TURBOKILLERS

IT IS A COM­MON MIS­TAKE TO VIEW A TURBOCHARGER AS AN ADD-ON COM­PO­NENT TO AN EN­GINE, LIKE YOU WOULD AN AL­TER­NA­TOR. THERE­FORE, THE AS­SUMP­TION IS, WHEN IT FAILS, IT IS THE TURBO’S FAULT AND A NEW UNIT IS NEEDED. AS THE TURBO IS SUCH AN IN­TE­GRAL PART OF AN ENG

Car (South Africa) - - TECH -

1 LACK OF LU­BRI­CA­TION

The num­ber one killer is a lack of lu­bri­ca­tion. Ow­ing to the fact a turbo can spin quicker than 200 000 r/min means the bound­ary­layer lu­bri­ca­tion at the bear­ings is crit­i­cal. If for some rea­son the cor­rect-speci cation oil does not reach th­ese ar­eas at the cor­rect pres­sure, turbo fail­ure is im­mi­nent. Lu­bri­ca­tion prob­lems may in­clude in­cor­rect oil, faulty oil pumps and a blocked oil feed (or drain) pipe. When a turbo is re­placed, a dry start-up – if the cor­rect lu­bri­ca­tion pro­ce­dures were not fol­lowed – can kill a turbo in a mat­ter of sec­onds. Even at idle, the turbo spins at about 10 000 r/min.

2 OIL CON­TAM­I­NA­TION

It is not just suf cient for the turbo to re­ceive oil; the liq­uid also needs to be clean. As the tur­boshaft spins at such high ro­ta­tional speeds in the bear­ings, any par­ti­cles or de­bris in the oil act as grind­ing paste and wear away the shaft and brass bear­ings in the case of the jour­nal type. Foren­sic anal­y­sis of this fail­ure mode re­veals scor­ing on the shaft and bearing sur­faces. The wear can re­sult in bearing fail­ure and seizure but will ini­tially lead to other prob­lems.

3 EX­CEP­TIONAL OP­ER­AT­ING CON­DI­TIONS

If a turbo runs out­side its de­sign en­ve­lope, fail­ure can be cat­a­strophic. This in­cludes over-speed­ing of the turbo lead­ing to burst com­pres­sor and tur­bine wheels if, for ex­am­ple, there is a prob­lem with the waste­gate con­trol (or vari­able-noz­zle turbo ac­tu­a­tor). The turbo ma­te­ri­als are de­signed for a speci c tem­per­a­ture range; ex­ceed­ing this is ter­mi­nal. Hot shut­down is a known killer be­cause oil starts cok­ing to bearing sur­faces. Al­though modern wa­ter­cooled tur­bos with elec­tric wa­ter pumps are de­signed to cope with en­gine stop/ start sys­tems, Chris Kam­bouris feels there’s merit in let­ting a turbo cool down by al­low­ing the en­gine to idle af­ter sus­tained hard driv­ing.

4 FOR­EIGN OB­JECT DAM­AGE

Imag­ine throw­ing a rock into the blades of a room fan. The re­sult is sim­i­lar to a for­eign ob­ject en­ter­ing a turbocharger but the dam­age is am­pli ed be­cause of the el­e­vated speeds. Run the ve­hi­cle with­out an air lter and the dust par­ti­cles will sand-blast the com­pres­sor blades. On the tur­bine side, any de­bris the en­gine coughs out can be lethal. Even the sealant wrongly ap­plied by some turbo in­stall­ers on the tur­bine ange can harden and break off in tiny pieces, rip­ping the blades to shards.

Newspapers in English

Newspapers from South Africa

© PressReader. All rights reserved.