360 VS 390

[coletrain777]

so there really shouldn't be much problem with using the partial skirt pistons with the 390 crank and rods even with the pistons traveling higher up the cylinder becuase the rings shouldn't come into contact with the ridge?

[fomocoguy]

A good ridge reamer will cut a smooth surface. It will be barely noticeable once honed.

The problem is, most cylinders will not wear perfectly round, so if you use a ridge reamer, you end up either with some areas not cut enough or some areas cut too much.

Keep in mind that the ridge is at the top of the ring travel, so the rings will not be running on this surface. The only two reasons I know of for using a ridge reamer are 1) the ridge is so high that the pistons won't come out of the bore during overhaul, and 2) to keep the rings from hitting the ridge and breaking a ring land if the bore is still within tolerance during a rebuild.

so there really shouldn't be much problem with using the partial skirt pistons with the 390 crank and rods even with the pistons traveling higher up the cylinder becuase the rings shouldn't come into contact with the ridge?

The problem in this situation is that the rings actually WILL run up onto the ridge because the ridge that has been made by the 360 truck set up goes deeper into the cylinder than a 390 car set up. The pistons acutally travel up to zero deck, where the 360 truck motor stops the pistons short to achieve it's lower compression.

Removing the ridge and honing could work I guess, but it won't be near as precise as a proper bore. It's a lot of work to do to possibly end up with a rebuilt motor that loses compression and has a bunch of blowby. I would just do it right the first time.

[70_F100]