Howdy moparts

I finally started breaking in my fresh 400/512 that’s been built for a while. Everything went good for a few minutes until I heard a rattle and shut it down. Turns out the last two bolts on my rocker shaft were coming loose. What was shocking was that #7 exhaust pushrod was too short to touch the rocker once I tightened the shaft.

It’s my first big block and wow what a pleasure to work on. With no water in the intake I had the valley open inside 30 mins. #7 exhaust lifter puked its piston and the little pierced sheetmetal piece underneath was ripped in half. #7 intake had its piston stuck cocked in the lifter bore. Both lifters still looked brand new on the bottoms as does the cam so I just ordered replacements. I was only a couple minutes into fire up and break in before it let go and no pieces fell thru to the pan so I think I dodged the bullet on this one and it will just be a small setback.

Is that a normal thing to have happen when rockers let go? This is stock stamped rockers and a .507” hft cam, no crazy pressures or anything. I half expected to find a whole lifter ejected into the valley I don’t see why this would have broken like this?


Thanks!
Radar in Philly

Guess I better make sure those pushrods are not bent too...

Edit: yup the one that did all the smashing #7 exhaust has a wobble you can hear but not really see when rolling it on glass. Time for some pushrods too.

After having a moment to reflect I guess the shaft got loose enough to let the pushrod out of the pocket in the rocker, then did a little smashing while misaligned in the lifter, then the shaft finished loosening up until it wasn’t even opening the valve any more.

I got a brand new set of 16. Hy-Lift Johnson slow bleed HYD Lifters. If your interested in them.

Make sure that the pushrod is not to large for the cup. It pushes down on the retaining ring and pop goes the lifter. Check for pushrod rubbing as well. (look for shiny spots where it goes through the head.
Todd

As you surmised I'd say the rocker bolts coming loose caused all the carnage. As you are doing replace the lifters (make sure they ain't too tight in the lifter bore(s)/check/replace the pushrods & #1 find out/address how the rocker bolts were/came loose. As you go together you might check/note preload.

I would make sure the rocker arm shaft bolts are at least grade 5 or better and make sure to NOT over torque them
The FSM calls for 23 to 25 Ft. Lbs. and that is what I use.(although I convert those numbers to inch Lbs. and use my 3/8 drive 100 to 750 inch lb. torque wrench on any torque below 30 Ft. Lbs. 23x12=276 inch Lbs., 12x25=300 inch lbs., correct )
I do check them at least three times while assembling the motor and again after warming up the motor to break the cam and lifters in and recheck the valve lash and inspect for F.O.D. in the heads in case of something going horribly wrong like you had
Good luck on your deal

Thanks fellas

This is stock 1977 rockers shafts and bolts out of my donor 400 screwed into brand new stealth heads. I have screwed down a ton of stock and aftermarket rocker shafts and I always worried about deforming the shaft more than pulling the threads. I will admit I never used a torque wrench on them though. When it first happened I was worried that all the threads had pulled out of the rear rocker stand. I have to go inspect the hole more carefully and decide if a stud or a timesert would be necessary or good insurance.

I’m definitely thinking about at least covering the rest of the head and spraying out the holes with brakeleen so blue loctite can get a good bite.

Ok so I went out got a really good cleaning and look at the threads on my bolt and head. Somehow the rocker stand threads still look sharp and the bolt threads down nicely. Hard to believe the last two bolts would just work loose like that with almost constant pressure on them as the rockers work the valves. Break in rpm is definitely loud though so I can see how I wouldn’t have noticed it until it realls clattered?

Still I’m surprised. While I was trying to drift off to sleep last night I kept thinking how could the pushrod have slipped far enough out of the dimple in the rocker and simultaneously wedged either to coil bind or too far toward the fulcrum of the rocker to have good leverage? The pushrods don’t contact their holes through the head but don’t have a ton of room to misalign- the holes aim at the lifters pretty well. Or did the pushrod just slip over into the lifter’s snapring/retention wire area then the cocked piston in the lifter bore broke the little sheetmetal piece underneath before it spat out the piston? And how did the intake lifter piston get cocked in its lifter bore?

And if enough force was transmitted from the rocker, which was anchored by bolts that were unscrewing fast enough to cause problems in less than 5 minutes of 2500-2700 rpm, how did it not pull the remaining threads holding the shaft bolts right out of the aluminum rocker stand?! What a freaky thing.

I actually have a video of it from my wife’s phone I posted on yootoob- you can hear a hint of a problem starting in the middle of the video but it was tough to hear in the heat of the moment at rpm before it was too late.

Skip to 2:45 through to hear the carnage happen. I think after that it was still running on 7 cyls pretty well with the one cylinder only slightly opening the intake and the exhaust valve staying closed! The rpm didn’t change a ton and there were no additional horrible noises. On the other hand a healthy 448” V7 motor should make enough power to drag a dead hole along for the ride.

https://youtu.be/pyZlQqcrNkI

If it were mine, I would be checking the rocker shafts as well to make sure they are not bent.

I agree you dodged a bullet, it could have been much, much worse.

The shaft bolts get loose, then you have some clearance between the pushrods and the rockers/lifters, pushrods are jumping around in the lifters & rockers, hammering all the pieces involved....... and you’re gonna end up with a few broken pieces.

Stuff happens........ you caught it before it got real ugly.

To me it sounds like at approx 36 seconds in on your vid it dont sound well. Sounds like its already laboring imo.

Hope its a easy fix.

Does the Stealth head use heli coils for the rocker arm shaft threaded bosses ?

Never installed a Stealth head


Was nice to see that the Edelbrock E Street used heli coils and supplied studs for 2 and 4 bosses

However

Was not nice to see the some what broken off heli coil tangs left in the bottom of the holes in three spots when I was trying to torque everything down

Avoided a messy situation there

You might want to use some old NHRA "stock class" racer tricks with the stock rocker arms to check the lifter preload on every rocker arm and lifter, you may need to swap some of them around to get between .015 to .045 preload on all of the lifters on the base circle of the cam lobes , all 16 of them :wrench

I had my thumb on the throttle and couldn’t understand why my buddy wouldn’t spin the curb idle screw until I could let it go. Turns out he was trying to be smart and run back and forth to look at the tach but that dip in rpm was me checking to see if I could let the throttle go yet or not and yelling at him to zing up that curb idle asap.

My floats were way high and it was running super duper rich. I’m still not sure if I did it again if I would have heard it starting to let go and know to open the valvecovers. I’ve had adjustable lifters on solids open up before but always heard a tap and shut her down.

Guess it was my torqueing negligence mixed with a freak thing. The stealths have room to run 1/4” longer bolts without flirting with the bottoms of the blind holes. I’m gonna spray out the holes with brakleen and shop air a few times then blue loctite them in next time.

I got new pushrods, just waiting on lifters and gonna order some new grade 5 or 8 bolts off mcmaster.

I do NOT recommend loctite on the bolts

Don't do that

X2 no loctite & my Super Stealths have inserts so I would highly assume the Stealths do also. Not sure about grade 8 but I will defer to others on this. EDIT yes spray em out with brake kleen & eyeball em to see if the threads look good then run a bolt in there & see if it threads in/out good then we will see about advise on a lube. I usually dip threads in 30 oil then blow em off with shop air. On a side note I would pick a cyl that is on TDC compression & see what the preload is (not that I think it caused this) but it is important.

did you fill the lifters with oil before you started engine? Do you have adjustable rockers?

I soaked the lifters overnight but I didn’t take them apart and fill them or anything crazy. I also let the drill run for a minute when I primed the oil pump- dunno if it was clocked right to feed the lifter galleries but it didn’t noticably clatter on fireup.

I’m running a comp .507” hft cam with extreme energy lifters and I bought comp 5/16” pushrods that are nice fartory low deck replacement deals- 8.555” iirc. The rockers and shaft are stock late 70s truck pieces out of the 400 donor motor I stroked.

Haha I spelled factory ‘fartory’ oops thats a hilarious typo