[94cobra69ss396]

I was out shopping today and was almost back to my house when the Cobra developed a misfire and a tapping noise in the valvetrain. When I got home I pulled the valve covers which requires removing the upper intake manifold and discovered that one of the rocker arms broke. To be precise it was the exhaust rocker on cylinder 3. To my surprise the pushrod was fine. However, I pulled the intake rocker off the same cylinder and found that the pushrod was bent. So obviously something happened to cylinder 3 but I have no idea what as of yet. I went by Phil's house tonight and picked up his cylinder leak down tester to help determine what else is wrong. If I'm lucky the whole cylinder will be F&#%ed so I will have an excuse to build a 331 so that Eric's car won't be faster than mine.

[kdracer73]

Holly crap !

[09sscalicobalt]

damn that sucks lol is it a 4.6 or 5.0

[94cobra69ss396]

It's a 5.0.

[Redondo Jon]

Holy crap is right. The rod is trying to turn itself into the letter S.

[09sscalicobalt]

oh ok and haha yea it coulda been alot worse tho

[94cobra69ss396]

Originally Posted by 09sscalicobalt

oh ok and haha yea it coulda been alot worse tho

It might still be. I still don't know what caused the valves to bind up enough to break a rocker and bend a pushrod. I'm going to do a leak down test tomorrow and go from there.

Originally Posted by Redondo Jon

Holy crap is right. The rod is trying to turn itself into the letter S.

That's kind of what I'm use to seeing. The shocker was the broken rocker. The only time I've broken a rocker before this was when my dad and I first built the 396 in the Chevelle when I was 17. The guy who built the heads didn't set them up for the lift on the cam we had and the springs went into coil bind and pushed the pushrods right through the back of the stock stamped steel rocker. We then had the heads redone and my dad bought the Crower roller rockers that are still on the car today.

[94cobra69ss396]

This morning I pulled the plug from cylinder 3 so that I could run the leakage test. The plug looked fine so it doesn't look like anything was inside the cylinder. I did the leakage test and it only has 10% leakage. Not bad for having 80,000 hard miles on the engine. So going to order a new rocker and pushrod and put it back together.

[Damian]

Lucky. Did you see anything wrong with the piston at all? Not sure if you have a borescope or not. Or even just looking in there with a flashlight.

[94cobra69ss396]

I can't get down there to look into the spark plug hole and I don't have borescope. However, I did compress the valve springs down to make sure they moved freely. The 10% leakage tells me that there isn't a broken piston ring, blown head gasket, or even a hole in the piston. I'm not sure where the piston is at relative to the stroke but I probably should make sure it is at bottom dead center and do the leak down test again. That way I can make sure that there isn't a crack in the cylinder wall.