[Stan Weiss]

Originally Posted by Cliff R

I made the OP aware of the MAIN ISSUES with this engine about 400-500 posts ago. It went on deaf ears. Instead we are searching the Internet and various other sources to the brink of extinction to find another potential cause when the OBVIOUS problems were right in your face a couple of times and easy repairs made. You can Google all you want, and go all over these Forums and get BUTT LOADS of input on your issues, you can even wear out a few resident "experts" here to a point where they will tell you piston offset the wrong direction and rods backwards on the cranks throws is OK, but as with everything else on this planet it is NOT possible to get past the basic laws of physics with these things.

Somewhere in the history of this engine it got FUBAR'd. The problems from that deal are finally manifesting themselves to where the correct repairs are REQUIRED. Any other course of action is just wasted time/funds and additional "drama" on the thread at this point.

Getting mad and breaking up cinder blocks with your bare hands woln't help, neither will doing hand stands on your fingertips. If I were Mike I'd smoke a hog, get a keg of beer and invite over ALL your friends and even folks you don't know. If I lived closer I'd be the first one in line to help out and get some free smoked pork belly.

Have the car up on cinder blocks, hood off, and before you let everyone get drunker than monkeys have them help you remove the engine again and pull it down to parade rest. Once all the pistons are out locate the chamfered side of the rods and "notch" on the pistons. Put them all back in the right bores with both the rods and pistons facing the right direction. No honing needed, no new rings, etc. You "knurled" the valve guides for crying out loud so throwing more money at rings and such isn't going to be worth the additional expense.

If the rings don't seal up well just get some Comet cleaner and drizzle some into the carb/intake with it running on fast idle at 1500rpm's or so. That'll either get them to "bite" into the bores or give it a miserable death. Either way you'll be a LOT further ahead than you are at this point......IMHO.......Cliff Out

Cliff,
Since I like many here want to learn. Just what laws of physics does installing the piston with the offset reversed break?

Stan

[Cliff R]

That question has been answered at least three times now if I counted right.

Drop back a few pages and read my response and what I did to correct the issues after installing a set backwards (and the connecting rods were installed correctly BTW) and dealing with the drama that caused for 10,000 miles.

If that's not good enough read the copy/pasted response from GTOFreek about why we do NOT install pistons that have offset pins in the wrong direction in these engines.....Cliff Out.....

[JSchmitz]

Originally Posted by Stan Weiss

Cliff,
Since I like many here want to learn. Just what laws of physics does installing the piston with the offset reversed break?

Stan

I would say that the piston installation didn't break any laws of physics. They are merely complying with the laws. The laws dictate that the pressures and angles act on the pistons in a certain manner. The engineers, that designed the pistons, understood this better than anyone in this discussion. They designed an offset to minimize unwanted movements of the pistons and maximize efficiency. Choosing to go against this is most likely causing the noises in this engine. But he wants to blame it on the moon, stars, and everything else. I say, GOOD LUCK!

[Stan Weiss]

Originally Posted by JSchmitz

I would say that the piston installation didn't break any laws of physics. They are merely complying with the laws. The laws dictate that the pressures and angles act on the pistons in a certain manner. The engineers, that designed the pistons, understood this better than anyone in this discussion. They designed an offset to minimize unwanted movements of the pistons and maximize efficiency. Choosing to go against this is most likely causing the noises in this engine. But he wants to blame it on the moon, stars, and everything else. I say, GOOD LUCK!

How many times does it need to be said the engineers only put that offset there so that people on a cold stop wouldn't hear piston slap. You do understand that with that offset the piston and crank journal are not at TDC at the same time?

Stan

[JSchmitz]

Originally Posted by Stan Weiss

How many times does it need to be said the engineers only put that offset there so that people on a cold stop wouldn't hear piston slap. You do understand that with that offset the piston and crank journal are not at TDC at the same time?

Stan

Yes I think I understand it pretty well. Piston slap is bad. It causing ring wear, sounds bad, etc. The offset is there help eliminate this. Are you saying that his knock isn't from improper assembly?

I know that my dad owned a 1969 Chevy pickup. He had the engine rebuilt. The guy put the pistons in backward. Guess what, it had a strange knock.

[Stan Weiss]

Originally Posted by JSchmitz

Yes I think I understand it pretty well. Piston slap is bad. It causing ring wear, sounds bad, etc. The offset is there help eliminate this. Are you saying that his knock isn't from improper assembly?

I know that my dad owned a 1969 Chevy pickup. He had the engine rebuilt. The guy put the pistons in backward. Guess what, it had a strange knock.

So does this mean you will never run an after market piston that doesn't have any offset?

Stan

[Shiny]

As a spectator (or maybe in this case an observer of a spectacle), gtofreek's explanation of offset was the most helpful for me:

https://forums.maxperformanceinc.com...6&postcount=24

[JSchmitz]

Originally Posted by Stan Weiss

So does this mean you will never run an after market piston that doesn't have any offset?

Stan

No, I'll order custom pistons with the offset. Then I'll install the backwards to break the laws of physics.

[Stan Weiss]

Maybe someone who has worked on a SD 455 stock engine can confirm the information that I have that Pontiac used pistons with no offset.

Stan

[Cliff R]

Having 7 out of 8 backwards and who knows how many rods facing the WRONG direction is plain and simple FUBAR. We can continue these discussions and feed this thread for days, weeks, months and even years and NOTHING gets better until the fundamental issues that have been discovered here are corrected.

I certainly hope that the OP is getting all this down in my over 500 pages of notes, and plans on addressing the issues at some point.

I've purchased and installed sets of pistons with zero offset. Most were the two valve releif variety so you had to pay close attention to how you hung them on the rods as the larger reliefs needed to end up under intake valves, the smaller ones under exhaust valves. At the sme time the flats of the rods end up running together and chamfered portions out agains the filet in the crankshaft.

Not overly difficult but does require exact precision to get all eight in where they need to be.

I suspect what happens with these Pontiac engines is that having #2 as the lead cylinder instead of #1 throws some folks off some and why we see this sort of thing happening more than it should. I seen some very well experience engine machinists and pretty smart folks mess that deal up and why I loved to see the aftermarket start offering affordable full floating forged rods. At least you didn't have to get the press out and collapse a few pistons when they got hung on the rods incorrectly........FWIW

[Cliff R]

"Maybe someone who has worked on a SD 455 stock engine can confirm the information that I have that Pontiac used pistons with no offset."

I've done a hand full of them and with my bad cases of CRS can't remember. I do remember that the original 455 SD pistons were forged, hung on pretty heavy forged rods, and small valve reliefs in the shape of a "trough" maybe, not four like most factory and aftermarket replacement type forgings used.......

[johnta1]

I'd agree with Cliff that the pistons had a trough, so thinking they were not off-set. Also seem to remember Pontiac had complaints about piston slap when cold on the SD Birds?

Also having CRS, I thought they did not have any off-set.

[Stan Weiss]

Originally Posted by JSchmitz

I would say that the piston installation didn't break any laws of physics. They are merely complying with the laws. The laws dictate that the pressures and angles act on the pistons in a certain manner. The engineers, that designed the pistons, understood this better than anyone in this discussion. They designed an offset to minimize unwanted movements of the pistons and maximize efficiency. Choosing to go against this is most likely causing the noises in this engine. But he wants to blame it on the moon, stars, and everything else. I say, GOOD LUCK!

If that is the case then why does ever Pontiac engine from a 326 ci to a 455 ci having different bore size and strokes all had the same 0.063" offset? (Based on the information I have)

Stan

[JSchmitz]

Originally Posted by Stan Weiss

If that is the case then why does ever Pontiac engine from a 326 ci to a 455 ci having different bore size and strokes all had the same 0.063" offset? (Based on the information I have)

Stan

That's a good question. Maybe they chose a standard offset that minimized piston rocking and thrust loads on the piston. Maybe it's the maximum that they could justify. Maybe it just works well for all. Maybe the guy was mental. LOL

[242177P]

Originally Posted by Stan Weiss

If that is the case then why does ever Pontiac engine from a 326 ci to a 455 ci having different bore size and strokes all had the same 0.063" offset? (Based on the information I have)

96,946 GTOs built in '66. Eight pistons each... 775,568.
Pistons were mass produced, fixed offset makes sense.
455SD was already receiving extra attention because of
the rods, 326 just needed a slug to fill a hole.

[MatthewKlein]

Originally Posted by Stan Weiss

If that is the case then why does ever Pontiac engine from a 326 ci to a 455 ci having different bore size and strokes all had the same 0.063" offset? (Based on the information I have)

Stan

Things have progressed to the point I prefer this thread to be more comedy oriented and less well thought information

In the beginning I had genuine concern but it has evaporated

[JSchmitz]

Some good reading about piston pin offset and overall piston design:

https://www.jepistons.com/je-auto-bl...haracteristics.

https://courses.washington.edu/engr1...ylinder%20bore.

https://www.quora.com/What-is-a-pist...20power%20loss.

https://www.speed-talk.com/forum/viewtopic.php?t=20391

[steve25]

Something related to piston noise is being overlooked here I think.

Prior to the the first 400 motor in 67 Pontiac pistons where fully round and in my mind other the the issue of having the rods facing the wrong way on the crank if you had a piston in a motor the wrong way I don’t think you would hear much added noise when cold.

Now let’s look at the 350s, 400s, 428s and the 455s with there inventive usage of a Cam ground piston.

Now if you reversed these pistons, yes to me you would be in for a good amount of cold slap noise, and along with the noise comes ware.

Just some food for thought here.

[Murf]

Turn it up to 11 and rip the knob off! ��

Seriously tho, Stan keeps mentioning SD’s & custom piston having zero pin offset. Wouldn’t a turned around stock piston be different with the same amount of offset, just in the opposite direction?

Thanks
Murf

[Jay S]

Big stereo and loud pipes solves those problems. I think this might need both.