AMA passenger car specificatins - 1969 z28 "Locked in rod" piston pins

[69er]

I was looking through the AMA passenger car specifications that someone posted in General Discussion and the GM Archives link. Page 94 indicates that the piston pins in the 302 v8 (z28 engine) were "Locked in rod". According to this GM document the piston pins were pressed into the rod, i.e. not "Full Floating" as the legendary rumor has been touted since the start of time.

If you look at this document it clearly shows that this line and column has the option to be "Locked in Rod", "in piston", "floating etc". 

Over the years I have contacted several CRG members that according to them were the original owners of a 1969 z28 and were in the process of having the engine rebuilt. I asked them to post or send me a picture of the connecting rod, especially the small end. I never heard from them again.

Maybe I'm misreading this document, but if anyone can comment on this I would appreciate it.

Saying that it's a misprint is not enough.

69er

[z28z11]

I pulled my '69 apart in 1974 and rebuilt it - standard bore, floating pins. I had the rods rebuilt before I reinstalled them with bronze bushings by Howard Douglas Machine in Nashville; when I got them back the shop manager told me that they were the toughest rods they had ever seen, apparently because they drilled the pin oiling holes out in the small end, and broke 2 dozen drills drilling them ("pink" rods were shot peened). When I ground the forging flash off the sides, the pink paint was still visible on the sides of the beams. I used TruArc retaining rings to reassemble, not Spiralocs.

My '68 rods are pinks, but pressed pins. They are polished as well - wish they weren't (and I wish I hadn't polished my originals), but that was a step back in the time when you couldn't trust materials and engine construction as much as you can today. Elimination of stress risers is still important, but more modern manufacturing techniques minimizes the risk to a great degree.

Regards,
Steve

[69er]

z28z11,

Great comments.

The General Motors "AMA Passenger car specifications" has printed detailed engine information on the 69z28 302cid engine. Its clear it states that the piston pins were the "Locked in Rod" type. The Chevrolet chassis service manual (Page - specifications 7) also indicates that the 69 302  - Piston Pin: Fit in Rod had an interference fit of .0008" - .0016".

I have pointed out the General Motors documentation that reflects that the 1969 z29 302 had "Pressed Pin" connecting rods. I have read many comments from members indicating that the connecting rods in their 69 z28 were full floating. But, NEVER ONCE, has a member posted a picture of the connecting rod showing the small end with "Babbit" on it. A picture would even show the type of machining on the small end of the connecting rod.

I realize the GM parts books shows piston pin retainers to secure the piston pin in the piston boss, and thus float in the connecting rod. But, this could be no more that GM showing the parts availability so that full floating piston pins could be used for the racing circuit.

Just looking for proof of facts. A picture is worth a thousand words. Just want to see pictures of  "full floating"  connecting rods before they are modified.

As I mentioned previously, I had contacted CRG members whom claimed they were the original owners and were about to have their engines rebuilt. I requested that they post or send me pictures of the small end of the connecting rods during the rebuilding process. After that request, I never heard from them again.

In the past I contacted the person whom did the machining work for "Dean's 1969 Z28" the website address is, "http://69camaro.20m.com/index.html". The machine shop told me during the tear down, the connecting rods were pressed pin type and not full floating"

And as I said before, saying its a "Misprint" is not enough proof.

Can some one post pictures of these connecting rods. Please have a close up also of the small end.

69er

[jdv69z]

Original 69 302 pistons are full floating. I've got my originals. In fact, when I had the engine redone in 1993, the machine shop broke the boss out of the side of one of the pistons. How? Trying to "press out" the pins on full floating pistons with the retainers in place. The rebuild then used press pin pistons. The rebuilder specifically indicated to me that he had to "bush" the rods in order to make the piston pins "pressed".

[1968RSZ28]

Jerry MacNeish states in his '69 Camaro Z/28 Fact Book,

"Full floating, forged-aluminum pistons were used in the '69 302 engine. 1969 pistons were actually introduced in late-production '68 Z/28s."

Jerry has probably seen the insides of original '69 302 engines more than most people.

Paul

[69er]

jdv69z,

Great comments as well. First I would like to say any competent engine re-builder should know the
difference between a pressed pin connecting rod and a full floating rod. Not acceptable that the re-builder did not know how to remove the piston pin. Makes me wonder how the rest of the rebuild went. I'm not sure if GM made a "pressed piston pin" and a "floating piston pin" design. Just to clarify, full floating piston pins move freely in the piston pin boss and in the small end of the connecting rod.

Since, you have your originals, if their not installed in your engine could you please post a picture of the connecting rod small end.

Picture worth a thousand words.

Hi 1968RSZ28,

Thanks for commenting. Yes, I'm aware of the "69 Camaro z/28 fact book". But, I supplied quotes from the manufacturer, "General Motors",  "The holy bible of z28 302 cid facts", their is no higher source. Book writers, bloggers etc. can write what they want, but I would like picture proof.

Let Jerry then post pictures of the connecting rods including close ups of the small end, untouched.

Again, picture worth a thousand words.

69er

[jdv69z]

Never said the engine builder didn't know how to remove the pins. Probably was done by a youngster who happened to work there. Engine builder must do something right. He's still there building racing engines, 23 years later.

Not really sure what the point of this anyway. Sounds like you mind is made uo.

[z28z11]

If GM is the "ultimate authority" on the cars, would someone please look up the proper part number from a '69 dated parts book and confirm this ? I can't trust my '74 printing to be close enough to the build date of '69 Z's to be unimpeachable. Everything I have ever read, seen or suspected points to full floating rods as being Flint correct in 1969 built 302's, including the ones in my car.

Regards,
Steve

[69er]

jdv69z,

I have no axes to grind with anyone, and my mind is always open to what ever the truth is. But, with truth comes evidence and not here say.  I was just looking through the "AMA passenger car specifications" that another member had posted and I was surprised to find the information regarding the 302's piston pins.
I remember seeing other posts before regarding this topic, so I thought it was fair to bring it up.

It's also not fair to a owner of a 1969 z28, who is passionate about the vehicle that he owns, and during a possible engine rebuild finds that the piston pins are pressed into the connecting rod. And then he wonders, maybe my car is not an original z28, its supposed to have full floating piston pins. We'll that's where evidence and truth comes in.

Its like the early 69 z28 had 1968 Camaro spoilers installed due to the 69 spoilers where not yet available. I remember reading some where on the CRG that members where replacing the short spoilers for long spoilers so that their z28 would be more authentic to to others, maybe even judges. And of course we now know that early 1969 z28's did come with the shorter spoiler.

So, let the truth out and be free and false facts.

z28z11,

Could you post any pictures you have of them, with the original machining. I so want to believe that the 69 z28 came with full floating piston pins. But, I have to see any evidence, here or trade shows.

69er

[KurtS]

The AMA doc has several errors. It's a form the manufacturers still submit.
GM issued listings of the Z28 features and the floating rods are listed there, IIRC.

[Stingr69]

3946841 is the original GM part number.  You can Google it, search it on ebay, or find it in Chevrolet parts manuals from back in the day for more detail.

[jdv69z]

OK, here's a pic of the underside of my original 302 pistons. If you zoom in, you can see hopefully the pin retainer grooves. Required to hold the pin in on full floating pistons. Pressed pistons have no such grooves, as the rod holds the pin in place.

[69er]

jdv69z,

Thanks for you contribution. But, most/many pistons are manufactured with the grooves
in the piston boss to accommodate retainers. What really differentiates between full floating
piston pins and pressed piston pins is the connecting rod. If you have your connecting rods available please post pictures of the complete connecting rod and then a couple of close ups of the small end of the connecting rod.

69er

[69Z28-RS]

When I disassembled my original 302 in 1976 for rebuilding, all parts were factory original and included 'fully floated pins'.  I bored the engine and installed Forgedtru pistons (0.030" overbore) also with fully floated pins (using the original rods).  My understanding has always been that the '69 302 included factory fully floated pins, so a better question for you might be....  Someone who has factory parts which are NOT fully floated should post data/photos of those... 

[jdv69z]

jdv69z,

Thanks for you contribution. But, most/many pistons are manufactured with the grooves
in the piston boss to accommodate retainers.

69er

Huh? OK, it's your turn. Show me evidence of a factory pressed pin piston with machined retainers grooves that were machined and then not used. So Chevrolet would only punch the holes necessary for a specific Camaro firewall, but they machined unnecessary grooves in pistons?  Stick a fork in me, I'm done.