Engine Machining

Decking the Block

• The deck of the block should not be warped to insure a sufficient head gasket seal.

• Concurrently, block deck should be parallel to the main bearing bores.

• Block deck is checked with a straightedge and a feeler gauge at six different positions, check manufacturers specifications.

(a) Checking the flatness of the block deck surface using a straightedge and a feeler (thickness) gauge.

(b) To be sure that the top of the block is flat, check the block in six places as shown.

Decking the Block

• A block that has been “decked” will have it’s surface(s) sanded parallel with the crank bore. Pg.446– Decking the block will raise static compression.

Cylinder Boring• Cylinders are usually tapered after

extensive usage.• Most of the wear will occur at the top of the

cylinder, just under the ridge.– Though not highly advised, the ridge may be

removed with a “ridge-reamer” for piston removal.

• The engine must be “bored” and new pistons fitted if the cylinder is out of specification.

Most of the cylinder wear is on the top inch just below the cylinder ridge. This wear is due to the heat and combustion pressures that occur when the piston is near the top of the cylinder.

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Ridge being removed with one type of ridge reamer before the piston assemblies are removed from the engine.

Cylinder Boring

• Maximum bore oversize is determined by cylinder wall thickness and piston size availability.

• An ultrasonic test may be performed to determine cylinder wall thickness.

• Cylinders should be machined to the smallest oversize possible.

Cylinder Boring

Calculating oversize diameter …

• One method is to factor the maximum amount of taper, double it, and add .010in. This will give you your piston size.

Cylinder Boring

• A boring bar is used to bore the cylinder diameter.

• The cylinder must be perpendicular to the crank-shaft bore before boring is attempted.

• Main bearing caps must be installed and torqued to specifications prior to boring.

Cylinder Boring

• Cylinders are bored .002” - .010” under the finish bore size.

• Torque plates should be used on the deck for bores larger than .030”. Pg.451

• Boring leaves a finish too rough for service.

After boring, the cylinder surface is rough and fractured to a depth of about one thousandth of an inch (0.001 in.).

Cylinder Honing

• The cylinder finish is, in effect, sanded to a proper finish and/or size.

• Deglazing hone – removes the hard surface glaze remaining after normal engine usage.– A flexible hone that follows the shape of the

cylinder wall.• Ball type

• Stone type

Cylinder Honing

• Sizing hone – used to finish a bore procedure, straighten cylinder taper and provide a suitable surface for the piston rings.

• While size honing, the cylinder must constantly be checked with a bore gauge to check for size and taper.– Cylinders will generally hone quicker closer to

the deck of the block.

Measure the bore diameter at the top just below the ridge and at the bottom below the ring travel.

Take measurements in line with the crankshaft and then repeat the measurement at right angles to the centerline of the block in each cylinder.

TECHTIP

An engine being honed. The block is equipped with a torque plate to stress the block the same as if the cylinder head was attached.

Dial bore gauge

Sizing hone

Torque plate

Cylinder Honing

• While honing, it is important to constantly move the hone in a vertical motion.

• This vertical motion insures that a cross-hatch finish is left.– The crosshatch should be between 20 and 60

degrees. • Too little crosshatch will cause excessive ring wear.

• Too much may effect compression.

The crosshatch pattern holds oil and keeps the rings from wearing excessively.

Cylinder Honing

• Plateau honing – using different grit stones, in succession, to achieve proper size and finish. May be done in two or three steps (different size stones).

• The grit of the finishing stone will be determined by the ring composition.– Chrome - #180 grit– Cast iron - #200 grit– Moly – #220 grit

Cylinder Honing

• The top edge of the cylinder should be chamfered prior to honing.

• Cylinders are finish honed to specific piston diameters to insure proper clearances.

• The finished hone should be within .0005” of desired size and taper

Piston diameter being measured using a micrometer.

Cylinder Honing

• The cylinder must be thoroughly cleaned after any honing is done to remove dirt and abbrasives.– This is done with a brush, soap and water.– The cylinder can be wiped with a clean, dry

cloth to check cleanliness of the walls.

Lifter Bore Honing

• Lifter bores are deglazed with a finishing stone to remove wear patterns.

Lifter Bore Sleeve

Main Bearing Bores

• Final machining of the main bearing bores (align bore) and cam bearing bores is done with the main caps torqued.

• FOR THIS REASON, MAIN CAPS ARE NOT INTERCHANGEABLE NOR UNIDIRECTIONAL.

Main Bearing Caps

• Designs include …

– A Girdle design. (pg. 440 fig. 19-24).

– A two bolt main cap (pg. 439 fig. 19-21).

– A four bolt main cap (pg. 439 fig. 19-22).

• Mostly high-performance and truck designs.

Girdle-type Cap

Main Bearing Caps

– A six bolt main cap design. (pg. 440 fig.19-43)

– A bedplate design (pg. 435 fig. 19-10).

• Attaches to the bottom of the block and supports the crankshaft.

Bed Plate

Main Bearing Caps

• The main bearings are held into place by the main bolts and enlarged areas of the block called bosses.

Main Bearing Bores

• M.B.B.s may elongate over time and become egg-shaped (pg. 441 fig. 19.27).– This out-of-round can be checked with a bore

gauge in 3 different positions. 0.0005 variance is considered acceptable.

• The main bearing bore not contained within the cap is called the saddle.– The saddle will be part of the engine block in

most cases.

Main Bearing Bores

• If the M.B.B. is measure outside of limits, the saddles can be checked with a straightedge and feeler gauge (pg. 441 fig. 19-28).

• If the saddles are within limits, the face of the caps may be block sanded to compensate for out-of-round.

The main bearing bores of a warped block usually bend into a bowed shape.

The greatest distortion usually occurs in the center bores.

Main Bearing Bores

• The main bearing bores must then be align honed to restore its symmetry. (pg 458 sequence).– Note: the depth of the saddle cannot be

altered because this will alter the centerline distances between the crank and cam.

Cylinder Sleeves

• Cast iron or steel sleeves are installed at the factory on some aluminum engine blocks.– They may be cast or

pressed into the block.

• Silicon-aluminum blocks have no sleeves installed.– Pistons with zinc-copper-

hard iron coatings are used in this design (Porsche 944).

Cylinder Sleeves

• A dry sleeve is completely supported by the engine block and does not come in direct contact with the coolant passages (Saturn, Ford, Northstar (pg. 434)).

• A wet sleeve is in direct contact with the water passages. Therefore, they must be thicker to withstand combustion pressures (Cadillac 4.1, 4.5, 4.9).

Cylinder Sleeves

• A sleeve may be installed into a cast iron block if a cylinder is badly damaged. – Typically, the cylinder is bored to the exact

outside diameter of the sleeve. A ridge is left at the bottom of the cyl. To support the sleeve.• The block is then heated and the sleeve

frozen to aid installation.

Crankshaft Grind

• The crankshaft must be ground if not within specification– Generally speaking, if the groves on the crank

journal can be felt with your finger-nail, it should be ground