1979-1993 & 94 Conv [Subscribe to Daily Digest] |
Engine knock at idle while cold could be a number of things. If it is a tap or tapping, it could be a lifter not pumping up, till the oil is warm and circulating easily. It could be a rod or main bearing, these really do sound like a knock and in the early stages of failure and are most noticable at idle when cold. I do not want to scare you, but the varibles here are almost endless. If the timing, mixture, etc, isn't right, hot, cold or in between, the engine will produce sounds that don't sound right. It's an unusual person that pays attention to this to begin with and I commend you for doing that. Many things happen as an engine warms up, there are many different kinds of metal involved that expand at different rates, but in general, clearances tighten as the engine warms. If it is more of a rattle, it could be the timiming chain (but that would probably not go away, might even worsen as the engine warms); or it could be piston slap, this is when a worn piston kind of slops around in the cylinder, until the aluminum expands enough to fill the bore properly, this is unusual with cast pistons though, as the rings will usually go first. Forged pistons (which are not stock for SAAB), are a different story, since they expand so much more than cast, the clearances are greater and piston slap while cold may be normal. These are just a few maybe's.
Todd, if it really sounds like a knock, not a rattle, tapping, etc, it's time to do some serious investigating. You really need to figure out where it is coming from; also determime the freguency of the knock, is it the same as idle rpm, slower, faster? Use a screwdriver, piece of small diameter pipe, etc, held to your ear and touch it to the motor, starting with the head and working your way down, don't forget to throughly check the transaxle too. Don't stop listening, until you have found the place that is producing your knock the loudest. Let us know what you find and we'll go from there.
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