DOHC Timing Belt System (60k/120k)

Preamble

One of the most critical maintenance items on your 3000GT, Stealth or GTO is the timing system. Failure of the timing system is from my observations responsible for a minimum of 20% of the cars that get parted out or stored indefinitely.

Required Parts

  • Timing Belt (OEM, Gates or Contitech heavily recommended)
  • Timing Belt Tensioner (OEM or Gates heavily recommended)
  • Timing Belt Idler Pulley (Koyo heavily recommended)
  • Timing Belt Tensioner Pulley (Koyo heavily recommended)
  • Timing Belt Tensioner Pulley Bolt (OEM with head marking 8 recommended)
  • Water Pump (OEM, Hitachi or Aisin recommended for full pump | Gates or Contitech recommended for rebuild kit)
  • 1/4″ Inner Diameter Flat Washer, ~1/16″ Thick
  • Water Pump RTV (If You Don’t Have the OEM Metal Gasket)
  • JB Weld (For Tensioner Washer)
  • Grease (For Lubrication of O-Ring and Reinstallation of Rear Turbocharger Intercooler Pipe)

Required Tools

  • Floor Jack, Jack Stands and Wheel Chocks
  • ~2 Foot 2×4 (Supporting Engine)
  • Selection of Ratchet Wrenches, Sockets and Extensions
  • 1/4″ Drive Torque Wrench (Setting Timing Belt Tensioner Pulley & Torqueing Pulley Bolts)
  • Timing Belt Tensioner Pulley Tool (Platform-Specific or Generic)
  • 1/2″ Drive Torque Wrench (Torqueing Harmonic Balancer Bolt)
  • 2x 1/2″ Drive Breaker Bar (Two Required for Harmonic Balancer)
  • Harmonic Balancer Holder (Platform-Specific or Generic)
  • 3x M8-1.25×40 Bolts (Locking Cam Gears)
  • 3x M8 Fender Washers (Locking Cam Gears)
  • Pick (For O-Ring and VICS Clip)

Nice to Have Tools

  • Serpentine Belt Tool with 14mm Socket (Removing Alternator Belt Idler Pulley Bolt)
  • Large Impact Wrench (Removing Harmonic Balancer Bolt)
  • Bench Vise (Resetting Timing Belt Tensioner)
  • 10mm, 12mm, 14mm and 17mm Gear Wrenches (Making Everything Easier and Faster)
  • Bungee Cords (Keeping AC Line / Cruise Control Out of the Way)
  • Prybar

Potential “While You’re There” Maintenance Jobs

  • Camshaft Seals (Guide Coming Soon)
  • Oil Pump (Guide Coming Soon)
  • Harmonic Balancer (Guide Coming Soon)
  • Accessory Belts (Guide Coming Soon)
  • Accessory Pulleys (Guide Coming Soon)

Walkthrough

Preparations

Before you do any maintenance on your car you’re going to want to do a few things.

  1. Disconnect the battery. At a minimum the negative clamp should be completely disconnected from the terminal and tucked somewhere that it will not accidentally bump the terminal. Ideally, disconnect the positive terminal thereafter and completely remove the battery. This prevents accidentally energizing circuits when you expect them to be powerless. Even on purely mechanical jobs, it’s always a good idea to do this as a precaution.
  2. Safely lift and support all areas of the car you’ll be working on, if necessary. Any time both front wheels are off the ground the parking brake should be on and the rear wheels should be chocked. Any time both rear wheels are off the ground the front wheels should be chocked and the car should be in park (if automatic). Never get under a car that is supported only by a hydraulic jack! If you do not have jack stands, put a wheel under each side of the car – damaged wheels are better than a funeral. Once supported, push on all 4 corners of the car (being careful not to dent panels) to ensure it is well-supported and does not wobble or creak.
    1. All 3S cars have a jack point on the front cross member marked with a raised kidney-shaped area with a lattice pattern. This allows you to raise the front of the car enough to put a jackstand on either or both sides of the jack point on the same cross member, or on the pinch welds.
    2. The rear differential serves as a jack point for all AWD 3S cars. This allows you to raise the rear high enough to put jack stands on the rear sub-frame or the pinch welds.
    3. On FWD 3S cars, there is a small jack point in front of the gas tank in lieu of the differential, access to it isn’t great, but it is an option to allow both rear wheels to be lifted at the same time.
    4. All 3S cars have mildly reinforced sections on the pinch welds at the front and rear (under the side skirts between the wheels). It is highly recommended to use a pinch weld adapter (many types available, here is one option from Amazon) to avoid bending the pinch welds, and only attempt lifting in the non-reinforced areas of the pinch welds as a last resort.
  3. If you are working in the engine bay, consider removing the hood to give better access and lighting. If you do, remove only the bolts from the hinges into the hood or the bolts from the hinges into the frame. If you separate the hinges from both the frame and the hood, you will be introducing two alignment points during reassembly instead of one and it will very likely cause you to spend an extra half hour fiddling to get the hood lined up with the bumper, lights and fenders again. With a layer of foam padding, the hood can be set on the roof so that it is out of the way and unlikely to fall over. If that isn’t possible, rest it on its points (being careful not to bend them or chip the paint) and lean it against the wall with the exterior facing out.

For this service, only the front left side needs to be lifted. Hood removal should be considered. Consider supporting both the front cross member on the left side as well as the front left pinch weld support, as large amounts of torque may be required to be applied to the engine which may dislodge the car from poor support.

Disassembly for Access

There are several items that must be removed before we can even access the main timing belt components by removing the lower timing cover.

  1. Remove the front left wheel. Any time you remove wheels, always set them flat, with their exterior facing up. This prevents the face from getting scratched (resting face down) or them from falling onto their face (resting on the rubber).
  2. Remove the front wheel liner. Be careful as the 3 bolts along the outside edge are likely to tear the plastic of the bumper if they are rusty.
  3. Remove the inner splash guard with the ~1″ diameter rubber plug (or hole if it’s missing). There should be two bolts facing upwards and one or two facing the side.
  4. Remove the throttle cable. Mark the position of the bracket with a sharpie so you can reinstall it in the same place. Unbolting it from the back of the plenum makes removal from the throttle body much easier.
  5. (Twin Turbo Only) Remove the intercooler pipe from the rear turbo. There should be one bolt on the top of the turbocharger, one bolt on the intake plenum, and a clamp joining it to the braided hose. Put some shop cloth in the outlet of the turbocharger to prevent any debris falling in and damaging the compressor wheel.
  6. (Naturally Aspirated Only) Unplug the connector for the VICS, located above the rear upper timing cover on the intake plenum. It should have a metal spring clip retaining it, be careful not to lose it as they like to fling themselves into the neighbour’s lawn when they come out.
  7. Unbolt the cruise control box. Under the cover there are 4 nuts retaining it. Lift it out of the way and bungee cord it up if you have any available.
  8. Unbolt the large air conditioner line from the firewall (2 nuts), headlight bucket (1 bolt) and frame near the wheel well (1 bolt). Bungee cord it up so that it is approximately 90 degrees up above the engine if you have one available.
  9. (Twin Turbo Only) Remove the short metal intercooler pipe from near the left headlight bucket. One bolt retaining it is shared with the line from step 7.
  10. Remove the left radiator fan. There should be two 10mm bolts on the top and two on the bottom and it should then slide up after unplugging both connectors near the headlight bucket.
  11. Support the left side of the engine. I typically use a vertical section of 2×4 on the lip of the oil pan where it bolts to the block. Under no circumstances should you every lift or support the engine from the sump of the oil pan no matter how much wood or padding you use!
  12. Remove the engine mount. There are 2 nuts on the front side and one nut on the back side to allow you to remove the pin bolt. There is a prying location on the left front side of the frame-side bracket where you can fit the beveled end of a prybar behind the face of the pin bolt and pry it forward if necessary, but if the engine is supported at the right height it shouldn’t require much force. Once the pin is out, remove the 3 nuts and lock washers holding the mount to the engine-side bracket and slide the mount up and out.
  13. Remove the alternator drive belt. Break the torque on the tensioner pulley (to the lower left of the harmonic balancer) and then loosen the upward-facing bolt behind the pulley to slacken the belt until it can be removed. The pulley and tensioner assembly do not need to be removed.
  14. Remove the power steering drive belt. Break the torque on the two bolts of the power steering belt tensioner (fork shaped arm, one bolt has a very long and strange looking hex component and one is a normal bolt) and then use a breaker bar in the end of the fork to release the tension on the belt.
  15. Remove the power steering tensioner assembly. Remove both bolts you loosened in step 7, and remove the tensioner assembly (noting which bolt went in which hole).
  16. Unplug the alternator. There is a normal push-tab plug to remove, as well as a ring connector on a stud with a nut to remove. The harness is retained by another small bolt into the body of the alternator.
  17. Remove the alternator. There are two upward facing bolts and two left-facing bolts. The alternator comes up with part of its bracket still attached. Be careful not to drop the alternator, it is heavy, and can crack the radiator. It may be beneficial to put a sheet of cardboard on the radiator to protect the fins.
  18. Remove the alternator idler pulley. This is possible with a shallow 1/4″ drive breaker bar and a shallow socket, but a serpentine belt tool makes it a breeze. You might be able to fit a 1/4″ drive ratchet in if you unbolt the power steering fluid cooling lines and move them up slightly.
  19. Remove the engine-side engine mount bracket. There are 2 small bolts and 3 large bolts of different lengths, remember which one goes in which hole. It may be hard to see one or more of the large bolts if there is a lot of oil sludge or dirt caked into the bracket.
  20. Remove the harmonic balancer. The torque spec of the center bolt is over 100ft-lbs so expect it to put up a fight. Use the harmonic balancer tool to prevent the engine from turning over while trying to break the torque. I find bracing the breaker bar holding the tool against the frame helps. Do not use the 1/2″ square drive in the bolt to break the torque or you will risk cracking the bolt. Use the exterior hex drive with a socket.

Disassembly of Timing System

  1. Remove the upper timing covers, front and back. Each has two 10mm bolts on top and one is also retained by a fifth bolt in the valley therebetween.
  2. Remove the lower timing cover. There’s a lot of bolts so if it doesn’t feel like it wants to come out do not force it. The ones most often missed are the two behind where the harmonic balancer was, and the one at the far back near where the power steering tensioner was. Some are longer than others so once again keep track of which one goes where.
  3. Thread the bolt from the harmonic balancer into the crank sprocket after removing the washer so as not to damage the roll pin. Turn the engine over clockwise until all 5 timing marks are aligned (or if the motor is out of time, the majority thereof). Each camshaft gear has a punch mark in a tooth that aligns with a diamond on the cylinder head behind the gear when viewed at a perpendicular angle. The plate behind the crank sprocket has a notch cut into it that aligns with a ridge in the oil pump at approximately the 2 o’clock position.
  4. Lock the camshaft gears threading the M8 bolts and fender washers into the holes conveniently placed behind the gears (1 per gear). One washer will need about a 1/2″ section bent forward with pliers or a bench vise in order to clear the gear. Apply enough pressure that the washers will hold the spring tension of the gears, they shouldn’t need to be more than hand tight. One of the rear cams will be unlocked as its spokes obstruct the holes, that’s fine as there is no spring tension on the rear head at TDC (when the timing marks are aligned).
    1. If any camshafts are out of time, leave them unlocked for now.
  5. Turn the crankshaft back one tooth so that the notch is one tooth behind the timing mark on the oil pump.
  6. Examine the timing system. Your tensioner pulley (looks like a surprised face) should be perfectly up and down (“eyes” at the top) plus or minus about 20 degrees. There should be no evidence of hydraulic oil on the tensioner near the pin.
  7. If you want to keep the old tensioner as an emergency spare, put a small drill bit, allen key, or bent cotter pin through the key hole (if it’s aligned, if not it’ll need reset on a bench vise – if you do this, do it very slowly at approximately a quarter turn of the vice every 20 seconds so you don’t blow the internal seals).
  8. Remove the tensioner pulley. This will slacken the timing belt and allow it to be removed as well.
  9. Align any camshafts that were out of time and lock them down. If the misaligned camshafts are on the front head, you will likely need to hold them in place with a wrench on the nut in order to get the locking bolt in, as the spring tension will try to fling them ~3-4 teeth in either direction from the timing mark.
  10. Remove the idler pulley.
  11. Remove the tensioner.
  12. Remove the water pump.
  13. Remove the o-ring from the coolant crossover pipe (behind where the water pump was).
  14. Clean up the area behind the timing covers if necessary to remove any build up of dirt, oil sludge, etc. This includes any debris that may have fallen near the crankshaft sprocket.
  15. (93+ Only) Inspect the crankshaft sensor trigger wheel for any damage from foreign debris.

Preparation of New Parts

  • Use a thin bead of JB Weld around the edge of the tensioner body to secure the washer to the timing belt tensioner around the pin. Ensure the washer is not touching the pin. Allow it to cure fully before installing.
  • (Rebuild Style Water Pumps Only) Disassemble your old water pump by removing the series of bolts as well as the P3 philips screw on the opposite side. Use a plastic scraper to remove all of the old gasket material from the static half of the old assembly which will be reused. Mate the new water pump impeller half to the old static half, with the included gasket in between. Tighten all of the bolts to finger-tight in a star pattern, and once all are hand-tight proceed to torque them. Do not over-torque the bolts that hold the assembly together. Factory spec for the “water pump” is 17ft-lbs which WILL strip the threads on the housing, that spec is to mount the water pump to the motor. Start at about 6ft-lbs and go up to 8ft-lbs if you feel confident.
  • Clean the metal water pump gasket that was removed with the old water pump. If it was not present, clean any paper gasket or RTV off the mating surfaces of both the motor and the water pump.

Reassembly of Timing System

PartTorque Spec
Timing Belt Tensioner Bolts17ft-lbs
Timing Belt Tensioner Arm Bolt30ft-lbs
Timing Belt Tensioner Pulley Rotation
(With Timing Belt Tensioner Pulley Tool)
7.2ft-lbs
Timing Belt Tensioner Pulley Bolt35ft-lbs
Timing Belt Idler Pulley Bolt40ft-lbs
Water Pump Bolts17ft-lbs
  1. Confirm the torque of the timing belt tensioner arm (was not removed).
  2. Install the timing belt tensioner (do not remove the pin) and torque the bolts.
  3. Install the timing belt tensioner pulley and leave the bolt finger tight.
  4. Install the timing belt idler pulley and torque the bolt.
  5. Install the new o-ring on the coolant crossover pipe and apply a small amount of grease to it so as not to tear it during water pump installation.
  6. Install the water pump and tighten all the bolts to finger tight, then torque them in a star pattern.
    1. If you do not have an OEM-style metal gasket, apply a thin bead of water pump RTV along the same path as the paper gasket the pump came with, then throw out the paper gasket.
  7. Install the timing belt.
    1. Start at the rear camshaft gears, loop it over the back and pull the slack out of the space between the two gears, and loop the belt under the water pump.
    2. Pull the belt down around the idler and crank sprocket, expecting a small amount of slack to remain (this will be taken up by the crank being one tooth backwards).
    3. Tuck the belt around the tensioner pulley.
    4. Pull all of the slack out of the water pump area and wrap the belt around the front two camshaft gears, you should have just enough slack to do this and the remainder of the slack should be located at the tensioner pulley.
  8. Ensuring the bolt in the tensioner pulley is loose enough to allow free eccentric rotation, use the timing belt tensioner pulley tool to apply tension to the belt (torque spec above).
  9. As soon as the torque wrench clicks, snug the bolt up with a second wrench.
  10. Torque the timing belt tensioner pulley bolt. You should now have minimal slack on the rear side of the crankshaft sprocket and no slack at the tensioner pulley. The timing tensioner pulley should look like a surprised face, with the two key holes nearly perfectly above the bolt.
  11. Using the crankshaft sprocket, turn the motor forward one tooth until the crankshaft sprocket is aligned with the timing mark. All 5 timing marks should now be aligned. If they are not, reset to the beginning of step 7 and try again.
  12. Remove the camshaft locking bolts and washers.
  13. Using the crankshaft sprocket, turn the motor over completely two times. Verify that all 5 timing marks are still aligned. If they are not, reset to the beginning of step 7 and try again.
  14. Test to ensure the pin in the tensioner moves freely, it should have minimal force being applied to it by the tensioner. If this is the case, remove it. If it has significant resistance, recheck the previous steps.
  15. Remove the tensioner pin.
  16. Using the crankshaft sprocket, turn the motor over completely two times. Verify that all 5 timing marks are still aligned. If they are not, reset to the beginning of step 7 and try again.

Reassembly of Parts Removed for Access

Long story short, follow the Disassembly for Access section backwards. I’ll be expanding this with torque specs and a step-by step in the future, but I’ve run out of authoring time for now and want to get this released ASAP.