hi all I'm new here and have 96 Honda Civic hatch with a H23a swap.i was having starting issues and idling problems after one night of racing. So I pulled everything apart and found the pistons and valves looked to be bad. I posted pics and would like a second opinion.

 

Would I be able to ground down the piston replace the bent valves and head gasket? Or would I need to replace the piston head??

 

That motor is shot. All that damage was done by detonation. Most likely due to a poor tune or not being tuned at all, possibly wrong octane fuel or poor fuel quality. That's what happens when you cut corners. Now the head needs to be redone and good luck finding pistons for that motor if you intend to rebuild it. Probably just cheaper to buy another imported engine and start over. Get it tuned this time.

 

It looks like something metal went through it to me... spark plug pieces, valve pieces, valve guide pieces... or an outside object. Detonation can certainly do this level of damage over an EXTENDED period of time in an N/A application, however, it is unlikely that this level of damage would be present in two cylinders and apparently non-existent in the other two if detonation alone was the sole contributing factor.

I do agree with Aradin in stating that the engine is in really bad shape. The pistons need to be replaced, the combustion chambers would have to be welded back up and smoothed, replace the valves that you (OP) mentioned, and double check the cylinder walls for any damage... over bore and replace all four pistons if necessary. It is likely that the rebuild would be more costly than a used JDM H23A engine from a quality used supplier like HMotorsOnline.

 

It's possible it was from debris. I mostly see damage like this from substantial amounts of detonation though. Maybe it detonated the plug tip off and then it beat around in there for awhile? Who knows. I would think there would be more damage to the actual valves if it was from debris though. If you look the pitting is only in the typical spots for detonation damage, right on the edges of the crowns and combustion chambers. I've seen a couple of these engines basically meltdown from detonation just like this. They don't like excessive timing advance or even a remotely lean mixture under load. Looks like #3 got the most damage which is the hottest running cylinder as well. Could be improperly flowing fuel injectors that would cause an individual cylinder lean condition.

Either way....That thing is a boat anchor now. Not worth fixing when a fresh one is $650+shipping from an importer. I would probably part out what was left of the one I had and put it towards the new one.