QuestionI have a 1955 Fleetwood. I't seems to be under powered and knocks when I depress the gas heavaly it knocks loud but not when I nurse it (very little gas). Also when going down hills it starts knocking but in a diffrent fashion more like a loud clicking and goes away after sitting idle for a couple miniutes. It seems worse with low grade fuel. Does this car need leaded gas is this my problem? Puzzeled since it goes away at times. Is this mechanical or somting simple? Any info would be great. Thanks Tim
AnswerOne thing to suspect is pre-ignition or "ping", but since you also say the car feels underpowered, I suspect there are more serious problems. I owned a 55 Cadillac myself until recently, and no one would call that car underpowered!
However, before you get into more expensive diagnostic techniques, try this: Retard the ignition timing about 10 degrees from where it is now set.
If you do not have test equipment to do this, there is a poor man's way to accomplish this: With the engine off, remove the distributor cap, and have a friend tap the starter momentarily. Note the direction of rotation of the rotor. That tells you which way to move the distributor to retard the timing. Mark the position of the distributor body in some way so that you can tell how far you are moving it, and loosen the hold-down clamp at its base. Move it 5 degrees in the SAME direction as you saw the rotor moving in the previous test. 5 Degrees will be about 1/16 of an inch at the outer periphery of the distributor body. (5 degrees at the distributor body is 10 degrees at the crankshaft, which is what you want.)
Now, reinstall the distributor cap and repeat your test drive as closely as you can to see if the noise has lessened. If it has, you may be using the wrong gasoline in the car - try putting premium gas in it, and make sure you have fresh gas in it. Lead isn't the issue, it is octane number. Your car was designed to run on "high-test" gas, and today's highest grade of gas should be sufficient unless the engine is badly loaded with carbon deposits in the combustion chambers.
If doing this makes no significant difference to your symptoms, you are going to have to take the car to a skilled mechanic and have him do a full work up on it - compression test, hot oil pressure, and most of all, an experienced ear listening to the noise.
The above addresses the noise you are hearing when pulling a hill, it will have no effect on the downhill noise - I suspect that is a sticking valve lifter, which I would attack with a detergent booster in the oil - I prefer the "CD-2" oil additive for this problem, if often cures the "tick" as you are pouring it in the oil fill pipe with the engine idling.
Considering all the symtoms, I think you may have a well worn engine, but none of these things are fatal as long as the oil pressure readings are satisfactory - you can safely keep driving it. Satisfactory means at least 30 PSI at 1500 RPM, hot engine, and at least 10 PSI at idle, hot engine. You need to install a mechanical oil pressure gauge to get these readings - which you can do or have a mechanic do for you. Also, these reading are based on using SAE30W oil, which is what your engine was designed to run on. If it has the modern 5W30 or 10W30 oil in it, that is too thin, and is part of your problem.
Post a follow up question to me as you diagnose this problem - I'd like to keep track of it. Those are beautiful cars!
Dick
