hydrolic144

iTrader: (2)

Another knock thread. I've read a few others but didn't gather much from them

All stock 5.7. Nothing done except smog pump removed and Flowmaster exhaust.

I got what appears to be a knock on start up, for a split second, and then it's pretty obvious at 2k rpms. Anything before or after that and it's gone. Just did a oil change yesterday. Started the car and the knock went on for a few seconds until the oil built up and poof it was gone. I've noticed the knock ever since I put my exhaust on. Which previously was just a y-pipe, so you could imagine how loud it was.

I've also got some blueish smoke coming out of the exhaust on every other start up, smells pretty funky as well. If it sits overnight it's more noticeable.

Anyone have and clues as to what it could be? Here's a video I took of under the car.

silentkillzr

iTrader: (2)

Sounds like possible rod bearing/wrist pin failure. In my opinion of course.

built91Z28

I can't watch the video on my phone but blue smoke on start up is usually just leaking valve seals. Not saying you don't have knock, but I don't think the two are related. I'd offer to come listen to it, but I honestly don't know much about what certain knocks sound like.

It's not a lifter tapping though is it?

hydrolic144

iTrader: (2)

Yeah I figured the seals may be gone. It's every other time though so it's weird.

I don't believe it's a lifter. But who knows? It's intermittent and not constant. It also doesn't knock every time on start up and the temp of the engine doesn't affect when it wants to do it.

I have zero loss of performance even at the hottest temps. Great oil pressure even at it's hottest. So I'm stumped.

built91Z28

Dumb question then but the exhaust isn't hitting anything is it?

hydrolic144

iTrader: (2)

I'm open to any suggestions. But nope, exhaust isn't hitting anything. It all has a very clear path actually.

I added some marvel mystery oil cause that stuff normally works, but didn't do a thing.

built91Z28

Huh. That sucks then. That's why I leave my exhaust short and with no mufflers. I can just pretend there are no weird noises, lol.

I have seen front accessory brackets loose and a torque converter loose and a broken flex plate sound like an engine knock.

hydrolic144

iTrader: (2)

Yeah it's a crazy one. I've yet to pull off the belts yet and try it that way. Got the v-belt setup so there are like 3 damn belts. And gonna pull the flywheel inspection cover to see if anything is up there.

Which reminds me. My starter used to grind whenever starting the car, it used to be every other start but it doesn't do it anymore. Don't know what that was about.

I've resurrected this car from sitting about 10 years. So things here and there are to be expected.

Hey built91Z28, do you have a brother and did he at one point have a red firebird?

built91Z28

Yep. My younger brother had a red 85 but parted it out just before it was done.

hydrolic144

iTrader: (2)

Yeah I remember him. Bought a few parts from him awhile back when I had my other GTA. Got the Demon carb, wires I think, and a few other things. Did he ever get back into another one?

built91Z28

Lol, that's cool. Small world. Wonder if we met? I was there when several people came over to get stuff. He didn't want a car like that any more so no more 3rd gens. The car was driveable and he just all of a sudden decided he didn't want it. Which sucked for me because I built most of the car.

hydrolic144

iTrader: (2)

Haha yeah. I think we may have but for a split second. I remember him telling me the story and he did mention you pretty much built it. But hey things happen.

If you'd like to have a listen I'm all for it. I know I've got some engine vibrations and the fix would be new motor mounts. Only thing is I'm kind of intimidated by it from all the fuss I've seen on here about them. At around the same time as the knock, is the peak of the vibration. It's not fierce but it's noticeable.

built91Z28

Yea I could probably stop by either mid Saturday or sometime Sunday.

built91Z28

You can message me your number and I'll text you when I figure out when I could stop by. Not sure if I have to work Saturday or not yet and I have somewhere I have to be by 6:30ish. But I could probably come by for an hour or so around 4. Or Sunday sometime if it works better. I can bring the car too if you want.

poloaa008

Sounds like possible rod bearing/wrist pin failure.

gmstrong

+1 rod bearing.

freaky

what are you tunning w/ monitering knock with ?

hydrolic144

iTrader: (2)

Just curious, for the guys that say rod bearing, what are the full symptoms?

hydrolic144

iTrader: (2)

Thanks for coming out built91Z28. Was nice meeting ya man.

built91Z28

Not a problem. Hopefully next time its not because of engine noises.

hydrolic144

iTrader: (2)

Haha yeah!

Which btw, I found that the oil filter can cause such problems and guess what I used on my last oil change.

FRAM!

Hope nothing is too far gone but I bought another one and gonna put it on.

hydrolic144

iTrader: (2)

Back from the dead but,

the problem was rod bearings. Crank was so bad it couldn't really be saved. Also a few compression rings fell apart after pulling the pistons out.