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Last Tuesday, my timing belt sheered off several teeth. I got one on order and replaced it, and the car fired right up. I was able to hand crank the engine several times after re-timing it and it turned without any sort of binding/difficulty beyond fighting the springs.

Now, I've noticed while driving it, it sounds much deeper at the exhaust end of things. I didn't actually take apart anything along the airflow path. I just took out the spark plugs (so I wouldn't fight compression when hand cranking it) and the serpentine/timing belts.

So my question is, why would replacing the timing belt (and tensioner/pulleys/water pump) change the sound of the engine? Is it possible a worn out tensioner could be the culprit here, or perhaps a stretched belt?

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    It is possible that you slightly damaged the exhaust valve or valves when the belt had it's issues. I don't know if this is common with your vehicle, but a thought to look into.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Oct 6, 2014 at 18:46
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    Would a compression test be the first place to start with this?
    – Sidney
    Oct 6, 2014 at 19:46
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    I believe a leak down test is in order.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Oct 6, 2014 at 21:30
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    Agree with @Paulster2. It appears that virtually all Mitsubishi engines except one (the 3.0L SOHC 12 valve) are interference engines. bit.ly/1F7PgmE In an interference engine, the piston can strike the valves when the timing belt or chain breaks (or even if the engine just jumps time). That said, I kind of doubt the engine would run at all if that were the case. I suppose it just depends on the circumstances. I had an old Mitsubishi pickup jump time when the valve adjustment nut came loose and fell down in the timing chain at freeway speed. Result was NO compression an any cylinder.
    – bobfandango
    Nov 20, 2014 at 19:31

2 Answers 2

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There is a chance that your belt had some offset (1 tooth for example) and your exhaust valve was opening earlier/later. Now your belt is ok and sounds different.

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Tighter valve adjustments sounds like a choked motor and will stall when low on gas, looser valve adjustments sound more like a Harley but too loose and you will hear clatter(bad valves are slapping against something, this can also happen if you run 87 in a 10:1 ratio cylinder) or a diesel sound, which isn't necessarily bad. If by messing with your timing belt, you made your valves operate by a slightly different time, that could be the reason. Also if the teeth keep wearing out, you may be experiencing delayed firing of certain cylinders or gasoline igniting in places it shouldn't like your exhaust. It also could be that you have your boost adjusted or one of your spark plugs has a burn mark on the end of it.

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