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Old 06-26-2012, 05:30 PM   #1
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Unhappy Sad day for any Miata

I figured I would share my story to brighten some of your days, and hopefully to encourage the Miata gods to spare me some grief. So, after taking the past couple weeks to have my spare engine rebuilt, supercharger serviced, rebuilt engine installed (along with an endless list of new parts), then numerous hours solving idle issues... I decided to celebrate my Miata's renewed life by going for a ride with the top down on a recent sunny afternoon with my fiance. I had driven the car several times already after fixing the idle issues to ensure drive-ability before allowing my fiance to ride, I did not push the engine at all. Maintained desired oil pressure, engine temp never budged thanks to new aluminum radiator, ride was much smoother thanks to new AGX's; all was well, or so I thought. 30 minutes into our trip, I begin hearing a steady tapping noise. The road had become rough, so I assumed it was that. After realizing the tapping was not only indeed coming from under my hood, but was also load/rpm dependent (only took a few seconds to realize this), I immediately pulled off the road. Sadly, my "new" engine has knock. From what, I will not know until tomorrow when I can pull the engine. If possible, throw some smiles and crossed fingers my way. My poor Miata will appreciate it.
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Old 06-26-2012, 05:42 PM   #2
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U faacked bra!
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Old 06-26-2012, 06:05 PM   #3
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be sure its not an exhaust leak first... they can sometimes sound like knock
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Old 06-26-2012, 06:23 PM   #4
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Improperly tensioned SC belt can sound like a knock as it flaps around. Check that first.
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Old 06-26-2012, 07:14 PM   #5
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Last time I put my motor in I apparently forgot to torque the flywheel down, as it worked its way loose it sounded like horrible rod knock. Thankfully I still have my legs. Good luck man, hopefully it's something stupid... looks like there are several things it could be.
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Old 06-26-2012, 07:23 PM   #6
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Also, make sure it's not spark knocking / detonating. All your plug wires are on and down all the way.

Pretty sure that sounds like knock.
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Old 06-26-2012, 08:09 PM   #7
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Old 06-26-2012, 09:16 PM   #8
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Unfortunately, it seems far too loud to be any sort of spark plug problem. Although it never lost oil pressure while driving, when I pulled over it immediately bottomed out, then rose again when I pressed the gas. I have had the car towed to a local shop whose owner surprisingly drives a Miata, so he is more than happy to let me utilize his space to find my problem.

I apologize Hustler, I assumed if I pressed Enter it would submit my post prematurely. Silly me.
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Old 06-26-2012, 09:19 PM   #9
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spun bearing? rod knock?

good luck either way. I know the feeling: it blows
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Old 06-26-2012, 09:27 PM   #10
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I am assuming spun bearing per the way the sound started softly and gradually increased. Thankfully there is no rod sticking out of my block, or oil leaking. The thing that confuses me was the circumstances that it happened in: Driving at a constant speed, no boost, <4k rpm, no loss of oil pressure. I was very careful to drive with sense as to break in the engine/parts correctly. We will get it figured out though, no worries.
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Old 06-26-2012, 09:43 PM   #11
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you dont want to keep the motor at constant speed during break in. but I dont think thats why it failed
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Old 06-26-2012, 10:25 PM   #12
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I failed to mention I had been driving it for nearly two weeks before this point. The Mazda dealership offered this in response to my idle issue: "the ecu is trying to re-learn how your car should run, all you need to do is drive it". So I drove the car around locally (15-20 minute trips around small towns) every chance I got for the previous 2 weeks. No long trips right off the bat. After I found and solved the MAF issue, I suppose I just got excited that it was running properly for the most part.

Also, although the car idled correctly after fixing the MAF problem, the MAF was still holding 2.2-2.3v at idle. This cannot be right. What would cause it to run so high?
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Old 06-26-2012, 10:59 PM   #13
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Old 07-05-2012, 02:00 AM   #14
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Was able to take a look at the engine yesterday, had nothing to do with the bottom end. What I thought was a knock, was actually just a tap from a clearance issue in the head. Hopefully it will just warrant fixing the clearance, but the cam lobe does look a little worn, so I will investigate a tapped valve.
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Old 07-05-2012, 11:53 AM   #15
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Collapsed lifter?
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Old 07-06-2012, 05:20 AM   #16
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wow hopefully its not so bad afterall!
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