My first timing belt was lost at 102,000. All valves were bent except one! This happened about 10 years ago, and at that time I had no knowledge of these type of engines (Chev 350 mouse motors and 427/454 rats was where I had been). I rebuilt the top end myself to the tune of $1400. There was no apparent damage to the timing belt,(broken teeth, worn areas on the belt etc.) and I can only relate it to stretching of the timining belt. This is my only my experience and I do not know the answers to any timing belt problems except this: It is a lot cheaper to replace the belt whenever you have to tear down the front of the engine or the top end; my last Gatorback (My God It's not a Nissan or NISMO) cost $14.95 from Autozone and that is cheap insurance. Even if your pay their listed price of $25.99 for the belt, that is still cheaper than losing the top end and although I read where someone on this site could get his timing belt problem (with bent valves) fixed for $1100, I doubt it.
This probably does not answer your problem; But, if you have 90,000 on your original belt, change it, they are hypotheticaly only good for 60,000.
This is not your problem, but if the belt hasn't been changed, avoid headaches and replace it.
Hmm, well I took a real good look at my hayns manual and a good look at my z and decided that that is about the boundry of my mechanical ability... how much roughly would it cost for a mechanic to do the job?
I have never done the timing belt myself...But it isn't that bad...In order to change the water pump you have to take off everything as if you're going to change the timing belt (which is why a lot of people just change everything while they are at it). It really isn't hard to GET to the timing belt if you have a torque wrench, a harmonic balancer and a pry bar to save you trips to home depot and your local parts store P Red October seems to be really knowledgeable on how to line up your timing belt right. So just do a search for timing belts and/or set up an annoying title for your post to catch his attention P Either way...There's this guy I know in Illinois that'll do everything for $500...Or you can just take 24 hours out of your busy life and be a MAN P j/k.