Exhaust connection help

I replaced the front catalytic converter for my girlfriend’s 2010 Honda CR-V. It’s the type that is integral to the exhaust manifold. Everything is good except for a seeping exhaust leak where the unit bolts to the piping for the rear catalytic converter; it’s a flanged connection with the spring bolts and donut gasket. I can’t hear the leak but can see and smell the fumes.

I am trying to get installation help from the mfr rep and haven’t found online instructions regarding the correct arrangement of the gaskets. As shown in the attached picture, the mfr provided two flat gaskets and one donut gasket. I tried using one flat gasket and the donut gasket, because that is what most closely matched the connection I disassembled. Was I supposed to use just the donut gasket and no flat gasket, or am I supposed to use both flat gaskets and the donut gasket?

I could see the extra flat gasket causing the donut gasket to be pushed farther into the connection and possibly seal better. But it also seems that more hard-to-hard surface connections would be more likely to leak. I suspect that if I use only the donut gasket, the pipe stub on the bottom of the converter would bottom out inside the next pipe and not allow the flange faces to get close enough together.

The two spring bolts were tightened to the Honda-specified 16 ft-lbs, I went side-to-side to avoid cocking the donut gasket. The pipe being connected to is stainless steel so I don’t think that roughness of the joint is causing the leakage.

1 Like

Try tightening the bolts more to see if that stops the leak.


1 Like

I found it odd that there’s two flat gaskets. Looking online at genuine Honda parts, only the donut is shown and that would be consistent with my expectations. I would see if the flat gasket inner diameter is interfering with the donut gasket seating in the pipe flare…

Perhaps there are two variations in the converter assembly. One is flare to flare and the other is a flat flange to flange. In your kit, they supplied both gasket types??


Yeah, none of the cats on Rockauto show those two flat gaskets, just one with a cone shape on one side, flat on the other, along with the manifold gasket. Many just show the manifold gasket.

Looks like 2 spacers and a seal-ring. An aftermarket part intended to fit multiple applications.

I will try that first as it’s surely the least intrusive. However the bolts have a sholulder where the threads stop so they will not effectively close the clamped connection by much. The nuts are not used, these thread directly into the catalytic converter flange.
Screenshot 2024-03-27 161112

Those springs are what apply the clamping force to seal the joint.

Over time, the springs lose their tension from heat, so sometimes the bolts have to be tightened more in order to create a seal.


Thank you for explaining that. The bolts and springs are new though. Plus that shoulder controls the compressed height of the spring.

Are you really saying that I should get different bolts that are threaded farther toward the hex head?

Then I would try adding flat washers under the bolt heads to see if that creates a good seal.



I’d make sure the correct number and orientation of gaskets were used (maybe check a youtube), and then add some washers. Just don’t add to many, there needs to be a gap between the spring coils to let them supply the ‘give’ needed by the joint. If they’re fully compressed that can’t happen.

No experience w/that configuration, but my guess is the two flat gaskets are supplied to (by trial and error presumably) move the exhaust manifold away from the engine slightly, allowing the other end with the round gasket to line up correctly, directly inline, with what it bolts to. Suggest to try again, this time, test if using no flat gasket at all improves things. If that makes it worse, try again using both flat gaskets.

Mechanical fuel pump replacements for older cars often come w/multiple gaskets. The less space between the pump and the engine results in more pumping action and more fuel flow. So if you want a hot rod presumably you use one gasket, and if you just want a daily driver you use more gaskets. The instructions don’t tell you how many gasket to use. When I did that job myself I used the same number (1) that was used originally, and this seems to work ok.

The extra tightening, especially with some washers may do it. If not (or even if so) consider that if you bought generic after-market parts that the springs might just not be up to snuff as compared to OEM. They might just be too wimpy. I can’t imagine that an OEM Honda bolt/spring set could be insanely expensive. But I didn’t go look either.

I’m doubtful the problem is either the bolts or the springs or that they aren’t tight enough. More likely the gasket isn’t seating properly, either b/c the parts aren’t aligned or there’s carbon deposits on the mating surfaces. The new gasket could be defective as well.

When my plumbing-expert friend helps me solve a stubborn plumbing leak, the problem has always been w/the pipe alignment, or a warped part, never that the fasteners are tightened enough. He seems to be able to just look at the pipes and tell that they aren’t aligned correctly. I’m not able to observe any clear difference.

Thank you everyone for the input. I was hoping to learn that I did something dumb that would be easily corrected in the next step but it’s unclear. It is unfortunate that there is not enough room to get this joint apart to change the gasket arrangement without also disconnecting the manifold joint, so I will go through a manifold gasket for each iteration of the trial-and-error method. I will first try the washers and will let ya know how it goes. I presume I can reuse the same donut gasket a few times?

I won’t be able to get to it until this weekend or more likely Monday. And no it is not being driven in the meantime.

I wonder if it would help to put the donut-shaped gasket in a bowl of warm water for 15 minutes to warm it up & make it more flexible prior to the install?

Using all the supplied gaskets as shown in the photo was the correct configuration - who woulda thought :grin: I had to get a new donut gasket after so many iterations of testing the various configurations.

I was able to connect my shop vac blower output to the tailpipe to reverse-pressurize the exhaust system to more easily detect leakage without having to run the engine. And thankfully I was able to get the affected flange apart without disassembling the manifold gasket. Glad to have this behind me.

1 Like

Another reason that I’ve always believed the only proper way to repair an exhaust system is to take it to a weld shop.

Just be aware there are quite a few exhaust shops out there who do pretty bad work

You are correct.
Whenever my car has an exhaust leak I seem to have this nasty habit of trying to rig it up using various pastes, clays and whatever else I can find at the auto store.
Of course they all burn off within a matter of days because of the incredible heat.
Finally I give up and drive it to our local exhaust shop.

Partly because I’ve been in Texas, but the last exhaust work I’ve needed was actually a bad cat on a '96 Suburban. Our more recent cars haven’t needed anything.