There does not appear to be any single source of running changes/improvements made to L88 engines from 1967 to 1969 (I am not talking about obvious changes such as going from closed chamber to open chamber heads, or the carb changes, etc.) What I would like to determine are things such as rod bolt size changes, push rod size changes, crank changes, etc. And specifically, were all L88 pistons retained with full floating wrist pins, or was this a running change (possibly in '69?)? Thanks for any info.
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Re: L88 Engine Chronolgy
Everett-----
Regarding the parts you mentioned, there were 3 different connecting rods used for L-88s. 1967-68 used rod GM #3909846. This rod is forged from 4340 steel, uses floating piston pins, and uses 3/8" OD rod bolts. It was originally colored coded "pink".
Early 1969 L-88s used rod GM #3959187. This rod is also forged from 4340 steel, has a slightly larger cross section than the earlier rods, and is designed for use with 7/16" OD rod bolts of GM #3959186. These are high quality, ground shank rod bolts, but they were not boron steel like later. These rods are designed for use with floating piston pins, just like the earlier rod. It's also very possible that some very late 1968 L-88s used this rod, too. I don't know exactly when the changeover occurred.
Later 1969 L-88s used rod GM #3969804. This rod is also forged from 4340 steel and is similar in cross-section to the 3959187 rod. It is 100% magnaflux inspected and shot-peened. It was supplied with extremely high quality, ground shank, 7/16" boron steel rod bolts of GM #3969864. These bolts were 100% magnaflux-inspected and shotpeened. This rod is also designed for use with floating piston pins like all other L-88 rods. It was color-coded "green".
1967 L-88s used crankshaft GM PART #3879621. 1968 and 1969 L-88s used crankshaft GM PART #3942411. It is possible that VERY late 1969 L-88s used crankshaft GM PART #3967811. However, I think that 3967811 was actually only a SERVICE crankshaft that replaced the 3942411. Both the 3942411 and 3967811 were forged from 5140 steel, had nitride-treated journals, and were cross-drilled. I don't know how the 1967-only GM #3879621 crank differed from the later.
All 1967-69 L-88 used pushrods of 7/16" diameter. The 1967 pushrods somehow differed from the 68-69, but I don't know how they differed. Functionally, they are interchangeable with the 68-69. The 68-69 7/16" OD pushrods were GM #3942416, intake, and GM #3942415, exhaust.In Appreciation of John Hinckley -
Re: L88 Engine CHRONOLOGY (spelling corrected)
Awesome summary Joe! This is exactly the kind of info I was looking for. Thank-you.Comment
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Re: L88 Engine CHRONOLOGY (spelling corrected)
Joe, thanks for your very informative post. Is it true that the later 69 L88s used the same camshaft as the ZL1 engines?Comment
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67 pushrods used welded ball tips
Later pushrods used a pressed in endComment
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Re: L88 Engine CHRONOLOGY (spelling corrected)
Steve-----
Not that I am aware of.In Appreciation of John HinckleyComment
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Re: 67 pushrods used welded ball tips
Joe,
Did I miss something here? Your analysis didn't list the '7115 crankshaft
for the L-88.
SteveComment
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Re: 67 pushrods used welded ball tips
Steve-----
"7115" is the FORGING or ID number which was likely used for ALL of the crankshaft PART numbers that I mentioned.In Appreciation of John HinckleyComment
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