Warning: Cracking Frame on 818R at Track

[Mulry]

Good afternoon everybody. Wanted to pass along a warning about a non-contact frame crack on an 818R. Two weekends ago I was attending the NASA races at Motorsport Ranch in Cresson, Texas to help a buddy with his ST5 Miata. Turns out that Wade McBride had his 818R out there and was racing in ST2. We got to talking and as he was showing me around his car, he said that he had a problem with a frame crack during Friday practice but a shop at the track was able to repair it overnight by sleeving the tube with solid bar and then welding it in place. I didn't get a photo of it, but here's the location (on my chassis) where Wade described the problem:

IMG_6638.jpg

Wade said that it cracked right behind the weld at that angled joint (toward the rear of the car -- looks like the photo is getting rotated 90 CCW by the forum software) and that it was the flexing of the transmission that he thinks was responsible for causing it. Wade is not running a wing on his chassis, and didn't get hit, so there is little stress at that junction other than the transmission. We are working on a solution for our chassis to reinforce that location (the bolt in that photo is an attachment point for a wing), I'll add to this post when we have the design implemented. We think we are going to gusset the triangular area so that the weld isn't in tension and also weld some tube underneath to increase the strength of the bar overall and increase the angle of (something my mechanical engineer described but I can't remember now). But I wanted to get this warning out to other 818R builders. Cheers.

Pat