Looking for advice/opinions on best route to take.

I picked up a used JDM B18C. It had a couple sticky spots when turning the crank. Upon disassembly, I found piston 1 rod was bent and hitting the crank. It caused some damage to the very bottom of the cylinder wall (picture attached). Wondering if the damage is acceptable to run since it is isolated to the very bottom of the piston travel. Just looking for a reliable N/A motor to run on 91 pump gas.

I did a bottle brush hone on the cylinders to clean up some of the rust and glazing. Below are my current bore diameters. I have a set of used P73-00 STD pistons.

Cyl	Thrust Plane Near Top	Piston	P-to-Wall
1	3.1915	3.1881	.0034
2	3.1920	3.1882	.0038
3	3.1920	3.1882	.0038
4	3.1925	3.1882	.0043

For taper let's call it about .001" and for non-thrust plane about .001" smaller compared to thrust plane.

Assuming the wall damage is ok, these numbers still mean I need to run an oversize piston. Wondering if I can get away with Arias 81.08mm (.003") over pistons Arias Link? Or if I should go 81.25mm over and get the slight taper and out-of-round taken care of.



Cylinder 1 bent rod damage. Showing deeper gouge on thrust side.

 

I don't see why not. That area gets cut out to clearance for H beam rods. Have that area cleaned up and inspected for cracks and then send it.

 

If you have to buy new pistons either way imo just bump up to the next size and get a nice fresh bore.

 

Agreed with the above. As long as the cylinders aren't cracked in that area you should be OK. I would personally just bore over 0.50 mm instead of trying to keep the existing pistons. ~$300 in machine work (bore/deck/hone).

 

Thanks. I dropped it off at a local speed shop. Having them mag the block and hot tank to make sure there are no major cracks, then can decide on the correct oversize. Likely, 0.25mm over should be sufficient and leaves room for rebuilding later on. It'll be a week or so out before the shop has time to inspect the block. Assuming everything checks out, I'm thinking to get a set of US P72-A0 0.25mm cast pistons. I know there are far more options when going to 0.5mm oversize, but I'm not planning on anything crazy; more or less a stock build for now. This should put me right around 10.0:1 compression with P72 head and stock head gasket and crank. Block deck was nice and straight, so not needing to shave anything there. Main goal is to run a nice reliable build on 91 octane and stock ecu. I've got the OBD1 JDM P72-003 ECU that came with the motor; hopefully it powers on ok. I assume a C/R difference of ~0.6 will be fine especially going down in C/R.