Recently we had a customer bring his car into our shop because his car wasn’t running right. He also wanted us to add a set of roller rockers while we had his car in our shop for tuning. He just recently had another shop install a hydraulic roller camshaft into his 396 Chevy and since then it seemed like it was running out of fuel under acceleration it just didn’t want to rpm no matter what size jets he put in the carburetor or where he set the timing.
So we pulled the valve covers to install the new roller rockers and what do we see? Valve springs that looked like they were the originals installed by Chevrolet in 1967. The springs were so weak that you could spin a valve spring in its spring pocket when the valve was closed. When we measured the spring pressure, we only had about 40 pounds with the valve closed! Open pressure was only about 150 pounds, so that’s why the engine wouldn’t rev. For reference, the valve spring specifications for the new roller cam installed were 150 lbs. closed and 380 lbs. open so the original springs were grossly inadequate.
So we really have two lessons from this experience. First, always install new valve springs when you install a new camshaft it’s cheap insurance. Secondly, make sure you are dealing with a reputable shop or at least verify that they did indeed install the new parts that you purchased. A lot of times we see these tough lessons learned situations when backyard mechanic friends do the work at a discounted price. But in this case our customer did initially take his car to an automotive repair shop but they did not specialize in engines or vintage cars.