What scares unbelievers most about your FED?

[janjon]

And I think the $5000 part of that post was obscene as well. Can we edit that down somewhat? It's a little too close to the truth for me... Can we get these darn costs down???

[Dave Koehler]

CHRISMAN had a rear end break loose on him and resulted in very serious groin injurys. build it to stringent SFI or better spec's and inspect all tubes/welds after each weekend racing in especially critical areas. be safe and have fun.
bob

Hi,
New guy here. Just tripped over the place. This thread got me to thinking about an old friend and Bob's post triggered it.
This is meant to be a teaching moment so bear with me.

In the early 70s as a pup I raced a Jr Fuel car. The real version with 97% nitro. There were a lot of them back then with circuits everywhere. A friend of mine managed to lose his life in a grisly way to a rear end and it was senseless. There was a line of thinking that "light is right". This is cool as long as it doesn't become unsafe.

This took place at Motion Raceway in Assumption IL. We were running with the TF class. Yup, weekly TF shows were the norm then and we could run with them and win also but that's another story.
My friend was making his pass as I was sitting on the roller starters waiting my turn. I heard the car leave, the rpm climb, he pedaled then silence, then more rpm, more silence, etc. It was obvious something was wrong and then I heard a crash. My crew guy who was watching down track dropped his head, turned and signaled me to call it a day. This is not good he said.

The rear end had broken loose from the mounts and had rotated in the car over and over. I leave the image to your mind as to what took place.
Let's put it this way, this was a unique event for all concerned and afterwards the teams were in the tower deciding whether to go on or not. They did, I didn't as I was just too bummed out. While we were in the tower we all could see this wide swath of blood going down the center of the track. The track owner quietly said to me he wasn't sure how he was going to clean that up. Oddly enough a few minutes later a pop up rain storm rolled through followed by intense sunlight and the problem was solved. Come to your own conclusions on that.
 Another friend that was the track go to guy and EMT was just a year back from Nam in country. He was the one that had to do the extraction and had that "look". He never went to a race track again.

End game: Remember I mentioned "light is right"? Let me add that "cheap is deep".
Well, what happened here is that the rear end was held in with not enough 3/8" bolts and the above go to guy found some of them later. Off the shelf stuff. When he lifted and got bite again the bolts gave up. That's all it took.

Now, the teaching moment and Roo will likely concur. We have pretty stiff rules for rear end mounting in place for this today but I don't think they mention the type of bolt used. You first thought is grade 8 right? Ok as far as it goes but not any old grade 8 will do. You need the NAS type bolts like the airplane guys use. These bolts come with different length shanks and short threads on the end. The rear end mounting must have a the shank portion engaging both the rear end and the mount. IF a threaded section of the bolt is in contact with the metal it will move and eventually give up. Those of you building your own cars will also want to make the holes a just fit, precision fit. A gnarly drill bit won't do. Also, no kidding, check the torque on these as part of your weekly maintenance program. Might even want to replace them on some kind of schedule. A double shear design is a good thing also.
 Roo likely has these bolts on hand or maybe something even better.
I don't need to lose any more friends to stupidity.
Thus ends today's life lesson.

[masracingtd1167]

Dave Very interesting and scary story . Some times we complain when NHRA comes out with a new rule or regulation and then you remember some of the guy's that lost there lifes because of these things . I guess we need to save our self's from our self's some times . Thank's for the tip about the bolts 

[rooman]

If you use fully threaded bolts (and some so called professional shop do just that) the only thing that is really holding the rear end tightly in place is the torque on the bolts and if that falls off even slightly then the threaded portion of the bolts starts to "machine" the holes out, or the threaded portion of the bolts starts to wear away as there is very little surface area to fill the holes in the brackets. Either way the fit gets sloppy. Strictly speaking "Grade 8" bolts are not the best as they can be a little brittle. Allen bolts/ socket head cap screws are in the same category--not good for shock loads. As Dave K mentioned the best solution is to use NAS bolts. They are expensive but they are also the best quality bolts that are readily available. An cheaper alternative is to use Grade 5 bolts  by getting longer bolts with shanks and then cutting the thread portion down until there is just enough to suit the nut thickness. You may have to add bosses to the brackets to take up the shank length but that is a good idea anyway as it beefs up the bracket in a critical area. I use fine thread bolts in all applications except for tapped holes in castings and either jet/K nuts (reduced hex size) or nylocs. Coarse threads and split lock washers are for tractors and other farm machinery (and NASCAR where they call them fast bolts because the come apart quicker. Stay away from stainless bolts as they are usually soft and the threads gall very easily.

Roo

[cdafoe]

Roo:  Do you have a preferred supplier for NAS bolts/nuts?  Seems like there is a million different types if those bolts, and many of the suppliers don't explain the sizing of them very well.

Thanks
Chris

[rooman]

Roo:  Do you have a preferred supplier for NAS bolts/nuts?  Seems like there is a million different types if those bolts, and many of the suppliers don't explain the sizing of them very well.

Thanks
Chris

I usually get mine from MPH who are right down the street from Indianapolis Raceway Park --317 858 9500-- but most good aircraft parts suppliers have them---ECAS, Aircraft Spruce and Wicks are probably the best. The diameter is called out in dash (-)numbers just like AN lines. Each number is 1/16" so a 3/8" bolt is a -6, 1/2" is -8 etc. The length is measured the same way but does not include the thread--in other words a -32 bolt has a 2" grip length plus the thread which comes in short and long versions as well as drilled, undrilled etc.

Roo