Case­book

Car (South Africa) - - CONTENTS -

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.

BY: Garage­man

In the in­ter­ests of pro­tect­ing him from un­wanted fame, stalk­ers and the pa­parazzi, CAR can­not re­veal the true iden­tity of the re­source­ful Garage­man

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