C3 Broken Valve Spring

[Steven E.]

A couple of questions concerning a broken #8 cylinder exhaust valve spring on my 73 L48, Could someone tell the correct spring length (free length) also , the valve doesn't appear to have dropped (retainers still in place) but could there be possible damage to the valve and or head.The spring let go while cruising on the highway and the motor was shut down pretty quick when I felt the loss of a cylinder.. The motor has 125000 on it and is going to pulled for a rebuild this coming fall..I would just like to get the remainder of the summer out of it if possible. Is changing the spring and hoping for the best the way to go.? Any advise on what to inspect before I change the spring would be a great help... Thanks Steve #44112

[Chuck R.]

Re: C3 Broken Valve Spring

I'd replace the spring Steve and pull a compression test and see what you get for numbers. At the same time you can watch the rocker/valve action and dissern if the valve is sticking or not.

If the valve didn't drop, it could be an indication that it's possibly bent and jammed or seized in the guide. That's why I say to closely inspect the valve's travel.

If the compression is good and the valve train is traveling properly, I'd fire it up and gradually run it up to see if it smokes, knocks, hangs the valve again etc.

Chuck

[Duke W.]

Re: C3 Broken Valve Spring

1973 was the first year that valve rotators were used on the exhaust side and spring geometry is different. The part number is 6263796, and the specs should be in your CSM and AMA specs. The inlet spring is 3911068. The 068 spring was use on both sides of previous engines back to '67, and I recommend it to replace the earlier spring. With a properly lashed OE mechanical lifter cam these springs are good to about 7200. and I have never heard of one breaking.

I don't know how thoroughly you have inspected the damage, but the failure could be in the rotator or retainer rather than the spring. If the valve moves freely I don't see any problem replacing the broken parts and driving.

The above assumes the heads are still in OE configuration.

Duke

[Roger S.]

Re: C3 Broken Valve Spring

Had an intake spring break in March on my 73 L82. Found all the springs had a 0.030" shim under them. Anyway, install a spring on the valve and do a leak down test on the cylinder to test for valve seating and piston ring condition. A leak down test is a better indication of cylinder health than a compression test. A compression test is easier. If the valve is bent you probably can't put a new spring on it since it won't come up all the way. I put compressed air in the cylinder to hold the valve up while the spring was being installed. This air suppy was also used for the leak down test.
Roger