My build thread GTB2056VL, race1043 etc

TDIMeister

Phd of TDIClub Enthusiast, Moderator at Large
Joined
May 1, 1999
Location
Canada
TDI
TDI
Well, first of all, take this for what it is: advice given over the Internet. :p

Second of all, engine failures are rarely the result of a single factor in complete isolation; oftentimes it is a combination of things and failure analysis, just like a lawsuit, involves putting together facts to the case that led to the occurrence beyond a reasonable doubt.

It is very interesting to note that the fissure occurred almost parallel to the axis of the wrist pin.

The picture below shows the exaggerated deformation of a piston being subjected to thermal stress. High temperatures cause the top of the piston to thermally expand more than the cooler bottom part of the piston, but the expansion is also constrained by the pin bore and the webs of aluminium that support it. This expansion is therefore not symmetrical around the piston diameter axis but is preferential on the orientation of the piston as shown.


On the other hand, under gas pressure loading, the deformation of the piston crown tends to be 90° from the former case; on the right-hand side of the picture, the stress will want to split the top of the piston along the same axis as the wrist pin.


It would seem like it's absolutely clear that the crack you experienced, based on the above, was caused by gas pressure (excessive PCP), but again -- and this applies especially to pistons -- it cannot be considered in isolation from thermal stress. Aluminium alloys decrease drastically in strength as temperatures increase. Materials developed specifically for pistons (e.g. Mahle 124, 2618, etc.) are designed to better withstand high temperatures, but mechanically-stressed areas should still remain below 250°C, while areas like the bowl lip can see temperatures reaching 350°C.
http://bit.ly/eJodTW

I showed in my paper (page 15, in case the link does not automatically take you there) that piston heat flux scales with RPM and in fact correlates well with engine brake power.

A likely sequence of events is that high temperatures from sustained high-load, high-RPM driving (Autobahn?? ;) ) caused piston temperatures to increase to a very high level, which weakened the material sufficiently that gas pressure took over for final failure as we see:
 
Last edited:

TDIMeister

Phd of TDIClub Enthusiast, Moderator at Large
Joined
May 1, 1999
Location
Canada
TDI
TDI
Gross mechanical overload by itself in the absence of significant contribution from thermal stress would show in failures in other parts of the piston as well, possibly simultaneously, for example in the area of the ring grooves and upper part of the pin bore, like this (from StingrayRT)


Edit: Based on this picture and some calculations, I can determine to good level of confidence at what crank angle the crack took place. Hint: It likely did NOT occur at TDC, and it would not have been caused by a single power stroke but by low-cycle fatigue. Actually, more likely than a specific crank angle, if the picture were to be rotated to get a view of the top of the piston, I would bet that the piston bowl would be on the left hand side. The crack propagated in the direction of a combination of the weakest strength path and highest applied loading angle (after firing TDC). :cool:
 
Last edited:

chapelhill

Veteran Member
Joined
Aug 19, 2005
Location
Scotland
TDI
03 Ibiza pd13- 2260vk Turbo etc.., Merc E280cdi
How much of an effect will having some carbon build up reduce the heat transfer and therefore peak temperatures. Fabians pistons were presumably clean. I would have expected to see other reports of similar failures.
Regards chapelhill
 

Fab176

Veteran Member
Joined
Aug 25, 2009
Location
Minden, Germany
TDI
Golf Mk4 4motion PD+++
TDIMeister, I really appreciate your posts!

A little extra info on the situation when my piston cracked: The engine was warm. I used the car only to drop my daughter at a friends house, so the car didn't go any faster than 60 kph that day. The moment when it actually broke was while driving in a 30 kph-zone with those bloody "speed-bumps" for slowing down traffic in the street. I passed one and accelerated afterwards, thats when the piston actually cracked. So no high revs and no extraordinary temperatures at that particular moment. Before that, the engine usually ran as a daily driver, no etreme rev'ing or long-term high-speed-runs. But maybe the pistons have been "cooked" before and it was just a matter of time until they fail?

Fabian
 

Rub87

Top Post Dawg
Joined
Dec 10, 2006
Location
Belgium
TDI
Ibiza '99 90HP
Anyone has an idea about the valve to piston contact? was oem cam, and valves, springs, 3 hole gasket.. When the engine was assembled pistons prostusion was checked and was within limits.. pistons were oem BHW, so same pocket dept normal PD
 

Alcaid

Veteran Member
Joined
Sep 5, 2006
Location
Norway
TDI
See signature
Anyone has an idea about the valve to piston contact? was oem cam, and valves, springs, 3 hole gasket.. When the engine was assembled pistons prostusion was checked and was within limits.. pistons were oem BHW, so same pocket dept normal PD
Boost pressure or EMP too high for the stock springs so not able to hold the valve closed?
 

TDIMeister

Phd of TDIClub Enthusiast, Moderator at Large
Joined
May 1, 1999
Location
Canada
TDI
TDI
Failures of this type are cumulative in nature, so yes, it did not happen right while you were driving in a 30 km/h zone. But it had to initiate through some particularly abnormal condition...
 

storx

Veteran Member
Joined
Jan 16, 2006
Location
Earth!!
TDI
2009 Jetta CR140, 2010 Corvette Z06
when metal is extremely hot.. you can tap it with the slightest of a tap causing it crack.. when i was taking a class on mechanical engineering.. the teacher showed this with a steel bar that was held on the ends and being pressed in the middle with some pressure.. heated up with a torch tell it was glowing and then tapped it one time and it cracked broke into two peaces.. so maybe while the load caused the pistons to be so hot.. the touching of the valve.. caused the crack to happen...
 

b5converison

Veteran Member
Joined
Apr 4, 2010
Location
london
TDI
Audi A4 S , 2.0 PD 16v, 2060VKLR 280bhp & 550nm conservative ..
really bad news .. after all the work .. to build the engine up it is a nightmare to redo it again ...

yes .. playing with SOI maps can sometime be dangerous !

@alcaid

are them PD original valve spring springs this weak ? I mean the guy was revving the car only to 4200 rpm , I can`t believe that them springs would have problems with 2.1 bar boost at only 4000 rpm .

the picture looks like thermal stress to me and them 115 blocks were not the best in cooling AFAIK don`t know the most overheated engines were the AJM/ATJ engines and head gasket failures .

did you get any EGT readings what was the TOP reading at 2.1 bar ?

what SOI at what rpm did u use coz duration won`t matter whilst you have big bore PD`s.

probably some water meth would have helped you to keep things clean and cool .

I`m getting scared thinking that 2.1 bar boost does this to a PD piston thinking I`m going to install my 2060vklr soon .. in my 2.0 PD and on top of that I already had some valve to piston contact on mine when my timing stud that holds the timing tensioner snapped flush with the head .
 

b5converison

Veteran Member
Joined
Apr 4, 2010
Location
london
TDI
Audi A4 S , 2.0 PD 16v, 2060VKLR 280bhp & 550nm conservative ..
And I`m am sure he wasn`t using 2.1 bar at 4000 rpm !
 

JFettig

Vendor
Joined
Aug 18, 2010
Location
Blaine, MN
TDI
B5 Passat, 2010 Jetta
Upgraded valve springs are available finally, Rosten and RyanP have them over on your side of the world. Highly recommended for running 2bar or more.
 

brum

Veteran Member
Joined
Nov 30, 2009
Location
Bulgaria
TDI
Passat B5, 1.9 TDI, AFN
I have a question :) .

My assumption is that the correct SOI for power should be the latest SOI producing most torque. Of course in higher RPM we should also monitor the EGT. And probably the EGT should be cured by more air than by advancing the SOI as the SOI advance will result in serious increase in the cylinder pressure. So does this seems like correct approach for SOI adjustments?

Of course if someone have a cylinder pressure sensor and position encoder attached tom some of the shafts the approach would be different, but I think the results will be pretty close to the previous approach.
 

brum

Veteran Member
Joined
Nov 30, 2009
Location
Bulgaria
TDI
Passat B5, 1.9 TDI, AFN
Agree, but I think that too early SOI can easily beat the cylinder pressure generated by a 200-300mbar more boost.
 

Yucca

Veteran Member
Joined
Apr 13, 2007
Location
Finland
TDI
ALH 388bhp, Polo 6R 2.0TDI CR GTC1752VZ
S200V in action. Compressor wheel is 56mm / 80mm (50trim)

 

arazvan2002

Veteran Member
Joined
Sep 28, 2010
Location
Romania
TDI
Audi A4 B6 1.9TDI AVF quattro
There is a gasket for 2056vl downpipe? Someone has the PN for it?
I'm intending to buy a 2056vl and I'm trying to get all the parts for mounting it to my AVF.
Many thanks.
 

Alcaid

Veteran Member
Joined
Sep 5, 2006
Location
Norway
TDI
See signature
GTB2056VL downpipe gasket: Volvo part no. 1275549
GTB2056VL turbo to manifold gasket: Volvo part no. 8631549

Downpipe flange measurements:

[/QUOTE]
 
Top