pablocruise

OK friends, I'm fishing for some ideas. Pretty bummed out right about now.
Here's the story:
current L98 about 20K miles on the rebuild. Engine suddenly developed clacking sound around superram lid/lifter valley/heads. Car runs like crap. Check and re-adjust rocker arms many different ways, still clacks.
Pulled superram, heads, installed all new guides and a 3 angle valve job. SR back on. Still clacks.
SR back off, replace all lifters. SR back on. Adjust to many different pre-loads running, still clacks.
Clacking seems to quiet down at idle but gets loud upon application of throttle.
Clacking sound matches RPM. idle: clack............clack.............clack
1500RPM clackclackclackclack
I didn't put a dial gauge on the tops of the lifters to see how far cam is pushing them up when I was in the lifter valley.
Rocker arms all perfect, springs all perfect, actually the valvetrain is pretty quiet. Sound eminates like from cam area or lid of SR. EGR valve ruled out.
Lifter bores seemed ok but......? Flattened cam lobe? It's a hyd roller. The older roller lifters seemed alright. Minor scuffing on their sides.
I rolled all the pushrods on glass, all straight.
:cry
any idea welcomed! help!

TheCorvetteKid

I'm no expert here, but have you considered that you may have a spun bearing? I've never heard it myself, but from what I've been told, that's what it sounds like.

I hope I'm wrong and its something relatively simple (like a bad distributor or something).

Good luck with it.

pablocruise

oh crap. I didn't even consider that. I thought that might be an extremely loud metal on metal grinding/squeeling sound?
It's not the dist. A quiet whirr from the rotor inside.
Thanx for the wishes.

scorp508

Spun bearing sounds like a deep knocking down in the engine. At idle pull a single spark plug wire off the distributor and see if it gets quiet or stops. If not move to the next plug and keep going until you find one that seems to make the noise get quieter.

If it were me I'd probably pull the pan and see if I can move one of the connecting rods up and down any. Is the car an auto or 6-speed? If an auto could a torque convertor bolt have backed out?

pablocruise

what I thought to do was take the v/c's off and at idle remove an intake pushrod/unplugging the corresponding injector on one cylinder at a time trying to isolate cam lobes. Then replace it and on the same cyl, remove the exhaust push rod. Would this idea work while the motor is idleing? Never done that before. Too bad the starter died on me awhile ago too and can't even crank over the engine :cry

Mike's 86

:iagree: But I would not rule out a wrist pin going bad.

pablocruise

******DING DING DING!!!!!*******
SCORP GETS IT AGAIN!
update
Scorp, I tried your suggestion, no change at all in clack. I get car up on jackstands.........and..........
clack much more pronounced in oilpan area :cry
advise on oilpan removal? Subsequent inspection?
THANKS SCORP!
what did he win? thinking, thinking.....

CentralCoaster

Not fair.. i didn't get to answer in time. :smash:

Is there an easy way to measure the frequency of the clack? It seems like that'd be the best way to distinguish between valvetrain and bottom end.. valvetrain would clack at half the speed... of course the crank would clack only under load, every other rev. Oh well, it was a good thought.

It does sound like a bearing. My brother's truck made the same sound your describing shortly after he rebuilt it. Started clacking only under idle and load, and then got quickly worse over the next few days before we figured it out.

Luckily for him though, my dad was driving it at the time, and towing my Corvette at the time the symptoms started.. so my brother blames the two of us for destroying it instead of questioning his own procedures or dealing with the problem. :rolleyes:

Good luck. :cheers: :(