Fastener Finishes - 1970

[Stephen L.]

at this thread: https://www.forums.ncrs.org/showthre...ldest&uid=3961

Chuck wrote in a response:

"Your best shot at determining the original finish on fasteners is to examine the individual fasteners closely for any remnants of the original finish. This is best done during the disassembly process as they are cleaned, bagged and tagged.

[...]

Fasteners that were originally black phosphate or natural are the ones most likely to be rusted beyond recognition. Black oxide is a tougher finish, but application is more selective in my experience. Black phosphate will have a fine crystallaline structure in the finish that reflects light; its somewhat like looking at your concrete driveway in bright sunlight. Black oxide is a slick, hard finish compared to black phosphate. Be careful not to identify worn black oxide as black phosphate; the black oxide may have have near-microscopic flecks of plating missing that makes it appear as black phosphate (it's happened to me). Zinc plated fasteners should show some sign of the original finish under the worst conditions in my opinion.

[...]

If all else fails, feel free to apply my arbitrary rules of thumb on fastener finish. These are BFG (BIG FAT GUESS) or ALR (ABSOLUTE LAST RESORT) categories; USE AT YOUR OWN RISK: For chassis fasteners, say 1/4" and larger, use black phosphate. Fasteners 3/16" and smaller could be either black oxide or black phosphate. Zinc is used on the chassis sparingly, but you should be able to see where. Natural fasteners are also used on the chassis in a few applications; you will almost have to know these from observing restored cars or reference books."

I am trying to use this methodology - here is a case in point - I took off the axle shafts last night from a 1970 - the bolts that secure the outer shaft flange to the spinder dirve flange (UPC4A2 - 2; page K168 in the Mid America AIM) can serve as an example - they were dirty, but not rusty - I rinsed them for a few minutes in mineral spirits - the result, bolts that look "grey" - the first thing I did was consult the TIM (4th Ed., pp 103 and 110) - but I cannot find any reference to bolts at all - does the TIM not deal with what markings the bolt head should have and what finish? - if yes, I could not find it - Chuck's post says that for certain fasteners (e.g., "natural" finish), one has to refer to a reference book - assuming this is not the TIM, what is it? - I otherwise have searched the archives, and could not find anything on this specific bolt finish (bad searching?) - so, since all else I can think of has failed, I'll ask you guys...what finish should this bolt have? - and going forward, is searching here and if unsuccessful, asking, the only way to know about correct fastner finishes? - thanks and sorry for the long post! sl

[Terry M.]

Re: Fastener Finishes - 1970

I am trying to use this methodology - here is a case in point - I took off the axle shafts last night from a 1970 - the bolts that secure the outer shaft flange to the spinder dirve flange (UPC4A2 - 2; page K168 in the Mid America AIM) can serve as an example - they were dirty, but not rusty - I rinsed them for a few minutes in mineral spirits - the result, bolts that look "grey" - the first thing I did was consult the TIM (4th Ed., pp 103 and 110) - but I cannot find any reference to bolts at all - does the TIM not deal with what markings the bolt head should have and what finish? - if yes, I could not find it - Chuck's post says that for certain fasteners (e.g., "natural" finish), one has to refer to a reference book - assuming this is not the TIM, what is it? - I otherwise have searched the archives, and could not find anything on this specific bolt finish (bad searching?) - so, since all else I can think of has failed, I'll ask you guys...what finish should this bolt have? - and going forward, is searching here and if unsuccessful, asking, the only way to know about correct fastner finishes? - thanks and sorry for the long post! sl

A lot of chassis fasteners are not listed in the TIM&JG because they simply are not visible when the car is judged. The TIM&JG started as an aid to judging, and only recently was expanded to assist restorers. Share what you learn so that it becomes better.

The only chassis reference I am aware of is Joe Tripolli's chassis restoration book available from the NCRS office. The best chance for answers to your questions, besides this forum, is to look at original cars. Best place for that is the Advanced Judging School at the National Convention -- we have a lift and the best chance for real original cars.

Can't get to the convention?
No answers here?
Joe's book doesn't mention it?
Then Chuck's Last Resort formula is the only answer there is.

[Chuck S.]

Re: Fastener Finishes - 1970

Hi Stephen...I think you may have read more into my "reference book" comment than intended.

My comments above say that with natural fasteners, or black phosphate fasteners under the worst climate conditions, it will be tough to tell the difference. Both finish types will probably be rusty beyond finish recognition. What I meant by my "reference book" comment was, if your fasteners ARE rusted beyond finish recognition, you'll have to either SEE these original finishes on cars with low climate exposure, or be lucky enough to find a rare finish identification in some reference books like Tripoli's Corvette Chassis Restoration Guide, 1953 Through 1972, or the 70-72 Corvette TIM&JG (Yeah, it's there...see page 105...what you see is what you get).

The naked truth is THERE IS NO GOOD REFERENCE BOOK for fastener finishes. There are cursory efforts at chassis finish identification in the two named references above, but in both cases there is not enough descriptive detail, and there are more holes in the coverage than a fisherman's net. Frankly, it would be a gargantuan undertaking and exceeds the scope of the two named references...it could be a hefty reference book in it's own right; and then you could start building a book for 69s or 71s.

OK, now lets critique your methodology and see what should be concluded. You say the bolts were not dirty or rusty, and appear to be gray after solvent cleaning. From my previous post, you should conclude what?...they are either black oxide or black phosphate on a well preserved chassis...Right? Not natural that's for sure, or zinc either. Note that "black phosphate" or manganese phosphate will vary from a full black, to dark charcoal gray, to a medium gray. If it's a light gray, it's probably zinc phosphate.

I haven't seen the rest of the chassis for condition, so I can't really tell which of the two the finish should be...Did you apply the direct sunlight examination for tell-tale phosphate crystals reflecting light as I recommended in my previous post? Here are my comments about the two finishes:

Black oxide is a slick, hard finish compared to black phosphate. Be careful not to identify worn black oxide as black phosphate; the black oxide may have have near-microscopic flecks of plating missing that makes it appear as black phosphate (it's happened to me). Note: The missing flecks in the black oxide coating resulted from wire wheel brushing.

Since the bolts weren't rusty, the analysis should indicate black oxide, and in fact, I believe those half shaft flange bolts are black oxide Grade 8 bolts. You will find that high strength Grade 8 bolts are often black oxide finished. I didn't record these particular bolts in my plating records, lending further confirmation that they are black oxide. Since there are so few black oxide fasteners on the chassis, I had planned to simply replace them rather than introduce yet another finishing method.

At one time, Paragon had replacements that were identical to the originals as far as I could tell. If the bolts are black oxide, and are in good shape, you may simply be able to oil them to nearly new appearance and reuse them.

Sorry for the long post, but I'm trying to "teach you how to fish".

[Stephen L.]

Re: Fastener Finishes - 1970

Chuck - many thanks for taking the time - greatly appreciated as always!

Terry - thanks for pointer to Joe's book - sl (waiting for sunrise to check for disco ball sparkles!! )