How to diagnose if cracked front exhaust manifold 83 QV?

Youll smell it from the engine compartment.

If you need a pair of exhaust manifolds, I have a set from my 83 QV I'm converting I'm happy to sell off. Just PM me.

 

Start it up and look for smoke, you should also smell it. If you take the rear wheel off and the liner out you will see the pipes a lot better

 

Stethoscope. No tool box should be without one. Get both kinds for mechanical and air-induced sounds. If the crack is slight, it can be hard to see smoke and then when the engine heats up, the crack may seal itself up. If looking for hard-to-see smoke, try looking when it's dark and with a faint light in that area.

 

Smoke???? You cars smoke??? You guys need to drive more... No smell either in my case - but noise - yes!

One give-away of a cracked header is a rev-dependant exhaust sound under load only. Once you back off, that part of the exhaust sound would disappear. It's also often only 1 cylinder, so it's more like a Harley-Davidson type exhaust note under load only. It's an escaping hot air type of sound.

Here is how it could look:
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Might not even be a crack. I had an exhaust leak on my Alfa Romeo. Sounded like a ticking noise, almost like a lifter. I went snooping around with my stethoscope and it brought me to the exhaust manifold and a very specific area. Sure enough, a nut to the header was loose. Tightened it up and the noise went away completely.

No smoke whatsoever.

 

On a US version, I'd go with first looking to see if any of the exhaust gas analysis tubes have corroded and broken off .