7T3C3TTZ07

Several years ago 4-bolt 350/350 with 75,000 miles was turned over to an engine shop to be refreshed with a "hotter" hydraulic cam and a little higher compression ratio. After the rebuild, I experienced a broken valve spring and a broken valve while driving (OK WOT hot rodding) it in a fashion similar to before the rebuild. The shop repaired everything and touched up the valve seats at their cost. I think that the rebuild must have weakened the engine in some way.

For a different C3 with an L48 I am considering having an engine shop put in a stroker kit, new cam and increase the CR with new heads. I want to make sure that I do not weaken this engine. I don't want to revisit broken valves springs and other parts. I am curious as to the possible root causes and preventions for broken valves and springs apart from leaving it stock or driving it like it is a hearse.

A ZZ383 would be more than stroking the L48 work but I may opt for that to avoid problems.

Thanks,
Ken

Sigforty

It is hard to say, but I would think that the spring that broke was weak and could not handle the new cam. If you are considering a cam swap, always look at matching the valve springs to the cam. Often broken springs could not handle the pressure and either weak or undersized for the cam lift.

Gordonm

Broken valve springs have nothing to do with a stroker engine at all. The broken springs are usually a mismatched spring for the cam. Usually coil bind is a reason or to weak a spring for that particular cam causing valve float. I would never put in a new cam without at least checking the spring pressure but Iwould replace them as my first choice. Springs are cheap. You will not "weaken" the engine by doing modifications. The only thing that happens is mismatched components that are not up to the task of more HP and rpm. Get it right the first time and you will not have this problem.

JE Caudle

I'm sure Gordonm answered your question correctly.

If you are willing to fork over the money for a ZZ4 you could have
430hp at your finger tips.

1) ZZ4 short block
2) LT4 hot cam
3) Fast Burn 385 Heads
4) 1.7:1 roller rockers
5) 750 Holley

Rock and Roll...

gkull

If you end up with broken valve springs and like this other poster found that he had the wrong oriented pistons in some of the cylinders. The reason is Morons maximizing profits on the rebuilds.

midyearvette

..good post but you have to remember, there are more JUNK new parts out there now than ever before...you must by quality stuff and that usually means more $$........

Gordonm

I agree on the parts. Make your selection carefully with quality parts. Speed is never cheap.

jb78L-82

I had a spring break on my totally stock L-82 with 35,000 miles in 1986 on it cruising down the highway at 70 MPH!

gkull

You should not have waited 35,000 miles before you changed your oil or checked the level!

jb78L-82

Too funny-LOL!!

Just cruising down the highway at 70 MPH and then started to feel an engine vibration. Stopped at the toll booth that was about 1/2 mile away when the vibration occurred and the engine would barely idle. Limped it home for another 10 miles, pulled valve cover, and presto stock valve spring on stock engine broken-secondary valve spring held the valve up. Replaced it and never had a another problem. I do think that the insane OEM engine temperatures that the L-82 used to run from the factory (225-240 degrees) might have contributed to metal fatigue. Engine runs about 175 degrees today!

jackson

and water temp has little to do with spring life ... oil temp does ... but primary cause for broken spring is spring mismatch & coil bind ... just as Gordon says