CHAPTER 14 Engine Machining

Introduction Manufacturers analyze parts to determine why they failed. Less expensive to replace Ability to analyze helps technician advise customer.

Engine Machining Machining adjusts tolerance by adding or removing material. Precise measurements Not operating within specs Sublet machining to machine shop Restore engine parts to factory specs Automotive Service Excellence (ASE)

Engine Cylinder Block and Cylinder Head Mating Surface Composition (1 of 12) Surface roughness (Ra) Measures at microscopic level Ra classifies how rough mating surface is.

Engine Cylinder Block and Cylinder Head Mating Surface Composition (2 of 12) Surface roughness. A. 60 Ra. B. 60 Ra.

Engine Cylinder Block and Cylinder Head Mating Surface Composition (3 of 12) Cubic boron nitride (CBN) cutter Polycrystalline diamond (PCD) cutter Surface engine block parallel to mainline

Engine Cylinder Block and Cylinder Head Mating Surface Composition (4 of 12) Measure deck height from setting fixture. Measurements are taken from top of engine block dowel pinhole.

Engine Cylinder Block and Cylinder Head Mating Surface Composition (5 of 12) Rebored and honed to fit oversized pistons Cylinder sleeve must be installed.

Engine Cylinder Block and Cylinder Head Mating Surface Composition (6 of 12) Boring bar positions and aligns. Portable boring bar Semiautomated boring bar CNC-style boring machine

Engine Cylinder Block and Cylinder Head Mating Surface Composition (7 of 12) Corkscrew pattern on cylinder walls Crosshatch pattern helps trap oil in bores. Torque plate is bolted in place where cylinder head is fastened to engine block.

Engine Cylinder Block and Cylinder Head Mating Surface Composition (8 of 12) If cylinder walls only need to be deglazed, use a ball hone. If cylinder was bored oversize, needs to be honed to final size with rigid hone.

Engine Cylinder Block and Cylinder Head Mating Surface Composition (9 of 12) Ball hone reapplies crosshatch pattern. Honing is typically done by honing machine.

Engine Cylinder Block and Cylinder Head Mating Surface Composition (10 of 12) To correct main bearing bore alignment, engine block must be line bored or line honed. Remove main caps and cut mating surface.

Engine Cylinder Block and Cylinder Head Mating Surface Composition (11 of 12) Cutting main bearing bores ensures bores line up properly.

Engine Cylinder Block and Cylinder Head Mating Surface Composition (12 of 12) Proper oil clearance can be quickly checked using Plastigauge.

Crankshaft Grinding and Polishing (1 of 4) Crankshaft journals need to be inspected for scratches, pits, cracks, and grooves. Induction hardened Nitriding Fillet area radial or tapered Radius helps strengthen crankshaft. Oil passage holes must be chamfered.

Crankshaft Grinding and Polishing (2 of 4) Before machining, pistons must be removed. Proper piston support tool to cradle piston

Crankshaft Grinding and Polishing (3 of 4) Big end of connecting rod has two halves. Machined faces Fracture split faces

Crankshaft Grinding and Polishing (4 of 4) Bolts must be removed. Rod honing machine or rod boring machine Pressed-in wrist pins Floating wrist pin

Cylinder Head Machining (1 of 12) Cylinder head should be magnafluxed to check for external cracks.

Cylinder Head Machining (2 of 12) Ferrous metal can be tested using dry or wet method. Dry method: iron dusting powder Wet method: liquid iron and fluorescent dye mixture

Cylinder Head Machining (3 of 12) Overhead cam engines have camshafts that ride directly in bores in cylinder heads. If removable cam bear caps, bore can be machined. If bore one-piece cam towers, oversized cam journals might be needed. Cam bores must always be aligned.

Cylinder Head Machining (4 of 12) A. Cam bores using removable bearing caps. B. Cam bearing with one-piece cam towers

Cylinder Head Machining (5 of 12) If valves reusable, valve face and valve tip need to be ground. Valve stem end chamfered so centered when inserted into collet Slowly fed into grinding stone

Cylinder Head Machining (6 of 12) Before grinding valve seats, valve guides must be checked and repaired.

Cylinder Head Machining (7 of 12) Four methods for repairing valve guides Knurling Reaming Thin-walled bronze liner Thick-walled guide 26

Cylinder Head Machining (8 of 12) Hardened seats are used to prevent valve seat regression. Integral or replaceable Head shop is needed. Proper cutter must be used. 27

Cylinder Head Machining (9 of 12) Two basic ways to refurbish valve seats Grinding Cutter

Cylinder Head Machining (10 of 12) Valves are ground or cut half or one degree less than valve face angle. Interference angle

Cylinder Head Machining (11 of 12) Valve stem height after machining of valve stem and valve seat Critical measurement

Cylinder Head Machining (12 of 12) Cylinder head surface is critical. Combustion pressures, water passages, oil passages Surface grinder Broach-style surfacer

Engine Balancing (1 of 6) “Prebalanced” at the factory Internally balanced Externally balanced 32

Engine Balancing (2 of 6) Internally balanced completely from the inside Externally balanced weights added on harmonic balancer, flex plate, or flywheel

Engine Balancing (3 of 6) Engine balancing. A. Externally balanced harmonic balancer. B. Externally balanced flywheel. 34

Engine Balancing (4 of 6) Two categories of crankshaft parts Rotating weight The amount of weight that is moving in a circular motion Everything from the center of the connecting rod down to the connecting rod cap and all components of the crankshaft Reciprocating weight The amount of weight that is moving up and down Everything from the middle of the connecting rod upward, including the piston, wrist pin, and rings 35

Engine Balancing (5 of 6) To balance engine: Engine balancer Connecting rod balance fixture Gram scale Gram calibration weights Bob weights Lead shot Disc sander with 80-grit disc paper 36

Engine Balancing (6 of 6) The first step in balancing is ensuring that all pistons and connecting rods weigh the same amount. Lightest piston is identified and some of the aluminum from the heavier pistons is removed. Rotating rod is weighed on the connecting rod balance fixture. Some of the material on the balance pad is ground away as needed. 37

Summary (1 of 14) Most automotive shops and technicians send their engine machining work to a specialty machining shop where components are restored to factory specifications. The measure of surface roughness is based on surface valleys and peaks and is specified as surface roughness area (Ra).

Summary (2 of 14) The deck height of an engine block must be identical at each cylinder in order to maintain equal compression values. The engine cylinder block dowel pinholes are used as alignment guides for the cylinder head and cylinder head gasket. Damaged cylinders must be rebored to fit oversized pistons.

Summary (3 of 14) Boring bars, which position and align a single-point tool, can be portable, semiautomated, or CNC style. After boring, the cylinder walls must be honed to the proper surface texture. A ball hone may be used to reapply the cylinder’s crosshatch pattern.

Summary (4 of 14) Most hones are self-tensioning but must be adjusted to the correct speed to achieve the desired angle of crosshatch. A torque plate may be used to keep the cylinder true to the machined dimensions when honed. Main bearing bores must be properly aligned to prevent premature bearing failure and crankshaft failure.

Summary (5 of 14) The engine block must be line bored or line honed to correct a bore alignment issue. Oil clearance can be checked quickly with Plastigauge or by subtracting the size of the main bearing journal from the size of the main bearing bore with bearings installed. Crankshaft journals must have clean surfaces, with imperfections polished out.

Summary (6 of 14) Crankshaft rods must all be cut to the same size, as must all main journals. A crankshaft can be spray welded to add enough surface material for grinding. Crankshaft oil passage holes must be chamfered before journal polishing begins.

Summary (7 of 14) The big end of a connecting rod must be resized to ensure proper rod cap alignment; this can be done with a rod honing machine or a rod boring machine. Before disassembling a non-adjustable valve-type cylinder head, measure and record the valve installation height. Cylinder heads should be magnafluxed, using the wet or dry method, to check for cracks.

Summary (8 of 14) Aluminum cylinder heads cannot be magnafluxed; therefore, they must be pressure tested via water or a pressure testing bench. Overhead cam engines may have camshafts that lose lubrication if oil pressure drops or misaligned cam bores if the engine overheats.

Summary (9 of 14) Cam bores must always be aligned, typically within 0.004" (0.1 mm) of each other. The four methods of repairing valve guides are knurling, reaming the guide oversize and using a valve with an oversized valve stem, installing a thin-walled bronze liner, or installing a thick-walled guide (bronze or cast iron).

Summary (10 of 14) When grinding valve faces, be careful not to grind away too much valve margin. Hardened valve seats are installed to prevent the valve from sinking into the head. Valve seats may be made of nickel alloy, chrome alloy, cobalt alloy, stainless steel, cast iron, or tungsten steel (for CNG or propane engines).

Summary (11 of 14) Valve seats can be refurbished with stones or cutters. Check valve seat contact, valve seat runout, and valve guide-to-valve stem clearance. It is critical to measure valve stem height after machining to ensure that the valve will close once the valve train is installed.

Summary (12 of 14) Measure valve spring height and adjust to correct height with shims. Cylinder head resurfacing may be performed if the head deck surface is found to be warped or if there is excessive pitting. The majority of production engines are “prebalanced” before leaving the factory.

Summary (13 of 14) Engines can be internally or externally balanced. Crankshaft assembly parts are divided into rotating (moving in a circular motion) and reciprocating (moving up and down) weight categories.

Summary (14 of 14) Equipment needed to simulate balance of a V8 engine includes an engine balancer, a connecting rod balance fixture, a gram scale, gram calibration weights, bob weights, lead shot, a disc sander, and an equipment lathe or milling machine.

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