andylancaster3000
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| posted on 2/1/12 at 03:59 PM |
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Duratec Piston Failure
Currently trying to determine the cause of a piston failure on our 2.0 duratec.
The story:
Prior to the last meeting at Cadwell it was noticed it was breathing heavier than you'd expect. Not badly enough to not enter but probably worth
bringing the head off afterwards for an end of first season inspection!
At Cadwell we suffered a failure of all big ends due to oil starvation. When the engine was brought apart it was also noticed that the edge of the
crown of one piston had a rounded edge over about 10-15mm. When the piston was taken out we found that the 2nd ring had broken up and the lands
between rings 1,2 and oil scrapper had 'burnt' away over about 40mm below the rounded crown. The bits ring were contained but piston bits
were not to be seen. See picture below.
Whilst we're fairly sure what caused the big eng failure we struggling come to an acceptable conclusion why the piston has failed in this way.
Possible thoughts are:
- The bore was starved of oil causing the ring and land damage
- One injector is faulty possibly causing damage crown or bore wash.
- Foreign body has gone into the cylinder
I have a number of reasons why these don't seem sensible however. We have a replacement bottom end but am not happy to put it back together
without getting to the bottom of this one.
What do people think?!
Cheers
Andy
[Edited on 2/1/12 by andylancaster3000]
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owelly
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| posted on 2/1/12 at 04:11 PM |
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I'd say, lack of oil probably in line with your big end issues. The damage looks to be on the thrust side so wouldn't like a lack of oil.
Does the knackered shells coincide with that piston? If theres no oil getting through the journal and up the conrod, that would cause your fault.
http://www.ppcmag.co.uk
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andylancaster3000
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| posted on 2/1/12 at 04:18 PM |
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I'm erring on this conclusion mostly too.
Each of the 4 shells failed to a similar extent but the piston damage occurred one No2 only.
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stevec
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| posted on 2/1/12 at 04:56 PM |
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Looks like detonation failure to me.
Steve.
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Bare
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| posted on 2/1/12 at 04:58 PM |
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That the piston's thrust face?
Looks like either the ring land or the ring (less likely) gave up the battle. Can't tell which was first to go tho.
Are those oem style pistons (not familiar with the pistons on that engine) seem a bit short as if of aftermarket slipper types.
Rocking can be a problem with some
Forged pistons would certainly be worth looking into.
[Edited on 2/1/12 by Bare]
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ajw
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| posted on 2/1/12 at 06:19 PM |
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The only answer to failure is to dry sump the engine . Use a millington spec tank to avoid air in the oil. I have written off a duratec in cadwell and
oil starvation is a problem.
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pjay
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| posted on 2/1/12 at 06:29 PM |
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Hi Andy - what sump were you running?
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andylancaster3000
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| posted on 2/1/12 at 07:56 PM |
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We have been using a DIY job which I think with a bit of work could be made to work but have since bought an SBD/Titan/Raceline sump which should do
the job I hope.
[Edited on 2/1/12 by andylancaster3000]
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sebastiaan
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| posted on 2/1/12 at 08:19 PM |
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Can you post a picture of the rounded edge on the piston crown? It might indeed be detonation damage.
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andylancaster3000
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| posted on 3/1/12 at 11:28 AM |
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I've got one other shot of the piston installed (not to hand though) but it doesn't show a lot more than the picture above. There is no
other damage or pitting on the crown of the piston or head which is what I thought is typical of detonation damage but would be interested to hear of
otherwise...
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MikeRJ
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| posted on 3/1/12 at 12:59 PM |
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quote:
Originally posted by stevec
Looks like detonation failure to me.
Steve.
Agreed, that is detonation damage. Very much like this poorly piston from my Fiat that a previous owner killed by winding the boost up and not
checking the fueling:
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owelly
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| posted on 3/1/12 at 01:32 PM |
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I've never seen detonation that hasn't marked the piston crown. Detonation starts as a hot spot that then burns like an oxyacetylene torch
through the piston/liner.
The picture above looks more like the land has colapsed due to overpressure.
http://www.ppcmag.co.uk
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owelly
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| posted on 3/1/12 at 01:44 PM |
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This was caused by pre-ignition detonation...
http://www.ppcmag.co.uk
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sebastiaan
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| posted on 3/1/12 at 04:45 PM |
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quote:
Originally posted by owelly
I've never seen detonation that hasn't marked the piston crown. Detonation starts as a hot spot that then burns like an oxyacetylene torch
through the piston/liner.
The picture above looks more like the land has colapsed due to overpressure.
The pic in the first post shows damage to the piston crown, and:
quote:
Originally posted by andylancaster3000
it was also noticed that the edge of the crown of one piston had a rounded edge over about 10-15mm.
So my first port of call would be checking ignition timing, fuelling and spark plug heat grade as I still suspect this was caused by detination / high
speed knock initially. How was the fuelling and ignition timing set up?
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MikeRJ
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| posted on 3/1/12 at 05:08 PM |
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quote:
Originally posted by owelly
I've never seen detonation that hasn't marked the piston crown. Detonation starts as a hot spot that then burns like an oxyacetylene torch
through the piston/liner.
The picture above looks more like the land has colapsed due to overpressure.
Detonation causes a violent shock wave which can easily break ring lands. Once they have
broken, hot combustion gasses are relatively free to pass down the side of the piston and things start melting.
The whole reason for the use of forged pistons in high performance engines is that they are are more ductile than cast pistons (which tend to be
brittle) so can tolerate more of this type of abuse without breaking.
[Edited on 3/1/12 by MikeRJ]
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owelly
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| posted on 3/1/12 at 05:26 PM |
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I've had a better look at the first piccy on a proper monitor, as opposed to my phone, and you're right, the edge of the crown has
damage.
There's a few points in that link I dissagree with but I'm no expert, just someone who has been all over the world to investigate engine
failures (mainly marine and gensets) and my words come from my experience. What would be hard to establish, is the relationship between the detonation
and the bearing failure. Cause or symptom?
I doubt you could find out unless you had afr readingd at the point of faolure, or found an air leak or some other reason to run lean.
http://www.ppcmag.co.uk
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andylancaster3000
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| posted on 3/1/12 at 09:01 PM |
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I suspect that if the ring land damage is det then as we originally thought the bearing damage is a separate problem piston failure. This seems
sensible as it was showing signs of piston distress (by the heavy breathing) prior to the weekend of the bearing failure.
This does now mean I'm going to have to investigate the what is causing it, whether it be fueling or ignition related... 
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andylancaster3000
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| posted on 3/1/12 at 09:02 PM |
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Oh and thanks for peoples thoughts! Please keep them coming if you have more!
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coyoteboy
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| posted on 4/1/12 at 02:59 PM |
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Definitely looks like detonation damage to me, and the big end failure could be related - severe detonation causes impact damage to the bearing
surface which will damage the oil film, leading to metal on metal contact. Assuming the bearing damage was fairly uniform across all pistons or heavy
on one or two you might have had an overall effect of dropping available oil pressure under load.
[Edited on 4/1/12 by coyoteboy]
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MikeCapon
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| posted on 4/1/12 at 03:23 PM |
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Another vote for detonation. Seen way too many of them when racing a Colt Lancer Thundersaloon.
You only had to hear the slightest "det" noise and the piston(s) broke exactly the same way each time.
ETA Often without any damage or witness marks on the crown. The lands were the first thing to go.
HTH
Mike
[Edited on 4/1/12 by MikeCapon]
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