Boring out cylinders to accept oversized pistons or sleeves has long been a common practice in the engine rebuilding business. Boring allows worn blocks to be salvaged, and stock cylinder bores to be enlarged for more displacement. More recently, boring is also being used to install special cylinder liners with hard surface treatments in high performance racing engines. The hard liners almost eliminate ring and bore wear so the engine can run race after race with no increase in bore clearances blowby.
Like most other machine tools in today's shops, the equipment used to bore engines is also evolving to keep pace with changes in engine technology and the aftermarket. Small shops want equipment that is versatile and can do more than just bore holes. For this end of the market, combination boring/milling machines have become popular. At the other end of the spectrum, production engine remanufacturers (PERs) want equipment that works harder, works faster and requires less operator input. For this type of user, automated high speed boring equipment provides the needed boost in productivity and quality.
Tooling has also been improving. The latest generation of coated carbide inserts provides longer life and better cutting action. For high speed boring, polycrystaline diamond (PCD inserts) provides the longevity needed for this type of operation. The speed at which the boring bar turns has a significant impact on tooling life. High speeds just kill the bits unless you use a PCD or cubic boron nitride (CBN inserts) type of insert. The high speed boring machines that go up to 1,500 rpm need these type of inserts.
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