I am installing piston rings in my 4.6L engine. I bought goetze oe rings. Do new piston rings usually have to be ground down, or are they usually the correct size? If they do need to be ground down, what would I use to do it? (preferably something from harbor freight). I am also replacing the block, but the new one has not come yet. Can I measure the gap by putting them in the old block, or could the bore of the new one be a slightly different size? When measuring the gap is there a specific way to do it other than sticking a piston in to ensure the ring is perpendicular for measuring?

 

The rings are usually correct if you bought them spec'ed correctly. You need to check them though! Too small a gap and you WILL have a problem. This is what the tool looks like (not endorsing this tool, just a visual). The time tested procedure is to insert a piston into the cylinder you are grinding rings for, place it near the top of the bore, insert the ring and push it to the piston to square it in the bore, using a feeler gauge measure the end gap, if it is in spec you are done, if too big you need new rings, if too small the use the grinder to open up the gap.

If you believe that all of the bores are properly the same then you can do all of your measuring in the same bore. Instead of pushing a piston down in a bore, you can insert the ring then push an inverted piston down to it to square it to the bore. First paragraph is more precise, second paragraph is perfectly adequate if you are not blueprinting an engine...and you are not.

 

If they only need a few though off the ends you can just use a file clamped in a vice and put the ring on it and squeeze both tends together so you remove equal amounts on both ends.

 

All the new piston rings were within spec. Can the piston rings be installed by hand onto the pistons or is it necessary to use the tool? I saw a video where I guy installed the rings by hand on a 3.5L rover engine.

 

It can be done by hand. The risks are snapping one of the compression rings, and chingering up the piston and either ring. The oil rings are done by hand.