Having problems with your 1985 Nissan 300ZX ?

Starter turns crank but timing belt doesnt . but belt is not broke .almost like the bottom timing gear has a sheard keyway.when it stalled ,,just seemed like it ran out of gas..pistons didnt hit valves ...no bangs no back fires just stalled ...i was going slow at the time....

Posted / edited by AnonymousUser on : 25-03-2019

Answers :

Scrossley200: marionbagget probably hit the nail right on the head.
\015\012Being a Nissan Master Tech as well as road racing Nissan 300Z's, I am going to say that I is highly likely that if you were to look carefully at the crank gear and the timing belt, you will discover that the teeth are missing from the belt. Additionally, there is probably the remains of the timing belt teeth accumulated in the timing cover area. There is also another situation that occurs on rare occasions. When a tech and/or individual installs a timing belt tensioner, it is possible on some of them to get a part of the tensioner spring caught between the tensioner and the block causing it to tilt on an angle slightly. When this occurs, there is a side load created on the stud which normally pulls the tensioner flush with the block. After a period of undetermined time, the stud will snap causing the tensioner to drop which allows the belt to come loose, thus where ever the cams stop, they stay and the crank will continue to turn. What ever valves were open WILL BEND. This is an interference fit motor! The damage can be quite extensive, consequently the costs of repair far outweigh the cost of replacement. If you like the car and it is in good shape, you might like to keep your car. I get a lot of Z cars though my shop and the majority of the owners do not discard them unless they are in pretty bad shape and I do my best to talk them out of throwing their money away on the car. You can find used engines for this car for as little as $250-$300.00. If you decide to replace the engine, make sure you get a good warranty with it and find someone who knows how to look at used engines. Typically, pulling plugs and checking for their color and oil accumulation. Removing the oil cap and looking for signs of oil having mixed with water. A crusty accumulation of oil sludge when you look through the hole where the oil cap was removed.
\015\012Prior to installation do the following:
\015\0121.Inspect the motor mounts and transmission mount. The mounts were prone to collapsing and the primary symptom was when the engine was running, it would transmit a lot of vibration into the cabin area, especially at idle and low speeds.
\015\0122. Replace the front crank seal and cam seals.
\015\0123. Replace the rear main seal
\015\0124. Replace the water pump.
\015\0125.Replace the timing belt and tensioner.
\015\0126. inspect the valve covers for oil leaks and replace the gasket as
\015\012 necessary.
\015\0127. Inspect the exhaust manifold studs for breakage and missing
\015\012 nuts. They are 8mm 1.25 nuts with a 12mm wrench size.
\015\012 Do NOT over tighten them! Torque them to 12-15 ft pounds.
\015\0128. remove the plenum (the upper part of the intake manifold.
\015\012 There are a few small coolant hoses under there, replace them.
\015\0129. There is a metal tube which runs under the intake manifold.
\015\012 make sure it shows no signs of leaking.
\015\01210. Replace the thermostat. 180 degree unit. Don't buy a cheap
\015\012 one!
\015\01211. The best plugs I have found by far to run in the VG-30 is either
\015\012 the NGK's or the DENSO's, I use DENSO's in both my Nissan
\015\012 300Z road race cars because they don't blister or burn up.
\015\01212. If you decide to replace the plug wires or other ignition parts,
\015\012 I have found the OE parts the best quality or the Japanese
\015\012 manufactured components seem to last the best. If you look
\015\012 on the insulation of the factory plug wires, they are actually
\015\012 dated! Both Sumitomo and Yazaki do this. The only other
\015\012 plug wire I will use is made by NGK.
\015\01213. If your hoses are original, I would suggest replacing them.
\015\012 One way to tell if they are rotten, is to squeeze them and
\015\012 if you feel kind of a cracking inside of the hose, they are
\015\012 History!
\015\01214. Look at the clutch if you have a manual transmission and
\015\012 make sure the lining on the disc is not worn too close to
\015\012 the rivets. If your not sure, ask a professional.
\015\01215. Look at the flywheel surface where the disc mates with it,
\015\012 if it has blue spots on the surface and small lumps and/or
\015\012 grooves, have it resurfaced.
\015\01216. Inspect the mating surface of the pressure plate.
\015\01217. Feel the throwout bearing and make sure it feels smooth
\015\012 and makes no noise.
\015\01218. Clean out the sleeve the throwout bearing is pressed on and
\015\012 put a light film of grease inside of the surface which slides
\015\012 on the transmission.
\015\01219. Clean off the mating surface of the transmission where the
\015\012 throwout bearing sleeve rides.
\015\01220. Clean up the fork which moves the throwout bearing in and
\015\012 out to apply force to the pressure plate. There is a socket
\015\012 area which needs to be cleaned and have a light film of
\015\012 grease applied. Clean the part on the transmission which
\015\012 the fork pivots on. If I can help you further let me know.
If when you try to start it, it turns over very fast, no compression, the valves are damaged.
\015\012You will not hear the pistons hitting the valves.
\015\012If the timing belt broke or the drive pulley on the crankshaft has sheared off then the engine is dead.
\015\012I do not believe this engine is a 'free wheel" design.( You can call a Nisan dealer to verify),
Once this happens the piston hit the Intake/exhaust valves and the repair cost will exceed the value of this old car. You may be able to sell it for parts or scrap metal or like I did, give it away to anyone who will tow it away. And of course never buy another car with a timing belt.
Repair Help & Product Troubleshooting for 1985 Nissan 300ZX

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