are 4+3 case to bellhousing or bellhousing to block bolts hardened?
 

i ask because as im fixing items on my 86, i like to let the rusty fastners sit in a phosphoric acid bath. it removes the rust and forms a protective dark layer on thier surface. i typically hit them with flat black rustoleum too.

but!!!!

i just read that acid treatment while fine for normal steel....is deadly for “hardened bolts” or any hardened steel for that matter. it causes something called hydrogen embrittlement.

im not claiming to understand the implications but id rather not find out.

the 4+3 case to bellhousing bolts are both hex head and torx. anybody know if they are hardend bolts?? same for bellhousing to block.

there is a website called finishing dot com that does cover this topic in some discussion. https://www.finishing.com/291/72.shtml

the “cure” is a bake between 200-250 celsius 392-482 F with bake times “varying depending on cross section” i assume diameter.

and this needs to happen within one hour....im not sure if its within 1 hour from when they get pulled from the acid or if its 1 hour from first exposure to acid. if its the latter, im hooped as they were in there for 7 hours. if its the former then im good cause they are on a cookie sheet, on tin foil, in my bbq, baking away.

any comments welcome as im out of my league as a hobby mechanic vette lover with this one.

I'd think all are GM280-M spec Grade 5 (3 radial lines)

https://www.boltdepot.com/fastener-i...ade-chart.aspx

should be in the clear
 

Thank You, WVzr1, your post led me to this site https://www.fastenal.com/content/fed...rittlement.pdf

and it clearly states that hardness levels of >40 will have problems.

below that likely will not.

grade 5 bolts, which u r correct, thats what these bolts are, even the OD trans pan bolts, have a hardness between 19-34 dependent on size as per chart.

so i should be in the clear. notwithstanding that, they are baking anyway.

I think i can lay this worry to rest. VT.

https://cimg5.ibsrv.net/gimg/www.cor...cdb439199b.png

I bought a large selection of Grade 8 hardware at Corvettes@Carlisle and have been using it ever since. I would replace the bolts with quality U.S. made grade 8 bolts. Since my C3 has more HP than it came with I figure using grade 8 hardware was not a bad idea. I am not trying to restore my Corvette just improve it a bit with non-stock grade 8 hardware.

I also like to use anti-seize when working on places on the Corvette where the hardware is tough to get at. Anytime you have dis-similar metals you should be using the anti-seize to prevent galling and frozen fasteners. A good example is your spark plugs where you have steel spark plugs in an aluminum head.

Thanks Vikingtrad3r for educating us about the problems with "Hydrogen Embrittlement" and how it affects hardware! I guess I will still use my vibratory cleaner from Eastwood for cleaning my hardware, it makes the parts look new again, it just takes 24 hours....

Best regards,

Chris

thanks Chris.
 

funny u say that Chris. i just bought this.


what type of media do you put in the tumbler? i once heard that using cat litter was good.

Bellhousing bolts are torqued at only 35 ft/lbs. Grade 5 bolts are fine.