Today I finally bit the bullet and replaced the timing belt on my 2001 Frontier S/C 4x4. It had 111k at the time of replacement. I opted to do this as cheap as possible; I used aftermarket parts and only replaced those parts that had obvious wear to them.
Overall it wasn't the enormous project I was picturing. It was 8-9 hours of turning wrenches, some of that was head scratching or hopping online for research. In hindsight, I don't regret neglecting the water pump, seals and other odds and ends that most choose to replace at this time. If I had to go back in, no sweat. I'll take a timing belt replacement over spark plugs any day. At least this is 8-9 hours of productive work as opposed to 4 hours of cussing, frustration and throwing things.
Before I list the steps, word of warning: By the time you're done ripping things apart your driveway will be scattered with parts and dozens of bolts. Keep track of nuts and bolts, tag them, do something so you remember where they went! Don't rush the disassembly for this reason.
1) I took the battery out to make room. Might not be necessary but you'll thank yourself.
2) Next comes the radiator. Two bolts hold the brackets at the top of the radiator. Pop those off and the third bolt that holds the overflow bottle. Hoses will need to go. Pull the upper hose off the radiator. The lower hose can stay attached but will need to be removed from the pipe above.
If your vehicle is automatic there will be two A/T cooling lines going to the radiator as well. I found it was easiest to leave these attached to the radiator, but to disconnect them where they meet the engine (a short space away). I was amazed how easy the radiator came up and out of the engine. You'll have to snake it past the fan which can be done with the plastic shroud still attached. It took some head scratching and a couple attempts but was quite easy.
3) I removed all drive belts and fan at this point. All tensioners are easy to reach and should be quite obvious. Remove the fan *before* you remove the fan belt, otherwise you have no way to keep the pulley from spinning. I learned this the hard way. Fan has four PIA nuts where you can't get a socket into. Have a wrench or small crescent handy, not the 12" crescent I used.
4) Remove the idler/tensioner pulley mounts, there is a left and right. Start with the right first. These are pretty self explanatory, a few 12mm bolts and they're off.
5) Remove the crankshaft pulley. At this time I was met with major obstacle #1. Removing this requires a 27mm impact socket and 1/2" impact (might not be necessary if you have a manual in 5th gear). I had my trusty 1/2" Harbor Freight electric impact (which worked quite nicely) however I could not position it between the bolt and the A/C condenser (radiator looking thing) without fanangling with the bumper supports and such so as to move the condenser forward. Without completely taking the bumper off, I still had to jam the impact in there which created a noticeable bow in the condenser.
"Almost" major obstacle #2 was getting the crankshaft pulley off once the bolt was loosened. The puller I had (Autozone part number 27078), the screw would bottom out before hitting the loosened bolt. Plan to have a shim, block of wood, something for the screw to hit and position it between the puller screw and loosened crankshaft bolt. Mine could have possibly been pried out, but there's a thin metal washer behind it you don't want to ruin unless you have a replacement.
6) At this time you should clearly see the top and bottom belt covers.
Do the obvious and pull all the bolts off which will remove these. Take care to remember where the bolts went as there are several different sizes. The plastic air hose that's part of the PCV system will need to be pulled out of the way. Take the two bolts out that hold it, then remove the hose at each end. This allows you to pull it up out of the way (it's pictured in the above image). It will require you to remove the two plastic wiring harness fasteners.
7) Make sure cylinder #1 is at TDC. It is wise to do this before hand if you can. I believe I used the crankshaft bolt before taking it off. Use the camshaft bolts to turn the engine if need be. Timing marks on cam sprockets need to line up with the indents on the backplate. Position the drivers side so that it's dead on, but you'll notice the passenger side is a 1/2 tooth off. This is okay. You'll have to remove the plate in the back (held on by four bolts) to access the camshaft seals and bypass hose. Take the cam sprockets off first, impact is a must for this (unless you have the crankshaft pulley on still). I'd recommend replacing the bypass (small 90 degree) coolant hose with the Nissan part. I had to cut my aftermarket part and it was borderline short after cutting (my own fault).
8) Loosen the tensioner bolt to relieve the belt tension. There is a 5mm allen wrench hole which will let you swing the tensioner around to adjust. Pull old belt off. My belt after 111k showed noticeable wear:
I wasn't planning on replacing my tensioner, but sounded as though sand was in the bearings, so off to Autozone I went. I bought their 35$ tensioner which worked wonderfully. I didn't have a belt tension gauge so I remembered where the allen wrench hole was in relation to the block, and reinstalled accordingly. There was spring on the back of the tensioner that had me wildly confused. I think it's supposed to provide resistance for the allen-wrench adjustment, but I couldn't find where the end of the spring was supposed to attach. I finally gave up on that, making sure the end of the spring would not contact anything around it. Once you see it, it becomes clearly obvious how the tensioner works. Spin the pulley using the allen wrench hole to the desired tension, then tighten up the fastener (nut).
-- Reinstall --
Reinstall is essentially the reverse, except for the belt:
Note: If you had taken the camshaft gears off, install them with the bolts snug tight. DONT move the cams. Reinstall the belt so that there are 40 teeth between the marks on the cam gears. There will be 43 teeth between the drivers side cam gear indent and the one on the crankshaft gear. Your new belt should have lines similar to the pictures below.
Passenger-side cam gear:
Crank (it's hard to see the indent on the gear but it's there, you'll see it from underneath):
It will take some time to position the belt correctly, I found it easier to install the tensioner last. DO make sure the belt is on correctly, use the pictures for reference though your belt may not look the same as mine. COUNT the teeth between marks! This made checking the work very easy. I tightened the cam gear bolts after the belt was tensioned, a torque wrench is preferred though I used the impact. Before I replaced the crank pulley or covers I turned the engine a 1/4 revolution back and forth using the cam gear bolt just to make sure everything looked normal.
Belt on w/ bottom cover installed:
Things coming together. I chose to replace the two innermost belts as they are the two most likely to leave me stranded if they were to break (water pump and alternator). I could care less if my supercharger / A/C belt broke, I'd just drive and get one, takes 5 minutes to replace.