QuestionFollowing up on the 1954 3100 truck with the "backfire". It did sound more like the popping sound out of the back of the truck and it occurred when I idled the truck in nuetral with the pedal depressed for a while. Large plumes of black smoke came out of the back. That hasn't happened recently but I now have a more disturbing issue. I hear a distinctive, consistent metal "tinking" noise from the engine block. Pretty quick cadence. I haven't driven it since this started. I checked the oil and it was black. Did I just carbon-up everything inside with my rookie choke mistakes? I'm going to change the oil and spark plugs this weekend. How about de-carboning the engine? Any recommendations on which book to buy for working on the truck? Beyond simple things, I'm afraid to do anything without clear instructions (and photos).
AnswerI had to search back a few weeks to find the previous question - I've been somewhat buried here and had forgotten it.
Your truck is both tough and simple - I doubt very much that you could do ANYTHING to hurt it, short of driving it off a cliff, so quit worrying about that!
Black smoke is always a sign of a too rich mixture in the carburetor. This could be a simple problem with the choke setting, or it could be a more serious internal problem with the carburetor. I also need to know if this symptom only occurs when the truck is first started or if it persists after continuous driving for more than 5 miles or so.
I need to know if your truck has a manual choke knob on the dash. If it does, the problem could be literally in your hands.
If there is no knob with a "C" on it, you have an automatic choke, and it could be seriously out of whack if you are seeing black smoke.
The choke is the flap in the top of the carburetor, as you probably know, and it should be closed, or almost closed, to start the truck when it is first run, because a cold engine requires a richer fuel/air ratio to start. As soon as the engine fires, the choke flap should open slightly, and progress toward totally open (vertical) as the engine approaches normal operating temperature. In your area, I suppose this will take longer than I am used to in Southern California, but by the time you have driven a few miles, it should be open, in all but severely cold weather.
If you have a manual choke, you need to educate yourself on how far to pull out the knob when starting, and at what rate to push it back in, bit by bit, as the engine warms up. You will learn to listen to the engine, it will tell you when it has too much choke by stumbling and running rough, and too little choke, by feeling week and refusing to "take the gas" to accelerate.
The symptoms of a badly adjusted or malfunctioning automatic choke are identical to the above, but of course the cure is different. Tell me which you have and we'll go from there.
Modern oils keep all debris in suspension, so they become black very quickly after installation - if your oil has turned black, that can be normal or abnormal, depending on how clean the inside of your engine is, and how many miles since the oil was changed. I doubt very much that you have contaminated the oil because of the choke problems, but one way to quickly eliminate the possibility is to smell the dipstick. If it smells of gasoline, there is contamination and the oil should be changed immediately - it is dangerous to run the engine that way, both because of possible explosion, and because of additional wear to the engine parts (gas is not a lubricant!).
If that is what you have, I suspect more than a choke misadjustment problem - I think there is a serious problem either with the fuel pump or the carburetor. Either one can put gasoline into your crankcase if they are not working right.
Before we go off on that tangent, smell your dipstick and report back on that, OK?
The explosion out the tail pipe is caused by a temporary interruption of spark in the engine, or by an accumulation of unburnt fuel in the exhaust system which suddenly ignites spontaneously. The latter can be just a result of the choke problems, so let's set that aside for later, OK?
The noise from the engine can be somewhat analysed by an experienced mechanic from the sound only. If you don't have someone you trust to do that, listen to the noise and report whether it is best described as a thudding sound (dull and low frequency), a rapping sound (sharper and higher frequency, but still fairly solid sounding), or a tapping sound, something like a tiny hammer tapping in a thumbtack. In addition to that, I need to know from what part of the engine block the noise seems to be emanating. The way to determine that, assuming you don't have access to a stethoscope, is to take a short length of garden hose (4 feet or so), place one end at your ear, and wave the other end around near the engine (watch out for the fan!) until you localize the source of the sound. Typical places are along the sheetmetal cover on the top of the engine, along the cast iron piping near the carburetor (the manifolds), and on the other side of the engine, anywhere on the side of the engine block. Make those determinations and get back to me - your noise can be anywhere from inconsequential to serious, and I cannot guess at where in that spectrum it lies without information. I also need to know if the noise is affected by RPM, acceleration or coasting, etc.
I need to know if your engine has mechanical or hydraulic valve lifters - both were used in 1954, generally the vehicles with automatic transmission had hydraulic lifters and the ones with manual transmissions had mechanical lifters - so give me any information you can about that. I assume your truck is a manual shift, and would probably have mechancal lifters, in which case your noise may be very easy to cure, and not a problem in any case.
As for reference material, there are shop manuals for every specific vehicle, and it is a good idea to have the original shop manual for your truck. New ones are no longer available, but reprints are available from automotive literature dealers. For a good vendor, contact Ed Faxon at www.faxonautoliterature.com Ed is a good guy, and will have it. You might also want to order a copy of the owner's manual for the truck - it will help with choke instruction and other things you might like to know.
In addition to the shop manual, there are a plethora of aftermarket books on automotive maintenance, but of course the current issues are going to be too new for much help to you. There are reprints of the "Chilton's" or "MOTOR" manuals available - you can ask Ed Faxon about those - he may have one which covers the 54 Chevrolet (and your truck uses passenger car mechanical parts for the engine/transmission and many of the other parts of the vehicle). It is possible that there are similar manuals for light trucks, but I am not aware of them - ask Ed about that too.
Ok, that's enough for now - go forth and investigate!
Dick
