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Diagnosing Engine Noises - Too Low Octane, No Lead, etc.

Looking for tips on what different engine noises signify in the old 1960's American V-8's.

Specifically, what could be called deiseling or what I call valve clatter while accelerating, but only when the engine is fully warm on a hot day.

Also, can someone explain how knocking or pinging would sound different from the above?

Are they caused by low octane, bad gas, dirty valves, bad timing or ignition, no lead gas, or something else?

Bought a 67 Ford with a 390 2 barrel, 9.5 to 1 compression, and 31,500 original miles. When I test drove the car, it was making what the seller and his mechanic said was a "dieseling" sound, but only when accelerating; it sounded perfect at idle.

They replaced the distributor, condenser, and points, and that seemed to eliminate the problem. I know those parts were replaced, as I saw both the new and the old ones. The car ran and sounded great after that on the 5 mile test drive. However, when the engine is fully warm on a hot day, it still makes the noise, though much less so. I ran 93 octane with some valve cleaner in it, as the car has been barely driven in 8 years.

I just put in 89 octane, and the noise is worse, but again only on acceleration after the engine is fully warm. I am startin to put lead substitute in it, but does the timing need to be revisited?

What octane would a 1960's 9.5 to 1 engine need?

Since this is relevant to non-computer controlled cars, I thought the knowledge here would have suggestions.



  • What it sounds like you are asking is the difference between pre-ignition and post-ignition.

    Pre-ignition can be dangerous and nasty, depending on how severe. Mostly it sounds like a chain dragging under your engine. If there is just a little "pinging" or pre-ignition, and then it goes away as you accelerate, this may be okay. If it continues through the acceleration curve, you are going to lose that engine sooner or later. Pre-ignition, in simplest terms, is a premature as well as uneven explosing of the fuel, often at the wrong time in the piston's cycle, So you could have the explosive forces pushing down as the piston is pushing up...ouch! That "ping" you hear is not only valve clatter by any means. It is your internal engine parts rattling under severe stress, and possibly even the walls of your cylinders flexing in severe cases. Pinging can punch a hole right through a piston.

    Post-ignition is called dieseling because, like with a diesel, the fuel is combusted even though there is no spark. With your engine shut off, the fuel is still ignited, probably by hot carbon deposits in your engine. It is less harmful than pinging, but still indicates that some attention is necessary to your engine's internals.

    A 60s engine needs high octane, but should run on 91 I would guess. If not, your only alternatives are to buy special fuel if you can find it (some stations will pump 93 or 95), add an octane enhancer (some work and some are bogus), or retard your timing (less performance), or redo your cylinder heads for lower compression (sometimes a thicker head gasket will help).
  • The noise you describe is known as "pinging". this is the sound of the air-fuel mixture igniting too early. A valve clatter would indicate a bad hydraulic lifter. It would be a tapping that varied with engine speed.

    Older high compression engines need premium gas. 93 octane would be my choice. An octane booster would help more than a lead substitute. The lead substitute would mainly be to protect the valves. the lead in old gas prevented the valves from "microwelding" to the seats preventing erosion of the seats.

    If the engine pings on premium, try retarding the timing a few degrees.

    Another problem could be a carbon buildup in the combustion chamber. The carbon gets red hot and acts like a glow plug and igniting the fuel before the plug fires. When the plugs were replaced did the old ones have a heavy carbon deposit?

    There are gasoline additives to clean carbon. If the cleaner doesn't work the other option is to pull the heads and have them rebuilt. The carbon on the piston crown can be scraped off with a hard wooden tool. If you choose to do this have hardened valve seats installed. Hardened valve seats will eliminate the need for lead substitute.
  • It looks like we think along the same lines.
  • Thanks, guys. With these older cars that have sat around a lot, was not sure if it was bad ignition or intake system problem due to age.

    The engine as is sounds beautiful at idle and before the engine is fully warm. Once it is completely warm on a hot day, it starts to make what I call a rattling noise, but seems to be known as pinging.

    The 93 octane from Shell virtually eliminated it in the first tank of gas (had some valve cleaner as well as carb cleaner in the tank), though it was still did it occasionally on light acceleration. I thought maybe the intake system, carb, or valves were gunked. I just put in 89 to see if it was solved, but obviously not.

    The guy I bought it from told me to take it back to his mechanic to reset the timing, and he would take care of it. He did not seem that worried himself, and said he would take the car back and refund my money if it was something serious. If it is just a timing issue, that is simpler to fix than I thought. Eventually, I am going to upgrade to electronic ignition, or learn to set the timing myself.

    Thanks for all your suggestions.
  • andre1969andre1969 Posts: 21,590
    ...every time I've had a problem similar to what you're experiencing, it was either because the timing was over-advanced, carbon buildup, or just gas that was too low of an octane. The noise you're talking about, I always referred to as "clattering"

    As for adjusting the timing, I don't know how it would be on a Ford car, but on the Mopars I've owned, I'd just loosen the bolt at the base of the distributor with the car running, and slowly twist the distributor clockwise (looking from the front of the car) to retard or counter-clockwise to advance it, to where the engine sounded like it was running the best.
  • speedshiftspeedshift Posts: 1,598
    That does sound like pre-ignition and it needs to be fixed quickly, but the quickest fix--retarding the initial timing, the timing you set at the crank by adjusting the distributor--also brings its own problems.

    Less initial timing means less power, and that can make the engine more susceptible to overheating. Also it reduces fuel economy (probably not an issue or you would have bought a Honda instead).

    Depending on how those 31k miles were put on (just going to church on Sunday?) the cylinder heads may be carboned up. You can buy something you pour down the carb that supposedly cleans out the carbon. I tried it once and it produced impressive amounts of smoke out the tailpipes, but I can't vouch for its effectiveness. The best fix is to remove the cylinder heads and have a machine shop blast out the carbon with ground-up walnut shells (I think that's what they use).

    Octane booster can work but it gets expensive. I'm one of the few people who thinks water/alcohol injection works, and I think something like Edelbrock's adjustable injection is a much better long-term alternative.

    There are a few other things that can cause pre-ignition. On a hot day the air/fuel mixture is less dense and that can cause pre-ignition. If the carb is running lean that can do the same thing. Even the axle ratio can affect pre-ignition, since the typical cruiser ratio lugs the engine. You could put in a 160-degree thermostat instead of the 180 or 190 that's probably in there now, but that causes other problems--the engine never heats up to its proper operating temperature.

    Adding an extra cylinder head gasket reduces the compression ratio, much cheaper and easier than changing the pistons. You could add hardened valve seats at the same time, to compensate for the lack of lead, although I wouldn't pull the heads just to do the seats.
  • speedshiftspeedshift Posts: 1,598
    BTW I'm not telling you to change the axle ratio, pull the heads, replace the carb or anything like that. Just a) start using 93 octane, b) add booster it you need it (you probably don't put that many miles on the car anyway) and c) back off the timing if a and b don't work. If you're feeling ambitious install water/alcohol injection and play around with it.
  • From the condition of the vehicle, I'm sure the mileage is original, as everything but the top and carpet (which dry-rotted) is factory, including all the headlights (they were stamped Made in Canada - Ford - 1967, I just replaced them, but kept them). I'm not sure if just sitting all those years could gunk up the valves tremendously, so I'm thinking the timing may not be set correctly, or it is running lean when hot. The carb is original, and it may not have been adjusted for decades, it's been driven less than 2,000 miles in the last ten years.

    First tank of gas returned about 13.5 mpg in mostly city driving, and going 60-65 when on the freeway. The car does have a gas smell sitting in the garage, I checked and found no gas leaks in the lines or the carb, and I replaced the fuel filter. Maybe the bad timing is causing unburned fuel?

    Not using any oil, and the engine sounds perfect at idle. I'll pull the plugs and take a look at them, that may tell me something. I got into this hobby because I find all of this fascinating to figure out, and I'll have time to play around since it is almost time to put it away for the winter.

    I'll start with octane boost, the timing and the carb mixture. 93 octane does solve the problem for the most part, but I want to fix it the right way.
  • speedshiftspeedshift Posts: 1,598
    The carb won't need adjusting but it might not hurt to put a zip kit (minor rebuilt kit) in it. The gaskets and accelerator pump may have dried out over the years, and there's probably some varnish inside--soak the parts in clean parts cleaner. It's an easy rebuild and a great way to de-mystify a carb. Don't buy a rebuilt--it'll have way more miles than the one you've got, and no one will be more careful rebuilding it than you. I wouldn't adjust the float, the accelerator pump or anything else. If it worked for 31k it's probably all fine.

    I wouldn't be surprised if there's some gunk inside the engine but if you've got good oil pressure and the lifters don't tick I wouldn't be concerned about it. You might run a quart of ATF through the engine but with an old engine that's just sat around a lot it might cause more problems than it solves. The seals may have dried with age and it's the gunk that's keeping them from leaking.

    It doesn't sound like the timing is "bad", just advanced a little too much for today's gas. Very common problem. I went through this with almost all the '60s cars I owned.

    That 390 is one of the most durable engines around but it won't take much pinging, so take care of that before you drive it much more.

    You might to also buy a book on ignition systems, how they work and how to modify them. The problem is that your stock ignition timing is set up for 1960s octane, but by trading some distributor advance (mechanical and vacuum) for some initial advance you may be able to minimize pinging and still keep your performance.

    BTW the dieseling (running on after the ignition is turned off) may be because the idle is set too high. A quick fix is to turn the engine off with the transmission still in Drive.
  • I put a bottle of octane boost in it, and 4 gallons of 93 octane to go along with the 21 gallons of 89 octane already in the tank (it has a 25 gallon tank). It sounds great at idle, and under accelerating before the engine is completely hot. I was hoping the increased octane completely fixed it, and gave me an impulsive thought of driving it through the Lexus dealership near my house and laying a 90 foot patch, but I want this car to last a long time, so I decided not too. Had the car up to 80 on the freeway last night, steady as a rock and plenty of passing power.

    The octane quieted down the pinging substantially. Still not perfect when hot, so it is going back to have the timing and carb mixture checked. Read up on setting the timing myself, so I may buy a dwell light and mess around with it over the winter as well.

    Can't think of any other mechanical issues to ask about, so I thank all of you. Well, maybe lubing a speedometer cable.
  • speedshiftspeedshift Posts: 1,598
    Aside from having to stand on your head, lubing the cable isn't a big deal.

    The speedo cable runs inside a wide flexible tube that goes from the back of the speedo to the transmission. It's fastened to the back of the speedo by a large nut. You may not be able to see it, but you can feel it. Loosen the nut (you should be able to do it by hand) and pull the tube straight out so the speedo cable inside clears the speedo--the cable is a little longer than the tube. Squeeze some liquid graphite cable lube (I think Cable Ease is one brand) down the inside of the tube and re-install. The cable is square and has to mesh with the gear in the speedo--not hard to do.

    The usual symptom of a dry cable is a speedo needle that flickers.

    Man does this bring back memories. Man am I glad you're doing it, not me ;-).
  • It is another noise that doesn't appear until I've driven the car 10-15 miles. It's a slight grinding sound from the speedometer area, it really doesn't flicker. Speedo and odo work fine, and I assume accurately. Only makes the noise after it's been driven for a while, I figured lubrication issue. At least I can see if the cable has ever been disconnected, the car has the foot and knee room of a walk in closet, so I should be able to lay under the dash easily.

    It's funny, this noise and the engine noise appears after a while, the creaks from the vent window frame meet the windshield (weatherstripping is original, and looks old) happens when cold, but then goes away after a few blocks. Just nitpicky things on an old car.

    Going in for some minor paint touch up soon after the timing is fixed, the old guy who repainted it in 94 must have had a tight garage, a few chips and scratches from things bumping it.
  • Finally got an owner's manual ($8 over the Internet from, and in it, is specifies 94 octane as "regular" gas for all the 2 barrel engines, and 99.8 octane for the engines that require "premium" gas, basically any 4 barrel carbed engine.

    Is octane ratings done the same way now, so 94 octane from then is the same as now?

    BTW, retarding the timing solved the knocking, very simple adjustment.
  • speedshiftspeedshift Posts: 1,598
    Now that you've retarded the timing, keep an eye on the temp gauge if you've got one. If you've just got an idiot light, an aftermarket gauge is easy enough to install.
  • andre1969andre1969 Posts: 21,590
    ...sometime in the early 70's, I think they changed the way it's rated. One of my college professors, for some economics class, brought it up. Well, actually, I brought it up ;-) He was saying how high octane is a waste of money, and that no car that's running properly should require it. At the time, I was driving a '68 Dart with a 318. I didn't have an owner's manual, but a friend had given me an owner's manual to a '71 they once owned, and I'm pretty sure it recommended either 91 or 93 octane.

    Well, I brought it up with the professor, and that's when he said that they changed the way octane is rated. I don't know how, exactly, it was changed, or what would equate to what, but I discoverd not too long after that that the Dart's timing was way over-advanced, which probably explained why it wanted to puke up anything less than 93. I really don't know what exactly it SHOULD run on, but it does fine on 87.

    I just thought of '67 Catalina tends to run kinda hot, but also runs fine on 87 octane without knocking. And I'm almost positive something like that required high octane in its day! Guess someone along the line set the timing too retarded or something. Looks like I got something to keep me busy tonite...
  • speedshiftspeedshift Posts: 1,598
    Depends on the CR, but the '67-up Pontiac combustion chamber tolerates low octane pretty well, a sign that it's a good efficient design. But it does sound like someone backed off the timing--very common as octane ratings went down.

    If your 400 is a 2v it may still be a high compression engine. Check the engine code on the top front of the block near the intake manifold. It'll have two letters. I have a '69 Pontiac manual and I think they kept the engine codes pretty consistent from year to year, so maybe I can ID your engine if you tell me the code. Or it'll be in a Chilton if you've got one.
  • andre1969andre1969 Posts: 21,590
    ...just tried checking the block for that code. The only thing I saw was what looked like an upside-down "BB" on the passenger-side cylinder head. Is that the code? The car currently has a 4-bbl carb on it, but I know it was originally a 2-bbl. It was rebuilt just before I bought it, and the original 2-bbl and intake were in the trunk.

    I do know that Catalinas came standard with a 290-horse 400 2-bbl, but you could get a credit-delete 265-hp 400, which I'm guessing was the low-octane version.

    I think the rear-end ratio is something like a 2.56:1, so it that tall enough to also be lugging the engine, possibly making it run hot?
  • speedshiftspeedshift Posts: 1,598
    "The 8-cyl. engine code is located beneath the production engine number on a machined pad on the right hand bank of the engine block" says the manual. That's a little confusing because they really mean the left hand side of the engine block as you're looking at it standing in front of the car.

    The engine number is on a pad just under the left hand cylinder head. The engine code is on a smaller pad just underneath the engine number. Looks like it's just behind the water pump outlet.

    For '69 the 400/290 automatic code was YD with 2v and 10.5:1 CR. There's also a code YB 400 with 2v and 8.6:1 CR.

    The 2.56 gears do make it run hotter, but indirectly. As you say, they lug the engine, making it more prone to pre-ignition. So you have to back off the timing and then the engine runs hotter. My recollection is that the shortest gears you can put in that carrier are 2.73s, maybe 2.9 somethings. Anything shorter than that, say in the mid 3s, requires a different carrier--not that I'd change gears on that car.

    And this last part is all off the top of my head after fifteen years away from these things, so take it with a grain of salt.
  • After doing some research, I came up with the following:

    The common way of rating octane in the 60's was the Research Octane Number. This involved running an engine not under load at low rpm, not sure of the details. A rating was developed from that test.

    Another test was developed using a different kind of engine operating under load at a somewhat higher RPM. From this the MON rating was calculated.

    Gasoline today is tested using both tests, and taking an average of the two (On some pumps, it will show a formula RON+MON divided by 2)

    Typically, the MON octane rating is a little bit lower than the RON rating for the same gas, not sure why. Say 3 points. So if you needed 94 octane under the RON only method from the 60's, and the MON rating was 91 for the gas, the average of the two would give you a pump rating of 92.5 octane. It is not a direct parallel, but it seems you can take the 60's octane requirements and drop it by a couple of points for the corresponding current octane rating requirements. So 94 octane requirements should be able to run on modern 92 octane. I'm sure I grossly simplified this.

    The mechanic reset my timing purely using his ears and a wrench. He had me run the engine under different speeds in gear with my foot on the brake. At the time, I had 93 octane with lead additive in the tank. He has a lot of experience, but I still may invest in a timing light and mess around with it over the winter.
  • Timing an engine by "ear" ---good way to blow up an engine, especially a modern one.
This discussion has been closed.