Nuts & bolts 101

[xb-60]

Originally Posted by CompClassics

xb-60,

I believe that you meant to say that a bolts thread should never be subjected to a shear load under torque?

Both the shaft of the bolt and definitely the thread of the bolt should never be subjected to shear in a torque transmission situation. The bolts should be torqued up correctly so that the torque that the shaft/coupling is transmitting is only transmitted via the friction between the two mating surfaces of the flanges. In this situation, the bolts should always be in tension, never in shear. This is achieved by having a correctly designed coupling ie with correct number/size/grade of bolts, with correct nuts (non-nyloc) and correct washers (non-spring).....all to suit the torque rating of the coupling.

Cheers,
Glen

[CompClassics]

I pretty sure he's talking about these spring washers.......

[CompClassics]

This is how they were being used....

[CompClassics]

So I was nearly complete with this build went to prime the engines oiling system. I started priming the oil system when I went to look at the oil pressure gauges readings to see if oil was moving through the system I noticed a substantial amount of oil puddling on the Cobras carpet, WTH! I found that during the Cobras assembly someone had used a non-AN fitting to attach the hose to the oil pressure gauge! The hose fitting had bottomed on the limited amount of threads on the adapter fitting and not allowed the rest of the fitting to seat as it should have if the correct fitting was used. This is going to prompt me to start another thread on plumbing! Please, do not go down to your local Home Depot and expect to find AN fittings for your Cobra!

BY THE WAY WHEN I TALKED TO THE PRESIDENT OF THE MANUFACTURER THAT BUILT THE COBRA I WAS TOLD I DO NOT KNOW WHAT I AM DOING AND THAT HIS INSTALLER HAS DONE HUNDREDS OF THESE COBRAS.................

[1795]

Nothing that a grinder, hacksaw and some JB Weld can't fix

[CompClassics]

I'm almost of the opinion that people that undertake these projects, because of the personal safety aspect, have some sort of verifiabe certification in order for the vehicle to be licensed for street use. I HATE ANY KIND OF GOVERNING OR RED TAPE ESPECIALLY WHEN IT COMES TO HOBBIES. I keep useful resources close by if I have any questions, just some of my reading material......

[CompClassics]

I am revisiting this post as a new client just recently brought in his 600+HP 4000 CSX Continuation Cobra for a check up and have some routine maintenance performed. While inspecting the Cobra I found the same issue as the Cobra from the original posting, inferior hardware and the lack of understanding the proper use of fasteners in the first place. All of the inboard half shaft fasteners were loose. I am beginning to think that maybe people assembling these cars and the performance potential of these cars should require some kind of competency certification similar to an aircraft AP license, there's just to much at risk when these cars are unleashed and something goes wrong. Home many here have seen the carnage after a half shaft fails?
Here are some photos from the current Cobras previous assembly methods and the corrections taken. Please remember that when using any fastener that you should have at least three complete threads protruding from the assembly after fastening.

[Gaz64]

Originally Posted by CompClassics

I'm almost of the opinion that people that undertake these projects, because of the personal safety aspect, have some sort of verifiabe certification in order for the vehicle to be licensed for street use. I HATE ANY KIND OF GOVERNING OR RED TAPE ESPECIALLY WHEN IT COMES TO HOBBIES. I keep useful resources close by if I have any questions, just some of my reading material......

Fully agree.

1st qualification is becoming a Motor Mechanic.

[Mark IV]

We see many people have a complete lack of understanding of "thread length vs. grip length". While the local hardware store is handy, they likely do not have the proper grip length available in the size/strength needed for applications such as halfshafts, etc. We have I.D.' the needed hardware and carry an inventory from Aircraft Spruce for our internal needs. The AN screws and nuts (and a 'bolt' is a 'screw' until a nut is installed....) are also less expensive than the local ironmonger's pricing. The AN washers are also far superior to the thicker, softer washers from the hardware assortment.

[LMH]

Is there an issue with cutting excess threads off of a bolt that’s too long?
Grip length is correct, just too long on the thread length.
Larry

[CompClassics]

Mark IV,

Your post couldn't be more true about the AN hardware.
We had a local Tiger owner stop by that had fully restored the car himself. Mind you this owner had taken the car down to a bare steel tub and corrected everything that was wrong with the car while returning the car to an operational car again. He stopped by to show me the completed car and all the work he had done and everywhere I looked there were new grade 8 fasteners in place of the original hardware. When I asked him why he had replaced the hardware his response nearly floored me, "you can buy this stuff by the pound". Here's someone that took the time to, completely strip the car down to metal, refinish all the wood accents, have the drivetrain rebuilt, etc, etc, etc.

LMH,

There is no real issue with removing the length of a bolt as long as the process does not heat the material significantly.

As per my posting of the CSX Continuation Cobras it looks like a pattern that is taking place during a subcontractors installation of components while turning the car into a "roller".

[patrickt]

There's a ton of guys out there that know there's a difference between grade 5 and grade 8 bolts, but have no idea what an aircraft spec bolt is, what the different letters/numbers mean, much less why they should be on your car. Here is the simplest two page summary that I have ever come across that explains the difference between the different specs (airframe bolts, close tolerance bolts, NAS 624/MS 21250: etc.): http://www.coastfab.com/uploads/4/1/...s_general1.pdf

[Cobra #3170]

I use proper air craft grade bolts and nuts on my half shafts and have found that they do not maintain torque. I have to change them a couple of times a year. I think they may be stretching under the torque load. I did not have this problem when the car had lower power levels in the 1960's through 1990's.

[patrickt]

Originally Posted by Cobra #3170

I use proper air craft grade bolts and nuts on my half shafts and have found that they do not maintain torque. I have to change them a couple of times a year. I think they may be stretching under the torque load. I did not have this problem when the car had lower power levels in the 1960's through 1990's.

Now, this is an area that is just slightly beyond my expertise, but you might consider going with a NAS 624/MS 21250 Series bolt (as per that two page PDF I just posted).

[Cobra #3170]

Originally Posted by patrickt

Now, this is an area that is just slightly beyond my expertise, but you might consider going with a NAS 624/MS 21250 Series bolt (as per that two page PDF I just posted).

Certainly worth a try, I don't look forward to changing out those 16 fasteners every 4 months during the season. Thanks for the suggestion! I had a problem with steering arm bolts failing (Grade 8 from Air Craft Spruce) and switched to aerospace grade 160,000 psi bolts and it solved the problem, might work with halfshaft too.

[Morris]

Originally Posted by Cobra #3170

I use proper air craft grade bolts and nuts on my half shafts and have found that they do not maintain torque. I have to change them a couple of times a year. I think they may be stretching under the torque load. I did not have this problem when the car had lower power levels in the 1960's through 1990's.

Bruce

Are you using Jet Nuts on the AN-bolts on the half shafts......

We had that same issue on the GT-1 with the 930 CV Joints....switched to Jet nuts and Red 271 Loctite ....and it worked.

[Morris]

This is the bolt we went to

NAS 624/MS 21250 SERIES: 12 POINT EXTERNAL WRENCHING BOLTS
These fine-threaded, twelve-point head bolts have a minimum tensile strength of 180,000 psi and a minimum shear strength of 108,000 psi. Thread length is consistent within each diameter and standard grips are in 1/8” increments beginning at 1/8”. These bolts also have a large radius between the bolt head and shank for additional strength. This requires the use of the MS 20002C series beveled washer under the head. A “Superbolt” for the most demanding applications. Please note that odd number grips, i.e. –15, –23, etc., are not standard and may not always be available. Please inquire for specifics.

[patrickt]

Originally Posted by Morris

This is the bolt we went to ...

… alright, I'm now adding "Nuts & Bolts" as one of my official areas of expertise.

[Cobra #3170]

Originally Posted by Morris

This is the bolt we went to

NAS 624/MS 21250 SERIES: 12 POINT EXTERNAL WRENCHING BOLTS
These fine-threaded, twelve-point head bolts have a minimum tensile strength of 180,000 psi and a minimum shear strength of 108,000 psi. Thread length is consistent within each diameter and standard grips are in 1/8” increments beginning at 1/8”. These bolts also have a large radius between the bolt head and shank for additional strength. This requires the use of the MS 20002C series beveled washer under the head. A “Superbolt” for the most demanding applications. Please note that odd number grips, i.e. –15, –23, etc., are not standard and may not always be available. Please inquire for specifics.

Thanks Morris,
Using jet nuts but bolts are inferior to what you are using. Do you have a suggested source for the bolts and washers?

[CompClassics]

FYI,

Coast Fabrication was just bought out by a UK based company called Clarendon.