent in TB between Inlet and Exhaust cams on the front bank. TB no longer drum tight/ tappable.
So, all unhappy and HELP!

Is this slack normal, when the crank is aligned with the blue mark this is described as ‘maximum tension’, presumably therefore all other positions are at a lesser tension, is what I observed a manifestation of this.
Trying to think of a good reason not to re-expose TB and repeat the process.
Duncan

[goldnsx]

You'd better recheck the tension for sure before waking up in the middle of the night...

Just one elementary question: did you remove the (ignition) plugs while tensioning the TB?

The best references you can find are the videos of our master Kaz found here: https://www.youtube.com/user/kzukna1/videos esp. this one: https://www.youtube.com/watch?v=T3Ym3hj61ko but check all 6 videos.

Or you might do a video as well and show us.

Good luck!

[duncan]

Hi, the sleepless night was last night!
Plugs were out when I tensioned the TB, plugs were in when I observed the slack.

[goldnsx]

The reference point is with plugs OUT, regardless what it is with plugs IN. I'd expect that the slack or tension gets distributed all around the TB with the engine running due to the additional force to overcome the compression in each cylinder. Still, if the tension is set properly with the plugs OUT and the right procedure described by the SM or Kaz it should be fine. Others might chime in as well.

I've asked about the plugs because there was at least one guy in the US who tensioned the TB with the plugs IN which is a definite no-go.

[Kaz-kzukNA1]

Year model?
If very early 91 model, don't use the hole (where you insert the 5mm pin punch) at the FRONT EXH cam holder plate as the timing reference.
In fact, you should use only the arrow on the oil pump cover (for crank shaft/piston position), markings at the front/back face of each cam pulleys and the marker on the TB silver metal cover plate.
Pin punch purpose is more of restricting the cam shaft movement when there is no TB installed or when you are in the middle of installing the TB and not for the final timing check purpose although it will provide some level of backup.

Using your old TB as a reference is also hit and miss.
On several engines in Japan and UK, I already saw number of engines with wrong timing enough for me not to trust the exiting timing alignment.

Kaz

[britlude]

Silly question time.... When you fit the new belt, you rotate the engine a few times check the marks line up then rotate the crank forward to the blue mark and release/tighten the tensioner, letting it do it's thing to set the tension......

Now, why would that process be any different with the timing covers on?? they did make the tensioning bolt accessable from the outside covers after all..... Just thinking out loud (as much as you can in a forum post) and haven't got my manual to hand to double check!