350 Dead?

[Snowman420]

Hi, I have a 1980 chev truck with some engine problems. I had the engine rebuilt 1 1/2 years ago. It worked great until 3 weeks ago. I was travelling on the highway, pressed the gas to pas a car, and Bang! I heard a loud pop through the carb. The engine ran rough after that and my vacuum guage fluctuated wildly like I had a dead cylinder. I removed the valve covers and found a bent pushrod on the intake valve of #8. Replaced it and the engine was fine for 3 or 4 days. Then it bent another intake pushrod (Cylinder #3). Both times the intake pushrod was bent and the exhaust valve for that cylinder was hardly moving. #8 is fine now. I replaced all the pushrods and set the valves 1/2 turn from zero and gave the engine a complete tune up. I thought my rocker nuts were backing off but I have poly locks on the rocker studs and they're staying tight. I even rebuilt the distributor (I thought my timing was advancing too quick or sticking). Again, the engine ran fine for 3 or 4 days. Then, on my way to work I was on the highway again, pressed the gas and pop, pop, pop. After that, same thing. Fluctuating vacuum and rough at low rpm's but seems to get better if I get the rpm' up a little (Vacuum smoothens up too). Seems to run better when cold too. I'm thinking of replacing all the lifters but I don't hear the ticking usually associated with dead lifters. I just wondering if I'm missing something stupid. I don't want to spend $$ on lifters and have the same thing happen again. Cam looks good and the valves open all the way after every time i fix it. Any help would be greatly aprreciated. Oh yeah, one final thing, the compression is 180 psi across the board.

 

Heres the specs on my engine for reference:

 

-Chevy 350 4 bolt 14010207 block 0.030 over with stock crank and rods.

-9:1 pistons

-Comp Cams xe262h Cam

-Lunati performance Hydraulic lifters (Might be the problem)

-Clevite hardened pushrods

-GM Camel hump 3917291 heads with 3/8 screw in studs

-Comp Cams magnum roller tip rockers 1.52 ratio

-Stainless 2.02/1.60 valves

-Stock Distributor with a Moroso Advance curve kit

 

Thanks,

Kev

[ChevyTech007]

Check your oil pressure. Relief valve might be stuck causing to much pressure.