Author Topic: 302 Replacement Pistons  (Read 1211 times)

X33RS

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Re: 302 Replacement Pistons
« Reply #15 on: July 27, 2016, 03:43:58 AM »
Here ya go, a pic of my NOS piston and the new piston side by side.
You can see the dome configuration is slightly different but it was the quench area that caught my eye.  The new piston is designed for the more modern heart shaped combustion chambers.  Not of any real consequence for the build but interesting.


Z28Project

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Re: 302 Replacement Pistons
« Reply #16 on: July 28, 2016, 02:18:04 PM »
Thanks, that was a nice comparison picture (for a little while anyway). :)

I ordered those same pistons.

John

Bryan302

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Re: 302 Replacement Pistons
« Reply #17 on: July 28, 2016, 08:09:41 PM »
asm69, IMHO, the floating rods and the piston ARE one of the distinct sounds of the 302.  The solid lifter is the other half of the distinct 302 sound.  Changing parts could result in the loss of this legendary sound.  The 302 and other engines like the 435 h.p Corvette, you don't even have to see them at a show to know what it is, then when it come in sight, yup, I thought so.  The pressed pin Would make a lot of difference.

Bryan
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asm69

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Re: 302 Replacement Pistons
« Reply #18 on: July 28, 2016, 08:53:38 PM »
Byron302, I didn't  realize that the full floating pins would make a difference in the sound. I do realize that solid lifters do make a cool sound.

69Z28

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Re: 302 Replacement Pistons
« Reply #19 on: July 29, 2016, 03:34:49 AM »
I went with pressed pins myself on my current 302. Many years ago, mid 70's, I did a 12 to 1 piston 302 with the 2nd design road race cam with my first 69 Z. When that engine started up it was the noisiest I've ever heard. Turns out I had 3 pistons slapping the heads. Didn't even have a clue what it was until the engine shop that did the machine work checked it out. Not even sure what they even did to fix it now that I think about it. I was young dumb and full of you know what then, and was just learning about engines at the point of my life. But boy did that engine scream.
GaryC

'UNRESTORED' 1969 Cortez Silver Z28 X33 D80

Kelley W King

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Re: 302 Replacement Pistons
« Reply #20 on: July 29, 2016, 12:03:58 PM »
Put headers and Flowmasters on it and you will know the difference.
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Stingr69

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Re: 302 Replacement Pistons
« Reply #21 on: July 29, 2016, 01:05:52 PM »
The floating pins are there for ease of assembly and disassembly only.  No need for a fixture or a torch with floating pins and it saves the rod from being stressed repeatedly.  The pins do not sound different or change the performance in any measurable way.  If you plan on tearing down your engine regularly to replace pistons after every race event, or you just want to do the assembly yourself in a hobby garage then floating pins make sense.  Otherwise pressed pins are fine.

jdv69z

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Re: 302 Replacement Pistons
« Reply #22 on: July 29, 2016, 01:57:50 PM »
I'd be curious to know what Chevrolet's reasons for full floating pins really were. There must be some justification other than ease of disassembly/assembly. They obviously are more expensive to manufacture since there are extra parts (the retainers) and extra machine work required for the grooves to hold the retainers. And I would think they would be more labor intensive to assemble than pressed pins on as assembly line. I've been led to believe it had something to do with the high performance engines they were used in, but I don't know reasoning other than it possibly had to do with the pin being able to rotate in the rod.
Jimmy V.

X33RS

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Re: 302 Replacement Pistons
« Reply #23 on: July 29, 2016, 10:17:42 PM »
It's a debate that goes on.  Failures many years ago scare people, but I tend to believe assembly methods or subpar parts could be some of that blame.  Nowadays not much worry, and the big 3 are still using floating pistons in some engines today.
   There is balance weight to consider, and the fact that the pin isn't stuck in one position while the engine runs.  Some arguments made that floating pins are beneficial for short stroke engines, some say frictional gains, and many more reasons.  Pros and Cons with both.   The machine shop I used does dozens of high end racing engines every year that make well over 1,000 hp, and he makes your head spin with knowledge.  When we discussed the issue, by the time we were done I was comfortable with the choice.  Plus, that's the way 69's were and I liked the idea of keeping it that way.
   Excellent machine work goes a long way here too.  I bought new Eagle rods and he made sure he checked and "tweaked" each rod and piston pin to make sure clearance was spot on.  Even the big ends of the rods were also "tweaked" for proper bearing crush.  Pistons call for .002" to .0025 side wall clearance so they run very tight in the bore as well. That's snug for a forged piston.  Not only does that make them very quiet, but you also gain better ring control which means better compression and oil control.  Sloppy pistons cause all kinds of oil consumption and ring flutter issues.
   Lots and lots of details went into this build looking for HP as well as longevity while keeping things stock, or stock appearing, including coatings where applicable and other tricks that are trade secrets with these engine builders I'm not even aware of. 

red69

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Re: 302 Replacement Pistons
« Reply #24 on: July 30, 2016, 02:34:43 PM »
I am confused. I called JE and was sent to tech where I inquired about piston part #123567. Specifically ring width, the gentleman I spoke with claimed the top rings were 1/16", weren't the original pistons 5/64"? Is he misinformed? Or am I mistaken on original width?

Z28Project

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Re: 302 Replacement Pistons
« Reply #25 on: July 30, 2016, 03:12:31 PM »
I think the tech guy messed up.  JE literature says the 123567 piston uses the original ring sizes as mandated by NHRA, which would be 5/64.

The newer style JE/SRP pistons use the 1/16 rings.

red69

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Re: 302 Replacement Pistons
« Reply #26 on: July 31, 2016, 02:34:40 PM »
That's what I thought I'll call back
Thanks

asm69

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Re: 302 Replacement Pistons
« Reply #27 on: July 31, 2016, 05:58:31 PM »
So, is it agreed that full floating piston pins do not generate a sound that makes the 302 sound different than a 302 with pressed piston pins.

70L34

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Re: 302 Replacement Pistons
« Reply #28 on: August 07, 2016, 02:25:06 AM »
If a floating pin setup makes noise, something is very wrong with the machine work.

firstgenaddict

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Re: 302 Replacement Pistons
« Reply #29 on: August 10, 2016, 04:09:10 PM »
Full floating is to minimize the chance of destroying the engine if one or the other were to freeze up... either the pin in the piston or the pin in the rod.

Pin Freezing with push in pins will rip the bottom of the piston apart then the rod causes all kinds of block damage. Even if the locks screw up with full floating typically you get scoring in the cylinder, or if one or the other freezes there is no damage at all to the block - only whatever issue is within the rod piston assembly.
James
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