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Rust/corrosion issues on my NSX? Dacro bolts?

Joined
11 January 2021
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554
Location
Ontario, Canada
I figured there would be some threads, but my search turned up nothing related. Waffled on which forum it belonged in (Is it general or just for DIYers?) so please feel free to move if more appropriate.

I have a (Florida) 1995 NSX-T in Canada. It won't leave the garage until all remnants of road salt are long gone. Considering how much aluminum is used on the NSX, I figured rust/corrosion would be a limited issue, but there are lots of steel parts from striker latches to brackets for electrical/fuses to the rear sway bar & holder. Most look galvanized to me? Many of them are starting to show corrosion. I have 2 questions:

Galvanic Corrosion (brackets etc.):

Considering aluminum is more prone to galvanic corrosion than steel, (applications use aluminum sacrificial anodes to protect steel) I would expect the aluminum to corrode sacrificially, sparing the steel bolts/brackets etc. But many steel parts seem to be starting to corrode & the aluminum not, thankfully. When some bolts were removed, there were traces of what looked like white aluminum oxide powder, which I assume was slight corrosion, but could be dried up lock-tite or similar? Some steel parts are partially rubber coated and it’s splitting. Any suggestions for restoring these steel and/or rubber-coated steel parts other than replacing them? Many aren’t that expensive, but it will add up.

I tried electrolysis on some discarded parts. It takes off the rust, but still leaves black marks (oxide where the zinc is now gone?). I applied Krown rust inhibitor to the parts. While they look better than the surface rust, they still look substandard. I wanted to see about powder-coating them, but our local powder-coaters are on hold due to Covid.

So:
1. Just tape up the brackets and Plastidip them myself?
2. Wait & powder coat?
3. Stop being so vain?

Dacro Bolts:

I've noticed corrosion on quite a few bolts. The owner's manual describes "Dacro" bolts to reduce corrosion in many locations denoted by a star, but I don't really see those stars in my owner's manual in many places where a Dacro bolt came out, based on the flat grey color & mint thread coating. Dacro coating is a “ceramic” of sorts. Was the purpose to electrically isolate and thus reduce galvanic corrosion between the steel and aluminum parts or between the bolts and the aluminum, or to reduce the chance for the bolts to seize? These bolts measure very high electrical resistance. Are Dacro bolts even available any more now that Dacro coating has been restricted by the EU? Replacement bolts from my local Honda dealer seem to be regular steel, not Dacro.

I'd like to change some of these rusty bolts to titanium, which won't rust in the future. Titanium is a poor conductor, but it's not as good an isolator as Dacro?

So the question is, what should I do?
1. Brush the surface corrosion off the old bolts, spray with Krown rust protector (oil), and reuse? (a bit unsightly)
2. Replace the bolts with steel ones from the local dealer (prone to rust? But is it better to have the bolt rust than something else?)
3. Replace the bolts with JDM parts from amayama (many seem to be out of production or take a long time to source there too, not sure if amayama bolts will be Dacro either)
4. Replace them with titanium which will not rust but could allow other corrosion? (more expensive & increased conductivity)
 
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Dacro is/was a brand name of a specialized zinc coating that serves as a sacrificial metal to oxidize in place of the base material (bolt itself or threads). Plenty of people have zinc-plated their own hardware, but personally I don't think the results will last as long as Dacro did, it's proprietary for a reason.

Lots of the parts you mentioned are rust-prone, especially for cars from Japan or the UK. Protective coatings don't last forever. The white powder substance you see on bolts is corrosion, as to what substance it was before it turned into a lump of oxides, my guess would be aluminum but not totally sure. This is a big problem on plenty of Hondas with camber/caster bolts in the control arms, the eccentric bolt can seize inside of the camber bushing sleeve and won't allow any adjustment.

1) Nothing wrong with doing this, will be the cheapest by far. Do not plasti-dip, it will be destroyed the first time you remove the bolt again. This is more time-consuming than buying new bolts so is a tradeoff between how much labor you want to invest vs. straight money for new stuff.

2 and 3) I don't think new OEM Honda bolts are left uncoated. I've bought tons of hardware from Acura US and Amayama, there is no visible difference. The new bolts seem to be a matte finish with a blue-ish tinge. I believe they are still coated, and I trust them much more than generic zinc-coated or galvanized hardware from a box store. None of the new OEM bolts I've put on have rusted yet. The same can't be said for the new OEM tie rod ends which seem to be unprotected...

You will have trouble getting any bolts from Acura in the US or Canada, I find that most of them are backordered/etc 90% of the time. Amayama has had pretty much everything I needed when I needed it.

4) I'd much rather use an old OEM bolt or newly produced one over titanium, you might cause long-term issues with the threads in the body/etc. People like dress-up-bolts in the engine bay and all that, I've not seen evidence of accelerated corrosion from the titanium-aluminum mix but the risk is there, people posting their engine bays on Instagram are unlikely to post about when they removed a bolt and ripped out the threads with it. Titanium is one of the most noble metals (cathodic) which means the aluminum threads will be what is eaten away as the anode, exactly what you don't want. Water/salt/etc. contact will accelerate that process.

TL;DR clean up the old bolt heads and spray with rust converter, try to leave the threads alone if they still have coating. If you want to spend the money and save time get new OEM bolts from Amayama.
 
I agree with Tyler here- your best bet is to replace the bolts with new OEM. I've replaced dozens on my S Zero project and Tyler is right, they are identical to the original pieces in terms of coating and appearance. Amayama will have everything you need at a good price, or Marc at MITA too. A potential hack is to clean up the bolt heads and spray them with a dry silicone spray. It won't be close to the protection of a true Dacro coating, but if your NSX is driven only in fair weather, it should provide some protection from atmospheric moisture (humidity) related corrosion. If exposed to water, it will eventually wash away. I use that stuff on the chute of my snowblower and it lasts about three uses before wearing away. Just sitting on the head of a static bolt, it should last much longer...in theory. Still, I'd just replace the bolts and get the extra 20 years of corrosion-free use. :)
 
The main problem here is that this NSX, spent most of its life in Florida, hence the corrosion issue on the metal brackets, bolts etc.
Buying new one's will be the best option, and will be good for another 26 years.

A couple years ago, I started a thread here asking if anyone had any corrosion issues with the Aluminum body parts, and at that time now one indicated any issue with these parts on their NSX. So overall Honda did a great job with the preparation and coating on these Aluminum body parts & panels.

Bram
 
As noted, Dacrotized is a proprietary process for coating stuff with Dacromet which is a proprietary zinc based coating. You can get the gory details by doing a web search on Dacromet or NOF Metal Coatings. Dacromet is not a sacrificial coating. That would be a bad thing. If you check a galvanic potential chart

Galvanic Series (electrochemical series) (structx.com)

you will find that aluminum and zinc are cheek and jowl (almost overlapping depending on the aluminum alloy) so that the galvanic potential created with the addition of a little dirty water is minimal / none which means no corrosion cell in the space between the aluminum body threads and the bolt threads. The Dacromet is there to prevent the loss of aluminum if a corrosion cell was set up between the aluminum body and an untreated steel bolt. Dacromet is applied by spray or dip so the complete bolt is likely covered with the product; but, the important area is the thread interface.

True Dacromet as supplied by NOF coatings is a silvery color. There are other anti corrosion coatings available. I don't know whether Honda uses true Dacromet or uses dacrotized in a generic sense and are using bolts treated with some other process. True Dacromet being silver in color might look like a galvanized bolt. The NSX has a lot of bolts on the car which have a greenish - grey finish to them and a lot of those bolts are in locations where the service manual does not call out for Dacrotized bolts. I suspect that finish may be an anodized or similar anti corrosion protection.

In a pinch, galvanized bolts are a reasonable substitute for dacrotized bolts. Never use stainless steel where a dacrotized bolt is called out. Stainless steels are even farther away from aluminum than conventional steels on the galvanic potential chart which means that damage to the aluminum threads will be even faster if a corrosion cell is set up. Uncoated titanium bolts would be the absolute worst. In assessing whether you need to replace a dacrotized bolt it is the condition of the coatings on the threads that should be the primary area of concern.

For for the various fittings, brackets ... on the car that are suffering from surface corrosion I expect (but don't know) that Honda did not have these fittings dacrotized. Clean up followed by powder coating or 2K paint or perhaps anodizing are options. If you tried 'electrolysis' on any of the dacrotized bolts I would ditch them. You don't know what you have done to the dacrotized coating.
 
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Thanks guys. Of course I now found this, which seems to endorse Ti bolts, used with anti-seize:
http://www.nsxprime.com/forum/showt...rosion, titanium,, even stainless, to corrode.

It's interesting that despite all of the folks adding decorative Ti bolts, I couldn't find much mention of ruined aluminum threads in my web searching except where the person had overtightened the fastener. Lots of folks seem to think Ti bolts will not cause corrosion if non-conducting nickel-based (some say copper OK too) anti-seize is used. I've replaced many steel bolts with Titanium on my bicycles, where the weight can make a difference, with nary a seized bolt or damaged threads.

That said, I can't afford to damage some of these threads, so I've ordered all the OEM parts from amayama. The few bolts that had months of delays can get on the schedule for next winter, along with powder coating a bunch of brackets.
 
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The greenish Dacro is there to prevent corrosion between the threads of a steel screw in an aluminium part mainly. In the SM you see it several times that Dacro parts have to be replaced if unscrewed. People normally don't with no ill sideeffects. Ceramic paste is a good additional when screwing it back together. But don't rely on it only. Don't ask me how I know (not on the NSX).

But salt will let rust any steel part, with or without Dacro, esp. if the screw has been touched.

Honda did a good job on protecting the panels but I've also heard of 02+ cars where corrosion under the paint was a problem.

For any car: if you love it don't drive it in the winter/salt period. If you have to just live with the rust/corrosion.

If you want a simple but very effective rust protector you can mix it on your own: melt 10% honey wax + 90% white technical vaseline (grease). I used to use it on my older winter cars on the brake lines (big PITA to replace). Advantage: you can always see what's going on below the thin coat of wax/vaseline.
 
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Anti-seize would probably prevent some corrosion from happening, but it will also alter all the torque values you're using and in some cases might allow bolts to back out when they wouldn't normally do so.

Another tip, hopefully you made a spreadsheet of all the hardware you're ordering to keep track of it ;). In a few weeks/months when a box of 100 bolts shows up it will be very difficult to remember which one goes where, and plugging their part #'s back in to a search engine usually turns up other Honda models or different applications on the car you weren't planning for.
 
Yep, spreadsheet made. amayama just invoiced me and shipping went from $50 to $140, with duty & taxes still payable! Is this their MO?
 
Yep, spreadsheet made. amayama just invoiced me and shipping went from $50 to $140, with duty & taxes still payable! Is this their MO?

Yes- it's because Japan Post/EMS shipping is still suspended due to COVID. They are forced to use FedEx right now. I had to do this with a new transmission case a few months ago. :frown: Still worth it IMO.
 
They don't try to rip you off with shipping, but their automatic calculations of package weight & cost are off which is why you have to submit your order for review first. That's when they actually look at the weight & dims of the package to get a quote from FedEx for you. Unfortunately international shipping is still all messed up and that's just how much it costs for larger packages now.

The extra $90 can still be worth it for lots of situations, especially when a part isn't available in NA. Example, I tried to order a battery bracket and sensor not available in the US and shipping was $120, I made a new order with just the sensor and shipping was $30 instead, same thing with coolant hoses where the large ones caused shipping costs to increase 5x. Sometimes you have to experiment with your cart a bit.

Any shipper will have you responsible for taxes and duties from your local constabulary, fwiw I've never been asked to pay any of that in the US, maybe Canada is less lenient.
 
Thanks guys. Of course I now found this, which seems to endorse Ti bolts, used with anti-seize:
http://www.nsxprime.com/forum/showt...rosion, titanium,, even stainless, to corrode.

It's interesting that despite all of the folks adding decorative Ti bolts, I couldn't find much mention of ruined aluminum threads in my web searching except where the person had overtightened the fastener. Lots of folks seem to think Ti bolts will not cause corrosion if non-conducting nickel-based (some say copper OK too) anti-seize is used. I've replaced many steel bolts with Titanium on my bicycles, where the weight can make a difference, with nary a seized bolt or damaged threads.

As MotorMouth93 noted, you need 3 partners to do the galvanic corrosion dance, two dissimilar metals with a significant galvanic potential difference and an electrolyte. If you are not riding your bicycle around in the rain you are missing the third dance partner. If moisture is present, the anti seize may mitigate the galvanic corrosion problem on aluminum caused by contact with the non aluminum fastener. The anti seize has a grease base which likely prevents the ingress of moisture into the thread area. However, the bolt head / shoulder (washer if used) that comes into contact with the aluminum body may not sustain that protective grease coating and you may incur galvanic corrosion at that site if moisture breaks the grease barrier.

The thread you linked had references to the fact that aluminum forms a self protecting oxide barrier when exposed to oxygen. That is correct; but, depending on the alloy it is not a particularly durable oxide coating. I expect that the act of threading a fastener into the aluminum probably does a pretty good job of abrading the oxide and once the steel and aluminum are in solid contact I don't know whether you can reform the oxide barrier.

In my previous post I made this statement with respect to the protective coating on some of the other fasteners used on the NSX "I suspect that finish may be an anodized or similar anti corrosion protection". Although the term anodizing has been used for treatment of steel it is not the same process as used for other metals and appears to be pretty uncommon. There are a number of other anti corrosion coatings for fasteners, epoxy based finishes appearing to be fairly popular. I also opened up the service manual last night to check the references to the special bolts. Honda only uses the term "corrosion resistant bolt/nut", so those bolts may or may not be Dacrotized (which has a silver finish); but, some other non corrosion finish such as an epoxy.

You mentioned titanium bolts which I was definitely not keen about. Ti is one of the metals that will accept an anodized coating; however, it is pretty uncommon and seems to be mainly available in the high end bicycle market (small fasteners). If done well anodizing creates a durable oxide coating that might fir the corrosion resistant bolt/nut requirement. However, the only vendors that offered large anodized Ti fasteners that I spotted were from the west side of the Pacific ocean and looked dodgy.
 
Yep, spreadsheet made. amayama just invoiced me and shipping went from $50 to $140, with duty & taxes still payable! Is this their MO?

Interesting. Did you order some fairly large items that did not fit the current Japan Post shipping limits? I have been ordering packages steadily from Amayama for the last few months (last delivery was in December). All of the packages were smaller and arrived via Japan Post / EMS quickly and cheaply.

As a hint, if it is possible break the orders up in to multiple small value orders. If the declared value of the package is less than $150 - $200 Cdn, Border Services generally seems to waive the collection of taxes and any duties that might be collectable. Amayama calculates shipping by weight and as long as you remain within the size limits for the weight ranges I have not experienced a shipping cost increase because of breaking the order up into smaller shipments.

If the parts come by courier you will most likely get hit with administration and brokerage fees and collection of taxes and applicable duties. Couriers probably don't have the authority to waive the collection of taxes and duties and probably have a self interest in not waiving the taxes and duties because they then get to charge the brokerage fee which is a revenue generator for them.
 
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