Do I Have A Bad Lobe On My Cam, Or A Bad Valve

I have a brand new 427 Big Block Chevy motor in a 67 Camaro. Recently on my last drive, I heard a ticking sound from the valve cover. Having concern, I turned around and headed home, 15 miles back. On my way back the ticking got louder and it sounded like machine gun fire from the carb, motor was running 215 degrees water temp. I pulled over and messed with the timing until the popping went away. I nursed it the rest of the way home with the loud ticking still going, but no more popping and it ran at normal temp of 185 the whole way, seemed to run fine, but like it had a dead cylinder. I figured I had some rockers to adjust and a plug to replace.

When I got home, I pulled the valve cover and found a rocker arm sideways chilling with no damage, and a bent and broken pushrod (intake) on number 8.

After pulling the intake, I inspected all 16 rocker arms, pushrods, and lifters to find no other damage. I did notice the intake lifter from the broken pushrod cylinder was slightly smaller then the rest of the lifters. No discoloration, and the lobe on the cam seemed totally fine. I replaced the pusrod and lifter, adjusted all the rockers, and reassembled the motor.

I ran a compression test on all cylinders. They were all equal at around 126, except for number 8, the one that had the broken pushrod, came in at 119, still within reasonable limits but slightly low.

With the coil wire off, and no fuel or spark to the motor what so ever, when I turn it over, I can hear air coming out of the carb, and when I run it with spark and fuel, it pops continuously through the carb as well.

From what I know ive narrowed it down to a slightly bent valve or a worn lobe on my new cam. Its odd because I still have good compression at 119, but shouldnt it be much lower compression with a bent valve? and the only reason I think it may be the lobe on the cam is because when I pulled the lifter, it was smaller in length then the rest of the lifters and had a slight outer bulge on the bottom (wobbles when you set it on a flat surface), but the lobe on the cam looks and feels perfect. No metal shavings or anything anywhere in the oil filter or the motor. I have a 500 lift cam with 280 duration at 0.50, and 1.72 roller tip rockers. The motor has 54 miles on it and was built completely with all new parts. Im a little stumped and could use some help on what to do next. Im still leaning towards the bad valve but that small lifter has me worried.

Answers for The Question

  1. kelly_f_1999
  2. oldmanarnie
  3. cussos58
  4. Country Boy