Remedy for stepped cylinder bore

I was just getting ready to assemble pistons/rings/rods and discovered one cylinder has a step in the very bottom such that the piston cannot complete its full stroke. The last quarter inch of the cylinder necks down a little over .002". This is enough to stop the piston in the position shown:

Is there an easy remedy for this that does not involve dismantling everything and taking the block back to the machine shop? Maybe a loaner hone from Autozone, although I’m afraid of removing material above the step as well.

Rick OBrien
65 FHC in FL

I don’t think the piston travels that far down? Put the crank and rod in and make sure it does before going any farther

Unfortunately it goes about another 3/4" past there.


I would think that if it is tight now, while at room temperature, it would seize when hot. I do not think simply honing it would be adequate. I believe you would want the specified clearance. I would start by asking the machine shop what happened.

How in the hell did that occur?

Sorry to say but the only proper way to do that would be to have it taken apart and put on a Sunnen hone.

This begs the question, should the skirt extend past the bottom of the cylinder this far, if at all. So I put a wrist pin in it and got this at TDC. About .025" below the deck. This seems about right to me.

So if the skirt protrudes too far at BDC that would indicate the piston skirt is perhaps too long. Unfortunately I discarded my original pistons so I have nothing to compare. Here are the dimensions of my current pistons. Can someone review these please?


No, that piston looks to be correct, and almost always the skirts of pistons extend below the bottom of the bore a little bit.

The clearance is correct (about .002") everywhere except for this narrow band at the bottom. I think he just did not hone deep enough. He took 4 measurements per cylinder N-S and E-W top and bottom (as did I to confirm) but both of us took our bottom diameter about 1/2" from up the bottom edge. This undersize area starts about 1/4" from the bottom. I only discovered it by accident by sliding the piston full stroke (106mm) just for grins. Not grinning now:-((

So I take it removal of this small band will require the full machining set up again?


A Sunnen hone can be used on the bottom taper: at the very least, he should not charge you to fix his f**kup.