GASKET AS-CYLINDER HEAD 1620682 - Caterpillar

Reference: "Uprated 3500 Series Engines Use Stronger Pistons, New Connecting Rods And New Piston Pins" in this issue.Uprated 3500 Series Engines are now available. Design and manufacturing changes have resulted in improved structural and component capabilities. These improvements allow a rating increase of up to 25% above the previous levels, while the brake specific fuel consumption will decrease by up to 3%.
Improvements to some of the basic engine components such as the cylinder block, crankshaft, camshaft, valve train, pistons, rods, wrist pins, cylinder heads, turbochargers, inlet manifolding, fuel injectors and fuel lines have allowed the uprating of the 3500 Series Engines.
This article will address some of the improvements which have allowed the higher ratings. Part numbers of some components have changed and former parts should not be used to service the uprated engine.
Illustration 1. Location of the drilled oil galleries.Cylinder blocks have increased wall thickness in key locations to make the block stronger. The oil galleries are now drilled rather than cast. These improvements have increased the fatigue limits of the block. This allows the block to be used at higher ratings without decreasing the reliability of the block.
Crankshafts used in 3512 and 3516 Engines have improved heat treating. The manufacturing process for the crankshaft oil supply holes has been changed to reduce stress concentrations. These changes will result in stronger crankshafts.
Illustration 2. Former and new camshaft drive gear retainers.Camshaft lift, duration and profile have been refined to provide increased efficiency. The camshaft drive train has been improved to carry more load, as shown in Illustration 2. One larger bolt is now used, rather than two smaller bolts to fasten the camshaft drive gear on the end of the camshaft. This provides a stronger gear-to-camshaft joint and is simpler to assemble.
Illustration 3. Cross sections of the forged piston and the cast piston.
Illustration 4. Forged piston and cast piston.
Illustration 5. Bottom view of the forged piston and the cast piston.Two types of pistons are now used. One type piston is of all cast construction and is used in lower and intermediate rated engines. The other type piston has two parts; a forged skirt, pin boss and central crown with a cast outer crown. These two piston parts are electron beam welded together. This welded type piston is used in the new uprated engines.
Illustration 6. Connecting rod used with the welded piston and the connecting rod used with the cast piston.Due to the increased piston crown thickness, a new connecting rod with a different small end balancing boss is used. This will provide sufficient clearance between the top of the rod and the undersize of the piston crown.
Piston pins have been improved but the difference is hardly discernible to the naked eye. The improved piston pin is required for proper break-in and satisfactory performance under the increased load. The former pin is not to be used with the welded pistons.
Illustration 7. New and former intake and exhaust valves.
Illustration 8. New and former rocker arm shafts.
Illustration 9. New and former injector