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Interference vs non-interference Posted by Ari [Email] ![]() ![]() In Reply to: timing chain, stephen, Mon, 27 May 2002 13:57:06 Members do not see ads below this line. - Help Keep This Site Online - Signup |
There is no 'safety device' to protect the engine. If the timing chain/belt breaks, the valves all open partially, because they're spring loaded, and they're still connected to a cam.
In a non-interference engine, the head, crankshaft throws, and pistons tops are designed so that even if the valves are stuck, they won't hit the pistons. In an interference engine, if the valves are stuck, the pistons WILL hit the valves, doing damage to the valves and pistons.
So why not make all engine non-interference? Because you give up a lot in terms of performance. Cutouts in pistons, lower compression, and other possible compromises give up performance, weight, and fuel economy. If you have a relible way of driving the timing gear (a good chain, good belt), you trade off the remote possiblity of doing engine damage for improvements in weight, performance, and fuel mileage.
So yes, break a Saab timing chain (4 cylinder engines) or timing belt (6 cylinder engines), and you will do damage - they are interference engines. Breaking the serpentine belt will do no engine damage, because it only drives accessories - water pump and alternator.
The solution is to do frequent oil changes, as that keeps the timing chain healthy, and if you have a 6-cylinder, changing the timing belt at the recommended interval.
Why do you think the timing chain needs replacement? There is no recommended interval for replacing the chain, and most Saabs go their whole, long, lives with the original chain. There are many things that sound like a bad timing chain that really aren't. There are ways to check if a timing chain is worn. Replacing the chain is quite expensive, so it pays to really know why it should be replaced.
posted by 140.157.4...
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