besides measuring all the parts yourself...most machine shops will take your rods etc... and measure them for you and give you a report.
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68' 1602
98' ///M3 Sedan

88' ///M3 Sold *
06' ///M3 Competition Pkg Sold *

http://www.bmw1602.com/

you've got either a really high lift cam or pistons backwards... or out of time.

Those dings don't hurt the piston. Just smooth them over with a wizz wheel. Piston's probably 3/4" thick in that area. They're probably fine and you don't need to go overbore.

You do need to find out which vavles were hitting the pistons and why.

valve floating at high rev will cause that. the piston are not that much damaged, i would be more concerned by the valves and if they still close perfectly.

changing the piston orientation will not prevent that to happen again.
you have parts mismatch to beggin with, and a potentialy blown engine with worn out piston ring lands.
if and only if the piston ring lands are perfect, i would rebuild the bottom end and try to find the correct head to match thoses piston.
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1976 turbocharged 2002, 14psi, T3, 70%LSD, urethane bush, 36x15 intercooler, 63mm tby,SDS EM4F, 5sp overdrive. Bilsts. Tech edge wb02, datalogger, recaros.
1974 2002 auto (under resto)
1992 325i
1991 318is
1985 XR4TI, 22psi
1986 Toyota pick-up

Pistons are in the correct direction. Clean the raised portion off and you will find the arrow pointing forward.

PO probably got the cam/valve timing late because the dent is clean and valve has been touching recently or you have a heavy foot and go over redline a lot. Exhaust valves are probably bent.

Holy pants-
I suspect that that's left over from a previous problem.
If the valves really hit the pistons that hard, your motor wouldn't run.
All 4 would be so bent that it didn't have enough compression to start.

If you rebuild the bottom end, and have a refreshed head with new valve
springs, I think things will be just fine.

I WOULD get the rods reconditioned, the crank polished and checked for
true (2002 cranks take a LOT to kill) and you'll be fine.

t
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I have a car disease. There is no cure.
I'm not even managing the symptoms very well...

Agree with Toby that dings that deep would likely have bent valves resulting in very low compression. So much so that car would probably have not been driveable. Unless you have recently removed the head and cleaned things up, it seems that everything was burning evenly and there is very little in the way of deposits.

If the cylinder walls are round, even and unscored, and the piston rings are not stuck and in good shape, I would think your piston concerns should not be that great. Seals and bearing surfaces fail for all types of reasons, including something as simple as failing to lubricate them to prevent dry starts or installing seals slightly cockeyed.

You mentioned blowby, suggesting that this is purely the result of poor/worn/ ring-cylinder wall condition. While this is the most likely culprit, there are other possible causes.

I received an 02 with the oiliest of carburetors and manifolds. I discovered the dipstick was not reading accurately causing the previous owner to overfill with oil. By eliminating the extra oil the engine idled faster and the blowby virtually disappeared or at least became more manageable.

The fact that you claimed the rear main seal leaked leaves open the possibility (I did not say probability) that for whatever reason, you had too much pressure in the crankcase. Oil under too much pressure can result in leaks. Another very remote possibility is your oil pump. The spring that regulates the pressure or related mechanisms, may be fatigued or sticking , causing the pump to produce too much pressure. Too much pressure may make it easier for the oil in the crankcase to migrate elsewhere.

There is also the remote possibility that the oil you use is too light allowing it to make it around your oil control rings. Conversely, if the oil is too thick, that might result in too much pressure.

Lastly, probably the remotest of possibilities is that a head gasket or other gaskets were defective or installed incorrectly permitting the oil to pool in the head. It seems inconceivable that the headgasket could be installed incorrectly or be defective, but these things happen. I have a Fiat headgasket where the holes were not completely punched through the gasket.

Bottom line: Take all parts to machinist for consultation.

HTH