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71bmr02

engine detonation

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Sounds ominous. recently the 40 solex single bbl carb went south. I was driving from home and about a mile out. the engine stopped running as if out of gas. I coasted to the side and attempted to restart. It cranked and then on one revolution a terriffic bang. It was so violent it rocked the car and honestly thought I had broken a motor mount (turned out not). it finally started and I got it back home. At home it did the detonation thing again, once or twice. i pulled the carb, did a through cleanout and reinstalled. this time it wouldn't start at all. I installed a 32/36 and no problems since. does any one know if or what type of damage may have been done as result of the detonations? the car runs good better than before be the solex, but I have a nagging question about potential for bent connecton rod(s), broken pistion lands etc, stretched timing chain. Ireally don't want to pull the head or other wise get into the engine, I just did a complete rebuild and it seems ok but I still wonder if damage was done. any help suggestions appreciated

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There are tools that can look inside combustion chambers through the spark plug hole. It's a camera on the end of a rod. You can also measure if the piston is reaching top dead center with similar tools and thus determine if a rod got bent..

But even if it looks damaged, and the car seems to run fine, I would drive it until other symptoms start to emerge that would cause warrant further investigation.

Best of luck.

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What you had was probably a backfire. This happened either in the intake or the exhaust. When it happens in the intake system, it can blow off hoses and in some cases ruin the power-valve in the carburetor, if it has one. When the backfire happens in the exhaust system, due to accumulated fuel and air, it can ruin the muffler, but usually just makes noise. Either way, it does no damage to the engine. Backfire on the intake side is caused by leaky valves, incorrect (lean) mixture or wrong ignition timing.

If you're really worried about it, run a compression check. Be sure you open the throttle when you do that.

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As mentioned, do a compression and a leakdown test. If the numbers are good (which I'm betting they will be) forget it and drive the car.

Be sure to check all the intake/carb gaskets for leaks - start car and pass a propane torch (not ignited) around all the joints and vac lines to see if the idle increases through the introduction of the propane gas which would indicate a leak. Obviously, use the appropriate caution with the propane, but you're looking for any unmeasured air entering the system and causing a possible lean condition.

All cars eventually break/wear out. When it does, take the appropriate corrections, but until then, lose the angst and drive the car.

Cheers!

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I had this, blew out my muffler.  Are you running the correct coil/ballast resistor setup?  Do you have a Pertronix?  If a coil overheats and doesn't throw a spark when it's supposed to the car will die and/or the fuel will go into the exhaust unburned then ignite in there and scare the bejesus out of you.  Once it cools it will restart then fail again.  Worth checking into.

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awwwww, jeez.  Way to dig one up, Steve.

 

Funny coincidence... I had a voltage regulator go out on a '70 GTO, back in the day... battery voltage dropped and engine started running poorly... I had a BIG backfire (Ram Air III 400) and completely blew out both of my BRAND NEW mufflers...uggghhh.  what a pisser.

 

Ed

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