Che downpipe leaking issues fix

Thanks for posting here.

 Fist off you may have read some of my struggles with the Che downpipe which is surprisingly good quality in terms of welds, cat and flex section but all falls apart because the Chinese like to make a one size fits all exhaust flanges and that is why the damn thing sucks.  

At one point I thought of selling off everything and going PPE but I kept at it and finally found the solution that has been working the longest. 

1. First I tried the flat gasket and the screws provided and it blew out in a day because the bolts walked just enough and eventually created enough gap to leak and then blow out.  At the time I did not think the bolts walked and it was a gasket issue that could not handle the heat. 

2. I then tried to use a Percy CarbonX gasket which I cut out from a blank using the flat gasket as a template thinking this gasket would be able to handle the heat and that also blew out. At that time I discovered the bolts walking being the issue.  

3. I then decided to try special locking washers and went back to the original gasket that was provided and it worked for a time but eventually it created a gap and a leak.  

4. I then got frustrated and looked for a high temp thread locker and found a nice one.  This time it worked well for a good while but now I discovered a new problem and that was the other end (connection with the muffler) leaking because the whole assembly shifted causing the bolt to slide out which disconnected the joint. This is a stupid design where they should have added holes.  

 So now lets visit the downpipe to muffler connection and how I solved that issue. 

 Members with this pipe discovered that the Che downpipe has a flat flange requiring a flat gasket but the stock exhaust and some aftermarket exhaust use a donut gasket arrangement that crushes to form a seal.   If your muffler has a flat flange then a flat gasket will work, if not then you will need to perform the following modification so the gasket doesn't shift.  You have no other choice but to weld a tube onto the end of the Che flange to look like the stock downpipe.  In order to get the right size I had to go to Advanced auto and find the right size by trying on various size exhaust couplers that match up to the hole on the Che downpipe  and it needs to have a outside  diameter to pass the donut gasket so it fits.  Unfortunately I forget the right size you need.  I cut the pipe coupler to the right size so the top of the donut gasket will be flush and then welded in the tube to the Che downpipe.   If you don't have a welder take it to any exhaust shop and they can do this for you.  

 Once this modification is done then the donut gasket will not move around and is locked in place. I made sure to use the high temp thread locker so there was no change of the connection separating and its been very  sold for over two years.   

 At this point in time I thought I solved both issues   and the credit goes to the high temp thread locker.  

  Part 2. High tempeture gasket issues. 

 Everything was working fine and the high temp thread locker kept the bolts from turning at the header connection but I discovered a new issue and that was the gasket. Apparently the flat gasket they provide cant handle the heat and it burns up.  The gasket is a two piece metal mesh with some sort of high temp material in between. As the material burns out the two halfs separate and then it leaks in between.   This made me mad because I thought the issues were resolved. I then decided to use one of the many Percy carbon X gaskets that I made that has this carbon felt material that can handle the high heat which worked for a while but even that gasket material burned out.   

  Did some more research and came across another possible solution which is called a Rimflex gasket.  This stuff is made of graphite that can handle the high heat. It also has property of behaving like a spring under tension preventing the gasket from leaking due to a heat cycle.  

   With the material that they gave me I made two gaskets.  A local friend came over and needed his downpipe changed out so I helped him and then discovered that his new aftermarket downpipe cannot fit the ring gaskets so I decided to try the Rimflex gasket as a last attempt otherwise he would be suck and it worked without any leaks.  

Eventually I got around to using the last of the two Rimflex gaskets and it worked and continues to work without any issues what so ever.  Problem solved, finally.  

 Here is what you need.  

 High temp  thread locker-  Resbond 907ts

 Apparently this stuff is only good for a few months  so a lot of it will go to waste. There is a guy on Ebay that sells small quantities that is more then you need.  Apparently he doesn't have the blue right now and the listing is for the red but I think if you contact him he could make that available for you. 

https://www.ebay.com/itm/Resbond-907ts-High-Temp-Threadlocker-2mL-Red-Fast-Free-1st-Class-Mail-2020/113936707951?hash=item1a8728316f:g:0RoAAOSwCyFbLDfn

  The Rimflex gasket will come as a blank. I bought mine from Amazon.  Overlay a flat gasket and then cut it out carefully using an exacto knife. You should be able to make two gaskets 

https://www.amazon.com/Remflex-GS16511-Gasket-Sheet/dp/B006G30D6Q/ref=sr_1_4?crid=3AB8LDZEBU46K&keywords=remflex+gasket&qid=1577982567&sprefix=rimflex+gasket%2Caps%2C135&sr=8-4

The Rimflex is not a typical gasket.  It is very fragile and can crumble if you are not carful in handling it.  Those that have used it  and then complain about it afterwards  did not follow the directions and overtightened. 

  Once the gasket is in place and you applied the thread locker on the nuts you need to carefully apply pressure evenly on all three nuts.  It should just feel snug. Only use 25 lbs  per nut using a torque wrench.  It will seem very odd to use that low of torque because your first reaction is to over tighten to get the best seal possible but that will only break the gasket and leak.  The gasket acts like a spring keeping tension between the two halves.  

I know this is a long read but there is no other way to explain it without going into detail of the failures and what is causing the issue. I hope this will fix your leaking Che downpipe.  

Dev,

First, thanks for introducing me to mr2-spyder forums. This is great! I read up a bit on why you guys transitioned to here. and it makes complete sense. Much appreciated!

Second, thanks for the detailed explanation as it helps my engineering brain walk through the process.

I had five follow up questions:

1. Did you still use the same bolts and washers or the special ones you purchased? Or does the tread locker make that point moot? I'm think anti-seize or high-temp rtv may accomplish the same result (i.e., reduction of vibration) without making it hard to remove later on.

2. I see some mufflers use a spring bolt, any thoughts on those? Is that only for those with donut gaskets? I 'm nervous of bolt slipping from the slot (DP -> Muffler). How did you prevent that if at all?

3. If I remember correctly, I'm pretty sure my apexi muffler flange is also flat, so that should prevent any need for welding. Which muffler were you using? Mine looks like the one in the link: <a href=" removed link "> removed link

4. When you did weld, did you use stainless steel pipe? I heard many people do not prefer to weld stainless steel, which is why I was avoiding that route. I have access to a welder so I may give that a shot myself.

5. Did the position or angle of the hangers make or create any tension?

First off welcome to a great site with members that love to help.  

1.  I basically have a bucket of bolts from part out cars and previous repairs which I draw from to find what works for me in a pinch.  In this case I used two bolts that came with the Che downpipe  for the header side and one I found from my bucket.  
The Nordlock washers work great but in this situation it doesn’t because the material on the downpipe was too slick to grab and yes the high temp threadlocker makes those washers moot but you should still use regular washers to distribute the tension.

Antisize will only make things worse by lubricating  the bolts.  I tried  Exhaust sealant to gum up the threads and it seemed that there was more friction from the bolts turning but with heat and time they worked their way free.  The high temp blue locker on the other hand just works and when it’s time to remove it actually breaks easy.  I also think  it’s a barrier against corrosion.  Trust me on this one.  

2. The mufflers that use the spring bolt connector works to keep tension so the donut gasket doesn’t come loose when the exhaust shifts.  I got rid of the springs sometime in 2005 when I got a Team moon exhaust and the springs wouldn’t fit. Never had a problem afterwards. I can’t say that it is not recommended  but so far I haven’t had a problem.  
With the Che downpipe I initially used a donut gasket sandwiched in between. Since there was no support in the way of a tube that the gasket goes onto it caused the gasket to shift in time and I had the bolt on one side come off causing a major leak. After welding the tube extension it works great and I just used regular steel and welded it in and cleaned up the welds by filling it down using a cutoff tool so the gasket sits flat on the flange.  
I hate those slots and also had an idea of welding on some washers to the flange but never got around to it. It’s still holding great since the gasket has no possibility of shifting so problem solved for now.

3. I’m technically using a Team Moon muffler which is actually an older Magnaflow Camarro muffler body.  If you are using a flat gasket on the downpipe to Muffler connection I would suggest using the Rimflex gasket here as well. 

4.  As I mentioned before I used a non stainless pipe.  I didn’t see the need as long as it works as I was desperate at the time to solve the leaks.  Hopefully it doesn’t rust out.  

5. I basically recycled some of the parts, mainly the hangers from the old exhaust and transferred it  to  newer Magnaflow body.  I made new pipes to go out through the bumper. 

If you need any clarification please let me know and we can discuss.  

Just a quick update:

I decided to follow the same logic as Dev's journey and coming to the same results.

However, I used Vibra-Tite Threadlocker which can be found off Amazon ($15): https://www.amazon.com/gp/product/B07XW2ZTZL/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1

The leak is back (albeit tiny) so it's time to replace the cheap gaskets with remiflex and weld in pipe. Have both, but unfortuantely, the nearby Makerspace is closed so will have to wait to get my hands on a jack and welder. 

Thanks Dev again for all the support.

Zo

Good to hear. The rimflex gasket is still holding strong for me. About this time the other gasket materials would fail. I’m sold on this style of gasket but it’s so brittle it can easily crumble.