Piston failures

[Ragnarok]

Do you guys think that oil consumption might be an indicator for a defective piston ? Oil seeping trough and burning in the cilinder ?

Could be, but could also be a sign of turbo blow by.

Mine eats hardly any, though it's pretty "stiff" due to forged internals.

[Jero]

Well mine drinks 0,08 quart on every 700 miles (i hope i converted it right, 0,1 L or 1 Deciliter per 1000 km) On my citroen dealer they said, that unless it burns more than 0,5 L per 1000 km they wont even bother checking whats the cause and he started acusing me of not fully warming the engine before i start reving the engine and also because i drive fast. Now thats a hell of a way to talk to your customer

[Czar]

Since the THP was first installed into the BMW MINI back in 2005 there have been a number of component revisions, understanding why individual components are revised, has absolutely NOTHING to do with a word that is so readily banded around, that word being FLAW or FLAWED, accompanied alongside design.

What you need to understand is, let's keep this on track, and discuss the THP piston, the first incarnation of the piston, as produced by MAHLE, is not subject to a design flaw, I now hear lots of you shouting at me, it must be flawed as it breaks and there is a 2nd incarnation of the THP piston.

Let's ask a couple of questions:

Why does the first incarnation of the THP piston break, and break in the same place ?

Why was a second incarnation of the THP piston produced with a supporting shoulder ?

Before I start to answer the above questions, here is a little insight into the sensitivity of the THP engine, the combustion pressures, heat harmonic vibrations, fuel mixture control, camshaft timing phase and reversion, cylinder temperatures, firing temperature and a crucial factor which won't be commonly linked to any of this, intake temperature, interesting fact that last one huh !!

So why is all the above relevant to piston failure; let's see if we can shed some light on the issue.

When designing in this case the piston, crucial data is necessary at the designing stage, what is crucial is knowing the working combustion pressure and cylinder working temperature, without this you can't know what % of silicon to add to the metallurgy blend for the particular piston, you need to get the % mix correct to control the expansion ratio of the piston to fit within its tolerance working environment, same goes for the piston rings and cylinder liners.

There is so much more to add to the above, but I would be writing a very lengthy thesis, and most of you would loose the will to continue reading, so I am trying to keep it very brief.

Once the calculations are known, the piston design can begin, very crucial to get the fuel control seat correct, get this wrong, and the combustion will be off centre, and very quickly destroy the piston.

So we now have the first incarnation of the THP piston, (not a design flaw) it undergoes rigorous testing and casting control, to ensure no design flaws, otherwise it is rejected, it was after all designed and manufactured fit for intended purpose.

With the first incarnation in service, lots of variables many of these can not be taken into consideration at the design stage, come into play, issues within the individual vehicle manufacturers chosen ECU control, poor fuel quality, increased oil service intervals, leading to infrequent checking of the oil level, the customer and his or her choice to modify !!

Why is the oil level and frequent changes so crucial, the Pistons are cooled on the underside by oil injection.

ECU control, very important at controlling engine knock (pinking) incorrect detonation loads, place huge amounts of unwanted uncalculated cylinder pressure on the piston, the heat harmonic vibrations from excess cylinder pressure, sonically starts to damage the piston metallurgy, these incorrect detonation loads, can be from poor fuel quality, low oil level, infrequent changes, remapping (pushing up the boost) ECU control issues, especially with the timing and fuel phase.

As you can see there are lots of unwanted uncalculated variables that take their toll on the poor old piston, even such a simple air filter change alters the pre turbo air intake temperature on the THP, which is very sensitive to heat changes within the combustion chamber, and the wurst of all by far, are those vehicles which do very short journeys and never get to working temperature, this affects oil quality, the combustion process and the wear within the cylinder, piston, piston ring and cylinder liner suffer from premature wear, very cool cylinders, rapid wear from heavy high gear loadings, which lead to high oil consumption and very rapid carbon build up.

Along comes the second incarnation of the piston, and the first is deemed a design flaw, and what should be understood, is the real world data that is collected, from the uncalculated unknown valuables at the first design stage.

[cyclone]

So the perfect laboratory piston got a dose of the real world and went to hide in a corner. Then redesigned to stand up to the big bad real world conditions that those pistons were facing without cowering in fear.