Reuse factory nylon nut with loctitre or new thinner nylon nut... - Alfa Romeo Bulletin Board & Forums

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Old 06-06-2012, 04:00 PM
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Reuse factory nylon nut with loctitre or new thinner nylon nut...

I have a dilemma here right now...

I am in the process of putting my front suspension back together and I have bought all new nylon nuts to replace all the old nylon nuts.

However, I found out some of the nylon nuts from factory are a tad thicker than the one I can get new now (can't buy the thicker one), most of them have about 25% more usable thread on them.

Here are my thoughts -

The old nylon nuts are way pass their life (40 year old) and they are rusted, brittle and it's kinda unsafe to reuse them even though I would put loctite on them to replace the function of the nylon part.

The new nuts are thinner, but they are newer, manufactured hopefully with better/newer material and probably can withstand the same amount of force like the older thicker one do.

But I am not sure if my thinking is right regarding the strength. I would assume since the nuts are 8.8 rated, it should be designed to match the strength of the 8.8 bolt (even with fewer thread). So thinner or thicker nut won't matter since when it get past the breaking point, the bolt will break apart or strip anyway.

So, please help me with what I should do.


Reuse old thicker nuts (+ loctite) or just use the newer thinner one.


Thanks.
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Old 06-06-2012, 08:55 PM
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New nuts. I don't like to reuse nylocks even if they are new and used but once.

Robert
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Old 06-07-2012, 10:56 AM
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use washers?
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Old 06-07-2012, 12:32 PM
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It is the number of threads that matters. The first thread takes the most load and subsequent threads take less load.

The first 3 threads will take about 75% of the load alone. At 6 threads it is taking all the load.
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Old 06-07-2012, 01:36 PM
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Quote:
Originally Posted by alfa_chan View Post
The old nylon nuts are way pass their life (40 year old) and they are rusted, brittle and it's kinda unsafe to reuse them even though I would put loctite on them to replace the function of the nylon part.
I agree with others that newer is probably better. I'm sure the old nuts are rusted, and their nylon has lost its ability to lock. But, why do you say the old nuts are "brittle"? Steel doesn't go brittle with age - if it does, you should be concerned about ALL of the steel components in your 40-year old Alfa!

Quote:
But I am not sure if my thinking is right regarding the strength. I would assume since the nuts are 8.8 rated, it should be designed to match the strength of the 8.8 bolt (even with fewer thread). So thinner or thicker nut won't matter since when it get past the breaking point, the bolt will break apart or strip anyway.
How do you know what grade the old nuts were made to (e.g., 8.8) ?

I agree that the new nuts are probably made from higher-strength steel, and as such would have more load capacity than older, thicker nuts made from softer steel. But, I'm not sure how you would verify this.

Bottom line: I'd install the new nuts, torque them properly, and move on.
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Old 06-07-2012, 05:04 PM
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Quote:
Originally Posted by Alfajay
How do you know what grade the old nuts were made to (e.g., 8.8) ?

Bottom line: I'd install the new nuts, torque them properly, and move on.
Agree. New nuts that is (I always use new bolts if possible).

The old Alfa bolts say 8.8 on the head, so I assume the nuts are 8.8 too.
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Old 06-07-2012, 05:04 PM
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Quote:
Originally Posted by caliscouser View Post
It is the number of threads that matters. The first thread takes the most load and subsequent threads take less load.

The first 3 threads will take about 75% of the load alone. At 6 threads it is taking all the load.
Great information. Thanks.
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Old 06-07-2012, 06:02 PM
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Hmmm. I feel like a salmon swimmimg upstream sometimes...

When I strip a car I take every nut, bolt and washer and have them zinc plated. Greasy, grimy, rusty parts go in, shiny, clean parts come out. I then inspect them carefully. The interesting thing is that the nyloc nuts come out looking new, including the nylon. Now I realize that it's not about looks but I have used lots of these fasteners for years without a problem. (I do cheat and use lock tight). If you think about it, in most cases these fasteners are static and far stronger than the components they are holding together. (I'm speaking specifically of the suspension items.). I really think that Alfa over designed this area for the small, lightweight cars they are used in. My point is that the fasteners are called on to perform at a fraction of their ultimate strenghth.

What really wears on these fasteners is when they are spun on and off multiple times. But unless you are dealing with a previously restored car or a race car chances are they've only been spun on once forty years ago.

I never reuse a nut or bolt (btw, never lock washers) that is stripped, galled, rusted more than light pitting, stretched or otherwise distorted . But I find surprisingly few like that. We also find very few fasteners that are rusted tight and cannot be removed without breaking or stripping. I'm not bashing american cars but if you've ever stripped a '69 Mustang you know the
difference. Alfa must have specified a superior fastener.

Which brings me to my final point: I don't think much of today's fasteners. Newer technology and materials in this case means cheaper and weaker. Just as noted, trying to find a nyloc of similar dimension these days is futile.

So I guess I'm saying if your fasteners are beat up throw them out. But i would not just throw them out because they're old. Many old nuts still have a lot of life left... If you know what I mean.
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Old 06-07-2012, 06:45 PM
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I make the call based on each specific fastener and use. I believe that some old fasteners are fine to re-use (been doing it for years without issue) but sometimes I just don't like the look of them. There are many factors including type of load, vibration, cost of failure, service temperature and chemicals. Some new fasteners are cheaper but many are better. Unless you are racing and are on the edge of the strength of the fastener and with the advances in ways to keep nuts from backing off it seems like there are more options. Call them as you see each individual case!
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Old 06-07-2012, 09:22 PM
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Most nuts, bolts, and washers are available in a variety of grades. For all of the smaller ones on my Alfa, I just buy a few boxes of them brand new. Any nut that has been torqued has the threads deformed slightly. New 8.8 and 10.9 grade fasteners are cheaper than any of my local platers would charge to renew used ones.

You do have to avoid most home-store fasteners. Threads are made in a variety of depths, and common fasteners found at these places are often only 70% - makes them easy to put on, and the wide tolerance makes them cheap to make. But the higher graded nuts are 80%+ thread engagement.

NASCAR teams and some of the big race teams use 90 - 95% thread fasteners. Very expensive (the bolt threads must match the nuts), but they can be used safely with no locktite, allowing them to be removed in the middle of a race.

Robert
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Old 06-17-2012, 05:58 PM
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So would any fastener specialist store be able to provide the type of nuts/bolts we require or is that a standard that is no longer adhered to and therefore NLA over the counter ?
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Old 06-17-2012, 10:02 PM
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Quote:
Originally Posted by Alfajay View Post
... why do you say the old nuts are "brittle"? Steel doesn't go brittle with age...
Actually, steel goes soft with age. The crystal structure grows slowly with time, softening the austempered internal structures, or the work-hardened surface structures. Old bolts, especially, will tend to stretch when torqued to spec, which will indicate a part that needs to be replaced. Nuts are similar but less sensitive - it's almost always the bolt that fails at a thread root near the edge of the nut. It's that elongation failure that is often called "going brittle".

Robert
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Old 06-18-2012, 12:08 AM
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Robert, you sound like you know about metallurgy. I have read in the past that you need to 'de-embrittle' replated fasteners by baking them in an oven for a couple of hours. Is this correct?
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Old 06-18-2012, 08:19 AM
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Electroplating does not change the grain structure of the underlying metal. What does happen is called "hydrogen embrittlement". If the plating current is a bit too high, you generate hydrogen gas on the plating surface - bubbles in the plating process. Atomic hydrogen gets into the microstructure of the metal (it's a tiny molecule) and reduces the bonds in the grain boundaries, which can weaken the structure - a bit like rusting or oxidizing, only deeper and with no visible effect ( there are other effects too).

Generally baking in any oven available to us mortals has no affect on metal structures - it can barely get to 500F. But the temps of an oven can help drive out the residual hydrogen gas. It's just a shallow surface effect, so it doesn't take much in temperature or time. Also, an hour at 500 won't cause any harm. However, don't use your kitchen oven - other gasses, including cyanide, are involved and can be harmful. A welding torch can do fine - just keep away from the 'bright orange' heat to stay well below 1000F. A simple toaster oven is OK, but just barely at 450 to 500F.

SAE AMS 2759/9 Section 3.3.3.1 calls out the correct procedure for eliminating entrapped hydrogen. It should be done within 4 hours of plating to minimize the formation of molecular hydrogen - H2 - which is a much bigger molecule and harder to get out.

BTW - this happens with arc welding too. Post-heating welds will drive out the hydrogen.

Robert

Good question!
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Old 06-18-2012, 09:29 AM
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Superb detail, thanks Robert. I guess this is a far more important consideration for fasteners used in key structural applications. This particular topic really ought to be a 'sticky'. I only learnt about this phenomenon on the Yahoo 750/101 group some years ago, and I have barely seen it mentioned since then.

Now, how to persuade my electroplater to call me within the hour so I can get my fasteners in the oven within that four-hour period!

Thanks again,

Alex.
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