I had a sb that made a lower end noise, sounded like a rod, woulda swore it was a rod had you heard it, removed bearings in every rod, nothing perfect clearnace, not even a slight scratch from micro dirt, replaced them anyway.
Made the noise still...
pulled the mains, replaced all bearings even though they have no signs of nothing.
Still made the same noise.................
Went out of the shop cold, made a 1/2 mile pass on both stages (150/200).
Nothing flew out, noise didn't change, i come back to the shop on both stages and my buddy said well there ain't nothing wrong with it, just leave the radio on.
Well i did that and Ignored it for a year as best i could ignore it.
Only thing that bothered me was the oil psi, it wouldn't get over 65 psi, at 4k, or over 6k rpm, 65 psi was the max..
After a year of listening to this sob lower end noise i couldn't ignore it anymore and ripped it out, made many passes on 2stgs, never hi-cupped or anything.
Ripped the motor out, pulled it all apart, checked pistons and bores and rods, wrist pins and crank and mains....
NOTHING, now my temper flared and things started getting tossed and hit with a hammer, smacked the crank right on the snout with a 32oz BP hammer.
then i heard the crank hit the floor (eagle forged) pissed off it fell over i turned to see that only the TOP half of the crank fell over...
The bottom half with a exceptionally perfect crack was still standing there, right on the trust main.
It could be put back together and you couldn't see the crack, this explained the noise and the oil psi issues clearly now.
Eagle demanded the crank be returned for them to figure out what happened, i had wanted to keep it for another shop front counter look at this **** item, but they really wanted it back, so away it went.
But the new crank i hit it first before putting it in, didn't fall over and the motor stopped making noise.
It was amazing that it came out in one piece and needed my temper to hit it to find the crack, i was about to put it back together after having blowing off some steam, had i never hit the crank with that hammer i may never have found that