doritomiata

Long time lurker here, I have a weird problem today. I bought a fairly low mileage renesis and rebuilt it about a year ago. Apparently a coolant seal had failed, but I replaced apex seals, side seals, and corner seals(everything that comes in the atkins basic closing kit) since I didn't have a compression reading on it, plus I completely mixed up the seals and I didn't want to take my chances. I re-used everything in the block including the bearings, none of it was worn enough for me to consider it worth replacing as I wasn't trying to build a race or high mileage motor. The stationary gear bearings were showing a tiny bit of copper but from what I read a little copper showing is okay, so I didn't think I'd have immediate problems.

Here I am today, 3500 miles later, driving home and I decided to do a second gear pull to redline. The motor ran fine all the way to around 7000 rpm where it started to slow down and miss a little, but then went back to normal until around 8000 where it shot the absolute meanest backfire I've ever heard. I shifted at that point and drove it home keeping it under 4k rpm, but noticed it sounds like its knocking now:
https://youtube.com/shorts/iZhQRoXMy80?feature=share

And I found this when I drained the oil:
https://youtube.com/shorts/3ftKRQjY8Js?feature=share

I ended up identifying the reason it started to break up before the backfire as a bad connection to the ESS. I fixed that, but it still knocks.
There's also a slight knock that comes and goes that sounds very similar to the one in the video above, but it only occurs at idle. Its much slower too, maybe only 2 or 3 knocks per second. It's not throwing a knock code, it doesn't feel down on power at all, and it's still making the same consistent compression numbers that it was before this happened. I've been running 20w-50 conventional in it since its been built, and started premixing around half an oz/gal about 1000 miles ago. I haven't taken it past 4k rpm until its fully warmed up. It's also worth noting that the noise is gone under acceleration or deceleration, the knock only occurs in that brief window where rpm starts to drop after its been raised.

The knocking seems to originate from the passenger side of the engine bay, but I can't feel the vibration from it anywhere but the oil pan and the SSV for whatever reason. Moving the SSV in and out or open and closed doesn't affect the knock though. Everything other than the copper in the oil seems to be pointing to it not being the motor knocking, but I can't trace the sound to anything other than the engine. I'd love to know if there's a possibility that this noise isn't a bearing going out prior to me pulling the motor, but I'm going to assume the worst here.

I already know this is probably going to result in me tearing this motor down again and building it the right way this time. So my question is what do you think caused it? It never ran low on oil, I changed the oil 4 times in 3500 miles with the first two being done after 500 miles, I replaced that thermal pellet in the eshaft with the atkins one that's always open so there's no way that's stuck closed. I just don't want to make the same mistake on the next motor. Is 20w-50 too thick? Could a backfire cause a bearing failure? Can a rotary be knocking without having any sealing issues whatsoever?

Sorry about the long post, I appreciate your time reading this and any help anyone can offer.

Loki

iTrader: (1)

The metal in the oil is probably more telling than the knocking sound, there's really no great reason for that. It's hard to discern different sounds from the video, the phone microphone seems a bit overwhelmed.

Big high rpm backfire is usually associated with cat failure. Either the cat was clogged and failed under exhaust pressure, or it was ok but for whatever reason you had enough fuel in the exhaust to backfire, destroying the cat. If it was clogged that might be what killed the original engine.

Reusing worn bearings is a pretty bad idea, it's a lot cheaper to replace them than to tear down the motor again, so I'd avoid that on your next go around. It could be as silly as not putting bearings back in the location they were originally in, causing them to wear differently and quickly. Also make sure the big parts you're using are still in spec. If it had coolant seal failure, so it could have overheated and warped as well.

Before you go tearing everything out, I'd pull the plugs and see what they tell you, pull the exhaust and examine the cat.

You could also just buy a known-good engine from a rebuilder like Pettit who are in Florida as well.

doritomiata

I took a big metal pipe to the cat a long time ago, there's no concern for it being clogged lol. Sorry I forgot to mention the mods, It's got a Magnaflow exhaust, gutted cat, and a Racing Beat REVi intake.

I got it to do its high rpm misfiring again after that event and I could see the AFR leaning out like crazy. I imagine given the bad ESS signal, it was probably injecting & sparking at the wrong time too, maybe dumping the unspent fuel into the exhaust on the events where it missed completely. When I pulled the plugs to check the compression I noticed they were black, probably darker than I've ever seen them.

I definitely learned my lesson on reusing bearings, I'm not doing that again.

Where's the fun in buying a known-good engine though? I thought building & blowing engines was at least half the fun of driving a rotary

kevink0000

Reusing good bearings is fine.

Better than new sometimes.

Something else happened not related to the used bearings.

TeamRX8

iTrader: (25)

you need to verify fuel pressure, a fuel pump going bad or the internal filter in the fuel pump module would result in a lean condition

assuming it’s a 2004-2008 if it’s that then you need to replace the entire module, not just the pump

but you always need to specify the model year as there were changes; the 2009-2012 fuel pump module has replaceable everything so on those a new pump and filter swapped in might be an option over the full module

knocking can be a busted motor mount, but it sounded more like an exhaust leak to me, video sounds are hard to discern

overall it sounds pretty sad imo, like it doesn’t have good compression and/or a possibly exhaust blowby back into the intake, it’s got no punchy juice when the throttle is being blipped for sure
.

kevink0000

Also, the oil video is not definitive, I have seen fresh oil while draining warm look just like that. You have to let it settle and inspect the bottom dwellers to see what's up. Did you keep the filter? If its really bad you don't even have to cut open to inspect.

kevink0000

Grab a long solid rod and put up to your ear and try to find the sound with engine running by putting the rod against the engine in different locations. I use this alot. My son bought an 84 Supra recently with what sounded like a bad water pump bearing, and found it wasn't the pump at all but the harmonic balancer wallowed out and was loose on the crankshaft. We ruled out the pump being bad with the rod. I use a 30" (approx)3/8 extension.

TeamRX8

iTrader: (25)

you might also consider cutting open the oil filter to see if it was clogged or plugged up and then bypassing solids into the engine. otherwise anything loose in the sump should be getting picked up and filtered out.
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doritomiata

The lean condition was gone once I fixed the connection to the ESS. It is a sad motor though, I didn't build it properly when I should have and I'm now feeling the effects of that.

I've been using this method for the past couple of days, I can't trace the sound to anything. Both rotor housings sound fine and I can't hear a knock in the center/rear iron either.

I'm starting to wonder if the filter could be what caused this, I couldn't see anything in the filter from the outside but I didn't really care to check the inside once I saw what was in the oil.

After today I'm pretty well convinced a bearing is on the way out. The noise is getting louder and sounds like it's coming from the back of the motor, I'm suspecting the rear stat gear bearing failed. Pressing the clutch has no effect on the noise so I know it's not the trans. No clue what could have caused it though, maybe the oil pump is failing, maybe the filter started bypassing some bearing material through and allowed it to keep doing more damage. There's too many unknowns for me to get a clear answer. I've parked the car in a nice flat spot where it'll probably sit for a while until I get around to building one of the two rennies and swap it in. Whenever I get around to building it I'll make another thread on here detailing the noises it's currently making and the actual failure point once I find it for anyone in the future with a similar problem.

Thank you to everyone who took the time to respond, and sorry about starting up a thread just to answer my own question a day later.

FYI TeamRX8 you've got a keen sense of hearing, the exhaust has been leaking from the manifold gasket, probably much worse after the colossal backfire from a few days ago lol