65-66 Big Block Spark Plug Heat Shields-What is correct?
Not sure what is correct. Restoring a 66 that has had headers on it for years. I have gathered 2 sets of what I believe to be original spark plug heat shields and a set of NOS. One set of OEM are all the same (lighter color), the other set which was painted black has 2 that are shorter than the other 6. The NOS have a much wider opening, which does not look right at all. Need opinions on which would be correct for my 66 and what finish should they have. Thanks, Mike
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Re: 65-66 Big Block Spark Plug Heat Shields-What is correct?
Mike, the used ones you collected look correct. The one with the wide “tail” I’d say no. If you were to clean them up and replate them with plain zinc you should be all set. -
Re: 65-66 Big Block Spark Plug Heat Shields-What is correct?
If my memory is serving me correctly these are not correct for '65-'66 the barrels are more rounded and have a rolled bead on the end.Comment
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Re: 65-66 Big Block Spark Plug Heat Shields-What is correct?
Mike-----Not sure what is correct. Restoring a 66 that has had headers on it for years. I have gathered 2 sets of what I believe to be original spark plug heat shields and a set of NOS. One set of OEM are all the same (lighter color), the other set which was painted black has 2 that are shorter than the other 6. The NOS have a much wider opening, which does not look right at all. Need opinions on which would be correct for my 66 and what finish should they have. Thanks, Mike
None of these are correct for 65-67. All of the used examples are GM #336716. These were used for 1972-74 454. The NOS GM #465840 are a late 1970's SERVICE replacement for the 336716. They may have been used for some PRODUCTION application but never Corvette.
The 1965-67 shields were GM #3871266. These are completely tubular-shaped, end-to-end.In Appreciation of John HinckleyComment
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Re: 65-66 Big Block Spark Plug Heat Shields-What is correct?
Joe ...you are amazing...what a gift to the forum you are.Comment
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Re: 65-66 Big Block Spark Plug Heat Shields-What is correct?
All------
A little more on this: the 1965-66 big block spark plug shields are unique to those years although not unique to Corvettes. As I mentioned, these are tubular shaped, end-to-end (although the outer end is "cut-away", not "duck-billed" as seen in the 336716 or 465840). These shields have a small tab spot welded near the outer end and this tab serves as a fastening bracket. The shields are thus fastened to the heads with a 1/4-20 hex head screw which threads into a tapping on bosses on the heads. Only 1965-66 heads have these bosses and tappings. So, these shields can only be used with 1965-66 heads.
1967-71 big block engines used no heat shields.
1972-74 big blocks used the GM #336716 shields. These shields are differently configured. They have a "duck-bill" or "sugar scoop" shaped outer end. They have a fastening tab which is an integral part of the shield. This tab fastens to one of the exhaust manifold bolts so no separate screw is required.
The GM #336716 or its GM #465840 replacement can be used with ANY 1965-74 big block, although they were never cataloged by GM for any 1965-71 application. If any 65-66 big block is retrofitted with later heads or aftermarket heads and spark plug heat shields are desired, then the GM #336716 or GM #465840 shields must be used. If any 1967-71 big block is desired to be retrofitted with spark plug heat shields, then the GM #336716 or GM #465840 shields must be used. This is why the later style shields are found on earlier engines.
The GM #336716 and 465840 are actually functionally better than the 65-66 heat shields-----there's no spotwelded tab to break off and their design better protects the spark plug from manifold heat. However, they're not correct for any 1965-71 big block.In Appreciation of John HinckleyComment
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Re: 65-66 Big Block Spark Plug Heat Shields-What is correct?
Thanks Joe, now I remember the type you indicate are correct. Now, the search begins.Comment
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Re: 65-66 Big Block Spark Plug Heat Shields-What is correct?
Mike------
Good reproductions are available.
As far as used originals go, thankfully these shields were not unique to Corvettes. All 1965-66 big blocks got them. So, the field of donors is fairly large. Of course, a lot of those donor cars are Toyotas by now.In Appreciation of John HinckleyComment
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Re: 65-66 Big Block Spark Plug Heat Shields-What is correct?
Thanks Joe, now I remember the type you indicate are correct. Now, the search begins.Comment
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Re: 65-66 Big Block Spark Plug Heat Shields-What is correct?
Do you know who carries the correct repros? if I can't find originals.Comment
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Re: 65-66 Big Block Spark Plug Heat Shields-What is correct?
Here's my eBay set of 7. I'd say they're the "828's" but just a 1/16th shy of the 3.0" overall length shown for the "266's" in engineering dwgs (Noland Vol
2, page 285). No spot weld on the tab.
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Re: 65-66 Big Block Spark Plug Heat Shields-What is correct?
Noticed the rolled bead around the end. That is where the spark plug wire clips on.Comment
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Re: 65-66 Big Block Spark Plug Heat Shields-What is correct?
Do you know who carries the correct repros? if I can't find originals.Comment
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Re: 65-66 Big Block Spark Plug Heat Shields-What is correct?
Wayne------
I agree with Noland. I don't think the GM #3868828 was ever actually used in PRODUCTION; I know it was never available in SERVICE. It might be that it was never an actually released part number. I think that yours are the GM #3871266. If the tab on yours is not spot welded, how is it attached? Is it just an extension on the basic stamping used to form the shield? I always thought these were spot welded. The 3868828 drawing clearly shows it spot-welded; the 3871266 is unclear.In Appreciation of John HinckleyComment
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Re: 65-66 Big Block Spark Plug Heat Shields-What is correct?
Joe --- here's an old Bay photo of a "266" available in service. Notice that the reference to 2 spotwelds for the tab has been removed on the "266" dwg. in Noland's book. I'd have to clean up and examine several of mine to say for sure. Yes, the tab was part of the original stamping (not a separate attachment) and was bent back 180 deg.
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