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Has anyone restored the rusty bolts and nuts within the engine compartment? Looking to either order new bolts etc (zinc plated) or have them newly plated. Any suggestions? Anyone know the thread size?
Thanks!
Just have your nuts and bolts soda blasted clean. I have my own blaster from Harbor Freight. Then buy a tin-zinc plating system. Mine is from Eastwood. Once replated, fine wire brush them to polish the finish and use a car wax or other type of polish to seal. Good as new except slightly duller than new but way less expensive than buying new. I did almost all my nuts and bolts that don't take high heat.
Mike
The part numbers on hardware tell you the size and specs. Its explained in the psrt number thread.
the cliff note version, is that Mazda has a different part format for bolts/screws/etc
9978-60-612 as an example, the 99 tells you its a bulk item, the 7860 tells you want style of fastener it is. there are quite a few and you just have to go by example (we haven't figured out all of them yet)
the 612 is the size, so this one is 6mm by 12mm long. Mazda uses JIS fasteners, and a 6mm JIS fastener is 1.0 thread with a 10mm head.
9978-60-616 is the same bolt but 16mm long, 9978-60-816 is an 8mm bolt that is 16mm long.
sometimes they add a letter at the end, and that refers to the plating. 9978-60-616 is gold zinc, 9978-60-616B is a dark zinc plating.
etc etc. this really allows you to use the parts catalog to get the correct fastener.
Normally I'm all for a detailed restoration project. But before jumping in on something like this, I'd suggest asking yourself one question. Am I working harder, or am I working smarter?
If it were something vehicle-specific or difficult to find (example: brake caliper brackets), then I can see the rationale in giving it a proper surface treatment like this,
But let's be realistic here. These are nuts and bolts that were given a sacrificial yellow zinc finish so they wouldn't turn to rusty crap overnight. Zinc plated hardware is the cheapest of the cheap at any hardware store because they basically guaranteed to rust. Anyone that has dealt with a FC's fuel pump knows just how "great" the factory hardware is, and the colorful language resulting from it.
Nobody in their right mind sees a bolt and thinks "Gee, let's see how hard it is to remove it after it breaks...". We're smarter than this. Stainless Steel hardware is readily available. Add some anti-seize if threading into aluminum and put your effort where it'll do the most good. I for one would be overjoyed to spend the extra 8 cents or so on a Stainless Steel Nut/Bolt if it meant not dealing with it breaking off and having to get the "oh ****" tools out and hope there's enough room to use them. Last time I had to do that was on a suspension bolt on my Expedition that had seized to the steel sleeve inside bushing it went through. When I finally extracted that bolt, there was zero change of salvaging the affected suspension arm. Thankfully, I was replacing that suspension arm so it didn't matter that it was in several pieces. As for the bolt in question, it laughed off every form of penetrating oil and stuck bolt removal trick. Pretty sure I still have the 8" C-clamp that bent into a V-shape from trying to use Archimedes' logic on it.
The only thing that made a difference was heating the sleeve for 30 minutes with a propane torch. Now imagine that scenario on your FD's fuel filter...
Here's the same flange head style M6 bolts as Mazda used, but in stainless steel for $0.36 a piece. 25mm long is $0.38 a piece too.
Thanks to everyone who responded. All great advice. Temporarily I soaked the obvious ones in vineger for a few hours and the came out like new. I know this won't last so rusts when I'll hunt down the correct replacement.
If. your car isn’t some low-mileage uber-OEM version, I second stainless. They’re as close as most hardware stores, easy to change, not expensive and will look nice forever.
FWIW in most cases I used a little anti seize going back on.
I have actually restored quite a few bolts a while back. I do agree with the consensus here that for small M6 type nuts/bolts just order new stainless. For larger/non standard bolts I did the following:
1) Sandblast the bolts clean.
2) Paint with caliper paint. I used silver and it looked nice and clean just not original.
3) Wrapped up in tin foil and cooked in a toaster over for about 30 minutes.
At the time I was painting my rotor hubs/calipers and had the idea to paint the caliper bolts and then just kept going since it looked pretty good. I was mainly focused on the under carriage and did quite a few. The bolts held up nicely for the 8 years I owned the car. You could argue that I went too far
Painting bolts is somewhat short term. It's just a coating sitting on top of the bolts and it's easily scratched off. Actual plating is a chemical bond and a change in the outer layer of the material. This will last far longer and is far more resilient.
Electroplating isn't super hard but it is involved with a lot of chemicals. In many cases it's far easier just to get new hardware - cheaper too some times. But a freshly plated bolt or bracket looks AMAZING.
I went through a complete “restomod” over the last couple years and have replaced about 99% of the original hardware on the entire car. Most of it was either stainless steel or black oxide nuts and bolts from McMaster-Carr. In some cases, like the large suspension bolts, I went with the zinc-plated stuff—basically, I got the best I could find in whatever size I needed. In many cases I was able to get 10.9 grade hardware which is stronger than OEM. Total cost to do the entire car was about $300 including some odd-size stainless hardware on the engine. As stated before, if you’re keeping it pristine and original that’s one thing, but don’t be afraid to buy off-the-shelf hardware.
