Henry, thank you for the in-depth info. That clinches it for me. My cylinders all mic out at .001 or less taper except the one that has worn through in a small spot at the top of the ring travel on the bottom (installed) of the cylinder. That one measures .0025 taper and .003(25) bore wear at the top where the wear spot is. I am measuring with a rolling bore gauge so the dial gauge measures reliably down to .0005 but I can read the span between marks to get an idea where the measurement falls between marks.

I'm assuming that this particular cylinder had a heat issue and caused the problem. There are no other anomalies with the other 5. I will replace this bad cylinder and of course a full set of pistons. The honing info is excellent info. I'm thinking I will hone lightly with 600 and then do a hand wipe with 1000 to get close to the RA with my equipment. I will be honing on my lathe.

I would caution you against relying on a 0.0005" resolution bore gauge in the cylinders to establish a size for your replacement JE pistons. I have been bitten by this and ended up with pistons that don't fit the cylinders- too much clearance. PLEASE use a 0.0001" resolution gauge and check your measurements again.

Realize on 2.7 Mahle also made Alucil cylinders and the piston casting numbers reflect alucil pistons.
Bruce

Kevin, are we on the same page here? My .0005 DI reads to 1/2 a thousand on the dial face and it is very easy to read "between" the indicated lines to judge where it is.

Bruce, Yes, Nikasil.

With JE pistons you want 0.0015" clearance and I don't believe 0.0005" resolution gives you the accuracy you need to get that clearance right. I used a 0.0005" Fowler dial to spec out set of pistons for a low mileage set of cyls. I sourced. Recently I measured the cyls again with a 0.0001" CDI dial (using the same 0.0001" micrometer) and my measured cylinder bore dimensions were drastically different. So now i have pistons that don't necessarily fit my cyls. I have too much clearance. Which is better than not enough, but still not good/acceptable.

I don't think it's advisable to read between the dial increments. That's what a higher resolution indicator is for. Plus, most 0.0005" indicators will have + or - 0.0005" accuracy- one increment. So if you're off one increment on the indicator? You're off by + or - 33% of your clearance spec. That's a lot.

Kevin, I'm with you on that, and for the most part agree, but I am checking the bore gauge with my mitutoyo 3-4" micrometer and it is matching perfectly for reading (on an even number) so I am not expecting a discrepancy in the reading. As for in between the lines, this particular DI has 1 line between the 1/2 thousands lines, so indicated is down to 1/4 thousands (visual) and I can definitely see where the needle falls between those lines. I agree, this particular gauge is a little strange like that. It is marked on the face as .0005 and has lines at 00025 in between the 0005 lines. My Starett 0005 DI does not have those lines but has a much smaller face.