356B Exhaust Leak

[Paul Giganti]

My Coupe has gradually developed a nasty backfire. It started out as occasional, but now it happens while idling, acceleration, and deceleration. My best guess is that I've developed an exhaust leak. I'm going to get underneath and besides carefully examining my exhaust system, tighten the exhaust bolts at all the exhaust ports. I can see the rear ones, but I don't know how to reach the front ones. I wish I had a lift, but I'm going to have to rely on jacks and jack stands (multiple).

I prefer not to learn by trial and error so I'd appreciate any advice for both locating those exhaust fittings and how to reach them with wrenches.

[Dick Weiss]

Searching for exhaust leaks, look at the slip joints of the exhaust pipes (#1 & 3) for a black color--if the pipes & muffler are painted Exhaust Gray--kinda difficult if the exhaust system is colored Black!

Proper OEM clamps should be barely positioned over the slotted muffler inlets so the clamps can squeeze
the joints--they won't do the job if the clamps are placed over the uncut part of the inlets. the same goes for the S-pipes. To prevent age rust, use a Hi-Temp anti-seize paste on the slip joints & bolt threads.

Don't use the U-bolt clamps as they'll crimp the joints and if you ever need to remove the muffler,
it'll be difficult!!! They look ugly, anyway.

Overall, leaks in the muffler shell itself may need a "weld job"--& hope it's not under the sheet metal
sleeve--if it still exists. Exhaust port gaskets should have metal reinforcement & only 12mm nuts.
Aftermarket exhausts may develope cracks and I won't go into the Dansk systems; That's another story.

[David Jones]

Get yourself a cheap automotive test stethoscope from a parts store then remove the metal portion and use the flexible tube as a wand and place it around the engine until you hear the leak. It will be very obvious. Do not try and remove the "J"pipes with engine in car, that is a mistake as it will take longer to do that than removing the engine and replacing it and a lot less frustrating.

[Dave Wildrick]

My Coupe has gradually developed a nasty backfire. It started out as occasional, but now it happens while idling, acceleration, and deceleration. My best guess is that I've developed an exhaust leak.

I have used the Maestro's method for locating exhaust leaks with success. This dates back to 1999:
[To find where an Exhaust Leak is coming from (Some Exhaust leaks sound
EXACTLY like Rod Knock!), try this (takes 2 people, or very long arms).
While YOU are under the engine shining a Strong Flashlight up
at one particular Cylinder/Head Junction or "J" tube/head Junction (Easy
with Euro Heaters. Harder, but possible with Double Flapper Heater Boxes.
Difficult with Single Flapper Heater Boxes), an assistant drops a couple of
'cc's of TWO-STROKE MOTORCYCLE OIL ('cause it burns clean), down the throat
of the carb of THAT PARTICULAR CYLINDER you're eyeballing.
If there is ANY pinhole leak at any junction, copious quantities of White
Smoke will bellow forth therefrom forthwith.
Repeat this test, eyeballing the Head/J Tube connection of
that cylinder. Again a Great Blast of white smoke will come out of the
Head/J-Tube junction if there's a leak present.
Repeat these tests on the other three cylinders.
A blown-out exhaust gasket is very common these days, thanks
to those damned non-asbestos exhaust gaskets in all the current gasket
sets. And like I said, a badly blown exhaust gasket sounds just like Rod
Knock. So does a leaking Head!

Keep the 356 Faith
Maestro]