JeffreyyyD

Just bought this 8 for $800, mainly just wanted a roller with a good body to work on for autocross. Expected the engine to be completely dead, but it does occasionally crank and even drives! Dies at stops and red lights though. Thought it was compression, but compression in rear rotor seems pretty decent (enough to drive) and front rotor is just above failing. Can’t figure out this noise though. Sounds like a bearing to me possibly, here is the link:


Thanks

NotAPreppie

That's a very weird sound for an '8 to make. It sounds too loud (to me anyway) and on the wrong side of the engine for the SSV/VDI actuator tick. Also, that tick wouldn't be RPM dependent.

Are all 4 spark plugs present and intact? I can't see how it would be the plugs but that's what is on that side of the motor.
Any belts falling apart and slapping something?
Does the sound go away if you remove the A/C belt?

JeffreyyyD

All 4 spark plugs are there, but the alternator/battery are toast (maybe both, need to test) so I haven’t been able to test ignition yet. The belts look good to me, but I am considering trying to remove them and see if there is any improvement.

NotAPreppie

Honestly, I wouldn't worry about it too much. I mean, this motor is already effectively shot so you're going to have to remove it for rebuild or replacement anyway. That will probably solve the problem even if you don't figure out what exactly it was.

CaymanRotary

That sounds really bad wow. Any engine codes?

JeffreyyyD

No engine codes. I’m hoping it’s maybe a pilot bearing, since clutch was replaced in December so it’s still under warranty. That leads me to another question though if you don’t mind:

The clutch doesn’t seem to “grip” by itself like my miata does, it requires a good amount of gas or the engine will stall out. Is this just due to low torque on these engines? It feels super weird to me, like there is no real feedback from the clutch (doesn’t start vibrating the car like on any other manual I’ve driven, especially my Miata since I have the most experience with it).

Loki

iTrader: (1)

Partially the nature of the engine, partially that your engine is dead. "good enough to drive" and "stalls out at stops" don't go together. What are the actual comp numbers? When it stalls out is it easy to restart?

JeffreyyyD

When it stalls it is pretty much impossible to restart without a jump, which leads me to the alternator/battery being at least partially the issue. Comp numbers are normalized at 250 rpm (starter motor gets about 210 RPM max):

Front rotor:
96 97 96 @ 250 RPM

Rear Rotor:
101 101 101 @ 250 RPM

Loki

iTrader: (1)

Does it start OK when cold?

210 rpm is too low to be useful, so it's either the battery, battery terminals, or starter motor.

However that doesn't explain why it stalls. What mods are on it, hold is the ignition and have you checked your idle fuel trims?

JeffreyyyD

Starts cold fine (as long as battery is charged), which is why I checked compression first.

Ignition is supposedly new, and it certainly looks new, but I haven't really had the chance to test it fully yet. The last owner spent some time trying to track it down and poured money into it (including a rebuild roughly 15k miles back), and had a new clutch installed as well as new ignition (wires a plugs for sure, I believe coils but I am not certain they look clean enough to be new but who knows).

As far as mods, it appears that there are none, everything is stock except it's missing the engine cover. Stock wheels, everything. The only real mod I want to do anyways is gut the cat, but I am waiting until I can get it running to register it first.

Not sure about idle fuel trims, how do I check that? I tried the reset (pumping the breaks 20 times, moving wheel to left, then to right) but didn't notice any difference, plus the battery was dead again by the time I looked at it the next day, so any "reset" would have been wiped anyways. It's hard to do the reset as well because it stalls out after a couple of minutes of idling.

myon

To me it sounds like the noise is coming from the combustion. At idle it sounds like something hitting something else, but when you rev it up it seems clear to me that it comes from the intake and is correlated to the combustion.

It sounds a bit like a 2-stroke that is "4-stroking"...

Have you double checked the wiring from the ignition coils to the spark plugs?
If you unscrew the oil-refill cap when the engine is on and place you fingers on the hole, can you feel any puffs?
Have you tried running the engine without the cat?

Also, can you try and see where the noise seem to originate from?

mazdaverx7

iTrader: (6)

That sound is rotor bearing failure. I had one fail on me in an 05 GT I had a couple years back and took it to Mazda as it was under warranty. They diagnosed it as rotor bearing failure on the front rotor. It's time to replace the engine and flush the oil coolers and lines to ensure no metal debris is present that could contaminate a new engine.

CaymanRotary

It does sound like a bearing failure. But I still have some hope it could be transmission related due to him having issues with the clutch. That would be the first thing to do would be to drop the transmission and see if that's what's causing the issue.

The compression numbers seem too good for it to be the bearing. It's one of the two I suspect.

NotAPreppie

I don't think the bearing is a sealing surface.

CaymanRotary

Wouldn't a bearing failure also ruin compression? Could be wrong, I've never had a bearing go on me.

JeffreyyyD

This weekend I'll have a chance to look at it for a while, so I'll try removing the cat and checking ignition first. If it is a bearing failure I should be able to see metal bits if I drain my oil right?

CaymanRotary

An oil analysis would be a good idea, also drop your oil pan as fragments more likely to stick in there than drain out. If you do find a bearing went out and you see metal shavings everywhere the engine is not salvageable so you will need to replace the engine.

Edit: could also cut open your oil filter.

motodenta

Bearing failer so-called "stationary bearing failure" more common on 4 port engines.

kevSpencer

i bought a 2007 6 speed auto that had a broken off stud on the mounting plate for the torque converter, and it made a sound that was impossible to find until i ended up removing the starter and there it was, loose rattling away in the oblonged hole. i dont know how it broke it was like this when i got it. rev up it stopped, at idle it sounded awful. just thought id mention it

Pai7077

Hi guys. Recent bought a rx8 with 50k mileage on it and came across with this issue, so i started my 8 one morning and it made this weird sound. Mileage of the engine is 40k and did a recent compression test it came out around the 120s both front and rear rotor. What could be the issue?