Casebook
BAD OIL
Larry Mccreedy made quite name for himself as a guitarist and he still strums the chords from time to time but his life changed when he inherited the family farm. He has a relaxed manner of speaking and moving that no doubt make him a good meditation companion but this did not endear himself to teachers during his schoolgoing years. In fact, the music teacher referred to him as “Largo” (slow and stately in music terms).
Largo Larry recently bought a 2011 Audi and brought it in for a service. When the car turned up, we discovered the camshaft covers were leaking and the idling was erratic. When August drained the engine oil, it wasn’t just dirty; it looked like it was beginning to form sludge.
August knew a blocked crankcase breather could cause the oil to deteriorate fast and also form an oil leak, so the next step was to remove the positive crankcase ventilation (PCV) valve and shake it. There is a pintle inside which should move and make a rattling sound but the silence told him the valve was no longer operating correctly. This would have to be replaced.
A PCV valve can block with an accumulation of oil varnish and impurities often a result of using the wrong oil. This will cause the moisture and blow-by gas escaping past the rings to stay inside the crankcase and not be sucked out. The oil will deteriorate and crankcase pressure will build up suf ciently to cause gaskets to start leaking. It may also affect the mass-air ow sensor, which has an in uence on the air/ fuel mixture, thus increasing fuel consumption, emissions and affecting the idling.
August suspected the sump did not contain the remains of fully synthetic oil. This is essential on turbocharged engines because it is more capable of dealing with the high loads and temperatures such an engine is exposed to.
The Audi ended up with a proper service, a new PCV valve, new camcover gaskets and a ushed engine containing fully synthetic oil. I explained to Largo Larry many oils carry a percentage (usually quite low) of synthetic oil but the good stuff, suitable for turbos, needs to be fully synthetic. These oils are modi ed (chemically converted) and puri ed according to processes developed in a laboratory.
WRONG PLUGS
Most locals know they should never ask Ponty Pienaar to make a speech. If he gets the chance, he’ll adopt a Pope-like tone and ponti cate about subjects he knows nothing about. And he’ll do it to such an extent even his enemies will start to feel embarrassed. He farms mainly with sheep, so his irritating habit is not a disadvantage when dealing with his ock.
Ponty has a more endearing side to his character: he is a real motorcyclist, not just a commuter, and that makes his company acceptable. Some years ago, he bought a damaged 15-year-old BMW at-twin, repaired and restored it. Over the years, he found the spark plugs needed replacement far too often and eventually came in to have a chat.
Both Hannes and I used to own BMW motorcycles, so I gave the job card to him. He checked on a comparative chart and found the plugs on the bike had the correct heat range but were the cheaper copper-cored variety. Rather than the more expensive type with platinum on both electrodes lasting for up to 160 000 km on water-cooled engines, these plugs needed replacement at 45 000 km. Ponty claimed he had to replace the spark plugs before 12 000 km and this was worth investigating.
Hannes dug into some spark-plug literature and discovered engines employing a wasted-spark ignition system (thereby eliminating the need for a distributor) devour copper-core spark plugs; he knew later BMW motorcycles used such an ignition system. It means there is one doubleended ignition coil with an HT lead coming out of each end going directly to one of the two spark plugs. When the circuit is interrupted, the spark at the cylinder ready for combustion sets the mixture alight but the other spark res into the exhaust gas and is therefore wasted.
The live spark jumps from the central electrode to the side electrode and the current then travels through the engine to the other plug gap, where it jumps in the opposite direction a fraction of a millisecond later. Copper-core plugs erode faster than the platinum type under this reverse-current situation.
What this means is dead-spark systems have to use platinum-tipped plugs.
Ponty has an endearing side to his character: he is a biker and that makes his company acceptable
puncture mystery
My Volvo has a slow puncture which no one can fix. It has been taken to the tyre shop six times and the cause of this slow puncture couldn’t be found. The search for the leak included the removal of the tyre to look for a piercing object on the inside of the tyre and tyre walls. Every time, the valve was replaced.
The last time, the tyre was removed for the umpteenth time, some security film was placed on the inside (according to the technicians, a necessary step on Michelins). Needless to say, the persistent slow puncture has remained. Can you please help with a solution? ROBERT NEETHLING Alberton We do not buy the excuse it’s a problem with Michelin tyres.
Logically, the puncture is located in either the tyre itself; a valve; the tyre-rim interface; or the rim. Because the tyre has been removed so many times and checked without success, I would propose a final check: swap the two tyres on the same axle. Therefore the “leaking tyre” would be on the other rim and the “good tyre” on the rim where the leak occurred.
If the leak is transferred to the other side, i.e. has travelled across with the tyre, the problem is definitely tyre related. If the leak is present on the “good tyre” on the same rim where the leak first occurred, the leak is related to the rim (or valve). This should at least narrow down the problem. A tube is another solution but we are not in favour of this, as it hides the actual problem and can be susceptible to wear and heat build up on the tyre-tube interface.
piston movement
Let me state I am not a technically minded person.
I do, however, enjoy doing some maintenance work myself on vehicles and have come up with an interesting (or possibly unrealistic) idea: what will the effect be if an engine is designed to move every piston seperately? I suppose maximum power output will be less because two pistons together will produce more explosive force at one time, but can there be any other useful consequences? HERMIE DE JONGH Calvinia In a four-stroke engine, there is a power stroke on each cylinder only once every two revolutions of the crank (720 degrees). The crank design determines the firing order and it is rare in a modern engine for two pistons to fire at the same time.
In a multi-piston engine, meanwhile, it’s more common to spread out the power pulses over the two revolutions to provide smoother power delivery with less engine vibration. The engine’s power output is not linked to its firing order but rather the amount of air-fuel mixture which can be efficiently burnt to convert the chemical potential energy in the fuel to motive force.
Although many enthusiasts have thought of different mechanical designs for the pistoncylinder assembly (connected to a conventional crankshaft), it’s mostly more complex with little to no additional benefit. The reason is the current internalcombustion-engine design is able to extract more than 98% of the chemical energy in the fuel during combustion, leaving less than a 2% possible improvement. Unfortunately, only around a third of this energy actually reaches the wheels, with two-thirds wasted down the exhaust and to the engine’s cooling system.
CREAKING SUSPENSION
Recently, my vehicle’s front suspension started creaking in the morning and when it’s cold outside. I have deduced this started after I took my car to a carwash that makes use of a high-pressure system. My theory is, when the person washed inside the wheel wells, the pressure and soap washed away any “lubricant” and thus the creaking resulted. Is there a product that can be sprayed on to eliminate this noise? GREG HAND East London Because the creaking is worse when it’s cold, that means the rubber bushes in the suspension become hard at low ambient temperature. A good way to locate the creak is to spray the suspension joints one by one with a lubrication-oil-in-a-can product and test if the noise disappears. If it does, you’ve found the guilty joint. You can either replace the rubber bush (rubber also hardens with age) or try another lubricant, as the spray-on oil is thin and soon wears. We would guess a dry lubricant, grease or even wax type (as used for motorcycle chains) may last longer. Please explain the use of rev counters in vehicles. They serve little purpose to the nontechnically minded motorist who changes gear by ear or necessity. PETER REYNOLDS Pretoria We agree a rev counter means more to petrolheads, as it is important for them to know: • Where the redline of the engine
is to optimise performance. • At what engine speed the torque peak is for towing purposes, hill scalability and fuel consumption. • The engine speed while cruising on the motorway to ensure top gear is selected. This applies mostly to a car with a manual transmission but it is still use ful (and interesting) to follow the shifting patterns of an automatic transmission. For non-technical people, it may simply show the engine is running. This is useful in modern, wellinsulated cars. The rev counter also shows when the stop/start function is active. Interestingly, there are many other instruments that also mostly speak to technical people such as battery voltage, oil pressure and even engine temperature.