20V (RR) rods

[Phil Payne]

The piccie's high definition (ca. 1MB) so I'm hosting it to save S2 bandwidth:

http://www.isham-research.co.uk/quattro/images/20v-rods.jpg

#1 to #5 - left to right.

The immediate history is a massive oil overfill - ca. 30mm above the 'Max' mark - causing heavy oil smoke. Drained, replaced filters, refilled and within 50 miles or so: "Bang, bang, bang".

I think the reason is obvious.

86k miles. The internal bore micrometer is easily within specification. #5 and #2 - the most obviously bent - had piston ring gaps aligned almost together.

Everything else seems undamaged.

[S2central.net]

Ouch.... Fyffe cylinder engine ?

Get it - do you see what I did there ?

I'm claiming that if its original !!!!!

[Phil Payne]

I'm claiming that if its original !!!!!

I'm prepared to bet that no one else will want it.

[S2central.net]

Story of my life - LOL

[220bhp]

So did the exsess oil hydrolic the engine, or was it to much boost,these are the same rods as 3b aby adu and aan are they not.

[s2driveruk]

someone care to explain 'hydrolock' to a numpty like me - heard it mentioned several times but noooo idea what it actual means

[Jamo]

someone care to explain 'hydrolock' to a numpty like me - heard it mentioned several times but noooo idea what it actual means

Basically liquids don't compress to well so fluid in the combustion chamber trying to be compressed equals, well see top pic

[s2driveruk]

makes sense....will avoid

[Billman]

still can 30mm above max hydrolock the engine? for hydrolocking dont you need liquid in the combustion chamber?

[Phil Payne]

still can 30mm above max hydrolock the engine? for hydrolocking dont you need liquid in the combustion chamber?

That's what I'm poking around at.

(The engine is 100% stock, BTW, no boost mods.)

30mm above 'Max' will almost certainly cause crank-induced foaming and the undersides of the pistons will quite likely slap down against the foam.

I'm wondering - why #5? Is it because the foam (above the 20Vs cast-in baffles) would slurp to the back of the sump under acceleration? Is it because the piston ring gaps were aligned?

To cap it all - I thought I needed one conrod, but ETKA says they only sell them in sets. Fair enough - probably balanced. Then I pull off the pistons and see I really DO need five. And in response to the order (by part number) for a set - Audi ships just one!

[Billman]

Number 3 rod seems also bent.

[Error404]

You'd have thought it would have smoked massively before it blew if it ended hydrolocked, if the chambers were filling with oil?
Maybe the misaligned ring gap let the foam get sucked up into the chamber from the crank case? But then why did the others bend too?
I'm sure there will be tons of decent sets of OE rods knocking about if they are the same as all the other 20vt engines?

[newsh]

maybe the oil burning caused massive detonation?

[S2central.net]

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 ?

[Phil Payne]

You'd have thought it would have smoked massively before it blew if it ended hydrolocked, if the chambers were filling with oil?

Well, yes. Read the first post again.