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Old 06-16-2014, 10:15 AM   #1
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Default 97 built motor knock noise from valve cover

well, i dunno how else to epxlain this so i will try my best.

the motor is a '97 1.8l
Supertech 8.5:1 pistons
Mahely rods
MSPNP2 running a base map for turbo just to get it to idle
base timing set up correctly and can verify by commanding timing and it matches.
car itldes at 13.5 AFR (if that matters)
550cc RX7 Injectors
IAT (no MAF)

the engine still in it break in stages.

now when cruising or revving the engine at idle at about 2500 RPMS i can hear a lout knocking sound coming from the engine.
this only happens at that RPM.
i re did my timing about 5 times thinking it could've been it
but the noise is still there.
i started fiddling with pulling timing around that area and i get the noise to lower, but i'm at about 10*
it doesn't do it at any other RPM

what i really want to know is...is my engine having rod knock?
i rather know now before i throw a rod through the side.
removing the engine is easy...but the fact it only happens at a certain RPM leads me to believe is timing related...but even at 10* i can still hear it.
engine revs freely to 6000RPMs and idles perfect
no smoking, no rough idle...nothing...

any thoughts?
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Old 06-16-2014, 11:09 AM   #2
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Get a mechanics stethoscope from HF for $6 and have someone rev the engine at the point where you think you get knock and use the stethoscope to listen. That is a strange rpm to be getting knock at, I am betting some other metal thing is just vibrating against something at that RPM.
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Old 06-16-2014, 11:23 AM   #3
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Maybe the downpipe/exhaust hitting the side of the bell housing??
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Old 06-16-2014, 12:05 PM   #4
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it sounds inside the motor.
i barely have anything in the engine bay that would rattle.
at first i thought it was the flapper for the turbp but i held it tight and it still does it.
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Old 06-19-2014, 01:01 PM   #5
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found someone's video that mimics the same exact noise as mine.
yep, it is rod knock
will be taking the motor apart this weekend.

his reposnse was:


Finally got around to getting into the motor a few weeks ago and I found my problem.

Ripped the block apart and started to pull off the connecting rod bearing caps. To my surprise, none had spun, unless they somehow managed to spin perfectly and not scratch any of the surfaces, which I believe is impossible All tangs were lined up, and all bearings were in the correct orientation. Instead they all had pretty nasty wear/burn marks from, what I'm guessing was, running too low on oil for any given amount of time. As an experiment, I only replaced the connecting rod bearings, polished/measured the crank journals, put it all back together, and started it up. Ran perfect, actually smoother than before. No noises or anything. I then knew that is what my problem was. I went ahead and did all the other stuff while I was in there, bearings and wearables, and replaced my front main seal, oil pan gaskets, and the camshaft seals. It's been a few weeks now, car runs great, and no more oil leak!

So for anyone that is experiencing the same symptoms as I was, I would say it's worn bearings, which I would much rather have than a spun bearing. And as mentioned, in my case, it was the connecting rod bearings that made the noise. My crank bearings were fine.

Thanks to everyone that chimed in!
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Old 06-23-2014, 08:30 AM   #6
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I had exhaust resonance at exactly 2500rpm

It wasn't hitting anything just ringing at 2500rpm and making a scary noise that I thought was something in the engine.

I had to change its resonant frequency by adding a flexi section.

Maybe something to look at if your pipe is rigid all the way ?
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Old 06-23-2014, 09:18 AM   #7
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Loose flywheel.

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Old 06-24-2014, 11:47 AM   #8
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update: after shitting bricks thinking the noise was a stuck filter, i rmeoved the engine.
i also suspected it to be a bearing issue because of my low oil reading.
well, it turned out that when 12 of 16 filters are stuck, it makes a pretty scary noise!

so that was fixed.
all bearings were intact as well as rods and pistons
still, needed to find out the reason for my low oil, so i measured all bearing clearences again...and found that i was using std size crank beraings instead of .025 over.
i must've made the mistake when putting the engine together as i had the STD and .025 boxes in the same pile...thank god i found out early enough to not cause any major issues.

replaced the bearings and re-mesured the gaps and now they are good.
that must've been my oiling issue...i'm glad i was just in the break in period without pushing too hard on the engine.
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