20V (RR) rods

[Phil Payne]

I'd go with newsh. If I understand that the piston rings were all aligned then you can visualise how overfilled oil could make it's way into the chamber. The fumes would increase temp of mixture considerably. Even if the ecu was pulling back timing as a result of knock - it must have been so severe that it pinged itself to destruction.

Any bearing damage as well as rods ?

There's really no sign of pinging at all. The tops of all five pistons look much the same - a thin film of what might once have been oil, scoured by the incoming mixture and the ignition point. The head seems completely undamaged.

The bearing shells from #1 to #4 are normal for an 86k mile engine - no scoring at all and the usual slightt wear discolouration.

The shells from #5 are worn through to the backing - essentially the bearing surface has pretty much gone. Again no scoring, but the wear pattern is slightly asymmetric.

My (Chinese) digital caliper says the crank is still round - I'm amazed at what Audi cranks will sometimes put up with. Once I get new shells I'll Plastigage all the journals at 90 degrees.

I won't be at the car again until Tuesday - I'll take and post piston top and bearing pictures then.

[Phil Payne]

Number 3 rod seems also bent.

Agreed. I suspect that accurate enough measuring equipment would show they're all bent to some degree.

[JP]

Overfilling causes three things to happen inside the engine.


1st it reduces air volume in the crankcase causing increased crankcase pressures. As the pressures increase the oil control ring (2nd ring) looses its ability to seal due to its unique stepped shape designed to scrape oil of the bores. Allowing the engine to start burning oil. This reduced ring pressure also results in the potential rotation of rings as a side effect of having reduced wall pressure.

2nd the increased volume of oil coupled with the increase in crankcase pressure will throw oil until the breather system filling the intercooler, pipework and intake manifold.

3rd and last it prevents the turbo draining back freely to the sump causing the turbo seals to fail dumping oil into the exhaust system.

All of these items cause smoking at different levels of severity.

As a rule of thumb once the engine has been overfilled all pipework should be removed and cleaned otherwise you will continue fooling the intake air quality.

Rod failure as shown can happen for several reasons, however to assess it properly you would also need to see the piston sideskirts, ringlands and crowns. Along with the big end bearings in particular the rod side. It's also very difficult to assess from a picture at times as the tale tale sign may just be at the point on the other side.

As for checking which rods are straight and not without precise measuring equipment. Take a rod that visually looks the straightest fit it with a wrist pin. Then take as rod you wish to check and fit it onto the same wrist pin overlaying the first rod. Now visually compare the alignment of the big ends. Repeat this using various combinations of rods until you eliminate all the faulty ones.

[JP]

Almost forgot don't confuse pre ignition with detonation, they are two completely different items.

Pre ignition comes from hot spots in the chamber burning the fuel early resulting in deposits and melting away of the spark plug ground strap and the nibbling away of the piston.

Detonation happens when the main combustion cycle doesn't burn all the fuel and has a subsequent explosion in the chamber due to the remaining heat. This will show up as tiny little hotspot marks on big end bearings and scoring on sideskirts.

[caterpillar]

have a controll of the VOLT at the generator( when in car)...and battery...low volt may cause this too; bad ignition,bad evrything..14,4-14,7 volt WITH lights an heater on

[newsh]

Good point, also was the engine washed down after the oil was overfilled? Water in the electrics can cause bent rods. Perhaps the oil overfill and bent rods are not so closely related..

[Phil Payne]

Good point, also was the engine washed down after the oil was overfilled?

No, but the ashtray was emptied.

[JP]

No, but the ashtray was emptied.