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Original Message
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| Bore taper. |
| By Dave Shoe - 05/05/2002 8:33:43 PM; IP 216.243.191.33 |
Bore taper becomes an issue in engines with lots of miles on the most recent cylinder boring.
Since there is little oil that makes it to the top of the bore, the bore tends to wear more quickly at the top than at the bottom where the cylinders run wetter with oil.
After a fresh bore job, cylinder taper is typically zero. It'll remain near zero for many thousands of miles. Because the piston is able to slide up and down in a perfectly fitted bore, the piston tends to rock less and also the rings do not have to expand and contract as they move in the uniformly sized bore.
It generally takes a year or two for cylinder wear to start showing up. The "cylinder ridge" at the top of the bore is a precise indicator of what kind of taper you can expect to find in the cylinder, since maximum wear occurs at the top of the ring travel area, and zero wear occurs above this position. Generally, the lower portion of the ring travel area offers a practical approximation of zero wear, as well.
Since the ring must expand and contract with existing taper, and the piston will also tend to rock just a little bit more, a ring in a tapered bore will tend to seal less efficiently than a ring in a freshly bored cylinder properly fitted to the piston.
Typically, a cylinder with .0005" of taper or less is considered to be like new (if I recall correctly). Taper of .0020" or less is often times considered to be satisfactory for certain types of rebuilds. Taper exceeding .0100" can sometimes be problematic (blowby, oil consumption), but if you're just looking for a cheap rebuild to have fun with, this kind of taper can work O.K.
If you're engine has been freshly bored, cylinder taper is not a likely problem. If it's only been honed, taper needs to be measured.
As for "thin spots" in the block, for an .060" 427 block, those look like reasonable numbers. Expectations for any .060" factory 427 block should be pretty low - I'd expect worse numbers than you've got. You didn't mention whether it has cloverleafed cylinder jackets (squared cylinder jackets which help translate head bolt torque to the cranksaddles), as this makes a difference.
I'm not much of a cylinder sleeve person, so I can't really give much opinion on what you should do with the block.
Shoe. |
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This thread, so far...
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