BimmaKid

My younger sister picked up a 09 2dr gti and it needed a rebuild as it had a lot of km's (canadian) and the valves hit the pistons. I work as a mech so I figured I can help her rebuild it. The engine has the 21mm small end of rod // 21mm piston pin bore. I bought a rebuild kit on ebay labelled with the 21mm wrist pin pistons and connecting rods and somehow they shipped me one with the desired specs for everything except the wrist pin diameter on the new connecting rods, that being 23mm. I did a little digging and found that some of these 2.0t's had oil consumption issues due to ring issues, and that most people upgraded to the 23mm pin bore pistons and a different oil ring, and these 23mm pin bore pistons I accidentally received are the "newer" 3 piece design.

So this is where I am a lil confused. My brain tells me I should either get the proper size ones or the assembly balanced (I know I should regardless but I'll pay the consequences).

Does the extra diameter of the piston pin add extra mass to the connecting rod and piston assembly?
Does the engine balance now have to be re balanced to counteract this increase in mass? (Shave a few g's from the rod assy if its heavier?)
Or is the difference negligible enough to pop it in and send it. I understand more pin = more meat = more power handled but this car is going to live its life pretty much stock.

Feels like a dumb question but I can't seem to find an answer about what you are to do when changing from the 21mm pin bore assembly to a 23mm pin bore assy.

Thanks!

SMac770

"21mm wrist pin". 21mm was replaced by 23mm around 2011, at least for the CAEB engine. The 23mm in place of the 21mm is a straight swap task, no one doing a piston replacement on a 21mm with 23mm is doing anything but replacing the conrods, wrist pins, and pistons as they would do if the car had come 23mm. If I were rebuilding and didn't want to buy new conrods, I'd get 21mm pistons, such as what they installed when they did the oil consumption work on mine. But for a lot, they went with the newer 23mm, but had to also fork out for new conrods to do so.

No idea what "assembly balanced" concern is. Yes, the 23mm was introduced for the flex fuel, but it ended up replacing all the 21mm regardless. If it's just a stock ride, not sure what all the concern is about. Maybe the people that do more engine internals work can relate to the concerns.