Knockin' On Heaven's Door, what to do for a rod knock?
- Thread starter MrSony
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This sounds lilke a GREAT idea. Glad to hear you're tearing it down.
WELP. I tore the thing down to the short block. Good news, no bent valves, no signs of valves, or anything hitting the pistons. Bad news, on two cylinders that I could see there were weird black marks. Are these scuffs from the rings? I must've rotated the thing a million times when it was just the short block before I put it together the first time and it never scared or scuffed anything. Maybe the oil pressure problem upon break in caused it? Also, I found a crap ton of bearing material. Actual chunks. I suspect it's cam bearing. Forgot to take a look at the cam itself. All my lifters fell the f*** out on the floor once I rotated the motor over, so they weren't mushroomed which leads me to believe the cam was ok but as good practice I'm gonna replace it anyway. There was a lobe however that had two spots on it that look like metal was ground in...bearing material most likely. With the exception of #7 (shown, darker of the set) and #8 (also shown), all the bearings, main and rods, looked almost new.
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Also, I forgot to mention, the locking tang on #7 ripped off of the bearing! You can see it there in the rod! Never seen that happen before, but I suppose how else does a bearing spin in a rod?
I assume this is 7 and 8 rod bearings, when you checked the bearing clearance did you check both halves and the center and both edges? What does the last main look like...
7 on the right, 8 on the left. Every bearing clearance was within .0023 to .0025 on the rods and mains. Damn, I didn't get a pic of the mains at all. I also had to clean up my mess in the garage so I was on a time limit.I assume this is 7 and 8 rod bearings, when you checked the bearing clearance did you check both halves and the center and both edges? What does the last main look like...
I hope you don't take my posts as criticism, it's just an engine blows for a reason and I'd hate to see you put time and effort into rebuilding it and missing the problem. I froze a Buick engine decades ago thanks to my brother in law and had to change the head gaskets. I was in a hurry and forgot the head gaskets on a Buick were right and left. Finished the job around 1 in the morning and had to be back at the aircraft plant to start work at 7 am. Started the thing up and water was pouring out of the drivers side block at the head. Had to redo it to switch the head gaskets and just finished in time to go to work. It's easy to overlook things....
Criticism, bad or good, has it's roots in good intention. I never messed up that bad. Worst thing I did, aside from the dumb oil pressure thing, was drop my damn feeler gauges in the motor on the stand so I had to take the 67lb intake off for a 4th time that day. Since the motor was fine up until I started really beating on it, WOT for minutes at a time on the highway, revving it to 6k all the time, I think the engine just had enough of my shenanigans. And as I found out, it ripped the tang right off the bearing. Whether that tang ripping off was just a normal part failure, or a 6,000 rpm wot for minutes at a time failure, I don't know. But knowing what I know now, I think I can prevent it happening again. With a rev limit of a safe 5200-5500, and less jackassery, if the next rebuild goes the same way, then something needs to be addressed. It was a BONE STOCK bottom end nonetheless. Just new bearings. Clearances checked out good so I slammed it together. Buick never designed this motor to go over 5,000rpm, let alone to 6k and beyond. It's completely different from any of it's GM stable mates in the oiling department. It was just meant to be a "fuel efficient" engine to carry a large car down the highway at 55mph tops.
Steve, you might not have seen, but he indicated above that other than these two rod bearings, the bearings (mains and rods) looked 'almost new'. I applaud your efforts to try to help him avoid suffering the same failure again.I assume this is 7 and 8 rod bearings, when you checked the bearing clearance did you check both halves and the center and both edges? What does the last main look like...
I realize he said that the other bearings look new. It looks like #8 rod is bent with the wear on one side of the bearing. When I check the clearance on bearings I check from edge to edge. Also it's hard to tell but it looks like the #7 rod is wearing a mark on the crank face beside the #7 rod. I wonder what the side clearance was on the #7 and #8 rods
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