Weird crankshaft in my AAN engine

[AANton]

Hello everyone! Some urgent help needed.

Friend and I have disassembled my AAN engine from my 1994. UrS4 and we ran into a weird problem.

Crankshaft has number 034 105 101, with imprinted letter D on one of the counterweights.

We measured pistons and rods and they are AAN stock, block is AAN, cylinder head is AAN, everything is alright, except that the piston is 6 mm below TDC - it is not aligned with the block surface.

Anyone has any idea what is happening?

We’ve never seen something like this.

Pictures are in attachment.

[Tractor Dave]

Maybe AEL crank ?

[AANton]

But AEL has longer stroke, and this is shorter stroke, as seen in photo.

[Tractor Dave]

Very strange. Maybe someone ground the crank and put standard shells in

[AANton]

What do you mean “ground the crank”?

[Tractor Dave]

What do you mean “ground the crank”?

If the crank is very worn a machine shop can grind the bearing surfaces down to make good then you fit oversize shells to make up for the material that's been removed. Seems unlikely it would make the gap you have though. We are talking tiny amounts removed. Are you sure rods and block are AAN? You haven't got a tall block?

[K Simmonds]

I'm guessing someone has used the crank out of another five pot with a shorter throw on it, something like an MC engine or even an old Carb motor.

The part number should tell you what it's from.

A very odd discovery!

[AANton]

I'm guessing someone has used the crank out of another five pot with a shorter throw on it, something like an MC engine or even an old Carb motor.

The part number should tell you what it's from.

A very odd discovery!

I don’t think so. At least it doesn’t seem like that to me.

And the crank is forged if you look closely. Not sure that old carbs had forged cranks?

Not sure about MC though.

I posted the part number, but it doesn’t help a lot.

[AANton]

If the crank is very worn a machine shop can grind the bearing surfaces down to make good then you fit oversize shells to make up for the material that's been removed. Seems unlikely it would make the gap you have though. We are talking tiny amounts removed. Are you sure rods and block are AAN? You haven't got a tall block?

Yes, but they would grind like 0.25 mm, not 6 mm(!!!).

Yes, 100 % sure about rods and like, 99.9 % sure about the block. Dipstick and everything is AAN.

I’ve posted block pictures in the attachment.

[K Simmonds]

I don’t think so. At least it doesn’t seem like that to me.

And the crank is forged if you look closely. Not sure that old carbs had forged cranks?

Not sure about MC though.

I posted the part number, but it doesn’t help a lot.

I'm not 100% sure but I think all the Audi five cylinder cranks are forged even on the old carb engines.

I'll have a Google with that part No a bit later when I have some spare time, I might be able to find something.

Your block certainly look's to be stock AAN so if your sure the rods and pistons are also stock then the crank must be from another engine, the 2.1 10V motors are a shorter stroke so perhaps it's from one of them out of something like a C2/3 model. 6mm is quite a big difference so I doubt it's a stock AAN crank that's been machined.

Obviously all your rod's are straight? As I've seen engines that have been driven through water and hydrolocked with all the rods bent, but even then it's normally only between 1-2mm.

[rxl]

2.0 liter engine crank

[K Simmonds]

2.0 liter engine crank

From an NM? That would make sense.

[AANton]

2.0 liter engine crank

Are you sure? Is that why the piston is not aligned with block surface?

I mean, does this affect anything except the volume?

Can I rebuild it freely as is?

[K Simmonds]

A 2.0 NM crank would explain the shorter stroke...

It must seriously lower the compression being 6mm off deck height so unless you want a much lower compression ratio for some reason then I'd want the correct crankshaft.

7A, RR, 3B, ABY, AAN and ADU all use the same crank.

[rxl]

did you run this engine or buy it used ?