Knocking sound in 496 big block

[ljfen]

Here are the particulars. Friend is running a 496 big block. He bought the stroker kit for his 454. It has an Eagle crank with aftermarket rods and pistons. Stock heads with new valve guides and valves and seats replaced on some valves. He raced it a couple of times after the rebuild but for the most part it's been run on the street. It has less than 1000 miles on it. On cold start there is a considerable knocking sound coming from the motor. It sounds like a rod. It gets slightly less noticeable as it gets warm but it is still there. Car runs a electric fuel pump with a return line.
We tore the motor apart last night expecting to find a loose bearing or flywheel, something that would cause the noise. Nada. Bearings looked good, mains and rods. Took the heads apart looking for a loose seat or possible broken spring whatever. Found one valve with a broken keeper. The one keeper was cracked in half the other was good. That valve spring looked like the inner spring had been pounding the shim under the spring, not bad but you could see that it was contacting it. Spring was not broken. Under some of the other springs the shim was upside down. This was all that we found on the motor. The strange thing is my SBC had a similiar noise and I found nothing wrong with it either. One common denominator, both had Eagle cranks.

 

[grumpyvette]

Without being there to carefully inspect the engine its rather difficult to say, EAGLE, makes decent components, its far more likely to be a clearance, or valve train geometry issue than a bad crank,
Ive seen this dozens of times and with several different causes.
the most common cause is VALVE TRAIN clearance or geometry issues, a bad rocker (ESPECIALLY STOCK STAMPED STYLE ROCKERS) can make an incredible knocking sound at times, you would bet large sums of money was a rod going bad.
ID also look at the motor mount bolts and bell housing bolts as those can also cause noise at low rpms that goes away as rpms increase
many guys install a cam, spin the engine over by hand and if nothing binds they feel thier home free on checking clearance issues, but you might be surprised at the difference between the correct clearances and something that will still alow the engine to rotate without binding up.
Ive also seen busted valve springs, retainers hitting valve seals and rockers hitting retainers make very noticeable noise, rocker clearance slots hitting rocker studs, rockers hitting valve covers or rocker girdles and even exhaust leaks, or detonation due to low octane or non-correct ignition advance curves at times can sound like a rod knock..
next most comon was lower end clearance issues, very careful inspection might reveal rods just touching the block, oil pan, a looser than ideal,loose piston to bore side clearance, the wrong dome design too match the cylinder heads combustion chamber or windage tray,dip stick, or some other clearance issue.
rarely youll see pistons just kissing the cylinder heads but thats generally only at high rpms and not at idle if the combos been correctly clearanced

links might help, or give you ideas where to look.

viewtopic.php?f=52&t=181&p=2283&hilit=+guide#p2283

viewtopic.php?f=50&t=801&p=1542&hilit=+list#p1542

viewtopic.php?f=52&t=181

viewtopic.php?f=52&t=1092

viewtopic.php?f=52&t=528

 

[ljfen]

Thanks for the reply. We are going to mic all the clearances along with checking the piston to wall clearance. He runs a roller tip rocker. We haven't seen any evidence of the valve caps getting hit. Something else I found out about the block. A friend of ours drilled and machined the block to accept a 4 bolt main bearing retainer. He was not familiar with how to drill the block. He drilled thru the block. You can see where the hole came out of the side of main webbing near the bottom of the cylinder. The machinist friend tapped the hole, screwed a small stud into the bottom of hole with sealer, then machined what threads were showing at the bottom away. You can see about 1/4 of the threads were machined away. It was done on only one side as this was the side that went thru an oil galley. Makes me suspcious about any loose shavings or leaking bolt holes. The oil would simply fall into the pan but possible starvation of the cam bearings?

 

[ljfen]

Update on the 496. We think we found the knock. When the engine was assembled by my friend, the wrist pins were full floating with dual spiral locks to keep it in place. #2 piston had no spiral locks on the wrist pin. The pin was able to slam back and forth in it's bore. Because the pin was located so far up the piston, the bottom oil ring land runs thru a portion of the bore of the wrist pin. So in effect the oil ring was keeping the wrist pin from contacting the side of the cylinder wall. You could see where the inside of the oil ring was beat up from the wrist pin hitting it. Talk about lucky. :roll: I think he needs more than one set of eyes when assembling to stop this from happening again.

 

[grumpyvette]

IM amazed the ring didn,t break if that piston pin was not locked in place with TRU-ARCS or SPIRO-LOCKS or in rare cases piston pin buttons