G'day, Hoping for some advice on the following.
I have SR3 chassis 981 here in Tasmania, and have found a small crack in the chassis on the left rear top shock mount. The crack has propagated from an undercut at the end of the weld, where the top shock mount is joined to the main rear chassis tube, and runs out toward a hole that is punched in the fabricated plate to reduce weight. The location of the weld (and undercut), right where the bending moment is highest on this part of the chassis, and adjacent to the nearby punched hole seems silly to me... but I guess I don't design race cars for a living....
See pictures attached below...
I intend to do a repair in that area buy removing the powder coating, tracing the crack to identify where it ends (dye penetrant test), drilling a 2mm diameter hole in that location, and then getting a TIG weld repair done to fill the hole I drill, and then running the weld back over the crack line towards the edge of that section. If I am still unsure if that will be good enough, I could get a fishplate made that would bridge the cracked area and have that tigged over that part of the chassis.
Has anyone else experienced this problem, and if so how did you approach the repair?
Finally, does anyone know what material this section of the chassis is fabricated from? I'm guessing 4130 or 4140 Chrome-Moly but I'd like to be sure so that I can get the right welding rod for the job.
Any help/advice appreciated
Rod
Hi Rod (@rjbender), cracks in this area are very common and the method you described is how I have seen them repaired in the past (strip, stop drill, weld, paint). Spring Mountain did this repair on one of my previous cars but I am not sure what welding was used.
Charley
The tubes are not 4130 or 4140, just ordinary mild steel. I use ER70S rod. You can use either ER70S-2 or ER70S-6 for the repair.
If it were my car, I'd add a fishplate reinforcement too.
Flitch plate not fish.
@levo...take your pick...??
https://en.wikipedia.org/wiki/Fishplate
https://en.wikipedia.org/wiki/Flitch_beam or https://www.structuremag.org/wp-content/uploads/2014/09/D-From-Exp-Flitch-Plates-DeStefano-pac-5-10-071.pdf
Seems that the 'Flitch Plate' is more commonly used with reference to strengthening Timber beams (using steel plates), while Fishplate derives from railway terminology for joining/strengthening steel tracks....
@parsonsj - thankyou John... that's very helpful and I appreciate your advice re the reinforcement idea too. I'll continue down that path and see where I end up.
Haha!
Fishplate is what I've always called it -- I always thought that term comes from the typical diamond shape of the reinforcing material. Had no idea of its railroad origins. I learned something today, many thanks!
Maybe both are wrong and reinforcing is the term we should use.
@levo - you may be right Paul!... ultimately doesn't matter that much as others were able to provide the help I needed. I'll use the ER70S-6 tig rods for the repair and include a 'reinforcing' plate.
