Hey folks, Our catalytic converter got stolen, again. First time we had a local shop install an OEM replacement, but this time I decided to DIY a Walker 16337 to save some $$$. Unfortunately, I ran into a couple hiccups and now have a slight leak at the exhaust flange. Looking for advice on how to proceed from here... The first issue was that one of the two nuts welded to the back of the exhaust flange was already stripped. So on that side I ran a 5/16 class 8 bolt through the stripped nut (M10 x 1.25), and placed a 5/16 nut and lock washer behind the factory nut. Unfortunately the only 5/16 bolt I had to hand wasn't fully threaded, and I ran out of threads before reaching the recommended torque (32 ft-lbs). The second issue was that I think I felt the nut on the *other* side strip as I was torquing up the regular spring bolt. I stopped turning when I thought I felt it slip because I didn't want to strip it completely. While the situation is better, there is now a small leak at the exhaust flange. I think it's most likely because of the above two issues. I did use the Toyota gasket as recommended in other threads. Although I didn't have enough access to wire brush the flange before fitting the new donut. Is that another possible cause? The most obvious next step is to replace both bolts with two fully threaded 5/16 bolts, which should let me snug up the joint fully. Though I'm not sure if there's enough clearance to place a second nut behind the factory nut on both sides of the flange. Has anyone else been down this path?
Seems to me to be quicker just to swap out the exhaust manifold to be honest about it it just seems like that would be the way to go
@Tombukt2 hmm, replacing the manifold sounds like a bigger job. Does it require a car lift or high jackstands? I only have a 1.5T jack so getting the car more than 12" can be tricky. Do you think just using narrower bolts that fit through the stripped ones would work?
I know, it seems like such a basic problem to solve. I added as many washers as would fit, the problem is that the spring compresses by about an inch, so you really need longer thread on the bolt. I was using a regular class 8 bolt which only has about an inch of thread. A trick I read about on the forums this morning, is to compress the spring in a pliers or vice, and zip-tie it off, so that you're not fighting the spring to get the threads started (and in my case wouldn't need as much thread on the bolt). Then cut the zip ties once the bolt is started (or leave them to melt off)
There are some issues with putting washers under a nut when tightening it https://www.boltscience.com/pages/why-use-washers.pdf In some cases these washer related issues don't matter, not sure this is one of those cases though. I would suggest just getting better bolts and doing that part again. It shouldn't hurt anything to have a small exhaust leak for a couple of days, at least as long as the car is not parked and idling.
You can cut off the weld on nuts. Or source the proper length bolts. I have eliminated the spring clamp and hard bolted two flanges together but the stress on the flanges can make matters worse. But for this it seems getting a proper length bolt will be all you need.
I don't know man it just seems like with broken studs and stuff like that I'm not one to just stick bolts down holes and put a nut on them generally speaking to me with my extension and my flex socket that manifold comes off pretty easily he's like five bolts not screws whatever and then that whole manifold comes off right at the place it's broken for you the new manifold you'll bolt up has stud sticking out of it already you might clean them up with the thread chasing tool make them nice lubricate them whatever it is you do and maybe not get them broken again I guess some criminals did that better parking I don't know the answer not sure move to the country. But just for me they're laying here so I have them another point I guess then when I put all this back you see that big ugly heat shield and all that mess that's in the way that silver thing I am bolt that put it on a stack of other ones in the carport Bolt the manifold up now it looks like an old header bolted to the side of the big V8 engine that half the engine is missing when it's sitting in the Prius if you get the joke and then if you have to work on it again that heat shield is not in your way and all of that no nothing is going to burn up the heat shield is just there to irritate you when it gets half removed by rust and starts rattling
Thanks all for the replies. @MCCOHENS a little tricky to grind off the nuts as the exhaust flange is formed with a lip on the back to give it greater stiffness, that and the mounting points for the manifold itself kinda obstructs access (photo) Another thought I had was to use a helicoil. Anyone successfully used those in a stripped welded nut?
