As you last saw the '94 300ZX (NA, 2+0, 220,000 miles) I had mostly removed the window tint and replaced the rear shocks. Next I pulled the (cracked) front bumper and put the car up on jackstands for some serious engine bay surgery: timing belt, valve cover gaskets and associated bits.
We started by pulling the radiator, coolant hoses, power steering pump (leaking badly), alternator (coated in PS fluid and I was frankly surprised it was still working) and fan.
Which was cracked between every blade segment and somehow still held together by just the steel backing plate (dodged a serious bullet there!)
Next we removed the three-segment timing belt cover and the coolant inlet/outlet hardpipes that sit between the covers, which resulted in some carnage (if you are sensitive about your tools you might want to look away) because some Nissan engineer decided 6mm caphead bolts in deep wells would be easy-peasy to remove.
Yes, one of the downed soldiers is a torx bit, I was desperate. A trip to the hardware store for a proper 6mm hex on a 1/2in drive put an end to the stalemate and the last few coolant pipe bolts were removed, exposing the thermostat (outlined in red RTV in the picture below).
Next up, the always challenging crankshaft pulley removal and my surprise upon removal when I realized it's an aluminum aftermarket underdrive pulley... proof someone with some 300ZX knowledge has been here before me.
At this point, I went back up top to pull the plenum (the hoses, dear God why are there so many hoses? over, under and through the plenum!) and expose the four valve covers.
The red plugs in the picture are the injectors, the 5 rubber rings to the left and right (there's six, one was camera shy) are the spark plug wells and the carbonized ovals down the center are supposed to be the lower air plenum in shiny aluminum. Clearly someone's been sucking some serious oil vapors from the valve cover ports and EGR valve into the dual intake runners! What a mess (the upper air plenum is equally oily inside, that's going to be a challenge to clean without a dip tank). With no plan to pull the lower plenum for now, we moved on to clearing the valve covers and spark plug wells.
That's one side done and they don't look bad: the cams have some discoloration as do the hydraulic lifters, but no obvious wear and no signs of burnt oil in the galleries. At the lower edge of the above photo, you can see the closeup of the timing belt condition which appears shiny and the timing lines are well faded, leading me to think it may have been changed at 180k as recommended (60k intervals). The timing cover backing plate was oily, making me think the last mechanic skipped replacing the cam seals, so I had better keep going. No pics, but I proceeded to remove the cam gears, backing plates, water pump and crankshaft timing gear. Cam seals were pried loose and new ones tapped into place before replacing the cam gears. New water pump and thermostat were installed along with new idler pulleys and belt tensioner. Finally the new OEM Nissan timing belt was installed and carefully timed with the witness marks on each gear at #1 top dead center.
Since I didn't pull the spark plugs, I could feel the compression cycle for each cylinder as I hand-cranked the engine over to check the timing and seat the belt. Don't ask why I didn't do a compression check, but I could/should have. Shoutout to the legion of Youtubers who walked me through my first timing belt replacement (I faithfully liked and subscribed, free clicks for anyone who earned them!) Time for the timing covers to go back on with some new hardware (Nissan uses shouldered bolts with rubber crush washers and most of mine had disintegrated the rubber bushing due to heat and hydrocarbon exposure). Starting to look like an engine again!
Time to work on those valve covers. Lots of wire brushing and brake cleaner later, we had decent looking valve covers with acceptable gasket surfaces again. Recall the beginning of this post and the previous post: significant oil leaks from the exhaust valve covers which coated the engine sides and was actively dripping onto the exhaust headers was the primary reason this car is on jackstands in my garage only a month after my son bought it. The intake manifolds have a formed rubber gasket that sits in a deep groove, but the exhaust manifolds don't. Why, nameless Nissan Engineer, why? Instead of a proper gasket, the exhaust valve covers just have a shallow groove for RTV to seal the aluminum on aluminum surfaces. Oh well, RTV it is, then. I tried my best for a steady hand and a smooth bead, but I'm no cake decorator.
And that's where we stand: timing belt changed, water pump and thermostat replaced, valve covers resealed, plenum cleaned.
Along the way, the EGR system and the plenum coolant lines were deleted (standard mods for 300ZXs residing outside CA). The EGR delete was particularly tricky with the engine in-situ as it sits behind the block below the lower air plenum and access is mainly by feel, plus you have to remove both cabin heater pipes for access, but we managed it with only the usual sacrifices of skin, blood and sweat.
Next up is the addition of a catch-can between the valve cover vents and the intake plenum to reduce the amount of oil ingestion, reinstallation of the spark plug wells and upper plenum, replacement of the coil pack connectors (plastic clips were brittle and self-destructed upon removal), new hoses for the fuel system (already replaced the hoses under the plenum), reinstall the radiator, alternator and power steering pump (forgot to mention I rebuilt it already), say a quick prayer and attempt a cold start. Wish me luck, Oppos (and any and all advice welcome!)