[Dauntless1971]

After what feels like wasted money on the 326 I bought for my 65 Tempest ragtop. I found a early 75 400 engine. It was still running, with a few minor issues like bad gas evaporating in carb, vacuum leak. So I have been tearing it down to take into a shop. From what I was reading I just about stamped the connecting rods to match upper and lower. With numbers 21436587 starting in the front and working back. Seems odd Pontiac would be like that. But then I read that could cause stress fractures. It almost appears the cylinder bores are good enough to just hone and new rings. But as I called out to different shops it seems they really don't have much interest in doing that. All new everything is what the machine shops seem to be geared up for. Well I suppose I will find a paint pen to mark the connecting rods for now.

[25stevem]

Pontiac and some other GM motors have the passenger side cylinder bank ahead of the driver side.
This is why number 2 cylinder is ahead of number 1, and as such the last rod on the crank closest to the front of the motor is number 2 not 1 as on a SBC for example.

Don’t forget that a V8 is really just 2 V4s that happen to share the same block!

[tempest1964]

If you’re worried about stress fractures, could you use a vibra-etcher to mark your rods?

[25stevem]

Good way to go!

[Formulabruce]

You could ball hone and clean, clean and re ring as long as you keep pistons in same holes. And use NEW wrist pins too. No ridge up top of cylinders?
For a driver, its totally possible to do this on the cheap if its all in good shape

[Dauntless1971]

Down to just the camshaft and crankshaft to remove. Five of the top piston rings were broke in half but still where they belong.
I am hoping to get the parts down to a machine shop that will check the cylinders and crankshaft in the next few days.
If the cylinder bore is within tolerances was hoping to reuse the pistons though now not so sure.

[Sirrotica]

For many years Pontiac stamped the rods with codes on the flat area on the outside next to the rod bolts, not every set was stamped, but many were. I've never seen a fracture where the codes were stamped. I've seen them prick punched from rebuilders that didn't have number punches also, never seen any fracture from them either.

99% of the blown Pontiacs I've disassembled, spun a rod bearing then the rod broke after the rod bearing welded to the crank throw, or it hammered so long the rod bolts broke.

To me it's a non issue since it doesn't create a ragged edge, and that is usually where stress risers start, YMMV.

[Schurkey]

I number-punched for years. Heard about potential problems, have used the engraver since then.

A paint pen is NOT acceptable, the paint will be gone once the rods have been through the solvent tank or jet-wash cabinet.

If you have broken rings, the ring grooves are suspect. Probably time for pistons. Pay attention to compression height, most "rebuilder" and low-end performance pistons are too damn short by .010 or .020. Which then means you're paying extra to deck the block excessively. Which then means you're paying extra to get the intake manifold lined-up properly, and maybe paying extra for different-length pushrods.

IF (big IF) the rings broke because you pounded the pistons past a ridge at the top of the cylinder...you can pretty-much count on the pistons being junk, but that's ok--the cylinders needed to be bored and that means you'd have needed new pistons anyway.

[25stevem]

X2 with the above!
Careful check the top and bottom compression ring groove clearance.

Take a good ring and snap it in half , then use that a a set of feeler gauges to check the ring groove clearance around the perimeter of all 16 grooves.

Since you are using a used ring to make this check if you find more then .004” in clearance then that piston is done.

Word to the wise for used motors that are being considered for rebuild that you yourself have not
rebuilt is to start off by making a list of everything that could be needed and then scratch off what you find you don’t need!
Include the ball park cost of each item in your rebuild list also.

If you find you need to go for new pistons do not even consider the cast ones that are stated for usage with both early and late heads

Since you have found some broken rings the heads will need a valve job and even if by some stroke of luck they do not you should plan on replacing all the valves.

Depending on the valves you use this may also involve cutting the tops of the valve guides for positive type valve seals of the non Teflon type.

PS.
I can’t see why you would need new wrist pins if the piston skirts look ok.
Anyway the pins are one of the easiest things to check anyway.

[Half-Inch Stud]

Broken (428-455) Pontiac rings always sound like pinging damage. Never seen broken 326-350 rings.

[mgarblik]

Originally Posted by Formulabruce

You could ball hone and clean, clean and re ring as long as you keep pistons in same holes. And use NEW wrist pins too. No ridge up top of cylinders?
For a driver, its totally possible to do this on the cheap if its all in good shape

I would respectfully disagree with replacing the wrist pins if doing a super budget, ball hone overhaul. Removing wrist pins from factory cast pistons and then replacing them is a losing proposition from my experience. We have the high dollar Sunnen pin press at my shop. But almost always ruin 2-3 pistons pressing the pins out. Our rule is if the pins are pressed out, your getting new pistons. Pontiac rods take 1800-2500 lbs press typically to remove. Very hard to avoid bending the pin box. Full floating pistons a completely different situation of course. Our experience on a typical V-8 is: Ball Hone, re-ring with OE pistons vs proper overbore and plateau hone with torque plates = 4-6 HP loss per cylinder. So 32-48 HP loss doing a backyard style overhaul. Budget will determine which way you need to go.

[track73]

I don't understand why a torque plate would be needed on a "ball hone rebuild". I assume the cylinders would be worn in to the correct shape after many miles with the mains and heads torqued. I understand why it's needed if the block is being rebored. Ford did a study on that back in the 70's.

[Dauntless1971]

Yes the budget determines everything. I had planned on using the lowly 326 while saving up, plus the better machine shops at least by reviews left online have a 4-6 month wait here in Oregon. But I got took on the 326 and can't see pouring more money into the 326. Now as I get more information the stock 75 400 pistons may not be worth reusing even if within specs. Marking the rods if the engine was to be done on a budget. Now I may have to start a new thread on what would be a good combination of parts for my intended use of the 400 engine in my 65 Tempest.

[25stevem]

This is easy, no need for a new parts thread other then maybe for a cam pick and what to do with the heads you have.

Unless you have a shop that can both bore your block and cut your crank to get it right, then just order up a new rotating assembly without the rods which will cut your cost by maybe 400 bucks if you need to get the stock rods resized.

[67Fbird]

sorry mgarblk...if you are tearing up pistons pressing out the pin you might need to rethink your set-up. Pins only have about .0008-.0013 pinch in the rod IIRC. Yes PONTIAC even bank is FORWARD causing the 2-1-4 sequence. Stamping numbers is fine BUT stay away from te split line and stamp them while they are ON THE CRANKSHAFT! When you order new pistons pay very close attention the the compression hieght listed as each manufacturer has their own idea of what it should be (1.75) some go down to 1.720 others 1.730...this can lead to your new pistons .020 down in the hole...or .040" in the hole in a block thats a few thou tall. Needless to say .030 in the hole is LESS THAN IDEAL...now your adding $200 to deck the block.