8 cylinder front engine iconic vehicle
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By ChrisZ
#182922
Previously on Chris' 928S we had a case where the timing belt tension light popped when letting off the gas at redline in third a month or two ago. Drove car home, things appeared OK, no more light. Needed to check tension on the 70k mile belt. (pump and belt replaced at 70k, 140k now, last retensioned 2 years ago)

Yesterday while driving and revving it up in first I saw the light come on again. Not a good sign, drove 1 mile home and parked. This morning at about 40f temps outside and a cold engine I took the timing cover off and did a check on the tension.

It looks about where it should be. Pointer varies between the center of the window and on the front edge of the window based on how I hold it against the timing belt cover wall, but it doesn't appear to be too slack. Would like to verify I'm measuring it right.

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(Yes, #1 cam is at TDC mark along with the resonator/front of engine. Oddly enough though it does seem to be one tooth off when engine mark is at 0. This is not unusual (been like that before), but odd)
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By Addlight
#182958
My experience with my 86.5 is that it likes to be at the high-side of the window on tension. Just the slight move from the center like you show to the tighter end of the window is a good idea.
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By SeanR
#182961
Needs to be on the high side of the window for the Kemph tool. Otherwise, you need to tear down and see what is wearing and start replacing parts. Gears, tensioner arm bushings, etc. What belt did you use? If Contitech that could just be the result of why we call it a rubber band and not a belt.
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By worf
#182975
Don’t forget: bent carrier pivot bolt. Use inspection mirror to check belt tracking on main roller.
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By ChrisZ
#182996
Good data from all, thanks! I loosened the stop bolt and turned the tensioner adjustment screw one bolt face inward. Now the pointer is solidly past the end of the window...

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I'll get a mirror and check the tracking on the roller. Doesn't look like the belt is wandering on the gear, but will take a look before reassembling.

Note: This is the old belt, not a new one. I do need to replace it at some point, need to check with Stan to see if he can do it over the winter as it's getting cold....
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By ChrisZ
#183000
On a related note, what is that white thing on the belt? Manufacturer thing? Wear indicator?

Another shot of the gear, I wonder if it's one belt tooth off (engine is at TDC measured at front pulley) or if that's just normal-ish. Can't tell where the cams are without pulling the cam tops, which is dicey on an 86.5.... (oi)

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By Crumpler
#183666
Another can of worms, and I know it’s been discussed before.
My belt has always tracked forward like this on my 86.5. Several wp’s many belts, different cam gears, always comes back to that position.
I stopped worrying about it, but somebody tell me why ;)
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By worf
#183725
Crumpler wrote: Sat Nov 19, 2022 9:42 am I stopped worrying about it, but somebody tell me why ;)
Belt tracking is a function of the crank gear, the water pump pulley and the main roller. If belt tracking changes it’s because one or all of those is not where it used to be. Most likely the water pump pulley is in a different spot than was the pulley on the last water pump. This, assuming that the pivot bolt for the roller carrier isn’t bent.
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