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The growth in the valve seat insert market can be traced back to the early 1970s when the switch to unleaded fuel took place. Most of the engines in use or that were in core or inventory storage had to have replacement seats inserted in the exhaust side to prevent valve seat recession that occurred when the engines were run on unleaded gas.
Many people think that lead was a lubricant and somehow prevented wear. In fact, the lead caused a chemical reaction with the cast iron of the cylinder head and the stainless steel valve, forming oxides and halides that locally hardened the wear surfaces. This local hardening is what actually helped to prevent seat recession.
During the changeover period, it was not uncommon for a vehicle that had been initially run on leaded fuel to be switched to unleaded. The initial use of leaded fuel had created the local hardening required and the switch to unleaded created no problems. However, if these same heads were then reconditioned, the machine shop would machine away the protective layers and seat recession would occur very rapidly, sometimes in as little as 3,000 miles.
The OEMs used an induction hardening technique to locally harden the valve seat areas. This process was supposed to produce a hardness depth of around .070", but in many cases it was found to not be deep enough to allow for re-machining during head rebuilding. These early unleaded fuel heads also needed to have exhaust seat inserts fitted to them when they were rebuilt. The growth continues today in demand for rebuilt cylinder heads, especially with the extensive use of aluminum. With the exception of diesels and truck engines, almost all cylinder heads are now produced in aluminum. These heads have inserts already fitted at the factory; this has contributed to the growth in the seat insert market at the OEM level.
When the time arrives for these aluminum heads to be rebuilt, they are often cracked around the valve pocket areas; the factory inserts must be removed to weld up the cracks. New inserts are usually then required to complete the repair process. All of these changes have contributed to a replacement valve seat market that is estimated to be about 7 million units in North America alone.
PHOTOS ABOVE FROM LEFT TO RIGHT , ONE SELECTION OF THE PROPER SIZE SEAT FOR APPLICATION / TWO SETTING UP ADJUSTABLE SEAT CUTTER TO CUT COUNTER BORE LEAVING COUNTERBORE .007 THOSANDS SMALLER THAN VALVE SEAT RING, THREE LEVELING CYLINDER HEAD TO SPINDLE
LEFT TO RIGHT , INSTALLING ADJUSTABLE SEAT CUTTER ON PILOT , SETTING DIAL INDICATOR FOR SEAT DEPTH AFTER CUTTER CONTACTS CYLINDER HEAD , NEW COUNTER BORE CUT FOR SEAT RING
LEFT TO RIGHT , MEASURING INSIDE DIAMETER OF NEW SEAT RING , SETTING UP 70 DEGREE CUTTER TO OPEN UP COUNTER BORE INSIDE DIMENSION OF CYLINDER HEAD FOR A PERFECT PORT MATCH AT BASE OF SEAT TO CYLINDER HEAD TRANSITION , COUNTER BORE BASE HASE BEEN CUT TO MATCH INSIDE SEAT RING DIMENSION
LEFT TO RIGHT , NOTICE BASE OF COUNTER BORE AFTER BEING CUT FROM PREVIOUS PHOTO , ALL COUNTER BORES HAVE BEEN CUT IN CYLINDER HEAD TO THE SAME DEPTH FROM THE CYLINDER HEAD DECK , INSTALLING LOCTITE IN COUNTER BORES PRIOR TO INSTALLING SEAT RINGS
LEFT TO RIGHT , SMEARING LOCTITE ON SEAT RING , INSTALLING SEAT RING WITH SEAT DRIVER, VALVE SEAT INSTALLED IN CYLINDER HEAD
LEFT TO RIGHT , SETTING UP VALVE INTO SETTING FIXTURE TO SET POINTER ON VALVE FACE WERE THE SEAT IS TO BRAKE ON VALVE FACE , SETTING UP CUTTER TO POINTER FOR VALVE SEAT BREAK , CUTTING VALVE SEATS AND FORMING ALL THREE ANGLES ON SEAT RING
ESTABLISHING VALVE STEM PROTRUSION FROM SPRING SEAT PAD WITH DIAL INDICATOR WITH NEW VALVE AND SEAT INSTALLED TO DETERMINE VALVE SEAT HEIGHT SO ALL VALVES MATCH HEIGHTS ON CYLINDER HEAD , CYLINDER HEAD SEATS MACHINED BEFORE AND AFTER PHOTOS
BMW 1949 VERITAS 6 CYLINDER OHV , JUST COMPLETED ALL NEW SEATS , CUSTOM VALVES MADE WHAT A PROJECT@!!