Demystifying the ARP/Nord-Lock combination

Vuk

Vuk

Daily Driver
Hi all,

In my process of entirely rebuilding my Yugo, I decided to go with ARP bolts throughout the engine and suspension and naturally I've been looking for an effective locking method. Now, the best fasteners should be combined with best lock washers, right? I've read on different forums that people have ARP bolts with Nord-Lock washers and there is even a company that sells ARP + Nord-Lock kits for car restorations.

After reading about how Nord-Lock washers work, I conducted a simple experiment to ensure the condition for their usage was met: the hardness of the mating surfaces must be lower than that of the washer. Needless to say, this immediately precludes the usage of stainless Nord-Lock washers because they are much softer, however, their steel washers are denoted as compatible with fasteners up to class 12.9. ARP bolts do have tensile strength comparable to class 12.9 bolts, but their surface hardness is incomparably higher (if you knock two bolts against each other it sounds like socket rattle).

Photos below show that everything works as intended with a class 8.8 bolt, and that happens already at 35 Nm of torque. On the other hand, the Nord-Lock washer doesn't even put a scratch in the ARP bolt flange even at 95 Nm (which is right about the maximum torque for a steel M10x1.5 fastener). ARP assembly lube was used during these tests.

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I tried to get in touch with ARP technical support asking for surface hardness specifications to verify that they indeed are higher, but they never replied to any of my emails. Their catalog only lists tensile strength.

I suppose this leaves liquid thread lockers as the best option, and I am considering using Loctite 243 throughout my build wherever split washers are originally used. As per Loctite tests, thread locker should perform better anyway. Any shared thoughts are highly appreciated!

Thanks,
Vuk
 
Kind of hard to see in the picture how you have these oriented, but with "Nord Lock" washers the "ramps" face each other and the smaller serrations face the part/bolt or nut, it looks like you have the ramps facing out.

SteveC
 
The cams are facing each other as they should and the serrations are facing outward. "NORD-LOCK" insignia can be seen on first photo (both here and in my first post). They are properly oriented.

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Vuk
 
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Question, do the Nord-Lock retainers need to impregnate the bolt head to work correctly? Or is there sufficient friction from the design to work without necessarily having to mar ("bite" into) the contact surfaces? I don't know so I'm asking for more technical clarity. The amount of torque required for the specific application should also have an effect on this. Then there is the whole subject of fastener stretch and other aspects that go into creating the clamping load.

Regardless I agree, I prefer thread lockers anyway. But it can get a little complex. For example choosing the correct formula when using dissimilar metals, or when a thread sealant is needed, or if a thread lubricant is required. However there are a wide array of formulations for pretty much every need.

On a side note. I'm not really a big fan of ARP in general. From the research I've done I have the impression there is a lot of "marketing" that has made their products so popular, and not necessarily the level of quality. Having met the owner/originator of the company I wasn't impressed there either. Besides, in most cases that level of fastener is complete overkill anyway. Furthermore there are much more affordable alternatives with the same results. Just my opinion.
 
According to Nord-Lock technical specifications, yes, it is required that the washer "bites" into both surfaces, hence the requirement for surface hardness. I agree some time must be spent in reading technical documentation for thread lockers as the bolt material and particular application do make a difference. Good thing is, like you said, there are quite a few products to choose from.

I don't have much experience with ARP but just wanted a clean, unified look for a restoration of a lifetime - hopefully that gets me no bolt replacements in the future because the price point is quite high. I did notice that no matter how strong these bolts are, thread galling occurs very easily if one is not particularly careful during installation.

Thank you for chiming in!
Vuk
 
Henkel (LocTite) has some good technical materials that outline their threadlocker products and specific applications. Even if you don't choose their brand of products the reference materials are helpful to determine what type is best for each application. And their technical support people are more friendly/helpful than most. That's something I find increasingly rare these days. I see you are in Oregon, so I believe you are covered by the same regional representative as I am. I can send you his contact info if you like.
 
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I appreciate it! I actually already went though that process and found a couple of products that work for my applications. Like you said, local parts store may not hold Loctite but other products (like Permatex), however they will always have a cross-reference chart.

Thank you!
Vuk
 
By the way, good to know about the Nord-Lock / ARP combo. I'd never considered it but it makes sense that the retaining force is from the ridges biting into the fastener. Like how a traditional split washer will tear up the heads of normal grade bolts. I've read mixed information on this whole subject (fastener retention in general). And various product makers offer their own explanations, obviously supporting their products over all other choices.

I have to say between using all ARP hardware and Nord-Lock washers there would be more investment in just these than my entire car. :p But it sounds like you are doing a stellar restoration. Have we seen any write-ups on what you are doing?
 
Hi Vuk,
Have you had bad experiences with failling fasteners on Fiats?
I haven‘t and haven‘t read about this problem here.
The exception being cambox bolts, maybe.

How about using stock fasteners with NL washers?
 
I am indeed trying to redo the entire Yugo to the last bolt because I want my restoration to last many years and not just for chassis/engine, but throughout. I suppose I just don't have enough time to really document the whole thing on xWeb, but I am taking photos during the process. I'll post my suspension/brakes setup when I have everything squared away.

Nothing wrong with stock fasteners, really, (foundries for Yugo fasteners are different from the ones used on Fiats but regardless, no issues there), only they are not as pretty as stainless (especially as they age). Stock fasteners should work perfectly fine with NL washers, although I haven't even had any experiences of split washers going undone. However, I do know that split washers don't always cut it for lowered/stiffened suspensions and track use (from people who drive such Yugos).
 
I like to use stainless fasteners, especially button or socket head, around the engine bay. But just for the 'look'.
 
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I would like to extend my original post with some additional findings. These somewhat modulate my previous conclusions, but limitations still apply.

I never received the reply from ARP regarding surface hardness specifications. Regardless, since Nord-Lock stainless steel washers have higher surface hardness than their regular steel washers, I decided to put them to test. Notice that in the first post I stated that stainless steel Nord-Lock washers are softer and shouldn't be used in applications that require 8.8/10.9/12.9 fasteners. This still holds: stainless Nord-Lock washers are only surface hardened but have a softer core. Therefore, in the following tests, I will violate Nord-Lock recommendations that stainless steel washers are to be used with bolt grades up to A4-80 which ARP fasteners exceed in terms of tensile strength. I'll get back to this point later.

Here I am showing the same test as above, with applied torque of 95 Nm on an M10x1.5 bolt (I am using a new bolt and washer every time). Impressions on ARP fastener are visible, proving that stainless Nord-Lock washers indeed work. Additionally, during disassembly, sliding occurs between cam faces, clearly indicating intended lock washer operation.
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So where is the problem? Back to Nord-Lock specifications stating that stainless steel washers should be used with stainless bolt grades up to A4-80. A4-80 typically have tensile strength just around (or slightly under) class 8.8 fasteners, so we could say this is not an issue because most of our applications are fine with class 8.8 hardware. The issue for me is that, going through Yugo torque specs, most M10 hardware on the suspension is in the 25 - 50 Nm range (with some outliers above 50 Nm). Below I am showing a close-up of the fastener head contact surface for torque settings of 50 Nm and 25 Nm, Notice that the impressions of the washer are weak (especially for 25 Nm) which indicates effectiveness of the lock washer is arguably reduced. Even in the 95 Nm case, the impressions are not nearly as deep as in the case of a steel class 8.8 bolt (see my first post). It is worth noting that Nord-Lock provides a table with recommended torque settings, and they state 62 Nm for lubricated M10x1.5 fastening.

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Everyone can draw out their own conclusion, but I will just emphasize that some study of the application and requirements is needed, and the combination of ARP fasteners and Nord-Lock washers appears to not always be applicable. In my opinion, ARP stainless steel fasteners have just a bit too high surface hardness. I will also note that I have tested Nord-Lock "254 SMO" stainless washers, while a special purpose "INCONEL 718" version offers slightly higher surface hardness which may or may not make a difference with ARP fasteners.

Thank you all!
Vuk
 
Great testing once again, thanks for sharing. 🌟

Regarding stainless fasteners in general. Often it is believed that due to it being more expensive and more corrosion resilient, then they are a superior fastener. Naturally there are a wide range of qualities and alloy mixtures of SS out there. Some are rather weak, even well below a standard grade 5. The difficulty in many cases is not knowing what level of SS fastener you are getting (aside from some name brands, etc). So when it comes to something critical such as a safety item (e.g. suspension, brakes, steering, seatbelts, etc), I do not use a stainless fastener. But I also believe that many times there is a tendency to "over grade" (use much higher than necessary) hardware, so SS is fine for most applications. To be clear I'm not implying that any of this pertains to your intended uses; I simply wanted to make a point to go along with what you are finding in your excellent tests. ;)
 
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Absolutely agreed! Every application has specific requirements, and fastener specifications must be observed. I was just trying to get to the bottom of the whole ARP&Nord-Lock combination as there is not enough quantifiable information out there.
 
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