so about 2 months ago i got my 74 dialed in with a fresh tune up. changed oil, plugs, cap n rotor, new electronic ignition, set the timing to 36* and the motor has been running great. it starts easy every time and runs like a champ...

yesterday i was driving and going uphill i rolled into a stop and i started to hear a loud knocking noise, my house was only two blocks away so i tried to idled it home but it wouldn't run for more than maybe 10 seconds at a time unless i gave it some gas. i limped it home the two blocks and once i got in the garage the motor gave out.

can an engine knock develop this quick? the oil is full and very clean looking (just pulled the dipstick to see, i will drain oil this weekend)

neighbor said it could be fuel related since the motor didnt want to stay running but the loud (really loud) knocking noise was something i have never heard. maybe timing got out of wack somehow?

motor work is relatively unknown we have had the car about 3 years and previous owner didnt have much info on any mods to the car... as far as i can tell it just has a aluminum intake, edelbrock carb, and possibly a slightly hotter cam.... guys have any ideas or suggestions as to where to start diagnosing?

 

Sorry to say that usually indicates a spun bearing. Drain the oil to look for signs of bearing failure.

 

Ditto, I agree with SH-60B

 

Cut the oil filter and look for bearing trash. If your lucky it's the fuel pump and if it'll start you can use a stethoscope and listen to the pump.

My 2nd stock replacement fuel pump knocked for awhile and I finally just put an aftermarket pump & return reg on instead of another stock pump. I got maybe 5,000 miles out of both auto parts store pumps and the 1st one blew the diaphragm and filled my engine with gas.

 

Sounds exactly like what happened to my 70 Gto when it spun a rod bearing.

 

Can you post a short video of the noise? It would make it much easier to make an educated guess at. Unless it's catastrophic, a rod knock isn't usually super loud at idle.

 

What oil pressure were you indicating when this occurred? What oil pressure were you indicating before the engine quit when you got it home?

Good luck... GUSTO

 

The vette is at my parents house and I won't be there until Saturday so I'll post up a video over the weekend.

The knock was loud at idle and was louder as the rpms went up, as far as oil pressure I did no look at the gusts when this occurred. As soon as I heard it I knew something was up so I limped it home. The guage does not work too good, when the motor is off it shows 40psi and when running it will be pegged a little past 80psi so I know it's not that accurate but has oil pressure

 

Can you explain the how you set the timing at 36*?

Running w timing way advanced can destroy bearings...

 

A spun bearing will normally cause the oil pressure to drop from normal readings, sometimes significantly. If it were me, I would pop a valve cover (or two) and see if a rocker arm or stud has failed.

Cost is minimal and they can make a lot of noise when they let go. It will also cause a noticeable loss of power.

Good luck... GUSTO

 

disconnect and plug up the vacuum advance, set the timing gun advance to 36*, rev the motor to about 3500 rpms and turn the distributor until the timing mark on the balancer is on the 0 on the timing tab.... this is how i set up my 70 elco motor and it has been flawless for 2 years.

 

draining the oil and pulling the valve covers off are definitely the 2 first things i will be doing. im hoping its a simple fix to get it back on the street but if not then its rebuild time and im ok with that

 

Weird- my 78 did the exact same thing today. Barely made it home, and pushed it down the driveway and into the garage. My mechanic, who is a C3 guru, came by and though either rod knock or fuel pump.

Hopefully it's just the pump. Engine is an L48 that has never been cracked open other than putting on an L82 aluminum intake and air cleaner.

Like you, car was just tuned up, new plugs, wires, rotor, cap, etc... Engine oil is full and clear.

Had just bought a tank of gas a few miles before this happened at a place I haven't bought gas from before. I'll let youknow what they find.

 

Found the problem... Pulled the drivers side valve cover off first and found a rocker that was a little loose but nothing out of the ordinary....

Pulled the passenger side off and a rocker arm fell out when I pulled off the valve cover lol exhaust rocker arm broke at the seat on the #4 cylinder.... I'll upload pics later tonight.

Can I just throw a new rocker on, adjust, and call it a day?

 

Are you running cheap aftermarket aluminum rocker arms? When it comes to rocker arms you get what you pay for...................

 

I'd check the pushrod & stud for straightness and make sure the pushrod tip is fine. Also that the lifter is in the bore on the rocker that broke.

 

Rockers are stock stamped, most likely the originals but the head casting numbers are 333882 from what I've seen they are the best of the worst heads lol

Here's what I was looking at when I pulled the valve cover


Here's the rocker



Didn't find much shrapnel it looks like it was a clean break

 

Pushrod also looks straight and undamaged. Most likely we will replace all the rockers, anyone recommend any good ones or give me advice on what to look for