Incorrect ring gaps? KB Hypereutectic pistons, for example, require larger clearances than cast or forged, IIRC.

I have heard of a 383 sb chevy engine running for miles with a spun main bearing. Noisy, but still started and ran.

Spun, or misaligned, cam bearing will break the camshaft in half at that journal (brittle material). That happened to my dad's old 400M Ford.

he said he thought he gapped the rings a bit too large & they are forged pistons. I wont be involved in the teardown (I barely know the guy) but I am gonna call him soon & see what he has to say & I will find out if early Nov is still the plan to get something done on it

If he could turn it to get it apart, it should still run.

Its a spun Main, and nothing else.

A seized piston, crank can still move abit, clearances n bearings.

A siezed cam bearing, crank can still move with chain slop.

A vert bolt stuck to block, crank should still be able to move backwards, at least with a breaker bar. Besides the described sounds weren't right.

A bad vert, no way. You would still be able to get some kind of crank movement.

A spun rod bearing, crank can still move there too, clearances.

A spun Main,Yep, Locked up Tight.

So , there is my Out on the limb, Big Fat limb opinion.

Good news though, is there wont be a lot of carnage.

Could be bearings but I would expect more shrapnel in the filter.

I have seen a front pump seized up solid. Thought it was the crank until they tried to separate the engine from the trans. Took a 6 foot bar to get it apart.

If the trans is good my bet is still pistons.

Kevin

A guy I knew locked up a freshly rebuilt 383 one time. He said it ran about 30 seconds, and just quit running. pulled the heads, and all 8 pistons were locked in the cylinders. The machine shop he had do the bore, and who sold him the pistons did too small of a bore, cast pistons to forged pistons. The shop refused to help him, said he should have caught that in the build process! I told him they should have caught it before it ever got to him.

The new machine shop had to destroy all the pistons when removing them. They did a larger overbore, and sold him a set of pistons that matched the bore. The crank had absolutely no movement.

My guess is its piston related. Gene

IMO, That's a He said guy I knew, Story. IMO, No way, are All 8 pistons going to seize up at the same time. Less then a minute to boot too , come on.

I just got off the phone with him, he pulled the rockers & no change, still locked solid. He's gonna pull the heads & I suggested when he pulls the pan to undo the rods that are angled right & with a wooden dowel see if the pistons can be driven up. he may have a little time here and there before his Nov vacation week rolls around and I will update with any tidbit that he uncovers. thanks all, the extensive and I do mean extensive interest has made my day!

I edited my first post later to say you may need to remove the tranny if it won't spin over backwards or forwards with a breaker bar on the crank bolt

Ive got to go with a locked up rod, maybe main.

Pistons/rings should loosen when cooled off, but the crank welds itself.

Who knows.... should be interesting, but unfortunate it happened.

I had a BB dart lock the crank up at 40 mph (stick car) and it stayed welded. Chased a miss that morning but it was a tossed lifter...then lockup.

Likely a coincidence of all coincidences to have converter/transmission cause seize up if neither had been modified simultaneous with engine build,,,unless some quirk occurred at installation of engine time.

Like we forgot to fill the trans up or the trans had an issue.

My ex had a new 82 Camaro with a 2.8 that had a noise in it that the dealer was ignoring. I forget what the noise was but I figured about 20 miles in second gear at 5 grand would sort it out. 10 miles out and 5 miles back it did. It labored for about 5 seconds and seized solid with a bang.

Had it towed to the dealer and they assumed as did I that the engine was pooched. Big surprise when they couldn't get the engine and converter to separate. Front pump was what the problem was.

Kevin

A buddy had a similar engine issue with an 85 IROC - after about 10 miles red-lined in first gear the cat converter over-heated and set the car on fire. It took the dealer and his insurance 4 months to figure out who was liable.

Mains, still still my odds on bet,,,many other good possibilities on deck so would not bet the ranch.

I'm betting a piston seized due to heat. I would suspect the slight changes in RPM you noticed was due to the piston starting to scuff the wall, then ultimately seizing. Pull the heads and looked for a scuffed bore.

Did he fill the both the block and radiator with coolant before break in? Rapid temperature raise points to a low coolant level.

When mine jammed the converter bolt, the motor would not budge in either direction with a breaker bar and a pipe. Didn't really hurt anything except the bolt and the threads in that hole in the converter. Still has same flex plate, converter, no block damage,only very slight scratch.
Doug

I didn't check the coolant but I know he did & now that you mentioned it the temp did come up fairly fast (was at 160) and that was at the end of the ~4 minutes. I'll probably get back at him in a week or 10 days & if I hear from him first I will for sure post. He knows from my last ph call that I am concerned about it & anxious to help (find the cause & the solution).

I just spoke with him & he reports that it will turn now but very hard. He said the weekend after next he might have it out & possibly opened up. EDIT two converter bolts were clocked to where they could be removed then he turned the crank to get at the other two. He plans to pull the eng from the top. After talking last night I am going to be in on the diagnosis & I will post what develops. I probably should have waited for something more definitive before posting but I am bored & kinda anxious to see some progress

I had a rod bearing seize in a 400. Locked the crank tight. Was just thinking how bad that sucked getting out compared to normal. So i know a spun rod will lock one up.

My vote for piston.