So now having the engine out, I have managed to clean some of the carbon off the top of the pistons, and 3 of them are stamped ERR2412 and STD stamped next to the arrow, but number 4 is stamped with the same number but has FSB 42 stamped where the std mark is on the other pistons. Is this a replacement piston, and does this mean that that bore is oversize? I cant see it coming from the factory like that. They are also stamped KS so im guessing they were made by Kolbenschmidt. I have seen on the net that the stamped number is not a real part number and they should be ERR2410

I cant at the moment find my measuring kit, SHMBO has put it in a safe place, so cant check the bores...

I also have not got the sump off due to the amount of silicon that has been used, and also need some M10 bolts or all thread to mount the block on my stand, so i guess its a trip out tommorow to get some. But some progress has been made.

what are you going to measure with?bore comparitor ,most wear occurs on turbo side at top part of bore were rings cover ,one piston has been replaced as they allways come in a batched set from the factory,number of original wont necessarily be the same as number replacement part as pistons are matched to block during build std bore size is nominally 3.562 imperial or 92.76 in metric but often varies hence need to match the two together or if been rebored block is bored /honed to piston plus clearance size ,(about 1 thou on tdi )should allways be equal sized bores ,to know if bore is worn measure at top of were rings sweep across engine (were greatest wear will be)and fore/aft were no wear should be check by measuring bottom also were no wear should be ,2 std piston sizes used to be available but just one i think now plus over size pistons +20 ,+40 ,quality honing is critical for long life

As always you are a fountain of knowlege. Will get my mate back with his bore comparitor and when i can find my kit i will be doing some carefull measurements..

All measured up and bores all look good. 3 of the pistons were worn alot, one just a bit and all bearings were down to the copper. Crank is good though. So ordered:- pistons, bearings, gasket set, rear oil seal (oem), timing belt, fan belt and prob so other bits and bobs. Also had some more tools turn up today (always a good excuse to get some..)

Not been able to get the crank pully nut off yet ,bl**dy forgot to loosen it while engine was in so have not looked at the oil pump yet and timing gear yet.. Prob have to get one of my heavier mates round with a big breaker bar

Simon