Max cylinder bore taper for the 2.7 ?

[S4B5Quattro]

Hello everyone,

I´m working on a build and perhaps this has been posted before, but the maximum cylinder bore taper for the 2.7 liter engine, is it 0,08mm? (The difference between actual and nominal diameter as given by Bentley?)

Is the "out of roundness" limit value the same?

https://www.audizine.com/forum/showt...=cylinder+bore

I greatly appreciate any stories or experiences with tolerances to share?

Thx,

[julex]

0.08 mm max

bore diameter should be 81.01mm nominal

You measure the wear by taking/verifying nominal dimension at the very bottom of bore in the front-to-back axis where nothing ever works against the walls, I reset my bore gauge to zero at that position.

Then you work your way up in both front-to-back and left-to-right axis and take measurements in three spot along the piston travel section (you will see clearly where piston travels because this is where hatching will be worn down). The most wear you should see around 25-30mm from top in left-to-right direction (this would be pistons top and bottom respectively) because this the where the piston slides against the walls and rings exert the most forces on the walls during compression and ignition phase of stroke.

[S4B5Quattro]

0.08 mm max

bore diameter should be 81.01mm nominal

You measure the wear by taking/verifying nominal dimension at the very bottom of bore in the front-to-back axis where nothing ever works against the walls, I reset my bore gauge to zero at that position.

Then you work your way up in both front-to-back and left-to-right axis and take measurements in three spot along the piston travel section (you will see clearly where piston travels because this is where hatching will be worn down). The most wear you should see around 25-30mm from top in left-to-right direction (this would be pistons top and bottom respectively) because this the where the piston slides against the walls and rings exert the most forces on the walls during compression and ignition phase of stroke.

Thanks for the input julex.

Is this limit a bit on the high side? After asking couple of workshop machinists, they said normally when having around 0,03-0,05mm taper they would recommend an oversize rebore.

Just by doing some quick online searches for reference values, I´ve found the following:

https://ls1tech.com/forums/generatio...learances.html
"Bore Taper Thrust Side: 0.018mm Max. / 0.0007" Max."

https://www.autozone.com/repairguide...00c152800c2c17
"Any cylinder that has a taper of 0.0012 inch (0.0305mm) or more, must be rebored".

https://subaru.oemdtc.com/252/revise...later-subaru/2
"The “limit” specifications provided are radiusdimensions (1/2 of the diameter). Limit: .03 mm (.0012”)". (So basically 0.06mm)

Again, I´m no expert on this and these links might not mean much. Just wondering if Audi (Bentley) has it abnormally high?

[julex]

It is not really the bentley... the info I got you is coming from official engine rebuild guidelines from audi service manual - bentely might be rehashing these. Do you what you think is right. First measure and see where you are.