Oversized piston rings in standard bore

**zap.FREEDOM** · February 23rd, 2014 02:37 PM

Hello gearheads!

Just want to gather some opinion, We are about to overhaul a van of a friend (Kia Pregio) for the next week and I just want to ask if it is alright to use oversized piston rings in standard bore or just stick in to standard size? so far there were no signs of loose compression before its run out of oil and its valve tappet conked out that cause the engine to stucked up.

**jick.cejoco** · February 23rd, 2014 07:18 PM

Originally Posted by zap.FREEDOM

Hello gearheads!

Just want to gather some opinion, We are about to overhaul a van of a friend (Kia Pregio) for the next week and I just want to ask if it is alright to use oversized piston rings in standard bore or just stick in to standard size? so far there were no signs of loose compression before its run out of oil and its valve tappet conked out that cause the engine to stucked up.

if the bore is STD, the piston should be STD and so are the rings. if you O/S your rings, your engine will "stucked" up again. hehehehe. the piston ring ends are designed to have a gap provision for heat expansion, if you oversize your rings, you can not even fit the piston with the oversized rings even when the piston and the rings at 32 degrees fahrenheit

**innova2013** · February 24th, 2014 09:40 PM

Originally Posted by zap.FREEDOM

Hello gearheads!

Just want to gather some opinion, We are about to overhaul a van of a friend (Kia Pregio) for the next week and I just want to ask if it is alright to use oversized piston rings in standard bore or just stick in to standard size? so far there were no signs of loose compression before its run out of oil and its valve tappet conked out that cause the engine to stucked up.

your mechanic should be the one to suggest what to do or what are the needed parts for the overhaul.

rule of thumb: if its plus 0.25mm than STD size, you should rebore the cylinder wall to have it "straight" for the fitment.

and greater than or equal to 0.50mm to STD size, pistons are recommended to be replaced with the oversized spec (same spec with the chosen oversized rings). need to rebore or resleeve the block for fitment.

if cost constraint, you can invert the sleeve and use STD size rings. (this is only applicable to diesel engines). your mechanic should be good at honing the rings to fit perfectly. individual cylinder has different gap due to different wear rate.