1500 miles on a 3 year old 454 in my dad's LS6 clone. I was out driving it this afternoon in 90 degree heat (car was running great!). Car was up to temp and well warmed up. Got an open stretch of highway from a red light. I pulled out easy, took it up to 5000 in 1st, maybe 4500 in 2nd and 3500 in 3rd - shifting all gears relatively softly. Within 10 minutes of that, I started to hear a very slight knocking/tapping noise at idle. I thought I might have broke a valvespring or rocker arm. Made a stop for a few minutes to run an errand. From there, the car started right up no problem and drove great on the way home with all of the power and road manners it always has - I was taking it very easy on it though. As I neared home, the knock started to get a bit louder (could hear it at any rpm, though it was still pretty faint) and I started to hear a groaning noise from the motor that came and went several times, most often noticed at idle at a stop sign/red light. Knocking was consistent, the groaning faded in and out. Got it home and in the garage, left it running. Verified the noise was coming from the motor. Shut it down, looked over everything quickly, all looked fine. Cranked the motor again and just as it fired, I got a windup of loud noise to a loud BANG - all within about 2 seconds. I immediately shut it down, but it may have stalled at the same time. I have not tried to re-crank it since. By the way, round trip mileage on my time out with the car was probably 10 miles or less - 5 miles on the way home in stop and go traffic.

So I pulled the valve covers - all valve springs, rockers, and pushrods seem to be fine. Went to spin the motor over with a 1/2" long bar ratchet and could not budge it with all of the plugs out! There is about a 1/4" of a turn of freeplay in the crank right now. All of the plugs looked fine by the way, no bent electrodes and coloring looks normal. I was hoping to do a leakdown test but won't be getting that far!! Oil is clean, and new (10w40) - within 100 miles, and it is full to the full line, no evidence of any water or metal.

Is there anything that you would recommend I check before taking the motor out and to the machine shop? Luckily I have tomorrow off from work so I can pull it then, if necessary. My personal thought was that a main bearing spun, but that doesn't explain the knocking - or does it? Any thoughts?

Thanks for any help/advice you can give!
Mike

what was the oil pressure gauge doing??...errr..showing you while this was happening?

what was the oil pressure gauge doing??...errr..showing you while this was happening?


Not sure - there isn't an oil pressure guage in the car (but there will be one now I bet!!!)

I've got to believe you've spun one. From your description above. Have you drained the oil and looked for shavings? With the way it's acting sounds like you should start by pulling the pan and looking in the bottom end. It's going to need to be gone through...

Major bummer, sorry to hear about it.

What kind of cam/lifter combo were you using? May want to consider roller setup if you weren't using one.

Don

'70 Fanatic

Cranked the motor again and just as it fired, I got a windup of loud noise to a loud BANG - all within about 2 seconds. Went to spin the motor over with a 1/2" long bar ratchet and could not budge it with all of the plugs out! There is about a 1/4" of a turn of freeplay in the crank right now. Thanks for any help/advice you can give!
Mike
Sounds like you first spun a bearing. And then broke a rod or cap. The loud BANG and 1/4 turn sounds right. The only way to tell is to pull the pan.

just as well pull it out..you sure can't fix it in the car..probally have it out by the time you can pull the pan in the car.

I started to hear a very slight knocking/tapping noise at idle. I thought I might have broke a valvespring or rocker arm. Made a stop for a few minutes to run an errand. From there, the car started right up no problem and drove great on the way home with all of the power and road manners it always has


You should have stopped it immediately when you heard the first signs of a knock, not restarted it or, driven it.

When you pulled the valve cover were the copper colored pieces in the oil? sure sign of a spun bearing. Drain the oil and take a look or cut open the filter and see what you find.

...454 in my Dad's LS6 clone.... I was out driving it this afternoon ...Got an open stretch of highway from a red light.
I pulled out easy, took it up to 5000 in 1st, maybe 4500 in 2nd and 3500 in 3rd - shifting all gears relatively softly...
Within 10 minutes of that, I started to hear a very slight knocking/tapping noise at idle...
Sorry Mike,
If my son came home telling that story, I don't believe I could keep a straight face. :p

Sounds like how mine went last year. Drain the oil, it will tell you.

I blew up my Dad's lawnmower as a kid and he was ****ed - Now as an adult I'm able to point out to him that he did infact salvage the mower from someone elses trash - cleaned the plug, sharpened the blade and told me to get cuttin'.