Engine Rebuilding- Automotive Machine Shop- High Performance & Hot Rod
Engine Block Decking
Neponset Valley Machine Surfaces blocks for flatness and gasket sealing. High Performance Engines are generally line honed prior to deck squaring. Chuck utilizes the time tested and proven BHJ Blok-Tru fixture for block correction and squaring.Engine block decking.

Engine Block Decking Defined
The term decking is used for the machine process that trues the head-gasket surface of the block. Most of the time, the objective of decking is to end up with a flat surface cut that is parallel with the center line of the crankshaft and at the correct angle to the cylinder bores. Another use for this procedure when building a V-8 is to make sure the surface of each deck is the same distance from the crankshaft. Decking can also be used to increase the compression ratio by reducing the quench volume and bringing the piston closer to the top of the bore when at top dead center.

BHJ's Blok-Tru engine block blueprinting fixture corrects improperly machined deck surfaces, commonly caused by factory machine tolerances and production line inaccuracies. This precision-machined fixture has a true 45-degree angle machined at each side of its own centerline.

The Blok-Tru Index Plate, when installed on the cam-crank centerline of the block, is then referenced to roll over and correctly index the block into position for the resurfacing operation (upper photo).

When the Blok-Tru is set-up and used in the prescribed manner, all angular dimensions shown in the illustration above can be held within five minutes of one degree. Top engine builders across the country rely on the Blok-Tru to provide the level of accuracy necessary for today's performance applications.

Common issues improved after using the Blok-Tru include:

•Twisted Blocks: On a twisted block, it is necessary to choose a point on the deck surface to use as a reference point for set-up. As a result, you may be compounding the out-of-square condition.
•Uneven Deck Clearance: Deck clearance often varies between the top and bottom edges of the piston due to the deck surface not being at 90 degrees to the bore. On race engines where deck clearances are held on the verge of piston to head contact, any discrepancy in deck angle means lost compression.
•Bores Not At 90 Degrees: Since most production lines use the pan rails as the reference point, it is common to find the bores at angles other than the intended 45 degrees when referenced from the cam-crank centerline.
•Cam and Ignition Timing Variations: If you have run into cam timing variations between cylinders on opposite banks, it may not be the fault of the camshaft. Again, since most blocks are machined from the pan rails, the cylinder "V" may not be at 45 degrees when referenced from each side of the cam-crank centerline.
•O-Ring Groove Variations: If you are cutting O-Ring grooves on a boring stand which references from the pan rails, it is not uncommon to have drastic depth variations.
•Poor Intake Manifold Fit: This condition is usually blamed on the intake manifold. However, if the included angle of the deck surfaces is not 90 degrees or if the top of the block has the incorrect angle, the manifold may not be at fault.
•Block Deck-Height Measurements: The Blok-Tru is marked with the height from the crankshaft centerline to index surface. A simple measurement from the block deck surface to the index surface of the Blok-Tru plate, added to the Plate's marked dimension gives you the deck height. This measurement can be easily made using our Deck Height Micrometer.

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