If the timing belt snaps, they run into each other, causing bent valves (most common), cylinder head or camshaft damage, and possibly piston and cylinder wall damage. ... In a non-interference engine, the pistons and valves don't occupy the same space, so if the timing belt snaps, no valve or cylinder damage occurs.
nissan are all Interference engines
SOURCE: 1999 escort zx2 timing belt broke
The ZX2 Zetec is a non-interference engine. This means the valves are not capable of touching the pistons at any time. If your belt breaks, there will not be any valve damage. There are reliefs cut into the top of the pistons that allow clearance for the valves if the belt breaks. Most engines are interference and will cause several hundred or even thousands of dollars of damage when a timing belt breaks. Most shop manuals list the ZX2 as interference but it is not. Many people seek out this how-to because a mechanic has informed them that they have valve damage and quoted a repair price over $1000.
If you are doing this job yourself, check your pistons. Valve interference can cause small "eyebrow" contact marks on the piston tops. If these have any sharp marks where material was "pushed" by a valve, you need to use light sandpaper toi remove them, otherwise they can glow as cylinder temperature increased while running and can give you a pre-ignition problem when the job is finished.
If only a few valves appear to be bent, you should have all of them checked...even one thousandth of an inch bend can and will cause the valve to leak and burn. Any bent valves should also have the guides checked for damage. Don't forget to replace stem seals as long as you have the head apart...most become brittle with use and need changing. If you have a good machineist, he will know what to do!
good luck with your car!!
SOURCE: audi a3 2.0 litre fsi cylinderhead problem
ginorini, get back to me on my email if you still have this broken head. [email protected] thanks alot
SOURCE: Toyota Caldina cambelt broke. Valve damage?
Sorry to say there is most likely quite expensive damage to the valve train and pistons. A new cam belt can be installed and the motor rotated to see if it is turning freely after which you would do a compression check (lack of compression will indicate bent or broken valves). I've never seen a diesel break a belt and avoid damage, virtually always a catastrophic failure.
SOURCE: I have a 1991 Nissan Pathfinder with a 3.0 V6
You're probably in pretty good shape the valves on that engine have a short lift and, fast duration.
Put on a new belt and, pressure test each cylinder before you start the engine up.
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