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TR4/4A Grade 9 bolts

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Rut

Rut

Obi Wan
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Reading your article...it sounds like they are not recommended to me.

I investigated a jet engine failure many years ago. The engine specialist, rather than unscrew the 2,000 little bolts around the compressor and turbine sections, simply started whacking them with a hammer. One hit each is all it took! When I asked him about it, he said they were grade 12 or some such. The point being, they were extremely strong, but they had no ductility at all. When it comes to metal, to get more strength, you pay with brittleness and less corrosion resistance.

In short...you don’t need grade 9 to assemble a 50 year old car!
 
When it comes to Grade 9 and to a somewhat lesser extent Grade 8 for our cars, I'm more of the "just say no" position for the application. Note some of the things mentioned in the Fastenal stuff linked. The big deal to me is the loss in ductility which is the loss in elongation between the yield point and the fracture point, the bit about hydrogen embrittlement and increased susceptibility to fatigue failure are just the icing on the cake. For the most part that is the nature of high strength metals, as static strength goes up, elongation and fracture toughness goes down. I spent many a year dealing with materials professionally and lots of that was fastener related. If you want to do anything "special" with respect to fasteners, I would suggest that you use AN/MS/NAS hardware for most of your Triumph needs. Your basic AN stuff offers grip lengths in 1/8" increments as well as standard and thin washers so that you can adjust the grip length even further to make sure that you keep the threads out of any shear loads in shear type joints such as suspension pivots. Strength is between that of your Grade 5 and Grade 8 SAE fasteners. With much of the MS/NAS hardware, you get into more fasteners that are in the Grade 8 strength range and with several, you can get into grips that in 1/16" increments. Prices for AN hardware aren't all that bad. I can buy AN hardware from Aircraft Spruce for about the same price as getting SAE stuff (most grip length and fastener length increments there are 1/4" steps) from one of the local fastener places. Aircraft Spruce has a more limited selection of MS/NAS stuff, try Pegasus Racing and Coast Fabrication for a better selection of MS/NAS stuff, just expect to pay more for that type of stuff relative to the more readily available AN hardware.
 
Thanks for the replies and the reason for this post is twofold: 1, the specs on grade 9 and ARP fasteners are similar and the reduced amount of stretch at the same torque is appealing to me. The downsides when used in applications where grade 5 and 8 were used are few as far as these cars are concerned, imho. 2, Fastenal has them on sale in fine thread and I’ve been buying 1/4 thru 3/8 in a variety of lengths for $4-$6 a box. In a critical application I use what’s susposed to be used, but where grade 2 imported stuff is your only choice at the big box stores I like the grade 9...stronger and cheaper.
Thanks, Rut
 
Hmmm.

You also have to understand "stretch" with a fastener. Stretch is what provides the tension in the finished assembly to hold the bolt in place. Aircraft fasteners are very high grade, and therefor have little stretch when installed. To keep them from loosening and falling out, they are normally safety wired. If yoou do not have sufficient stretch, then you have to provide alternate means to retain the bolt, like a lock tab or safety wire.
 
CJD said:
Hmmm.

You also have to understand "stretch" with a fastener. Stretch is what provides the tension in the finished assembly to hold the bolt in place. Aircraft fasteners are very high grade, and therefor have little stretch when installed. To keep them from loosening and falling out, they are normally safety wired. If yoou do not have sufficient stretch, then you have to provide alternate means to retain the bolt, like a lock tab or safety wire.
Click to expand...

Actually the majority of fasteners used on aircraft have decent elongation. There are some specified applications where this is not the case and there have been other cases where a fastener was specified initially and for lack of a better term, a "recall" was issued to remove and replace the fasteners with something that had better elongation, better resistance to embrittlement, better resistance to stress corrosion cracking, etc. If we look at fasteners made from H11 steel as an example, they are not allowed for new designs where the government is the customer or has a high potential of being a customer as a result of problems that cropped up in service with those fasteners.

As for safety wire, that is another area where you see much less use, especially on combat aircraft, since there is a possibility of chem/bio agent use and ground support personnel in either encapsulated suits or even a basic Tyvek "bunny suit" can snag the suit on safety wire, tear it and be exposed. That's what thread locking compounds are all about along with torque stripes.
 
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