Which bolts/nuts DON'T we re-use?

[goldtop]

I'm in the process of removing the ancillary devices from my spare engine + transmission. Most of the nuts and bolts are pretty rusty, although nothing has stripped nor sheared. (Yet! I still haven't tackled the exhaust manifolds...)

Given the delays/unavailability of some of these little spares, which of them can we NOT re-use?

Part of me wants to save money/time by reusing the old fixings, but part of me also thinks it's really wasteful to bin serviceable fasteners. With that thought in mind, a bonus Q: how best to clean/rust-protect these steel fasteners?

[goldtop]

As an extra bonus question (and included here, as it's part of my engine deconstruction)...

I've just about got the wiring harness off the engine. Fiddly, yes, but got there. Except... for two seized bolt+brackets, one at the front and one at the rear. The rear one is attached to the gearbox and is (I think) part 16 on this diagram:

https://www.lingshondaparts.com/partscatalog/catalog/listing/catalog/hondacars/modelid/21760/block/17SW001/blockref/E__0700/

The one at the front fixes to one of the rear timing belt cover points.

In both cases, the steel bracket holds a metal clip which encircles the harness. The clip is held by screw with nut welded to the bracket. But the bracket is too thin and flimsy to take any torque from a spanner applied to the screw.For now I've used more WD40 and am waiting to see if it will penetrate well enough.

[Old guy]

I can't think of any torque to yield bolts on the NSX engine, so I don't think any of them are designated as 'must not be re used'. There are a number of bolts on the engine that have a sealant applied to them (the coolant pump is a location that comes to mind). These bolts are called out in the service manual with a recommendation that they be replaced with new bolts. The bolts can be identified by a red coating on the threads. I expect that if you clean the sealant off the threads you can re use them following re application with a new sealant (I am sure that Henkel / Loctite / Permatex probably has some suitable product). I just ordered new from Amayama because they were fairly inexpensive (before singing the Covid shipping blues). I know that owners on NSX Prime have just reused them after cleaning.

Mechanical cleaning with a fine wire wheel is probably the safe way of removing surface corrosion from fasteners. Acid dipping is fast; but, can be problematic. Immersion in muriatic acid solutions is fast; but, can result in hydrogen embrittlement which would be a bad thing on a stressed fastener. Should be OK for things like metal clips and brackets that just hold things in place. Rust removal in a muriatic acid solution leaves the surface very active (no protective oxide coating) and it will flash rust very quickly (within hours). You need to spray with oil, paint or something almost immediately. POR 15 and others make rust removal chemicals that are phosphoric acid based and leave a zinc phosphate coating on the metal which prevents flash rusting and works as a primer for painting.

There are various cold galvanizing spray on coatings that you can apply to deter rust from reforming. Walter Zinc 100 is one of them

ZINC-100™ – Walter Surface Technologies (https://www.walter.com/products/-/producttradename/mro/corrosion-protection/zinc-100?setLocale=true)

They are semi durable. If you apply them to a bolt head and then apply a lot of torque with a wrench I expect that they will not survive that encounter. Probably fine on brackets. If you want to protect things like brackets I know people who have used the home zinc electroplating kits to get effective results on smaller pieces on classic cars. You need complete immersion in the electroplating bath which is what sets the limit on the size of the bracket.

Useless fact. Immersion in molasses will remove rust from ferrous metals if you have all the time in the world. Allow a few weeks to complete the process. The same back to the woods people who believe that apple cider vinegar is the fix for everything have adopted molasses as a rust removal tool. They purchase crude molasses which is sold in large quantities as a livestock feed supplement. Aside from being 'slow as molasses' it has the downside that it also provides an excellent food source for yeasts, molds and other unpleasant life forms. When it comes time to retrieve your de rusted parts from their molasses bath you may discover that you have hatched a bio hazard in the back corner of your garage.

[goldtop]

Hey OG - thanks, that's really useful information with a lot of promising leads to check out. I do work with a local plater for my business (tens of thousands of solder lugs at a time), so I can see if I can get mate's rates for a small batch of bits. The phosphoric acid approach looks like it's worth checking out first.

I'll leave the molasses idea. I've got a vague recollection of seeing 'miracle cure' videos on some other car forums a few years ago. :)

[Kaz-kzukNA1]

If the bolt/nut HEX is still in good shape and not something to be removed for the foreseeable future, I re-use most of them unless specified to be replaced.

For the seized bolt/nut, if it's safe to use, try 50/50 acetone/ATF mixture (thanks to the know-how by one of the member here).

Or, use Mapp, propane gas to heat it up.
Failing that, apply ice after heating it up to cause thermal shock but may require reviewing the fatigue effect on the object.

I always replace the bolts at the TB Lower and F&R mid covers at the time of Eng Refresh as they tend to get rusty by the next TB/WP service.

Be careful with the bolts around the trans/CL case.
Some of them could be oxidised and while the bolt body won't sear off, it can strip the mating thread.
Time to get helicoil, timesert (expensive), etc.

The worst case is that you may not notice the damaged thread until after starting the re-assembly process.
Always best to mark the thread and check it before re-assembly if you felt something not quite right during the removal process.

There are bolts that should be replaced and it is stated in the workshop manual.

Dacro coated ones or red sealnt/lock ones are most likely specified to be replaced with new ones.
However, some of them can be re-used after cleaning and treating them.

Still, I always recommend replacing the ones at the WP.


If you search here or on NSX Prime, there are several example of owners using the rust prevention chemical.
POR15 comes up several times.

Don't know the latest but if the noise and CO2 emission are not going to be too much of concern around your area, you can use dry ice blasting for rust removal.

I think someone on here used soda blasting during chassis rebuilding in the past.

My knowledge is very limited in this area but if you ask the professionals, I'm quite sure they can advise you on which blasting method would be suitable for your purpose.


Kaz