.50 over? can i find forged pistons?

[scottsi]

i bought my 240 a while back for 550 bucks, it had a engine from attarco in it, supposedly it has 36 miles on it, he drove it with no coolant and the headgasket blew.

fastforward to now, i pull the engine apart, the headgasket is fine, but the pistons are stamped .50 over, and the piston to wall clearance is HUGE, i mean HUGE. Now i see forged pistons that are .20 over, but this block has pistons stamped .50 over and they are completely flat and appear to be stock. I want to put some forged pistons for turbo in but i dont know if i can find any decently priced pistons that will fit, and it wil have to be somewhere in the area of .60 - .65 over, since the .50 overs are too small and have huge piston to wall clearance causing massive blowby and low compresson.

[deviousKA]

Those pistons are .5mm over, or in other words .020". You have the option of .75mm/.030", or 1mm/.040" total overbore. Some (most) manufactures do not offer .030", so look into going .040".

[scottsi]

sounds good thanks alot.

[Nismo_Freak]

At worse you can always have custom pistons made, alot of the manufacturers will do that. Especially if they have a shelf piston from the engine already.

[C-Kwik]

If you're going with a pretty sizable overbore, you may want to have the block checked for wall thickness. From discussions I had many many years ago, the KA can have some thin walls. The block is sand cast so if the cylinders were bored too close to a water jacket, it can make that cylinder quite weak. I actually don't recall the actual thicknesses mentioned and what the safe limits would be, but it was enough of an issue to have a pretty big discussion about it.

The person who had the most input on this topic suggested having the block sonically tested for wall thicknesses.

[fiznat]

^^ Def agree with C-Kwik. My block was bored .020" over, after it blew up (rods) I had the thicknesses checked to see if I could have leaked some water or something. Turns out that even with that regular overbore my walls were VERY close to the minimum thickness allowable for any sort of boosted motor. If you're going to go larger than .020 I would REALLY suggest you get those walls checked and measured, or just dont do it.