turbo whine

[neil mahoney]

why is my failing turbo more vocal on lower revs? what in the turbo is creating this whineing noise? thankyou for any help

[STEWY L]

why is my failing turbo more vocal on lower revs? what in the turbo is creating this whineing noise? thankyou for any help

the turbo consists of a shaft with basically a turbine wheel on each end of it. the exhaust wheel is driven by the exhaust gasses coming out of the cylinders,and this turns the shaft and obviously the compressor wheel on the other end.the compressor wheel draws in the inlet air.each wheel has a "snail"type housing around it,and very little clearance between wheel and housing.
the shaft rotates on two bearings which are fed with high pressure lubrication oil.
when the engine is at standstill,the shaft is basically lying on the bottom of the bearngs,save for the film of oil which has remained after stopping the engine.
when the engine starts,their is little exhaust gas to speak of and the turbo doesn't spin at all fast,relatively speaking,but the oil pressure has lifted the shaft into the centre of the bearings where it will spin quite merrily within the centre of the housings at each end.
as long as the oil is kept clean it will continue to do this for many miles,
but eventually,either through oil contamination,or normal wear,the bearings will wear and the shaft will no longer sit in the centre of the bearings as the oil can no longer support it. this causes the wheels
to catch the housings at either end creating the noise.
when the engine is at low revs,the oil pressure is less and so the wheels catch more because the shaft isn't in the centre.
another form of turbo failure is caused by the shaft snapping,,therefore the wheels at each end thrust into the housings.
this can be avoided by allowing the temperature along the shaft to "equalise" before shutting down by idling the engine a little before shutting off.
hope this helps
regards,
stewy.

[neil mahoney]

thanks stewey l, a great answer, understand it more now, do you have any recomondations where to get a exchange turbo from which i think i am going to need eventually, thanks again for your reply

[STEWY L]

you have to be talking genuine i would say, for the warranty( others may dissagree), but please do a search,as it is not just a case of changing the turbo.the oil feed needs at least inspecting(internally,in sump),better still changing.
crasher will be able to talk you through it,though you will again find his previous answers and description of this repair on the search facility.
regards,
stewy.

[neil mahoney]

cheers stewy, will look in to it.