Yo, engine geeks...
 

I popped into my dads work to say hello today, and he showed me a piston he extracted from a ford Ka. It was fubar'd, melted through and a right old mess. He's replaced the part and cleaned up the engine, but he couldnt explain why that piston had melted.

So here I am, opening up a discussion for reasons why a piston may melt in a Ford Ka engine. The only thing I know as to why a piston can melt through is a really hot burn from running lean, but it wasnt the case here

sooooo

what could have happened? I'm really interested in this sort of stuff, i find that when you discuss engine faliure, you end up learning alot

I'm gonna see if i can get hold of the piston as a paper-weight

Re: Yo, engine geeks...
 

pic

Re: Yo, engine geeks...
 

I forgot to take one. the melting-through occured at the edge of the piston, not through the centre

Re: Yo, engine geeks...
 

Yup, pics. Lots of possible causes, too lean, plug too hot, too much ignition advance. A bit of detonation can be survived but if it progresses to preignition then things melt very quickly.
Detonation can sometimes look like a rat has been chewing on the edges of piston.

Re: Yo, engine geeks...
 

YC, thats what it looks like. I'll get my dad to take pictures of the piston for me

just seems an odd thing to occur in what is really a reliable car. Goes to show that despite all the modern advances etc etc that drastic things still go wrong

and even though its expensive...its quite awesome, like face-plants

Re: Yo, engine geeks...
 

the engine in the KA is about 13 years old now, not what i would call modern......

Re: Yo, engine geeks...
 

But they are a simple design, usually fairly reliable.

Re: Yo, engine geeks...
 

I dont hear many tales of car engines failing this way, this is the first one that has seemingly done it of its own accord. The other engine destruction was due to a failed oil pump which wrecked all the big-end bearing surfaces on an audi engine.

Re: Yo, engine geeks...
 

Actually, it is a development of the ford kent engine that dates back to the Anglia of 1959, although most of it has had some extensive redesigns since, it is still the same basic design. I remember looking at a Ford Ka when it first came out and having a distinct feeling of deja vu when it first started up; it still sounded like my 20-odd year old fiesta 1.1L. The Ka uses a 1.3L OHV version with electronic ignition and fuel injection (early cars might have carbs but I can't remember).

MT

Re: Yo, engine geeks...
 

All for KA's were Fuel Injected IIRC. Tbh it's been around for donkeys years and still looks fresh and is still funky.. and it's a EVERY DAY, EVERY PERSONS car...what other car has done that?

Re: Yo, engine geeks...
 

Mini / beetle/ datsun 120y :smt102

Re: Yo, engine geeks...
 

Mini = falls apart from rust after 3 weeks (4 if you're lucky)
beetle = nuff said, worst car in history and looks like a squashed butternut.. simply terrible
datsun 120y = well, the first car to show that cars could be reliable! definatly not a looker nowadays but certainly a car the modern world should be thankful of!

Re: Yo, engine geeks...
 

fortunately others don't share your opinion

The Mini has won many awards over the years, perhaps the most notable include: "Car of the Century" (Autocar magazine 1995), "Number One Classic Car of All Time" (Classic & Sports Car magazine 1996) and "European Car of the Century" in a worldwide Internet poll run by the prestigious Global Automotive Elections Foundation in 1999. The Mini managed second place (behind the Model T Ford) for "Global Car of the Century" in that same poll.

In the end 5.3 million Minis were sold, making it by far the most popular British car ever made. Thousands of these are still on the road, with the remaining pre-1980s versions being firmly established as collectors' items.

Re: Yo, engine geeks...
 

I'm not arguing that the Mini isn't simply a brilliant piece of engineering, but cmon admit it..they rust.. xD

I never said it was a bad car. Just that it was a rusty one. :p

I seem to recall seeing on a documentary filmed by Jeremy Clarkson that each one of the original Minis were sold at a LOSS, also contributing to the whole decline of British Leyland.. among other things..

Re: Yo, engine geeks...
 

given a production run of 41 years and the last now being 9 years old, of course they'll be a rust problem by now, against the ford Ka, can't see them making that for the same production run :smt102,

given general advances in technology; any modern car will be more advanced in everyway, but it's not an every person car, as there has never been one as not ever person has one or would want one, but if you ment a benchmark, change it peoples perseption of personnal transport then there are many others that fit the bill far better, those three were the first to come to mind.

Cheers Mark.

Re: Yo, engine geeks...
 

Ahh, i seee now :).. well there was one that you forgot.. must have slipped your mind lol. :p

fiat 500, better than the mini IMO it has more soul... and it's italian you can't go wrong.. apart from electrics.

Re: Yo, engine geeks...
 

Far more than one; I assure you, Impact wise the Austin 7 was more a budget car for the masses than the fiat though, built under license in both Germany and America, probably the start of affordable motoring.

Re: Yo, engine geeks...
 

Seeing as over 21 million were sold, it would appear that yours is a minority view.

Not to mention utterly wrong.

Re: Yo, engine geeks...
 

:d:d:d:d:d:d:d:d:d:d

Re: Yo, engine geeks...
 

I always thought lean running did the middle of the piston because it means the charge is burning to quickly and to hot and it's the middle of the piston that gets the least cooling (it also has less mass than the edges where the skirts are). I've got some lovely examples from my two stroke racing days, neat 1cm holes straight through the middle of the piston.... I'm not so sure about pre-ignition though. This happens because the charge ignites before the spark tells it to, just like a diesel engine, and usually happens because it gets to hot during compression, so either wrong fuel or to high a compression ratio....
What are the other pistons like? I can't see pre-ignition affection only one cylinder, but lean running could be down to a dodgy injector on just one cylinder, or I suppose the ECU could be up the duff and telling the injector to deliver the wrong amount of fuel to that cylinder (don't know anything about Ka engines, do they have separate injectors or a common rail?) Either way sounds like an interesting head scratch moment.

Re: Yo, engine geeks...
 

The other pistons where fine. I'll get my dad to send me the piston so I can get pictures. Just so odd on an engine thats not really stressed.....i'd expect this from a boy-chaser's pimped out fiat that he regularly redlines and generally treats like a lump of poop

it;d be intersting if the car came back again with a similar problem

Re: Yo, engine geeks...
 

With a global population of over 6 billion I would have said his opinion was a hugely majority view.

Oh and right ;]

Re: Yo, engine geeks...
 

Mark II Rover 200 (with the honda engine) I still see aload of them. Shame theyre right ugly things now

Re: Yo, engine geeks...
 

Piston failures -
once you go into conditions where a failure will occur, the inevitable failure can take a number of forms.
Very often preignition is behind a piston failure like you describe, the reason for the preignition can be various.
As said previously, a reasoably well developed engine will withstand quite a lot of knock (detonation/pinking), though eventually it can lead to fatigue failure of the second land (the piece of piston between the top and second ring). Due to its very nature, the knock often occurs right at the edge of the chamber away from the plug, often near the exhaust valve but not necessarily. I have seen piston top lands "eaten" away with fatigue pits when I was involved in piston development, we were evaluating protective treatments for the top land, nickel plating/hard anodising etc.
Eventually the top ring can become trapped if the ring land material deforms or breaks, and this will often lead to torching through past the ring, then very quickly the material overheats locally and starts to weld to the bore and it's all over bar the shouting.
Alternatively the piston crown can just get too hot and expand to the point where it becomes an interference fit in the bore, then the friction generates heat, the material melts/welds, the rings trap, the flame torches through etc etc. Top land clearance is minimised these days in the interests of HC emissions, so the scope for tolerating overheating is marginal. Often simple crown overheating will lead to failures directly above the pin bosses since that's the direction the piston tends to expand more (heat paths away from the crown etc), and in a 2-valve engine like a wedge chamber or bathtub, the valves will be on this axis so knock will often be occurring directly above the pin boss.
Wrong plug grade or over advanced ignition or even loose spark plugs can be causes of pre-ignition. Combinations of conditions are often the cause, if for some reason the cylinder is running slightly lean (injector plugging is a common feature especially on earlier designs of FI engines, or if throttle body injection is used you can get lean cylinders (just like with single carbs), then if you run at full load the components get a bit hotter than normal, then you back off the load and the ignition advances and the plug overheats and hey presto.
Also with pressed gudgeon pin designs (pin is pressed into the rod and rotates only in the piston bosses) it's possible to get pick-up in the pin bores, or ovalising of the pin, and increased friction can cause excessive skirt loading, which can lead to failure.
I remember seeing an old Escort 1300 belonging to a friend which was rattling well but still running. When we pushed the pistons out of the block, on two of them the skirts fell completely off, it was only the fact that the breaks were like a jigsaw piece that the parts stayed together.