Author Topic: 1969 Z/28 DZ 302 overbore to .040? Piston Source?  (Read 7335 times)

doomer

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1969 Z/28 DZ 302 overbore to .040? Piston Source?
« on: July 19, 2013, 03:20:46 PM »
My DZ 302 is out and apart for the first time since I got it. The block is already at .030 and needs to go a little further. I'd like very much to go no further than .040 is possible, but my machinist's supplier seems to only have .060 for the 302. This is my first rebuild, and am depending heavily on my mechanics knowledge. He is a great guy, running an old school shop, and wants to help me keep her as true as possible. He asked that I check with you folks on a supplier to see if there are .040 pistons available? I'm looking for recommended manufacturers and item #'s if possible.

I found some via Ricks/Eckler's. http://www.rickscamaros.com/camaro-piston-set-302ci-11-1-0-040-over-high-performance-1967-1969.html Just not sure if these are recommended.

Thanks!

cook_dw

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Re: 1969 Z/28 DZ 302 overbore to .040? Piston Source?
« Reply #1 on: July 19, 2013, 05:02:02 PM »
Those will work just not forged which isnt a huge deal if this is strictly a restoration.  Also look at Icon Performance Pistons (summitracing.com).  Also if you call JE, SRP or Wiseco pistons they can custom build you a set if needed.  Hope that helps.
Darrell Cook

1967 LeMans Blue SS/RS L35 clone
1968 Rallye Green SS L78 - unrestored original
1968 Matador Red Z28

69Z28-RS

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Re: 1969 Z/28 DZ 302 overbore to .040? Piston Source?
« Reply #2 on: July 20, 2013, 01:56:49 AM »
one small nit:   you cannot 'restore' a 302 and not use forged pistons, fully floated pins, etc..  :)      you'd be doing only a semblance of a 302 if you used cast pistons.  JMO....
Gary W / 09C 69Z28-RS, 72 B 720 cowl console rosewood tint
69 Corvette convertible, silver/black 350 hp,
60 Corvette white/red, 72 Corvette coupe, '70 Mach I 
90 ZR1 red/red #246, 90 ZR1 white/gray #2466
72 El Camino, '55-'56-'57 Nomads, '55-'57 B/A Sedan

doomer

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Re: 1969 Z/28 DZ 302 overbore to .040? Piston Source?
« Reply #3 on: July 20, 2013, 07:01:13 PM »
I agree, wholeheartedly. I didn't catch that until after I posted the link.

These seem pricey, but does anyone have experience with them?

http://www.campbellenterprises.com/chevy-302-pistons-302-piston-sets/302-chevy-pistons-wiseco-forged.php


dutch

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68camaroz28

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Re: 1969 Z/28 DZ 302 overbore to .040? Piston Source?
« Reply #5 on: July 21, 2013, 07:21:01 PM »
Try:

http://www.jepistons.com/Catalogs/SRP/Chevy_SB/302-327_dome.aspx

Randy

Hi Randy! Must be more .04 over pistons than I was aware of as it always seemed the only two available were .03 & .06 over!
Chick
68 Z/28 NOR 01B Orig motor/trans/rear
69 Z/28 NOR 07A Orig Block & GM Cross-ram/carbs
69 L34 Rest. Nova Father/Son Car
69 L78 Surv Nova Purch 4/69 31K miles
67 L89 Corv Tribute
68 Corv 427/400 Orig motor
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R 68Z build- http://www.camaros.net/forums/showthread.php?t=182584

jims69

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Re: 1969 Z/28 DZ 302 overbore to .040? Piston Source?
« Reply #6 on: July 21, 2013, 09:39:15 PM »
Forged pistons..............Yes!

dutch

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Re: 1969 Z/28 DZ 302 overbore to .040? Piston Source?
« Reply #7 on: July 21, 2013, 09:41:28 PM »
Chick - Yea, there are a lot more lately than there ever were before - for sure..
I would like to try and get some at some point myself as my .030"s are pretty loose in the MO although when I last had it in the car they seemed still to work pretty well.
A 1/16 / 1/16/ 1/8 ring pack can't take too much rocking before they start leaking some I would imagine though..
I would also imagine anyone who doesn't want the full load that some of these full pop up pistons provide could also probably request the tops be cut some to lower the compression down to a somewhat more manageable factor like a shade over 10:1 if they asked J&E prior to ordering..

doomer

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Re: 1969 Z/28 DZ 302 overbore to .040? Piston Source?
« Reply #8 on: July 22, 2013, 09:09:14 PM »
These are what I've narrowed it down to. Anyone have a setup with these?

http://www.campbellenterprises.com/chevy-302-pistons-302-piston-sets/302-chevy-pistons-wiseco-forged.php


or

http://www.jepistons.com/Products/261357.aspx

Also, how do I determine from these web sites is these are narrow or wide bands?

69Z28-RS

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Re: 1969 Z/28 DZ 302 overbore to .040? Piston Source?
« Reply #9 on: July 22, 2013, 09:42:51 PM »
The Campbell Enterprises add for their forged pistons state:   "...... Wiseco Pro Tru Forged 302 piston sets for the Chevy 302 engine"
They call them Tru Forged... and it makes me wonder if they are building the same pistons as the old 'ForgedTru' pistons (which is what I've got in my 302), but which date to the 1971 timeframe or earlier.  Does anyone know?

dutch

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Re: 1969 Z/28 DZ 302 overbore to .040? Piston Source?
« Reply #10 on: July 23, 2013, 12:10:07 AM »
You may wish to check out the CHP site to see if it states what Jerry uses for his 302 rebuilds or racing engines - or better yet fire him off a call or email and see if he sells any particular ones himself - besides asking him of course, for particular preferences he has and why..
Randy

CNorton

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Re: 1969 Z/28 DZ 302 overbore to .040? Piston Source?
« Reply #11 on: July 23, 2013, 01:06:32 PM »
The Campbell Enterprises add for their forged pistons state:   "...... Wiseco Pro Tru Forged 302 piston sets for the Chevy 302 engine"
They call them Tru Forged... and it makes me wonder if they are building the same pistons as the old 'ForgedTru' pistons (which is what I've got in my 302), but which date to the 1971 timeframe or earlier.  Does anyone know?

Results of a Google search for <Forged True Pistons> indicate that the original Forged True company was absorbed by Bill Miller Engineering a number of years ago.  Inasmuch as Bill Miiller is still making pistons as well as other components, the use of that name by someone else is probably somewhat misleading. 

I'm sure that Jerry is using pistons from an aftermarket supplier for his race motors.  Modern piston/ring technology has far surpassed the era of the original parts.  Common suppliers of Stock Eliminator pistons are Diamond, Wiseco, Ross, J & E, or CP Pistons.  I'm sure that Jerry has a preference, as does the rest of the Stock Eliminator field.  "Stock" is a relative term under today's rules.

69Z28-RS

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Re: 1969 Z/28 DZ 302 overbore to .040? Piston Source?
« Reply #12 on: July 23, 2013, 02:39:37 PM »
Forged True was a very expensive piston in the late sixties, and the set of 30 over piston in my '69 302, actually came from a '67 302 that I had, which had been ran in a '67 Z28, which ran 11.6 in the old 'stock' class (prior to '71), which was right at or under the national record for the class at that time.  The only mods allowed were headers and 7" slicks.  mine were originally cut for dykes rings, but when I put them in my '69 302, I had them grooved for standard 1/16" compression ring, although that groove is higher on the piston than is typical.   It was blueprinted for the maximum allowable compression in the '67 engine, and was higher than 'stock' in my '69 motor, which is the primary reason I parked the car in my garage in 1980, due to the difficulty in getting suitable octane fuel.

z28z11

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Re: 1969 Z/28 DZ 302 overbore to .040? Piston Source?
« Reply #13 on: July 23, 2013, 10:53:01 PM »
My DZ 302 is out and apart for the first time since I got it. The block is already at .030 and needs to go a little further.

    Not trying to be nosey, or reinvent the wheel, but what does the block measure out as ? When I rebuilt my '69 in '75, the original pistons were worn, but the block was great after 50K miles - the high tin/nickel content in the block casting did what GM bumped the percentages up for; kept wear to a minimum in the block, pistons become the wear parts. Also, keep in mind forged pistons "grow" quite a bit when up to operating cylinder temps - the reason why wall clearances are different between cast (which run closer tolerances on the walls), and forged pistons, "sloppier". Depending on the wear, you could always knurl the pistons to tighten up the skirt to wall clearance -
    Stupid me put Manley 12.5:1's in the '69 engine; fortunately I kept a set of stockers, plus I bought a set of NOS GM .030's when they went obsolete. GM .030's ('67-early '68 narrow rings) in the '68 Z. Glad I don't have to buy 'em nowadays -

Regards,
Steve
1968 Z28 M21/U17 BRG/W
1969 Z28 X77/M20/VE3 LeMans/W
1969 L78 X66/N66 Cortez/BVT
1969 Z11 L48/M35/C60/C06

tmodel66

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Re: 1969 Z/28 DZ 302 overbore to .040? Piston Source?
« Reply #14 on: July 24, 2013, 01:43:38 PM »
My DZ 302 is out and apart for the first time since I got it. The block is already at .030 and needs to go a little further.

    Not trying to be nosey, or reinvent the wheel, but what does the block measure out as ? When I rebuilt my '69 in '75, the original pistons were worn, but the block was great after 50K miles - the high tin/nickel content in the block casting did what GM bumped the percentages up for; kept wear to a minimum in the block, pistons become the wear parts.
    
Regards,
Steve

Not according to JohnZ. All the added tin and nickel was dropped because it didn't improve the blocks.

" the "010-020" raised numbers that indicate the 0.1% and 0.2% tin and nickel content in some blocks; that was an extended tryout where the added tin was to improve machinability and the added nickel was to improve bore wear. It was discontinued when the promised warranty improvements failed to appear, and the added cost was no longer justified."
Daniel  
'69 SS 350/4 speed  Fathom Green--POP

doomer

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Re: 1969 Z/28 DZ 302 overbore to .040? Piston Source?
« Reply #15 on: July 24, 2013, 03:06:07 PM »
Well, got the bad news this morning that he had to go out to 0.060 anyway. I know this is not good, but can somebody share some wisdom as to what I should do at this point? This is not a trailer queen, I drive her on weekends to local shows and cruise-ins. I want to enjoy my car without ruining it for good. I don't want to put a crate engine in it. I'd rather drive a 'real' Z/28. On the other hand, If that means ruining what's left of a numbers matching '69 Z/28, I'd rather sell her to someone who will make a trailer queen. (A good home, so-to-speak.)

Pretty bummed out.

69Z28-RS

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Re: 1969 Z/28 DZ 302 overbore to .040? Piston Source?
« Reply #16 on: July 24, 2013, 03:11:37 PM »
You can always 'sleeve' it back to std..   it's expensive, but some racers used to do that with their race engines...

JohnZ

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Re: 1969 Z/28 DZ 302 overbore to .040? Piston Source?
« Reply #17 on: July 24, 2013, 04:32:24 PM »
My DZ 302 is out and apart for the first time since I got it. The block is already at .030 and needs to go a little further.

    Not trying to be nosey, or reinvent the wheel, but what does the block measure out as ? When I rebuilt my '69 in '75, the original pistons were worn, but the block was great after 50K miles - the high tin/nickel content in the block casting did what GM bumped the percentages up for; kept wear to a minimum in the block, pistons become the wear parts.
    
Regards,
Steve

Not according to JohnZ. All the added tin and nickel was dropped because it didn't improve the blocks.

" the "010-020" raised numbers that indicate the 0.1% and 0.2% tin and nickel content in some blocks; that was an extended tryout where the added tin was to improve machinability and the added nickel was to improve bore wear. It was discontinued when the promised warranty improvements failed to appear, and the added cost was no longer justified."


And, as it turned out after further research with the Saginaw Foundry (now called Saginaw Metal Casting Operations, part of the GM Powertrain Division), the old story many of us were led to believe about the 010/020 describing the tin/nickel alloy turns out NOT to have been true at all, although the magazines thought it was true and continued to publish the tale, and still do today.

Actually, the "010/020" cast into the front bulkhead under the timing cover turned out to be simply the identifier for the foundry pattern for the front bulkhead, which was shared by the 3970010 (350) and 3970020 (307) blocks; it had nothing to do with the iron alloy, which was never altered for any particular production block (although the alloy was altered for some later low-volume GM Performance Parts over-the-counter "Bowtie" blocks).
'69 Z/28
Fathom Green
CRG

z28z11

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Re: 1969 Z/28 DZ 302 overbore to .040? Piston Source?
« Reply #18 on: July 24, 2013, 11:56:47 PM »


Not according to JohnZ. All the added tin and nickel was dropped because it didn't improve the blocks.

" the "010-020" raised numbers that indicate the 0.1% and 0.2% tin and nickel content in some blocks; that was an extended tryout where the added tin was to improve machinability and the added nickel was to improve bore wear. It was discontinued when the promised warranty improvements failed to appear, and the added cost was no longer justified."

[/quote]

Mine must have been one of the trials - less than .0002 (read as 2/10,000's, not .002) taper in the bore after 50K plus miles - machine shop remarked it was extremely straight, considering the wear on the pistons. BTW - a lot of 010 blocks are around with just that percentage cast on the block surface. Bores usually look pretty good compared to blocks like my 2 - 678's - heavy ring lands that took at least a .030 overbore.

Regards,
Steve

z28z11

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Re: 1969 Z/28 DZ 302 overbore to .040? Piston Source?
« Reply #19 on: July 25, 2013, 12:09:46 AM »
Well, got the bad news this morning that he had to go out to 0.060 anyway. I know this is not good, but can somebody share some wisdom as to what I should do at this point? This is not a trailer queen, I drive her on weekends to local shows and cruise-ins. I want to enjoy my car without ruining it for good. I don't want to put a crate engine in it. I'd rather drive a 'real' Z/28. On the other hand, If that means ruining what's left of a numbers matching '69 Z/28, I'd rather sell her to someone who will make a trailer queen. (A good home, so-to-speak.)

Pretty bummed out.

Doomer -

If it's the original, build it and drive it. Or, build a driver 302 motor and enjoy it anyway. Hot trick when I was growing up was to build a poor man's 301 using a 283 block bored .125 over - they usually ran really hot, but if the cores weren't shifted, they would last decently under pretty severe duty (rods and bearings were the limiting factors). Later model blocks didn't seem to suffer the earlier block's tendencies for core shifts - I've known a lot of .060 engines that ran, and continue to run, very well.

Strictly my own opinion,
Steve
 

tmodel66

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Re: 1969 Z/28 DZ 302 overbore to .040? Piston Source?
« Reply #20 on: July 25, 2013, 02:16:13 AM »


Mine must have been one of the trials - less than .0002 (read as 2/10,000's, not .002) taper in the bore after 50K plus miles - machine shop remarked it was extremely straight, considering the wear on the pistons. BTW - a lot of 010 blocks are around with just that percentage cast on the block surface. Bores usually look pretty good compared to blocks like my 2 - 678's - heavy ring lands that took at least a .030 overbore.

Regards,
Steve




And, as it turned out after further research with the Saginaw Foundry (now called Saginaw Metal Casting Operations, part of the GM Powertrain Division), the old story many of us were led to believe about the 010/020 describing the tin/nickel alloy turns out NOT to have been true at all, although the magazines thought it was true and continued to publish the tale, and still do today.

Actually, the "010/020" cast into the front bulkhead under the timing cover turned out to be simply the identifier for the foundry pattern for the front bulkhead, which was shared by the 3970010 (350) and 3970020 (307) blocks; it had nothing to do with the iron alloy, which was never altered for any particular production block (although the alloy was altered for some later low-volume GM Performance Parts over-the-counter "Bowtie" blocks).

doomer

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Re: 1969 Z/28 DZ 302 overbore to .040? Piston Source?
« Reply #21 on: July 25, 2013, 05:41:07 PM »

If it's the original, build it and drive it. Or, build a driver 302 motor and enjoy it anyway. Hot trick when I was growing up was to build a poor man's 301 using a 283 block bored .125 over - they usually ran really hot, but if the cores weren't shifted, they would last decently under pretty severe duty (rods and bearings were the limiting factors). Later model blocks didn't seem to suffer the earlier block's tendencies for core shifts - I've known a lot of .060 engines that ran, and continue to run, very well.

Strictly my own opinion,
Steve
 

Thanks Steve. Good advice, and I'll be sticking to the matching numbers oath, to "do no harm while enjoying the hell out of it". :) Going with JE Pistons and rings. Thanks folks, for all the great advice. I'm sure I'll have more questions as I put her back together over the next few weeks.

Shane

rsr

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Re: 1969 Z/28 DZ 302 overbore to .040? Piston Source?
« Reply #22 on: August 03, 2013, 01:30:47 AM »
 Sure everybody wants a standard bore block but if you got a overbore .040 -.060 and need .010-.020 more to clear it up for a good fit why not just get custom pistons vs having sleeves installed? Many piston manufactures can easly make what you need and you don't spend the extra cash for new pistons and sleeves??A .125 is 1/8 of a inch! Just a different way to view this problem IMHO.............