2005 RX-8 Loud Knock - Needs a motor? - RX8Club.com



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Old 10-11-2017, 08:21 PM   #1
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2005 RX-8 Loud Knock - Needs a motor?

Hello all,

I just recently bought a used 05 RX-8 automatic for $650 which I knew might need a little work.
i was told by the guy that owned it that it was spitting oil out of the air box and that was the only issue he knew of...so I thought maybe it just had a bad seal somewhere causing it to spew out oil...or maybe a bad PCV
I towed it home, bought a battery for it, and fired it up. It spewed our white smoke, as expected, but also had a REALLY bad knock upon revving it up. And when I say knock, I mean like metal on metal (think full blown rod knock). My driveway is on a hill and I needed to reverse the car into the garage to work on it and inspect a little further...it didnít have enough power to even back itself up. I ended up having to come along into my garage. Oil pressure gauge read normal and car was not overheating. Oil at normal level. Changed oil, added Lucas oil, and started car again, same effect. Did find some very very minute copper looking particles (specs) in the oil.
Anyway...maybe itís just the optimist in me, but Iíve read on a few different forums on here that it might not be too serious...could just be a dirty SSV valve (which I took out and cleaned today but have not reassembled yet and started the car yet) or several other things causing it knock loudly.
So does it need a motor or not and how will I know for sure? Any chance I can just rebuild it myself for cheaper than putting a motor in it? I bought the car with the intention of reselling it.

Thank you! Sorry for the long post

Last edited by Jacobxryan; 10-11-2017 at 08:23 PM.
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Old 10-11-2017, 08:40 PM   #2
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How often at idle (# knocks per second)? I assume the car is at rest.

Able to record audio in the engine bay and upload?
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Old 10-11-2017, 08:46 PM   #3
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Compare these - your engine compression is likely low or SSV issue


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Old 10-11-2017, 10:55 PM   #4
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Does the knocking vary with rpm?

Can you localize the source of the sound? To pinpoint the source, take a wooden stick, one end to your ear, the other to various components until you hear the knock through the stick rathe than air.

None of this sounds great, but see what you find. People buy all kinds of previous owner problems, some are worse than others. Check that the spark plugs are connected to the correct coils.

Last edited by Loki; 10-11-2017 at 10:58 PM.
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Old 10-12-2017, 05:29 AM   #5
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Could very well be rotor bearing failure. The last 8 that I bought had a bad knock that sounded just like rod knock. I've owned rotaries since 1999 and after 35 RX-7's and 4 RX-8's, only one has ever made that rod knock sound and it was that 05 RX-8. Ended up being a bad rotor bearing.
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Old 10-12-2017, 07:46 AM   #6
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Thank u all

The knocking isnít perceptible when idling (also because it stalls after a short while). It is only pronounced when you rev it up. The volume of the knock and frequency increases with revs if I remember correctly. Once I get it reassembled, I will have to double check on all of this.
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Old 10-12-2017, 08:27 AM   #7
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At 650 purchase price you could do a lot of things, like converting to a manual if it needs an engine anyway. Parting it out ;( -sad but it keeps other owners on the road. Or simply rebuilding replacing the engine as a project.

I hope you end up keeping it. Even an auto rx8 is much better than most cars of that era. And the look! It's a special car that drives beautifuly. And I think it's worth the effort to enjoy that.
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Old 10-13-2017, 09:30 AM   #8
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Quote:
Originally Posted by mazdaverx7 View Post
Could very well be rotor bearing failure. The last 8 that I bought had a bad knock that sounded just like rod knock. I've owned rotaries since 1999 and after 35 RX-7's and 4 RX-8's, only one has ever made that rod knock sound and it was that 05 RX-8. Ended up being a bad rotor bearing.
Does this knock get louder or more frequent when you increase the RPM, load, and/or load at RPM?
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Old 10-13-2017, 10:45 AM   #9
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Quote:
Originally Posted by wannawankel View Post
Does this knock get louder or more frequent when you increase the RPM, load, and/or load at RPM?
I still have the car disassembled at the moment from where I took apart and cleaned the SSV. Once I get it back together, I will double check if it does so. I canít remember for sure if it does
i will take a video of what it sounds like as well
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