Re: Help Diagnose my engine tick/knock - Saab 9-5 Bulletin Board - Saabnet.com
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Former advice's and video takes into account parts that are really worn out and easier to spot, not the many subtle hints that something "might" be worn.
And like you said, if you don't know for certain what to feel and look for, you might be overlooking the problem as well.
Lifters for ones, you need to know what a filled and empty lifter feels like and you test them all when the cam lobe is off the lifter (released/resting valve). If lifter have a play pushing down, it is not filled with oil but here is the problem. If you allow enough time to go by with a valve standing open before you test, that constant pressure will slowly bleed out the oil and the test might not be valid.
Piston slap/wrist pin knock/connecting rod noise. Those are very difficult to spot when it is just a minor issue and not as in the video a pretty much worn out/gone connecting rod bearing.
As a tidbit note. I owned a 86 Volvo 740 turbo years back. Bought it from a customer that overheated the heck out of it when a radiator hose broke. I rebuilt the engine completely EXCEPT replacing the wrist pin bronze bushings. That engine had a wrist pin knock for the rest of its life. It could be heard during slight revs and idle but went away during deceleration of engine. These old Volvo "red" engines do have a tendency to create wrist pin knock after overheat sessions due to that the small end wrist pin bushing gets elongated with the heat. I just did not think hard enough about it.
There are also cases with the newer Volvo "white" engines where the big end connecting rod bearing slips and gets doubled up on top of itself. Almost impossible to understand how it is even possible since the bearing shelves are not really worn thin when you take it apart.
Since the clearance of the big end have not changed that much because the bearings are on top of each other, the knocking is very faint and you don't know the full story until you drop the oil pan and remove the bearings.
Have you killed one cylinder at the time removing the fuel injector connector while idling? That might pin point it even further to one cylinder. Removing the combustion explosion can relieve pressure on connecting rod and change or remove the sound. If there is no change at all in the sound disabling # 3 or 4 cylinder, you might be looking at balance shaft bearing instead. But also bad lifters could keep ticking when the cylinder is disabled.
Is it an automatic? If so you might have the rare problem of a cracked flex plate to torque converter?
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