Technical BBC top end noise and slight pop at high RPM.

Okay, so... I'm fairly confident I know whats going on, but I wanted to ask the gurus here if there is anything else I should be aware of.

My son's Chevy PU is equipped with a 454 (lucky little bastard), and since he's a an extra good kid who has always listened to me when it comes to this stuff, is always attentive when it comes to the performance of his truck.

So, he calls me last week and asked me to come out to where he works and listen to his truck. Said it had a slight top end noise.

When I get there, we fire it up and I hear the noise, then faded and went away. Before the noise left I was able to find it with my stethoscope and it sounded like it was emanating from somewhere around the #2 cylinder.

Anyway, the noise left and it ran great, no miss or anything so I figured there may have been some dirt or something in the pushrod or whatever.

Since the noise left and we couldn't reproduce it, I told him to drive it but pay close attention to it. A week later, still running fine and no noise, figured it was a fluke but still had some suspicions.

This morning, the thing shows up at my shop on a rollback. Top end noise is back but subdued, but now there is a slight miss and a pop when you throw fuel at it. No backfire but a little "pop" at high RPM.

So, I'm fairly confident that he's wiped a lobe off the cam. I'm going to get out my dial indicator and measure the lift at the spring before just blindly tearing it down on a hunch.

Since I've been a SBF guy my whole life, my question is, is there anything else I should look for while trying to diagnose this thing? Do BBC's have any quirks like the rocker arm nuts backing off or are prone to fulcrum issues or anything? Sure would be nice to NOT have to do a partial tear down to fix.

There is one other issue that I'm praying isn't anything, but the oil pressure gauge jumps a few pounds at idle.

I'm probably just grasping at EASY straws here, but I have this kinda sick feeling in my gut that we're going to be pulling this thing apart.

Some stats: Later model BBC, all stock, around 55,000 miles on the clock. No loss of oil, oil is as clean and full as it was when we changed the oil about 1500 miles ago.

So... what say you? Any help or insight would be greatly appreciated.


H.A.M.B. Tax: Here's Ms. Joi Lansing's fantastic vintage zoomers for your time and consideration.

 

Bad valve spring maybe

 

Look at the valvetrain....might want to do a compression test...but yeah, they do wear out cam lobes, and have rocker arm issues, and valve springs break, etc. Look it over carefully before taking stuff apart.

I've gone to using hydraulic rollers in big blocks that get driven a lot, and have a bit of lift.

 

If your son is romping on it regularly , bent pushrods & broken valve springs along with bent valves are likely candidates , BBC are notoriously hard on valve trains !
Forgot to mention , BBC are particularly hard on timing chains / gears !

 

I agree to evaluate the springs, rockers, and whatever you can see. If you remove the valve cover and start it up, can you see if the pushrod is rotating? That may indicate the lifter is rotating as it should, if it is losing a lobe the lifter is probably not rotating, or rotating less than the others. If excess clearance is detected, that is probably confirming your suspicions about lobe wearing away. Unless you find an obvious bad rocker.

Maybe a slight consolation, if you just pull the intake you can pull the suspected lifter to look at the bottom and the cam surface. Before you have to do further teardown, to at least verify if that is really your problem.

 

Wouldn’t a worn cam lobe cause a consistent issue? I’ve only had one bad cam, many years ago, but recall a miss and power loss.

 

Also.......if engine was ever overheated, BBC in late model trucks are prone to galling of valve stems and intermittant seizing of valves in guides due to galling/scoring

 

Lifter getting weak. Valve sticking in the guide.

 

Thank you guys for the heads up and info. I love it here.

Anyway. I'm gonna start diggin' around in this thing and see what comes up and report back.

Again, thanks!!!

 

HEI.

 

Pull the heads and look at the valves while replacing cam, lifters, timing chain. Check pushrods and rockers replace balls and nuts. Bet you find at least 2 burnt or warped valves.

 

Check the plug wires first and make sure there ain't no contact with the headers.. check inside the distributor cap and rotor tip.. make sure none of that is chewed up... plug wire leakage is best to check at night time... you never know if you have a fireworks display under the hood...

 

Alright you BBC gurus. Today I cracked this thing open and found almost ALL of the rocker arms on the right bank loose. The #5 exhaust valve rocker is REALLY loose -AND- the rocker arm nut looks to be backed off slightly (hardly any stud threads visible above the nut). I can replicate the noise with my finger on the #5 exhaust rocker. ALL of the pushrods spin a little too freely than I'm used to.

Again, this is the first time I've cracked into a BBC, so please, pardon my ignorance.

Not seeing anything else and this thing is stupid clean inside.

I'm wondering if I can get away with just adjusting the lash across the board and going from there.

My thing is... there is a reason there is so much play.
Collapsed lifter?

So, before I proceed, I wanted to run it past you guys for guidance.


Thanks!!!

 

Ideally you should pull the intake, pushrods, and lifters then inspect the cam lobes and parts for damage. Check the rocker studs are seated and tight. If all the parts pass inspection put it back together with some new rocker lock nuts and make the proper valve adjustment.

 

Might want to tell us what you define as "play" or "loose". If you can rattle the rocker arm, moving it in the direction of travel, then it's loose. If it doesn't rattle, but you can move it by hand side to side, then it's not loose.

The nuts do tend to back off when they get old and worn. You can buy new nuts. If a rocker gets loose and the nut is not backed off, that's a sign of cam/lifter/pushrod wear.

I would go through the firing order and adjust all the rockers, and see if it quiets down. I do one pair at a time, when that cylinder is at TDC in firing position (both valves closed), loosen the nut until I can rattle the rocker, then tighten slowly till all the free play is taken up and it doesn't rattle any more. It will still move if I push against the lifter spring, that doesn't mean it's loose. I can still spin the pushrod, that doesn't mean it's loose. Being able to rattle it means it's loose. Then turn the crank 1/4 turn and do the next cylinder in the firing order. After I finish adjusting all of the rockers to zero lash, I add 1/2 turn preload to all of them, starting at the front and going to the back, on each side.

This method of adjusting works, it's easy to keep track of where you are. This is for hydraulic lifters, with relatively mild cams. For solid lifters, you want to use a different method of adjusting them.

 

Hmm...almost just sounds like you have nuts backing off. Maybe swap to new nuts or poly locks and just adjust them for a first try? If that was mine, I would likely do that and change the oil so I could look for anything there before tearing it all down.

 

How much torque does it take to turn the nuts? It should take a bit to turn them. They could just be used enough that there isn't enough drag from the crimped part at the top to keep them from backing off. It would be pretty unusual for one bank to have all of the lobes going flat.

 

I haven’t played with a BBC in decades, but don’t they all have screw in studs to hold the push rod guides?

 

My lovely wife, and aspiring hand model, will now demonstrate.

Behold the looseness!!!



Yeah...

 

Yea, looks too loose from here.

 

I’m like you and can’t remember for sure, but these appear to have them.

 

I can see one section of the cam going flat, between journal's, but not one WHOLE bank! I'd try replacing the rocker nut's and adjust to factory spec's and see what happens... JMO... Also check under the pivot ball's for excessive wear and galling.

 

Well, I don't always trust my lyin' eyes, but it looks to me in that picture the screw-in rocker stud is backed out of the head a little. Also, when I was younger, I had a couple 396's that would eat lifters for breakfast...
And, since that's an exhaust valve, it would explain the pop at higher rpm.

 

Big block chevys all have screw in studs, that hold the pushrod guide plates.

I can't tell from the .gif if it's loose or not. If the lifter has bled down, but it's still adjusted properly, it will be loose like that, and all is well.

 

I agree new nuts, or better yet poly locks to prevent backing off. Also once you set preload and get it running, you can adjust the valves while hot and running. That way you ensure each lifter is set exactly at 1/2 turn preload. Or whatever value you want to use. Assuming the rockets and balls are not damaged. If you have clearance you can spend some money and put roller rockers on for fairly cheap since BBC are popular.

 

Man, you guys are the BEST! I love it here.

 

Seems like an awful lot of " replace this , replace that" all without knowing what's wrong ! S M H?

 

yup.

 

Maybe figure out what the issue is first, instead of shotgunning for a solution?

 

Do you what the lash was set at with that cam (041) and solid lifter combo????....