Author Topic: 1969 Z/28 DZ 302 overbore to .040? Piston Source?  (Read 24238 times)

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...
09C 69Z28-RS, 72 B 720 cowl console rosewood tint
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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
1968 Z28 M21/U17 BRG/W 1967 Chevy ll Nova SS 
1969 Z28 X77/M20/VE3 LeMans/W
1969 L78 X66/N66 Cortez/BVT
1969 Z11 L48/M35/C60/C06  1949 3100 5wd 235/6

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
 
1968 Z28 M21/U17 BRG/W 1967 Chevy ll Nova SS 
1969 Z28 X77/M20/VE3 LeMans/W
1969 L78 X66/N66 Cortez/BVT
1969 Z11 L48/M35/C60/C06  1949 3100 5wd 235/6

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).
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 #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.............

 

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