kamshaftz

I'm doing a timing belt change on my 300zx. the new auto tensioner is stuck at full extension and doesn't go down even when I turn the crank or anything. I previously did a 120k service on it about 2500 miles ago and did not replace auto tensioner (which was really dumb, but thank god didn't create any damage) and it ran great. but a couple of days ago I saw the belt was loose and the old auto tensioner was completely closed. no gap. so now I ordered a new one and this one is fully extended.
what do I do now? is there a way to compress it? or are you supposed to before putting it on? I know it needs to be at 4mm but it's nowhere close to that...

Skully

Yes you can compress it. "Common" practice it to carefully compress it with a C-clamp, and install the stopper bolt on the bottom when you compress it, put the belt on and undo the stopper bolt. Don't try to compress it with the stopper bolt as the casting is pretty weak and will crack if you try to turn it in, compress it first and then install the bolt to hold while you install everything.

kamshaftz

thank you for responding!
soo... I compressed it to 4mm exactly, put it on timing belt and when I unscrewed the retention bolt it went right back to where it was at almost full extension. so I out everything back together and took it for a test drive and felt like it lost a good bit of power. I am stumped. Is the loss in power from being off a tooth or so? or is it the auto tensioner being too tight since it is at full extension? last time I did the timing belt I was off a tooth and felt like a loss of power and then I redid it and it ran great! but now, ever since this ****ing auto tensioner it has been giving me problems? does anyone know why it goes to full extension??

Skully

You are suppose to set it to the 4mm, then bolt it down so its just taking up the slack of the belt and undo the bolt to release it. This should set it to its tolerance. There is a writeup here, read near the bottom.
90+ Nissan 300ZX Timing Belt Replacement

3. Set the timing belt in place. Make sure the arrows face forward.

4. Use a vise or clamp to adust the auto tensioner to 4mm of space
in the gap. ***Do NOT try to do this adjustment by cranking down
the screw.*** After you have squeezed the thing down to 4mm,
screw down the holding screw.

5. Put the auto tensioner in. You will probably need a big screw
driver to pry it over into postion to put in the bolts. Finger
tighten the bolts.

6. The manual takes a whole bunch of steps now rotating the
cams back and forth. I did this, but didn't really see the point.
You basically want to pry the tensioner over some more (not too
much) and tighten down the two bolts and nut that hold it in
place. I definitely did this section by feel.

7. Measure the deflection of the belt on both sides of both exhaust
cams. Make sure the average of these deflections is between
6 and 7mm.

8. Make sure the auto tensioner is tight and in place, then remove
the stopping bolt. The auto tensioner should not move much at
this point. Wait for five minutes then make sure the projection
of the rod in the tensioner is between 3.5 and 5.2 mm. Mine did
not move at all when I took out the stopper bolt. Lucky I guess.


Edit: I would highly recommend not driving it with a belt that is not properly tightened.

kamshaftz

Thank you! I finally got it. I wasn't pushing the auto tensioner far enough with the screwdriver/prybar to put tension against the belt but I have it now. it/s sitting at about 4.5mm.

Skully

perfect man!!