i just finished rebuilding a 350 for my car.
its a 78 truck 350 4 bolt mains. heads are off mark sheilds 350 crate motor that was cast in 2000. It thumps loudly about 5 times a second in a constant rythm. One thing i noticed when trying to set the valves was that the rockers wern't staying straight on the valve stems. I used the rockers off the stock 78 truck heads. I don't think that would cause this thumping but.. Can anyone help me please?
aaron

 

Are they SA rockers (self aligning). If not then you will definitely need them. Those heads require them because the pushrod holes are very large. I don't think its the rockers making the thumping your describing. Does it sound like rod knock or maybe a spun bearing?? Did you break the motor in? When did it start and what were you doing?

 

i think its been thumping all along. I just started it for the first time about 2 days ago, and haven't driven it. I just started it, and tried to set the valves. I don't have a lot of experience, this being my first engine.

 

Is the exhaust hitting the body of the car. Bad engine or tranny mount. Bad damper or flex plate. I too doubt it is the rockers they make more of a ticking sound. Did you tighten the tc to the flex plate if its an automatic. Just some things I would check

 

Looks like the torque converter isn't tight to the flywheel. I'm going to tighten it tommorow and make sure that its the problem. I got self aligning rockers found and i'm sending the money out for them tommorow. Thanks guys.
aaron

 

I'm not sure how your heads are set up, but if you have oush rod guide plates you do NOT need self aligning rockers (and actually cannot use them). However, you must have one or the other - guide plates or SA rockers.

Good luck in Wasserburg. Dodge county side, or the south side?