455 Stage 1 - Cracked rocker shaft - What would cause this?

A couple of weeks ago I was driving home with a warmed up engine. I rounded a corner and aggressively accelerated from 20 MPH to 60 MPH. I heard the sound of the engine change and noticed the mechanical oil pressure gauge was at zero. I shut her down and had her towed home. Upon further review, the rocker shaft for the #2 cylinder was cracked. What would cause this? The push rod is not bent. Any suggestions on additional areas to check? I was going to pull the intake and inspect. I'm trying to decide between attempting repairs or pulling the motor. Thanks in advance for any insight.

 

I’d say pull the rocker shaft and verify nothing else is broken. Put a new one in and repeat!

 

Cracked Rocker arm would not cause low oil pressure something else is going on.

 

No it’s the shaft, not the arm. That means it’s spraying engine oil from the hole in the top end

 

Stock shafts are pretty weak. Biggest issue is tightening sequence of the hold down bolts. They must be drawn down evenly and slowly. Especially when the the end rockers are up on the nose of the cam lobe. Replace the shaft ,check the rockers involved and tighten carefully.

 

The first push rod (exhaust #2 cylinder) was OK, but the second push rod (intake #2 cylinder) was pretty bent. The best I can see down the push rod holes, the lifters appear to be in place. I've got some replacement push rods and a new rocker arm shaft on their way.

 

Thanks for the heads up. I'll do some research and take my time.

 

X2. Crack could have been already started.

 

Sorry meant cracked rocker arm shaft

 

Yes that what usually happens, a small crack occurs and you don't notice it then over time the crack continues to migrate till the shaft fails.

 

My brother did the same thing with his 72 GS455, cracked the rocker shaft and bent a push rod. It was no big deal, he just replaced the rocker shaft and push rod, then added support brackets( I believe from TA Performance) on each of the rocker shaft bolts. That was years ago and still running great!

 

You may want to take the intake off and check the lifters. I was running the C 107 on the street bent
a couple pushrods and broke a lifter and was lucky that the parts didn't make it in the motor didn't lose complete oil pressure.

 

How big is the cam........much over .500 lift this cab happen often with stk parts. X2 of the shaft support clamps. Can find some off s 430/400 or order new.

X2 on the slow even shaft draw down to specs.....I never go more than a couple turns without moving around

 

I have heard of people having this problem with "fast-ramp" cams.

 

Cracked shaft wouldn't cause no oil pressure either. He has thru pushrod oiling. The lifter may be out of the hole or damaged otherwise.

 

Ohh that's very true. Something more is likely up then.

 

This happened to me in 76 on the drivers side front of the rocker assembly bar. Engine was also running up and pulling hard. ( i ran my car a bit harder back then. ) I went to a Buick dealer and bought all new stage one push rods, rocker arm shafts, and rocker arms. Installed em’ one afternoon and everything has been fine for 43 years now. Hope your situation is the same!

 

If you haven't done that to a set of rocker arms then you haven't been pushing your stuff enough. The end rocker shaft is unsupported so it is the first area to crack. A lifter out of #2 will cause a giant loss of oil pressure. There is a good chance that once the shaft broke the lifter pushed up but not all the way out of the hole and that allowed the oil to gush out of the bottom of the lifter bore. #2 is right there by the main feed to the whole engine which would cause oil pressure to disappear. After the engine was shut down the lifter may have just slid back into the bore. Keep your fingers crossed. The massively bent #2 intake pushrod is caused by the intake pushrod being forced to open the valve against the cylinder pressure without benefit of the exhaust valve leaving off pressure like normal. Nothing unusual there. Replace the rockers and pushrods and you probably will be good to go.

A heavy duty fix is to use the earlier 350 rocker arm shaft retainers.

 

If the push rod bent then it was not on contact with the seat in the lifter and that bled off oil pressure also.

To confirm that your lifters and Cam lobes are still good and did not get beat up in the failure , then once you get the new parts paint
The tops of the push Rods With a white verticle stripe.
Once the motor is back together and running you will see the push rod spin once every time that valve opens and closes if the lifter and Cam lobe are good.