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Loud Bang - HELP!
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Author:  60 Plymouth [ Sat Apr 17, 2010 11:14 am ]
Post subject:  Loud Bang - HELP!
I may be worrying over nothing but . . .

Was working on the car today and advanced the distributor a tooth to see if I could gain a little advance (Bosch distributor does not have the second nut underneath for initial advance, and even applying vacuum to the pod didn't reach the ping limit). Conclusion from this experiment - no - I can't, the idle is far too rough.

I then had a whole load of trouble trying to get her to start again (managed to skip a tooth in each direction before I got it back to where it was again). After trying to start the car again, there was a loud bang that sounded like a shotgun going off (not quite sure where the noise came from). After the bang I saw a lot of black smoke around manifold-head junction (I know the exhaust leaks anyway).

My initial fear was head gasket, but there's no bubbling from the radiator, temperature usually runs at 180-182, when I checked 20mins of running after the bang it was at 185, but it's also a hot day. Still seems to run fine.

The car runs, seems ok, but it's very loud in the mid range, around 2000RPM it hums very loudly. Sounds normal at higher speeds and at idle though.

Maybe somthing happened to the exhaust? Could the explosion have been in the exhaust and damaged the muffler?


Any ideas? I'm very concerned about this.

All the best,
60 Ply
Author:  sandy in BC [ Sat Apr 17, 2010 11:45 am ]
Post subject: 
You probably had some fuel fumes in the exhaust and muffler from trying to start it. Eventually you lit it off.

It is very possible to trash the baffles in the muffler doing this. As younger adults we used to do this on purpose. ( Coast downhill in gear with the key off......key on = KaBlamOh!). Now I only do it by accident.

The buzzing could be pinging. Try retarding the spark a lil and see if it goes away.

Watch out for volcanic dust........
Author:  SlantSixDan [ Sat Apr 17, 2010 11:45 am ]
Post subject: 
With the distributor off time, a spark fired with an intake valve open, and there was a spitback (backfire) that ignited all the fuel in the intake manifold. Big dramatic noise and smoke, but no real damage. See here.
Author:  slantrat [ Sat Apr 17, 2010 11:50 am ]
Post subject: 
It's only speculation, sometimes when you advance or retard the timming too far you will cause the engine to backfire through the carbeurater or the exhaust depending on which way you are going. My guess is that when you were tinkering you shut the car off when it was out of whack. There was unburnt fuel in the combustion chamber. When you restarted the car it back-fired through the manifold. This is more common on the older cars with points because they can fire when you initially turn the key and supply power. As far as the difference in sound you probably just blew out some old carbon that has built up over time. LOL
Author:  60 Plymouth [ Sat Apr 17, 2010 4:55 pm ]
Post subject: 
Hi All,

Thanks for the replies. It's good to know that there's no damage to the engine done.

Still a bit baffled by the humming at a certain engine speed though. It's noticeably louder at around 2000-2500 rpm. I don't think it's pinging - it's almost as if somone just turns the volume up as you approach the 'magic speed' then turns it down as you drive though it to higher rpm.

There is also the slightest hint of a dead spot at this speed. I'm going to hazard a guess that the muffler has been either damaged/constricted by carbon or somthing that has caused this 2000rpm resonance hum.

Could of course be volcanic ash in the cylinders :lol:
Author:  2 Darts [ Mon Apr 19, 2010 9:03 am ]
Post subject: 
Quote:
It is very possible to trash the baffles in the muffler doing this. As younger adults we used to do this on purpose. ( Coast downhill in gear with the key off......key on = KaBlamOh!).
LMAO. Brought back old memories. We do this sort of thing south of the border, too.

Couldn't do it with an automatic, so I removed the tailpipe and ran a 2" hole saw up the muffler outlet. Stuck back together and camouflaged the scratches. Had the old man stumped on that one.
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