The Stovebolt Site Forums The Shop Area Engine Shop Looking for the Big Bang Theory

Well some of you guys that have been active over the last year and a half know that I taint no professional mechanic, I couldn’t make a living at it because I get to hung up in the little teeny tiny details. But that said, I’ve been twisting wrenches in some fashion for most of my 65years and conceder myself a half way decent mechanic. At least I have a pretty good grasp of automobile physics in most cases. Now that I’ve twisted my arm patting myself on the back, I want to talk about something that happened today that I don’t, understand!
I’m approaching about 3,000 miles since I’ve done all my mechanical restoring and rebuilding chores and she’s been running just peachy keen. Starts first time over hot or cold, she hasn’t missed a lick in all those 3k miles, until today.
So it was such a beautiful day today, forecast to be 65°, 15° over the average for this time of the year, not a cloud in the sky and the whole weekend was supposed like that. I decided to reach way out and just do some motoring today and was about 75miles from home just cruising along nice and smooth not slowing down, nor speeding up and all of a sudden there came a VERY loud bang from under the hood. A single backfire through the carb, it was so strong that even though I’ve got the stock spark arrester fitted with a paper filter on the carb that the hood actually bulged up when she blew. A half block later when I got the nerve up to step on the gas to see if it was still running everything was just “Peachy Keen” again. There was a big empty parking lot in the next block that I swung into. By now I’m trying to recall the proper use of the fire extinguisher from my training that I had to have every year for 27years at the last job. With that loud of a bang I thought for sure that it had blown the arrestor clean off the carb and was probably ablazing under the bonnet.
I whipped open the hood and not’a, nothing wrong, the air cleaner was just fine not loose no burn marks, no fuel running out onto the exhaust, everything looked and sounded just fine.
The 75 mile jaunt on the back side of my trip was uneventful. Just that one single big bang and then all is well again. So I’ve been trying for the life of me to figure out what could have caused it but keep coming up empty. Rechecked the timing and took a read on the plugs when I got back home and she’s spot on the factory specs right where she’s been for the last 3,000 miles. Took a look under the distributor cap and everything looks is working fine under there also, nothing to loose or to tight.
I did a valve job back then also with every thing fresh, new valves, guides and hard seats and adjusted hot, dead nuts at .007” & 014”.
So I’m out of ideas as to the why! Any more suggestions?
Denny Graham
Sandwich, IL

fumes getting past the rings and exploding in the oil pan, like a diesel

Bill

Were you in Iraq?

LSD flashback?

I'm with Bill. Did you install a PCV?

Larry

I'll cast my vote for a errant piece of carbon in one of the cylinders that finally got into the perfect position to get red hot and pre-ignite the charge coming into that cylinder.

Doing so was an act of seppuku, as the little hunk of glowing carbon or steel was blown to oblivion.

This is the real deal...

Stuart

Dont have a clue - but very interesting, hope you find out and I will be watching, but the replys cracked me up!!! I would go with Stuart

a drop of water in the fuel....?

I wonder if you checked your outside fenders, cab, bed for a dent. It could be a rock thrown by a kid on the side of the road. If it backfired, might you have seen some resulting smoke?

intake valve may have stuck open or you may now have a broken intake spring or one of your friends was hiding in the bushes glad nothing was hurt

check your coil for loose wires, blew up a muffler that way on a F*rd.....

This was a one timer Bill. RVN Gazim. Only grazed on the Grass back in the day Tim. No PVC Larry, this is a 1950, we didn’t have pollution back then. Naw Alvin, the water up North here is nonflammable.

Now Stu, your probably about the closest yet, when I did the valve job I cleaned and vacuumed and polished the tops of the pistons and vacuumed and cleaned again! But its possible that a tiny piece might have still been wedged in thar somewhere. Also with the oil-burning problem that we’ve been discussing its very likely that the combustion chambers and tops of the pistons are carboned up some even in this short of a time period.

Jim this was a “backfire thru the carb”, it actually lifted the hood it was so violent. No mistaking it for a rock, it sounded like an M80 went off under the hood. Usually there isn’t any smoke if it’s a proper mixture just being fired out of time. Tending to think Stu has got the prizewinner today, it’s the most logical answer.

Highly unlikely that it was a valve sticking open or broken spring Duce. Chances are that it would have repeated itself if one of those were the culprit, anyway I checked the clearances when I got home and everything checked out fine under the VC. Oh, and all of my friends are dead by now, I’m the only one left!

Possibility Nut, but they are all clean, solid and in tact, I checked all the ignition related wires when I popped the hood in the parking lot and again when I checked the distributor at home.
Ok Stu, the contest is over and you win the grand prize. It’s a free trip to Hawaii, all expenses paid and all you have to do is send us your Credit Card, Social Security and bank numbers so we can verify your identity.
Thanks fur the input guys, think I'm gonna go for nice long ride now!!
Denny Graham
Sandwich, IL

Denny,You crack me up with your title, Big Bang Theory,but I see why the title after reading.
I sure wish those things didn't happen, but over the years since I've been wrenching and that started back in the early 60's, I've had machines do some strange things. A cough, a sputter,a loud pop,
or some other unexplainable short term event.
Like this Allis tractor I've got which runs like a stop watch 99.9 percent of the time, then all of a sudden it sounds like its running on 31/2 cyl.out of four. That will last for 10-30 sec. and its back to normal. I've checked everything and come up empty.
So now I just blow it off and live with it cause I don't have that much time to spend looking for this.
That's mainly because I have more than eleven more machines to keep running.
I understand your concern and I would feel the same as you do because I hate it when something ain't running right. People say I'm a bit of a perfectionist, I prefer to think of it as I just wanting it done right and running right.
When I was a kid my Gramps once said to me...A job worth doing is worth doing right. That stuck in my head for some reason.
Now back to your problem,I don't have the answer but I will be thinking about it and what I've said was only to ease your frustration over what happened to the Valdez. Sorry, you came up with that name, but I don't like the name. Hey, can't you call it your tinkle toy ! Cause it tinkles on your floor a little.
I sure hope you find the reason for this and let us know.
Oh, one more thing, I enjoy reading what you have to say. Hope you have another good sunny day.
Dan

I'm leaning toward Stuart's theory too although a momentarily stuck valve is a possibility however remote. One thing this does, it gives one an appreciation for the forces these old engines put up with hundreds of times a second every time we want to go for a drive.

Denny, check your fan blades,I had one come off and thats what it sounded like.
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Floyd

Denny, These truck do that occasionaly, just about the time you start to take them for granted, also to keep you awake and nervous. LOL
Cleon

Well guys we went for a spin and put another tank of gas and quart of Rotella-T into the atmosphere to day and she ran like a top, no misbehaving at all.
Hey Dan, you must have a Rochester ‘B’ carburetor on that AC tractor. And by the way, I agree 100% with gramps philosophy.
Iffin it were a fan blade Floyd I think I’d have noticed a tiny bit of a vibration on the way home and maybe a new hood ornament pokin’ through the bonnet.
Now Cleon, yours might do that occasionally but mine only did it ONCE and it better not do it again or I’ll take it out back of the barn and shoot it! After all, I loose enough sleep because of the cat and dog.
Denny Graham
Sandwich, IL

back about 40 years back i was a dishwasher well every night about 1 in the morning id be heading home and id come to this big hill with my 65 ford 6 automatic .that would do 105 most places and 95 at the intersections. well id get to that hill and id shut the key off id get near the bottom and hit the key didnt care that it split the muffler it sounded like a shootgun. well one night the guard told me the sherriff ! was waiten at the main road .i snuk out the back way and on comes the blue lights so he says you shooting a gun out your car. i told him what i was doing he told me to knock it off. he said when he was a kid they would mount a sparkplug in the muffler and run a coil wire back so i guess i wasnt the first ha!!!! but i bit you do that now and you would be in some trouble...

They call the sparkplug in the exhaust these days a flame thrower, thay are available and they illegal, but it does end tailgating. 8-]

That does bring up something that hasn't been mentioned. An intermittent connection in the ignition someplace.

Larry

I grew up around old chevies many years ago. Although I have never experienced it, I remember hearing that a defective condenser could cause a loud pop. Through the years I have experienced several things than made absolutely no sense. But they did happen, and never happened again.
meansam

Good stories... I remember in my youth I used to go out with an older teen who delivered a early morning Newspaper... He loved turning the ignition on and off and getting the loudest backfires out of his parents Vauxhall...I'm sure people sleeping didn't appreciate it at 5am... But it was FUN... Peter..

If you lost one complete fan-blade (most are two pieces on the original fan) the vibration MIGHT not be there.
I lost 1/2 a fan blade on my 48... Noise was so loud I thought I had been shot by a 460 weatherby ..............
The entire truck was shaking like a 5 lb hammer had been left in a front tire...(thats another story,,,hehehe ). I pulled to the side of the road to look and expected to see pieces of engine missing and oil all over eveything when I lifted the hood. Not a sign of any trouble with the engine. I pulled the dipstick while the engine was running to look for metalflake/glitter in the iol but none. Had a real fun time trying to put the oil dipstick back in while the engine was shaking all over like a jackhammer, so I tosse it in the bed of the truck and got the rig home which was a mile and a half down the road. Thinking the rocker shaft or a pushrod had bent or broke, I pulled the valve cover to look. I reached down to grab the fanblade to roll the engine over and watch the rockers and pushrods move,,, my hand came up empty ..
Only three blades on my fan,,, Hmmm WTF I looked up at the inside of the hood and not a scratch,,,, Looked down at the front crossmember and found a bent, twisted shiney object which use to be the fourth fanblade,,,,,, which luckily missed the brake line which crosses over to the right front brake,,,
I replaced the fan and engine ran great, no scared and shaking engine/entire truck

So ,, again, if you happened to lose both pieces of one entire blade, it MAY not have any vibration.


One more thought,, It COULD be possible for a hard object (such as a rock) to be
flung from a front tire, riccochet off the road surface and hit the underside of the hood or even the frame.

I remember once when I pulled into a gas station with my 84 Suburban, 350. A big German Shepherd was sleeping soundly right in front of the building and only 5 feet beside where I stopped. As I turned the ignition off, it let out a tremendous big BANG. It had never backfired before or since then but the dog was gone in a flash!

When we were kids we had a fifty four 3/4 ton chev. pick-up with the big six cylinder. Running back and fourth around the farm we used to key the ing. ( turn the motor off & on ) while running down the road. It was better than any M-80 fire cracker and enought to blow the muffler to pieces more than once. Being on the farm us kids always found another used muffler to replace before dad found out about it. We even buried a blowen out muffler one time to hide the evidence.
It's possible you may have a loose connection in the ing. wiring which caused the loud suprise when you hit a piece of rough road ??

Im leanin towards a loose wire in the Ignition also.

Im leanin towards a loose wire in the Ignition also.

Thanks guys, I think we can put this one to bed. There taint any loose/bad/corroded/broken/sticky fan blades, wire connections or valves on this one.
I'm convinced Stu hit it on the first day. He still wins the prize, just waiting for his identity numbers.
I’ve put another tank of petrol through since then and she’s purring like a kitten. At least like a kitten breathing through a Rochester ‘B’.
Denny Graham
Sandwich, IL

Did you have chili for lunch that day???

I addresed that already Dave remember, no smoke!
Denny G

At my age the attention span starts to go quickly. At least yours is still running. Mine took a dump and will hard move itself. Thank heavens I was only a hundred kliks up the road when it happened.