How to fix a hole in an exhaust silencer or muffler.

Using a tin can, some exhaust repair paste and rivets.

A small hole can cause a very big noise.

Our sixteen year old classic Saab 900 blew a small hole in its exhaust, which turned in to a large hole after I poked around!

The metal surrounding the hole was surprisingly solid after I scraped away the flaky rusty bits. So I thought I’d have a go at repairing it rather than replacing the whole exhaust section (very expensive).

First I jacked up the car and placed an axle stand underneath a strong part of the body. Talking about safety, goggles and gloves are pretty essential to to avoid injury from sharp or flying rusty metal bits during this repair.

To get a little better access I pushed a pair of rubber supporting mounts off their hangers and let the whole exhaust hang down a little. You need to make sure this doesn’t stress any part of the system by placing something underneath it to support it. I used a small axle stand but some bricks or wooden blocks will work just as well.

Gently lowering the exhaust might give you better access.

Next I used an old chisel to scrape away all the rusty flakes of loose metal. Don’t panic if this makes the hole bigger, as long as you still have access all around the hole. If the hole gets so big that you don’t have good access, then you either need to take the whole section off or replace the section.

Scrape with an old chisel at least 25mm or 1″ back to solid metal.

To make a really good job you can run a wire brush over the edges of the hole, the type the fits into an electric drill is perfect. This cleans away the rust back to solid metal.

Wire brush the rust away and get back to good metal. Goggles or glasses are ESSENTIAL!

Next cut a piece of metal around an inch or 25mm bigger all round than the hole. You can use any thin metal. I used some from a thick tin can, it won’t last forever but it needs to be thin enough to easily follow the curve around the hole and pull up tight when you rivet it to the silencer.

Use a thin metal patch to repair a hole in an exhaust silencer or muffler.

Next is to apply a special exhaust repair paste;around the edges of the hole which will set rock hard and seal any gaps giving you a gas tight seal. You should wear disposable gloves and try to use a tool such as the old chisel or a thin piece of wood and not your fingers. It’s very sticky stuff!

Don’t get this stuff on your fingers!

Then place your new metal piece over the hole and press it down. Using the right size drill bit for your rivets, drill a hole around 1/2″ or 13mm in from the edge right through the new metal piece and the metal below. Pop your rivet into the rivet gun and press the rivet through the hole. Pushing down as hard as you can squeeze the rivet gun to set the rivet. I riveted this patch along the bottom first to hold the metal in place, then I went up each side, finishing off at the top. Rivet each hole as you go to avoid misalignments.

All finished and gas tight. Not pretty to look at but it’ll last this silencer out.

Once all the holes have a rivet, smooth out the exhaust repair paste that has squeezed out. Now, it’s not very pretty, I can promise you that, but it does the job!

Use a heat source to start the drying process.

I did this repair during a cold snap and I worried that the silencer wouldn’t get warm enough to set the exhaust repair compound, so I placed an old lamp close to the repair for a couple of hours to speed up the process. The repair paste will finish setting on the road.

Repairing rusty exhaust pipes or silencers is always going to be a nasty job, but when they fail at an inconvenient time, you have no choice but to carry out a repair like this. If you have reasonable access to the area that’s holed, then you have a fairly good chance of being able to repair it.

Good luck with your own repairs!
Stay well

By Ian Anderson