When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Torque specs from exhaust manifold to stock muffle
A few years back I purchased and installed a high flow cat replacement. A few thousand miles later it started getting very loud. I could feel hot air coming out the front and back the the heat shield. I took it out and did a leak test by bolting plywood to the front and read and then blowing in compressed air. It whistled real high. Image attached of failed unit.
I saved all the previous original parts. My two mono cats are hollowed out and the main has been welded to fix leaks at the two front corners. It is all assembled right now and ready to install.
Search as I will, I cannot find a torque spec for the front mono cat to the exhaust manifold.
Any response would be welcomed.
i've never really used torque specs of the bolts on the exhaust, just tighten them up. it's more of the flatness of the mating surfaces of the flanges. they tend to warp slightly when welded up. a block of wood with sand paper attached usually fixes those gasket leaks.
Thanks Michael.
With compressed air, and all holes plugged up, the main cat to the long pipe was leaking. I just finished sanding the cat surface with 220 down to 800. I'll test later.
I thought getting the studs out would be a pain, but some PB Blaster and out they came.
don't really need to go that fine on grit. no need for polish smooth, just flat. 150 would probably be just fine. the discoloration on the flange in the pic is a low spot. new gasket gives false hope as it WILL start leaking over time....regardless of torque applied.
Thanks Michael.
With compressed air, and all holes plugged up, the main cat to the long pipe was leaking. I just finished sanding the cat surface with 220 down to 800. I'll test later.
I thought getting the studs out would be a pain, but some PB Blaster and out they came.
You can also buy remflex gaskets . They pretty much crush into place .
Most of my issues are turning out to be self-inflected.
I originally pulled out the long pipe up to the exhaust manifold as I suspected a leak in the main cat. I was correct and had it welded. When I reinstalled everything I did not put washers over the two studs in the manifold. Of course the gasket did not hold because the nuts were down to the unthreaded part of the studs. I then purchased the unit pictured in the first post. When removing the nuts, the right one came off, but the nut and stud on the left came off together. I installed a new stud on the left which had a much shorted portion of no threads. However, I did not replace the right stud and made the same mistake again. This account for the discoloration noted by rxtsay3. Unfortunately, the new unit developed a leak under the heatshield. I do not know where the leak is or if it can be repaired, so I decided to put the OEM components back in. The manifold studs have been replaced. The studs on the rear of the first mono will be replaced as one was bent (?) after I sand down the surface. When assembling the first and second mono cats, it is possible to tip one to the other while still in contact. I believe this is due to the higher parts of the flange to outside of the studs.
Now to sand down all the mating surfaces.
Thanks for the lead on the Remflex gaskets. I already bought the Mazda ones and I'll give them a try first.
After all, it is a 39 year old car and a blast to drive. Bonus when someone notices it and actually knows what it is. I have not seen another 1st gen on the road in the Dayton, OH area for at least a decade. I did meet up with an Rx8 on the way to work 2 years ago. Pulled up next to him and honked. He caught up with me at the next light and took pictures.
I do not know. I had 3 nuts frozen onto studs. One I got off, the other two the stud came out so I replaced the studs.
I live in California but I've always had good success cleaning each nut and stud with a wire brush putting a bit of anti seize and tightening and re tightening the nut a few times if i even feel a bit of resistance in the threads . You should be able to tighten a bolt by hand until unless it's one of those compression nuts. i feel alot of us just ignore the pre existing corrosion and then Pikachu face when the nut seizes . I also like to clean all my nuts and bolts with pb blaster lithium grease . Cut's all the gunk right off .
I went with the Remflex gaskets. I was never sure how flat I had sanded the flanges.
On the rear of Cat #1 the area around the stud holes was higher than the center. So much so that went fitting it to Cat #2 over the studs, I could rock it back and forth and leave a 3/32" gap.
Cat #2 to Main did not leak in a pressure test.
Main to rear pipe blew out enough to indent my finger tip. The front flange on the pipe had parallel thin black arcs. They looked like paint but were indentations. Sanding took some time.
I suspected the rear of the pipe. There was a pattern on it matching the gasket. When I first started sanding, only the area around the bolt holes and the top and the bottom of the flange sanded. This one flange took the longest to sand down as the surface was concaved.
One thing I did do to check if I as sanding level and identify low and high spots, was to mark the surface with a Sharpie. Then periodically check while sanding. Only when the marks disappeared at a uniform rate over the entire surface did I start to assume it was becoming flat.
05-26-23, 08:46 PM
Torque specs from exhaust manifold to stock muffle
