Technical Sudden lifter / rocker noise - Potential causes?

Afternoon all -

Yesterday I was doing some work on my SBC 350 (details below). Specifically, I was re-jetting my Holley 770 SA, changing out the power valve and switching to a bigger squirter. - so not doing anything with the valve train. I was testing throttle response, and then moved on to readjusting the Air/fuel mix screws. I just completed that process, got the A/F mix as good as I could and was again testing the throttle. I then held the engine at around 2000 - 2300 RPM to see if a miss had cleared up and suddenly, a rocker started clicking on the driver's side. Its loud enough to hear over the engine, from either side, and was not gradual - one second there was typical SBC engine noise, then suddenly the click of a badly adjusted rocker. Since I was standing right over the engine at the time, I took note of the vacuum readings, timing and engine "attitude" immediately after the clicking started....no change - if I didn't hear the clicking, I'm not sure I'd know anything was different.

I'm going to look at it tonight, there wasn't time to dig into it last night. On other engines I've had a clicking rocker that came on gradually, I've had ones that gradually got worse / louder or got better / quieter when the engine was warm. I've had rockers that you needed to keep adjusting to keep the tap-tap from coming back, but I've never had one go from "just fine" to "clearly needing adjusted" in the blink of an eye. Last week, I adjusted that entire bank (warm, engine running) to zero lash + 1/4 turn (I originally had them at 1/2 turn but the engine runs better at 1/4 - not sure why, I've always done 1/2 but this motor likes 1/4) so my hope is I somehow forgot to tighten a poly-lock and the nut has simply backed off - but I'm usually pretty good about that. So, aside from "nut backed off, you're an idiot", what else might explain a rocker that goes from adjusted fine to suddenly "doesn't sound adjusted at all"?

Engine details and other info that might be useful

Block: New 4-bolt main from GM. Lucky if it has 5 miles on it. Estimated 9.4:1 CR
Heads: Dart Iron Eagle, 180 runner, 64cc chamber
Cam: Comp Cams, 227@050 Intake, 241 @050 exhaust. 107 LSA, Valve lift: .479 / .465 (I /E)
Valve Train: Magnum push-rods, Roller tip rocker (standard ratio), Comp Camps lifters
Other: Edlebrock EPS intake W/ Holley 770 Street Avenger

Other issues: While likely unrelated, I thought I'd detail other issues it has:

- Timing: Timing mark likes to jump around 2 degrees, randomly. I have two timing lights, same design, does it with both lights. I've checked for vacuum leaks and tested the timing chain ( new, but tested anyway) only have 5 degrees of crank movement before the rotor moves - so within spec. Shimmed the distributor gear to 0.18. This helped, but not a solution. Distributor is also new, and issue was generally the same with three separate distributors, caps, coils modules and two sets of plug wires, three sets of plugs. Same condition regardless of initial advance, vacuum advance or mechanical advance settings. Confirmed balancer is not slipping ( its new, plus added a paint mark to check for a slip)

- Miss - Has a miss somewhere. Very difficult to pin down. It got much better when I switched to different plug wires and plugs, but not completely resolved. Miss occurs at all RPM, including idle. Engine improved when I adjusted the rockers to lash +1/4, as did vacuum.

Vacuum: Once warm, vacuum reads around 11 hg @1000 RPM idle . This is actually a very good reading for this cam, most report 9HG. The reading is not steady however. It has a rapid fluctuation of perhaps 1 HG. I've attributed this to the 107 Cam LSA - larger overlap playing with the vacuum signal. I've been able to vastly improve and steady the vacuum reading with valve adjustment, timing and carb changes, but cannot make it rock steady. Otherwise, it acts like any vacuum should when you rev the motor, etc.

I was just about to reset my timing curve (again) when the rocker suddenly started its tapping.

Thanks for any insight.

Allan

 

New flat tappet COMP cam , you used the correct break-in lube , correct oil-additive , correct procedure , right ??? Even w/all that , it's a crapshoot on cam/lifter failure [especially comp IMO}
dave

 

ran out of oil pressure? the cam went flat? something broke? a rocker nut backed off? it blew out an exhaust gasket?

 

Tossed a keeper in the lifter?

 

bottom of rocker arm cracked out?

 

Correct break-in lube yes, and comp-cams break-in oil, changed after 25 minute break-in run at varied RPM 2200 - 3500 and then refilled with more of the same. w/ new filter. In adjusting the rockers with engine running, I took note of an even and consistent movement in all rockers, both sides. I also discount this as prime suspect only because it was fine, then not fine, immediately - but I do agree its definitely a possibility. Though if it has flattened a lobe, it mush have done it in double quick time, the engine hasn't ran much at all.

Oil pressure - possibly, I didn't check that but I'd assume more than one rocker would start tapping - I left the engine running for a minute or so at least while I checked other things and only one rocker was tapping its little heart out.

Exhaust gasket - I definitely think this is a rocker tap, not an exhaust leak. I know they can sound similar but I probed with the stethoscope and I'd venture to say its the intake or exhaust rocker on #3 . #3 was also the plug that would carbon foul more than the rest before I got things running better.

Cracked rocker is possible, but I bought chromoly cast steel rockers - so if that's the issue, it must be defective. My engine hasn't seen any use or RPMs high enough to cause a failure like that - though if that is the problem, I'll take it because its an easy fix. Didn't think about that. I did once have a push rod punch a hole through a rocker.

As for a keeper in the lifter - that's a new one - wouldn't the spring pop and the valve drop if I somehow lost a keeper?

So far nobody has mentioned a collapsed lifter, bent pushrod, or busted valve - so....I take that as a good sign those things would present with different issues.

 

No, we just forgot about them. Hope you find it, and it's not serious

 

LOL....sort of...Given that the engine seemed completely unphased, with no additional noises, RPM drops or other signs aside from the loud click, I hope its a simple fix like a nut backed off. Knowing my luck on this build however, it will be a cracked block with a hairline fracture in the crank that has somehow held together just enough to make a ticking sound.

 

I had this very same thing happen to my "new" 283. Broken valve spring! Very easy fix and no issues since.

 

OK, that sounds more optimistic - a little irritating given that its a brand new head with new springs, but heck, I'll take it. Fingers crossed for an easy fix...

 

Something broke, pull a valve cover and it should be relatively obvious.
Cam lobe going flat immediately isn't too likely.

 

I had the same thing (or similar)happen on my new 327. Comp cams magnum rockers(1.52 ratio) and comp magnum pushrods. The balls on the pushrod tips where they went in the rocker were worn(hammered would be more the term)on several rockers. I replaced the rockers and pushrods with the stock components, and the noise is gone.

 

Do those heads have press in rocker studs? Or screw in rocker studs? I'd pop a valve cover off and set a straight edge across the tops and see if the rockers studs are all the same height or if one pulled, or loosened. Then check for a broken spring. Then leak it down, could you have dropped anything down the carb that then tagged a valve or piston?

 

I had a "self aligning" rocker on a 350 slip sideways on the valve, pushing one side until the keeper popped out, letting the valve drop. Only took a few seconds to happen, I had left the house, went 1/8 mile or so, starting tapping, by the time I got off the road, another 1/8 mile, valve had dropped. Limped it back home, when I pulled the heads found the dropped valve, damaged guide, and a bent pushrod. Luckily the piston only had a few small dents in it, cylinder was untouched. Had heads worked, put on a set of guide plates and roller rockers when it went back together.

 

Inspection should show it quickly. Sounds like a rocker that cracked, or the nut backed off, as you suspect. If your using poly locks, it pretty common if the procedure isn't followed exactly. i.e.; Set screw bottomed after backing off adjustment 1/4 turn, then tighten back up 1/4 turn, etc.

The reason your engine likes less preload on the lifters is that it increases the vacuum signal slightly. It will also reduce valve float at serious revs, but adds maintenance needing more frequent readjustment.

I'm assuming your pushrods length is correct for your cylinder heads and valve installed hieght?

 

I've
seen 2 cams wipe multiple lobes/lifters during break-in
dave

 

It happens plenty, but I think he's referring to the speed it happens making it less likely in this case.
Usually popping thru the intake, or a definite misfire, along with a vacuum signal indication, accompany a lobe failure.

 

Yes that's true, and I guess one could consider that immediate in a relative way but they do not go from ramps to flat in one split second. The loose thousandths each revolution.
25,000 or so cam rotations

 

If if is only one lifter than my though would not apply. I had an incident of sudden lifter noise and it turned out to be very simple. I reved the engine and click, click went the engine. It turned out that I was using a wire bail type dist. hold down and had not fitted it to the distributor properly. When I reved the engine, the hold down flexed and allowed the distributor to pop up about 1/4 off an inch which shut oil feed off to one side. A solid plate hold down And re positioning the distributor instantly cured the noise.

 

Morning - just closing the loop on this one -

Result?......nut backed off.

So in short - I just didn't adjust it right. I was able to move the polylock nut very easily and it was clearly too loose. So I understand why the lifter was clicking..Somehow I messed up the adjustment.....But I don't understand exactly how I managed it...here's what I mean:




The rocker on the right is the one that was clicking. You can clearly see that the lock nut is at least two threads further down into the polylock than the one next to it, and the one next to it is consistent with the rest, at about 4 threads showing. By my thinking, the only way I could have gotten the lock nut two turns further into the polylock, is if the polylock itself was two turns further out (so looser) which would have brought it up off the stud by two extra turns, creating the space needed to turn he lock nut in by two extra turns before contacting the stud and locking the polylock. HOWEVER.....if the polylock was a full two turns looser than the rest, it would have been clicking like mad the entire time, not after a good hour or so of run time. I check and double check each rocker when adjusting and there's simply no way it was making any noise at all. If the polylock simply backed out, I also don't believe there is any way for the lock nut to have spun itself in the opposite direction and go further in - surely it would just follow the polylock in an anti-clockwise direction. The only possibility would be that the polylock spun itself up off the stud by two turns at the same time it spun itself up and further onto the lock nut - but that seems highly unlikely.


In any case, the clicking is gone. The annoying miss and fouling out of #3 plug more than the rest is still the same. I'm really close to crushing my formerly beloved corvette into a cube of fiberglass and making it a table.

 

When you tighten these, how do you do it? I was taught to adjust the lock screw so that when I tighten the nut and lock screw together, it will end up with the correct lash. Takes several tries. If you adjust the nut first, then tighten the lock screw, it won't get very tight.

 

I've never used polylocks before, so I did a little reading and I came away with two recommended approaches from OEMs as well as folks like us on forums. The first way was to tighten the polylock to your desired setting, then while holding the polylock with a wrench, tighten lock nut. The other way is what you describe. I did it using a combo wrench that has the 5/8ths box end plus a guide hole for the allen wrench, and so did the the "tighten to setting, hold and snug" way. This is the only rocker I've had an issue with, but even If I did it wrong, I still can't figure how the lock nut turned itself clockwise and whet further in, while the poly lock turned counter clockwise and backed itself out...

I swear the engine hates me. Never before have I had such a collection of odd-ball one-off issues in a single motor.

 

Squirrel's right , you have to "cinch" the poly-lock after tightening the allen screw , wonder how many don't do this ??
dave

 

Engine harmonics make things happen randomly when a bolt or nut loosen. It's not surprising to see the loosened components spinning together or separately in either direction.

Your miss on cyl 3...have you tried a leak down test? I've seen valve seats not done properly and not seating causing low speed misfire. Even on new cylinder heads.
A leak down test will show it. Or use a compression test adapter and shop air with the engine on its compression stroke for cyl 3 to test for an air leak.

Maybe you've done it and I missed it earlier?

 

^^^^

 

I had issues on a few of mine because the studs had a slight recess on the ends, the set screw would lock on the edge of it and they would work their way loose, i filed them all flat and reinstalled the locks and stopped having the issues.

 

Adjust just like Squirrel said.

 

I haven't done a leak-down test yet - was trying to find a leak-down set locally today but no luck. I'll try that though.

Its odd, in many ways the engine acts as though it lean, yet fouls plugs with carbon - #3 happens to be the worst. 99% of the running time has been at idle though, So perhaps the plugs should look a bit rich. Its also started spiting at me - shut her down, half second run-on and some fuel gets tossed out the carb. Not every time and not much when it does...but still, its added another annoying trait. Its one step forward, two steps back with this engine. I'm going to look at my transition slots, make sure I don't have the throttle blades open too far (motor needs to idle at around 1000rpm) if I do, that might make the main circuit come in at idle and make things too rich, it would also explain the spit / run on that happens.

If this keeps up, there will be a 78 corvette with a $7000 motor / transmission at the bottom of Lake Washington.

 

50 yrs. ago I was thrashing furiously on my '57 chev. in my grandfather's driveway, after a strong line of curse words from me , he smiled & said ,"who's smarter , you or that lump of iron ?" PERSPECTIVE !!!
dave

 

I had one plug fouling on the first motor I ever built. After several cleanings and replacing spark plugs, I was talking with an older mechanic about it. He looked it over and told me to take out the Champion plugs and put AC plugs in it like it was supposed to have. I did and never had another plug foul.

When I worked at a Ford dealership in 79, a man brought in his pickup with 11,000 miles on it because it was missing. The Sun scope showed 2 plugs misfiring. When I removed them they were Champion plugs. I replaced them all with Motorcraft OE plugs and no more miss. The guy said he replaced the plugs to get more power.