By on May 5, 2010

TTAC Contributor David Holzman writes:

Sajeev, my ’99 Accord (2.4L 4cyl, 170k) when cold makes noises that sound like slightly loud tappets. If the engine is around 10 degrees (scan gauge) when I start the car, I’ll hear it. If the temp is more like 30 degrees or above, if I baby the car until it’s around 140-150, I won’t hear anything, but if I push it, I’ll get the noise fairly loudly. So I don’t push it. When I described it to Ray Magliozzi (Clack, from NPR’s Car Talk show) he thought it was piston slap. What do you think?

The noise is gone when the car is close to warmed up. The one thing that worries me a bit is that there was a point where I was driving much more than usual (though very easy driving, country roads around 40-50mph mostly, 23 mile trips) and I didn’t go to change the oil until I’d put 8000 miles on it, and the oil was around two quarts low.

I don’t remember having the noise right after the two quarts low, but when I first remember noticing it, it wasn’t very loud at all. It is loud now if I push the car at all when the engine is very cold (like 10-40 degrees), but as I said, I don’t hear it at all after the car is near warmed up. Uses maybe a quart in 3000 or so.

If it is piston slap, here’s one question. I consider it my duty to teach kids to drive sticks, and since I’m spending several weeks at my sister’s in February, I was planning to start teaching her younger boy to shift. (He doesn’t even drive yet.) Is this going to hurt my engine? Or anything else?

Sajeev answers:

Let’s get the easy question out of the way: a warm (operating temperature) engine is difficult to damage by a novice stick shift driver. I wouldn’t even bat an eye at that. The condition of your clutch, pressure plate and even flywheel is a whole ‘nother story. If all that stuff is quite old, the novice can send it to an early grave.

You might have Piston Slap, there’s some Internet chatter about Honda’s F22B1 motors to that effect. But I have my doubts, a bad lifter or a valve adjustment issue (address this at the next timing belt service) is my concern. And I say this not to contradict Ray Magliozzi.

Okay fine, maybe I am doing that just a little. But you mentioned the motor ran for a while missing 2 quarts of oil. Overhead cam motors (more so than other designs) are sensitive to low oil pressures when lubricating the top end (valve lifters, etc). It also explains the problem: cold engine oil, low levels, and the tough winter we recently experienced.

It is piston slap or just a worn engine? Tough call: either way, you gotta live with it. I’d throw a bottle of Lucas Oil treatment in there just for fun. I had good experience with Lucas silencing a noisy main bearing in one of my cars. If it doesn’t shut up that noise, you’re only out a few dollars. Good luck!

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22 Comments on “Piston Slap: “Clacking” About Piston Slap...”

  • avatar

    My ’97 Civic 1.6 SOHC does the exact same thing. I’ve heard that Honda built some motors with too-small of pistons but I’m not sure if this is true or an internet rumor. My car also drinks a quart every 400-600 miles. If I do a long highway trip in the summertime, it uses no oil at all so I’m guessing that the pistons expand and cause the oil control rings to work properly.

    I’ve owned over 25 cars (mostly 1970s American iron) and this Civic uses more oil than any other car I have ever owned. It runs fine, and I keep a spare quart of oil next to the battery under the hood. Just gassed up this morning and I’m getting 34-37 mpg for my daily commute, can’t beat that! Going to drive it ’till the wheels fall off and thumb my nose as all the Prius drivers with the extra $ in my pocket.

  • avatar

    I’d like to know whether piston slap is harmful to an engine’s longevity, and whether it’s considered normal or a defect. I’ve got an 07 Lexus ES350 that has a very pronounced clacking sound when cold for about 5-10 minutes, after which it’s only noticeable if I’m idling next to a hard surface (e.g., at the McDonald’s drive-through) with the window down. Putting the engine under pressure (e.g. giving it a little gas while in Drive and the brake is pressed to keep the car from moving) makes the noise really loud. ( Of course, the manufacturer tells me it’s normal, and it doesn’t seem to burn oil even after 50K miles, but it sounds defective to me.

    • 0 avatar

      My wifes 2006 Lexus GS300 developed a dull knock on cold start up after we had it about a year and it had about 10 k on it. The dealer said not to worry 3 or 4 times then last year a valve hit the piston and the sparkplug and created a dead cyclinder . THe dealer pulled the heads and replaced all the valve springs, exhaust valves and cam followers. Also they did a tec bulliten for the variable valve timeing cam sprockets that have been known to cause the symptom. The car runs great but still has the cold start dull knock/tapping that does go away when warm..I have one more year on the powertrain warranty and the car only has 30 k on it and my question is does any one have any advice on where to go with this. The ES with the 3.5 litre engine seems to have the same problem. I want to run this car into the ground as in 200k and keep it forever or till I croak whichever comes first LOL Thanks

    • 0 avatar

      I had a 2.2 litre Chrysler that had Piston Slap. All of the engines would develop it, the only variable being when. By 140K or so, I could clearly hear it at idle with a warm engine. I was told by a reputable wrench that as the engine aged, the slap would worsen to the point that compression would suffer and power would slowly deteriorate to the point that the car would barely break the speed limit. That never happened to me though. By 250K miles, the engine sounded like a diesel at idle, but still had most of the original power. Only a blown head gasket killed it 4000 miles later…

  • avatar

    I wouldn’t worry about a little clattering on a cold engine. It’s always a good idea to “baby” it until it warms up anyway. A modest ampount of piston wear is usually benign until the ring grooves wear excessively and then you can get stuck or broken rings which leads to rough running, very high oil consumption and plug fouling. It sounds like you’re a long way from that though. But perhaps you should consider checking the oil more frequently than at every change! 2 qts low is often the point at which the pump will suck air sometimes (when cornering or braking for example). If you didn’t see the gauge or idiot light expressing its displeasure then there was probably no damage done. Agree that the clutch is most likely to suffer from a beginning driver, especially in a modern synchromesh vehicle.

  • avatar

    In researching your vehicle I came across an interesting fact.. for the 1999 model year Honda did not offer a 2.4 liter size engine
    in North America for the Accord

    Are you familiar with the term silent shaft or balance shaft ?
    Some engines use counter rotational shafts to reduce harmonic vibrations caused by the natural asymmetric lateral imbalance of a 4 cylinder engine as the pistons reciprocate on the connecting rods.
    This causes a secondary imbalance that can not be corrected by weighing and balancing the internal (or external) reciprocating parts.
    My theory as well as others suspect the pistons attachment is key in the pivotal movement of the connecting rod as is at its lowest or highest point in the combustion cycle.
    All but if very few automotive engine manufactures use a press to fit piston pin.. this only allows limited movement and does not offer a free range of motion as a bushed connecting rod an locked piston pin.
    This is obvious to any one that has assembled both types of connecting rod pins The range of motion to either side is not available consistently with the press to fit pin placing pressure unevenly during the combustion or exhaust stroke likely causing your secondary vibrations.

  • avatar

    This is a trick I use for new drivers learning how to drive a stick:
    1 – Make sure car is turned off. Securely tie a very strong string to 1 inch below the top of the accelerator
    2 – Run the string through a small horizontally mounted ~ 1/2″ wide 2 inch long tube securely taped to the brake pedal. This will allow the brake pedal to act as a fulcrum.
    3 – Securely tie the other end of the string to middle of the clutch pedal. The string should be tight when one pedal is all the way down (preventing both pedals to be depressed all the way down at the same time). Practice with it yourself to adjust the string.
    4 – With the car still off have the new driver practice indirect relationship between the clutch and throttle. I.e. all clutch / no gas or all gas / no clutch.
    5 – When they get the concept and you feel safe – have them start the car and try driving. The brake will always work b/c once you depress it will have immediate slack in the string and work as normal. It just prevents drivers from doing the clutch bomb start.

    I’ve used this before and it works to get the concept to several drivers without significantly reducing the life of the clutch.

    • 0 avatar

      Another good technique is to have them push in the clutch, shift into first, then sloooowly release the clutch without touching the gas, to get the feel of where the friction point is. Do that for a minute or two til they know exactly where the clutch begins to engage.

  • avatar

    Can’t add much to Sajeev. For some reason mechanics really love the Piston Slap theory. It’s like when a rocket engine explodes, and the Failure Review Oversight Board cuts all branches from the fault tree, they blame “The Particle”. But in reality it’s probably the lifters, especially if they are self-adjusting like on all modern engines in the class.

    Take the valve cover off and check the cam surfaces. If there’s any flaking, that’s your reason right there.

    • 0 avatar
      Kevin Kluttz

      He has either an F23A1 or F23A4 and they had solid lifters and rocker arms with SOHC and V-TEC. Had a 2001 for 8 years. Said F23A1 on the engine. Never a hint of noise from the valvetrain…I’m going with the piston slap, because pistons are a different shape when they’re cold, especially that cold. And they’re aluminum and expand quickly, too. Also, it holds 5 quarts of oil, and I accidentally let mine run about a quart-and-a-half to two quarts low ONLY ONCE when my wife drove it for a year, and absolutely no valvetrain damage ensued.

  • avatar

    +1 on the lifters. E36 M3’s are notorious for this, although under different circumstances. The lifters will tick like crazy at idle after running the car hard, ie. autox. Overfilling the oil slightly quiets them down.

  • avatar

    I agree with Mr.Mehta, that sounds like a faulty lifter. It’s pretty common on 8+ years old overhead cam engines. Nothing to worry about really, it’s just annoying. If that’s the issue and you want it fixed, I’m sure the lifters are very cheap about $10 each,.

  • avatar


    That’s pretty much what I’ve always done, except I do it on a flat area, and have them pull engage the clutch, and do that multiple times, until they get it. I did have one clutch student, a female cousin who was then about 17, who got it right the first time, and ever thereafter.

  • avatar

    Good grief. At 170k mi, it sounds like good old-fashioned valve tap. Every OHC engine has this at some point (usually at a much lower mileage). You probably made it worse being down a couple of quarts. No biggie. Sajeev is right. Throw in some Marvel Mystery Oil or STP Oil Treatment and forget it. These engines are tough. You’ll have to do something much worse to kill this engine, and I’m afraid your nephew won’t be enough to do the job.

  • avatar

    I’m actually not sure it’s doing it anymore. After I put the new plug wires on, both a sound like a hole in the exhaust that he very recently started and the clacking seemed to disappear. Well, almost. I do get a very faint clacking even when the car is fully warmed up, just like I did before. But what I described to Sajeev, which I’ve gotten at engine times as high as maybe the 120s or 130s was quite loud.

    The car uses oil, but not heavily, no more than a quarter every 3-4k, and it gets about 32-plus mpg on the road.

  • avatar

    Sounds like lifter tick to me as well. A usual symptom of running a car too long low on oil. The good news is it can probably be fixed just with an oil treatment. Personally, I love Auto Rx. It has noticeably improved the smoothness and performance of the two engines I’ve used it in. It gets great reviews all around on

    To determine if is lifter tick for sure you can take a long screwdriver, place the handle against your ear and move the tip of the driver around the top of the valve cover (the top of the engine). It will amplify the noise and if it is coming from the valve cover you will hear it loud and clear and that’s most likely lifter tick. If it is coming from under the engine, that’s something else, a hole in the exhaust manifold can make sounds that are similar.

  • avatar

    If it’s a light tapping then it sounds more like a lifter, but if it’s more of a banging/clanging sound it could be a damaged rod or rod bearing caused by the low oil. Had an 90’s Tbird with lifter issues, that once I fixed those I made the mistake of going a while without checking the oil. Long story short, it ended up down a couple courts and threw a rod bearing and that was the end of that.
    I did learn something from the experience, now I check my oil every time I fill up with gas.

  • avatar

    My advice to people trying to teach kids to drive stick is NOT to use a car you value. Go out and find an old five-speed Civic or something for about $500, old enough that it’s basically finished depreciating. Have them learn on that, and then when they’re up to speed — assuming they haven’t wrapped it around a tree or grenaded the flywheel — just sell it. You’ll get most of your money back, and it will cost less than a clutch job on a newer car.

  • avatar

    ’99 Accord 2.3L engines do not have lifters, the rockers run directly on the cam and valve tips. First thing to do is have the valves adjusted. If the engine was once starved for oil, I’d think possibly one or more rod bearings has been damaged. Usually by disabling each cylinder one at a time (by pulling the plug wire) you can track down which cyl is the culprit.

    …and Honda has a Bulletin that says cold start piston slap that diminishes within 2-3 minutes is normal.

  • avatar


    Your Lexus is not defective. My wifes Toyota Avalon has the same engine, and makes the same noise. The noise is caused by the timing chain. The sound drove me up the wall until I tracked down what it was. When it annoys you, take comfort in the fact that you will not have to do a costly timing belt replacement further down the line. These engines have their quirks, but the strong power output and excellent gas mileage more than make up for these minor annoyances. Good luck!

  • avatar

    My 4.0L Jeep does this when it’s really cold. My mechanic thinks its a stuck lifter. Reving the motor a bit quiets down the clatter.

    I’m sure there is a top end rebuild in my Jeep’s future.


  • avatar

    I think most Honda, heck most OHC motors do this at one time or another. I’ve looked at a few G1 Legends that had tappets ticking. It’s perfectly normal. My father didn’t believe this until the 5.4 Modular in his company truck started doing it at 150K with no ill effects. He’s used to pushrod motors, so I quit trying to explain it to him.

    170,000 miles on a Honda four banger, you’re due for a timing belt in ~30K. If it truly annoys/bothers you, have the top end inspected when you have the timing belt replaced. Even better if you DIY.

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