[Half-Inch Stud]

Thus far the Press-Fit process is most suspect huh.

Door #1: Induction heated vs

Door#2: Draw-Bar or HYD arbor...leads to windowing the block.

Curious if antifreeze got into the oil.

[66geeto]

dipstick looks like clean oil can't see any antifreeze to speak of.

[slowbird]

You would know it if there was antifeeze in there.

[Half-Inch Stud]

wow, this really focussed quick on the rod/slug R&R process.

suggest you go the machineshop and ask about pressing pistons OFF then ONTO rods.
When Machinist pops the heads, YOU may need to verify that all slug-arros point toward the front.
When Machinist guts the bottom, YOU may need to verify the Slug-Arrow with the Rod dot/boss to assure they were clocked correctly.

[BVR421]

Whole lot of wildass guessing so far

[455Grandville]

Stock rods ARE NOT the cause of this - how could some people revving a stock rod motor to 6000 not break, yet a fresh engine breaks at 2000 rpms ?
If that were the case, can you explain stock rod engines going 200,000 + miles (my old 400 did plus it pulled a boat and a camper) then a new engine instantly blows up -
Millions of Pontiacs went many miles and years without blowing up - Im not saying they are good rods, but letting go that early that easily points to something else - Ive machined for years and have cleaned up alot of errors.
If it came apart that quick, there was either a machining error or a assembly error. Did the machinist even check the rods for cracks ? I wonder if he mounted the pistons (pins specifically) to the rods the correct way.

[Half-Inch Stud]

Brad says """...I wonder if he mounted the pistons (pins specifically) to the rods the correct way"""

we're all on the same page now. HIS

[hurryinhoosier62]

Brad,
Good point. I wonder if the rods were magnafluxed. A cracked rod or a piston
and pin installed incorrectly(backwards) are the culprits that come to my mind.

[455Grandville]

Originally Posted by hurryinhoosier62

Brad,
Good point. I wonder if the rods were magnafluxed. A cracked rod or a piston
and pin installed incorrectly(backwards) are the culprits that come to my mind.

As many stories as Ive heard of Pontiac rods going bad, I just cant see this causing the problem. Makes me wonder if the machinist checked to see if the rods were straight as well. Im pointing towards some sloppy assembly/machining on this. Ive even heard card-carryin' dumbasses say "well you should have built a Chevy" as if thats the problem,nevermind the fact millions of Buicks, Olds, Pontiacs, etc.,ran decades without Chevy engines.

[Pitch 400]

I had a pressed pin walk out of a bent rod and hit the cylinder wall. It was a 70 RA IV block too. Luckily I found someone that wanted the block and he had it sleeved. Lots of things could have happened here. I also have 2-389 standard cranks if you might be looking for one. I'm at Omaha, NE

[SneakyPete]

Hi Josh, i lived in lincoln for years, and know alot of machinists & mechanics there. If you want to PM the name of the shop, and it happens to be someone i know, i will try and help you get this resolved.

Pete

[66geeto]

just called machinist, forgot how nice of a guy he is since it has been 2 years since i got the shortblock from him. He was super nice about it and very understanding. "if it left here the clearences were right and i checked the torque on the bottom end 2-3 times." "tear it down and bring me the short block and i can take care of it for you, if the rod bolt broke or the rod broke i can't cover it but if it was somthing i did you won't have to worry about it."
Hopefully everything turns out ok. I get to tear it down now so i will let you guys know what the hell happened. or i won't and let this thread go on forever in suspense. Time to bag it and tag it. hopefully it all goes back together. later guys.

josh.

[Matt Danger]

He sounds like a good professional guy to be dealing with so now I'm even more interested to see what went wrong here.

[Will]

Agree with chiphead that stock rods that have NOT been rebuilt, checked, and had new bolts installed are a ticking time bomb waiting to go off.

Why someone would spend enough money to rebuild an engine and not at least have the rods magnafluxed, new ARP bolts installed, and resized is beyond me. Stock rods that are not badly out of shape when checked should be good to go for hard use after being rebuilt as above. If the journals are badly out of round or there is other evidence of hard use, I'd consider them suspect even if they pass mag inspection.

When you compare the price of a set of aftermarket forged rods (the cheaper ones available from some of the Pontiac vendors) vs. properly rebuilding stock rods, the price difference comes out to like $100. A drop in the bucket compared to the total price of the engine and the peace of mind they bring.

66geeto, you say the engine builder is much more familiar with Chevies than Pontiacs.... One VERY common mistake that chevy builders make is to install the rods backwards. On a Chevy engine the bearing tangs go on the outside, or oil pan rail side of the rod. On a Pontiac they should be installed to the inside of the engine. The rods have chamfers on one side of them and the bearing is slightly offset to one side to clear the radius at the edge of the crank journal. If he put the rods in like on a Chevy it's very likely the rod or a bearing seized on the crank.

I hope you can be there when the engine is torn down. Look carefully at the rods and note the position of the bearing tangs during disassembly.

[chiphead]

Wait. This shortblock sat up for 2 years?

[Half-Inch Stud]

"""""""66geeto, you say the engine builder is much more familiar with Chevies than Pontiacs.... One VERY common mistake that chevy builders make is to install the rods backwards. On a Chevy engine the bearing tangs go on the outside, or oil pan rail side of the rod. On a Pontiac they should be installed to the inside of the engine. The rods have chamfers on one side of them and the bearing is slightly offset to one side to clear the radius at the edge of the crank journal. If he put the rods in like on a Chevy it's very likely the rod or a bearing seized on the crank.""""""
----------------------------------------------------------------------
Add the effect of the Pontiac-specific Piston Pin Offset, and you know where my head is at on this diagnosis.
----------------------------------------------------------------------
Be sure to verify free movement of the slug pin on each remaining rod/slug assy.

[Mr. P-Body]

To add to what's being said about rod orientation, "TANGS" IN!! That is, the bearing tangs must face the cam, not the pan. If correct, they will "look" like a 302 Ford. As others have said, this is a VERY common mistake by Chevy builders. When backwards, the oil can't escape the bearing, overheating both the oil and the bearing. If there's blackened material around the rod and/or journal, that's the issue!

Jim

[joegio]

Oil pressure and temp were ??

Document everything as you open the motor with pics and torque readings.
It could could a non-obvious detail mentioned above. Maybe the rod bolts were not seated correctly or a bore or bearing clearance was out of spec or the block crank not cleaned .... The rod just "letting go" would imply that if the previous owner ran the motor 5 more minutes he would have had the same problem.

[66geeto]

not quite 2 chip, but it took a damn long time. It was in an engine bag for like 3 weeks with the heads off and then i put the heads and intake on. In a repair shop i worked in. Kept everything super clean, by the time i hauled it out of the shop my boss hated me cuz i *****ed everytime he came within 15 ft of it to do work.
Will, that sounds a bit more like an acusation than helpful information. I would have to find a reciept to see if he reworked the rods but i assume he did I was like 16 when i took the block to him and still very wet behind the ears. The block was with him for quite awhile because min. wage wasn't too high back then. I told him to do it right b/c I wasn't going for some damn stock rebuild for a 75 bonneville.
1/2 , I don't remember saying he was more familiar with chevy's but i am sure he is as there were only X50 more of those engines around, and he runs a business so obviously he works on alot of them.
ANYWAYS I'LL POST PICS SOON OF THE TEAR DOWN.

[66geeto]

he would have had to beat the bearings into place and flatten the tangs out as there would be no recessed area for the tang when the bearing would be installed. or he would notice and flip the bearing around. I'm not to conserned with the whole bearing on the correct side of the rod issue. He's been a machinist since God was a boy.