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Old 01-18-2017
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Loud knock before timing belt broke.

I have a 98 with the 2.5 auto with 159k on the clock. In the past few days it developed a knock that sounded like a rod.The knock would stop at higher RPMS and be less prevalent while in gear. On the way home yesterdayThe engine just quit. While turning it over I got the old no compression whir and knew right away that the belt let go and figured the tensioner was shot causing the knock. Tore it apart today but the tensioner spins free with no indication that the bearing went bad (I am going to replace it) My question is could the knock just have been the belt slapping the cover form being so stretched out?
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Old 01-19-2017
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I don't think timing belt slapping cover would be called a "knocking" noise, but sound descriptions are subjective so hard to say.

Rod knock noise is caused by the cylinder firing after TDC, at that time the worn rod bearing will have a gap between crank journal and rod, cylinder firing closes that gap quickly and you get a Knock noise when rod slaps crank

After new belt is installed you can see if knocking noise returns

Rod would knock at lower RPMs because of lower oil pressure, but load on engine shouldn't matter
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Old 01-19-2017
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Thanks for the info. This truck was never beat and previous owner babied with mostly in town driving. Oil was always changed when due.
Is is possible the belt slipped a tooth causing the cylinders to fire after TDC causing the knock. The knock started two days before belt snapped and was idling a little rough. I know its possible for a mid mileage engine like this to get a rod knock but I have seen Mazda engines go 300 k and never knock.
Guess I will find out after The belt gets here. .
Edit. Just wanted to add that I am pretty sure it is the original belt. Any Idea what company they used from the factory to make the belt?

Last edited by ricityranger; 01-19-2017 at 04:38 PM.
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Old 01-27-2017
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Got the timing belt on today even though it was a warm 35f degrees outside. Everything went well and she started right up.
Now back to the knock. It is not a rod bearing, I used a stethoscope to probe around and I am pretty sure it in the serpentine belt tensionor. The knock I am pretty sure is coming from it. It moves a lot when you give it some gas from an idle.
I cant seem to any info though on the tensionor removal. Is it just a bolt in the center?
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