engine pinging

[HAVABEER]

this might be a kinda wierd and stupid question.

what when peopel say your engine is pinging (tunner told me it was and i should run on premium) what should i actually be listening for.

been running on premium for a little bit now and last night i acceldently filled up with normal unleaded and the car is kinda sounding like a wipersnipper/lawn mower...could this be because i filled up with differnet petrol?

[YLD-16L]

Pinging/Pinking (called both by various bogans) sounds like you have a light rattle in your engine under load or at increased rpm. Similar to a small hammer tapping quite quickly inside your engine.

The noise is most commonly heard in standard cars when people try to drive out of a corner in 3rd or 4th gear at 500rpm, the rattle (pinging) sounds like the engine is a diesel.

It's a very distinctive sound once you know what you are listening for. It should only be evident in your engine under load. If you have an engine probelm across your entire rpm range including idle then it's a problem other than pinging.

For the actual details of what causes pinging and how it occurs look it up on google.

[ed]

pinging - sounds like a handful of rice in a 1kg milo tin (at full throttle)

when at low revs pulling away from the lights - sounds like somone is hitting your engine with a hammer quickly...

run it on premium and wind back the timing a few deg

[ed]

Wrenching with Rob--Chemical Soup: The Mystery of Detonation

By Dr. Robin Tuluie, Ph.D.

Editor's Note--This is part of a "Wrenching with Rob" series, in which Vintage Editor and Technical Writer Robin Tuluie will discuss, in depth, technical and theoretical topics that make motorcycles function.

Since the previous Wrenching With Rob, Chemical Soup: The Meaning of Gasoline we've been besieged with questions and comments regarding the combustion process occurring in an engine. In particular, the discussion focused on the problem of detonation, commonly referred to as "knock," which is a very serious and detrimental problem when it occurs - usually the pressures exerted onto the piston top during detonation are much larger (but of a shorter duration, like a pressure spike) than the mean combustion pressure. Nevertheless they are very detrimental to engine life, as the continual high shock loading of the piston, rod, crankshaft and bearings is quite destructive.

Detonation is the result of an amplification of pressure waves, such as sound waves, occurring during the combustion process when the piston is near top dead center (TDC). The actual "knocking" or "ringing" sound of detonation is due to these pressure waves pounding against the insides of the combustion chamber and the piston top, and is not due to 'colliding flame fronts' or 'flame fronts hitting the piston or combustion chamber walls.'

Let's look in some detail at how detonation can occur during the combustion process: First, a pressure wave, which is generated during the initial ignition at the plug tip, races through the unburned air-fuel mix ahead of the flame front. Typical flame front speeds for a gasoline/air mixture are on the order of 40 to 50 cm/s (centimeters per second), which is very slow compared to the speed of sound, which is on the order of 300 m/s. In actuality, the true speed of the outwards propagating flame front is considerably higher due to the turbulence of the mixture. Basically, the "flame" is carried outwards by all the little eddies, swirls and flow patterns of the turbulence resident in the air-fuel mix. This model of combustion is called the "eddy burning model" (Blizzard & Keck, 1974).

Additionally, the genus of the flame front surface - that is the degree of 'wrinkling' - which usually has a fractal nature (you know, those weird, seemingly random yet oddly patterned computer drawings), is increased greatly by turbulence, which leads to an increased surface area of the flame front. This increase in surface area is then able to burn more mixture since more mixture is exposed to the larger flame front surface. This model of combustion is called the "fractal burning model" (Goudin, F.C. et al. 1987, Abraham et al. 1985). The effects of this are observed in so-called "Schlieren pictures," which are high-speed photographs taken though a quartz window of a specially modified combustion chamber (Fig. 1, above).

Schlieren pictures show the various stages of the combustion process, in particular the highly wrinkled and turbulent nature of the flame front propagation (initially called the flame 'kernel'). A higher degree of turbulence, and hence a higher "effective" flame front propagation velocity can be achieved with a so-called squish band combustion chamber design. Sometimes a swirl-type of induction process, in which the incoming mixture is rotating quickly, will achieve the same goal of increasing the burn rate of the mixture.

As a general rule-of-thumb the pressure rise in the combustion chamber during the combustion phase is typically 20-30 PSI per degree of crankshaft rotation. Once the pressure rises faster than about 35 PSI/degree, the engine will run very roughly due to the mechanical vibration of the engine components caused by too great of a pressure rise. Sometimes, the pressure wave can be strong enough to cause a self ignition of the fuel, where free radicals (e.g. hydroxyl or other molecules with similar open O-H chains) in the fuel promote this self ignition by the pressure wave. However, this can still occur even without the presence of free radicals; it just won't be quite as likely to happen. This is why high octane fuels, with fewer of these active radicals, can resist detonation better. However, even high octane fuel can detonate - not because of too many free radicals - but because the drastic increase in cylinder pressure has increased the local temperature (and molecular speed) so high that it has reached the ignition temperature of the fuel. This ignition temperature is actually somewhat lower than that of the main hydrocarbon chain of the fuel itself because of the creation of additional radicals resulting from the break-up of the fuel's hydrocarbon chains in intermolecular collisions.

Detonation usually happens first at the pressure wave's points of amplification, such as at the edges of the piston crown where reflecting pressure waves from the piston or combustion chamber walls can constructively recombine - this is called constructive interference to yield a very high local pressure. If the speed at which this pressure build-up to detonation occurs is greater than the speed at which the mixture burns, the pressure waves from both the initial ignition at the plug and the pressure waves coming from the problem spots (e.g. the edges of the piston crown, etc.) will set off immediate explosions, rather than combustion, of the mixture across the combustion chamber, leading to further pressure waves and even more havoc. Whenever these colliding pressure fronts meet, their destructive power is unleashed on the engine parts, often leading to a mechanical destruction of the motor. The pinging sound of detonation is just these pressure waves pounding against the insides of the combustion chamber and piston top. Piston tops, ring lands and rod bearings are especially exposed to damage from detonation. In addition, these pressure fronts (or shock waves) can sweep away the unburned boundary layer (see figure 2 above) of air-fuel mix near the metal surfaces in the combustion chamber.

The boundary layer is a thin layer of fuel-air mix just above the metal surfaces of the combustion chamber (see figure 2, above). Physical principles (aptly called boundary conditions) require that under normal circumstances (i.e. equilibrium combustion, which means "nice, slow and thermally well transmitted") this boundary layer stays close to the metal surfaces. It usually is quite thin, maybe a fraction of a millimeter to a millimeter thick. This boundary layer will not burn even when reached by the flame front because it is in thermal contact with the cool metal, whose temperature is always well below the ignition temperature of the fuel-air mix.

Only under the extreme conditions of detonation can this boundary layer be "swept away" by the high-pressure shock front that occurs during detonation. In that case, during these "far from equilibrium" process of the pressure-induced shock wave entering the boundary layer, the physical principles allured to above (the boundary conditions) will be effectively violated. The degree of violation will depend on (a) the pressure fluctuation caused by the shock front and (b) the adhesive and cohesive strength of the boundary layer. These boundary layers of air-fuel mix remain unburned during the normal combustion process due to their close proximity to the cool metal surfaces and act as an insulating layer and prevent a direct exposure of metal to the flame. Since pressure waves created during detonation can sweep away these unburned boundary layers of air-fuel mix, they leave parts of the piston top and combustion chamber exposed to the flame front. This, in turn, causes an immediate rise in the temperature of these parts, often leading to direct failure or at least to engine overheating.

Scientists and engineers have recently begun to understand combustion in much greater detail thanks to very ambitious computer simulations that model every detail of the combustion process (Chin et al. 1990). Basically, a complete computer model includes a solution to the thermodynamical problem, that is a solution to the conservation equations and equation of state, as well as a mass burning rate and heat transfer model. In addition, a separate code (called a chemical kinetics code) models the chemical processes which occur during combustion and sometimes juggles several thousand different chemical species, some in vanishingly small concentrations! Needless to say these codes require huge amounts of memory and CPU time that only the largest supercomputers in the world can provide. They are far beyond the reach of the private individual and usually only employed by large research institutions or major car manufactures.

[Smokey228]

hmmm, wen i start my car up, occassionaly it sounds like sumfin rattling under the bonnet. i didnt really take notice of it, i jus gas it a lil to make it stop. but would that be pinging? i run regular unleaded with valve saver in my 18rc... sum1 said im spossed to use premium but i never do... to expensive

[chris davey]

Sounds more like low oil pressure on startup which could be noisy lifters.

[Nim]

Magna's are known for being noisy at startup. As far as I know, this is just the timing chain rattling around a bit. Other problems, as chris mentioned could just be parts not covered in oil yet.

[o_man_ra23]

smokey,
the noise you are hearing is timing chain rattle. Your timing chain tensioners run off oil pressure, so they will kick in when you rev up a bit. The other part of the problem is you probably have a stretched chain, which will be slack on the cog and rattle like that. The other item to check for the noise you have is the valve clearances. Also, switch to an oil filter that contains an anti drain back valve... works wonders at a couple of bux more.

Chris,
18RCs dont have lifters, they have an OHC running solid rocker arms pivoting on an oiled shaft. The valve clearance is adjusted with a screw adjuster.

Cheers, Owen