Decked Engine

[John C.]

Can someone please explain to me what this means. Thanks

[James W.]

Re: Decked Engine

John,

The engine block is milled to remove any waviness or deformations. The problem usually arises when they machine off your broach marks on the pad. My block was decked, but they didn't mill all the way to the end and hand-finished the block, preserving the broach marks. Can be done, but not by everyone. Also depends on how much material has to be removed.

Jim

[Gene M.]

Re: Decked Engine

This is when the top surface of the block is milled or surface ground on both sides to make the surface parallel and equal distance to the crank center line. As this relates to Corvettes the numbers on the deck will be lost or at least disguised.

[Mike M.]

Re: Decked Engine

decking of blocks not done to insure blueprinting by machine shops. owners occassionaly have a passenger car block decked to remove the pass. car pad data, prior to restamping the block with corvette pad data. mike

[Mark P.]

Re: Decked Engine

This means a machine shop has removed some material (5 to 20 thousands of an inch) off the top of the block from the head mating surfaces.
Many shops remove all or part of the numbers on the stamp pad doing this.

If you need to deck the block the shop should be instructed to not touch the stamp pad and they should square deck it so that the crank journals are parallel to the top of the block head mating surface. You should be there when they do this to make sure they don't wipe out the stamp pad.

I heard that deck height varied by quite a bit (sometimes 15-20 thousands) in the 50's and 60's which makes it tough to get consistent compression.

[Duke W.]

Re: Decked Engine

The nominal deck height of vintage blocks can be as much as .015" high relative to the nominal (SB) 9.025" dimension, and this can easily be determined on teardown by measuring deck clearance before block disassembly.

Any "slope" and variation is side to side deck height can be easily seen once the deck clearances of all eight cylinders are known. Since the crank throw radius, rod length, and piston compression heights are held to very close tolerances, most significant variation in nominal .025" (SB) deck clearance is in block deck height.

It's actually pretty rare IMO to find decks that are significantly out of parallel with the crankshaft axis, and variation in side to side deck clearance can be compensated by using different head gasket thicknesses to minimize side to side quench clearance and compression ratio variation. If the left deck is high, it can be machined down and no one will ever know, but never touch the right side deck!

Deck "warp" is not real common unless the engine has seen major overheating. Warp is easy to measure with a machinist's bar and .0015" feeler gage. Composition gaskets will usually tolerate up to about .003" warp, but OE type steel shim gaskets are not forgiving of much measureable warp. If the engine had shim gaskets and no history of head gasket problems, then there will likely be no problem.

Measure the head gasket mating surface of the head for warp. If there is none, don't machine the surface. Same with the main bearing saddles. If the crankshaft spins freely prior to disassembly, and there is no misalignment using the same tools as above for block and head mating surfaces, don't let them "align hone" the block.

Physicians have a credo: "First, do no harm". I have a similar philosophy when it comes to engine restoration: Do no remove metal unless absolutely necessary.

Unfortunately, many, if not most machine shops cut the deck, heads, and "align hone" no matter what - even if you tell them not to, so be wary. Make sure the instructions are on the work order and inform the machine shop that you will sue for lost value (several thousand dollars) if they screw up.

If the guy doesn't like your deal - go elsewhere.

Duke