Decking a block - OK to do?

[Greg F.]

I contact a reputable corvette specialist in my area about an engine rebuild. I have a 71 small block (numbers matching). He mentioned that the machine shop would deck the block but not touch the engine pad.

Is this possible? Is this suggested or OK to do? I am curious if this is common practice during a rebuild?

Thanks.

[Joel F.]

Re: Decking a block - OK to do?

Some shops can do this but I would recommend against it. Too much room for error. Plus most blocks do not need this, and it will only raise your compression (if only marginally), which I doubt you want.

What makes your shop thing it is needed? Unless there was a core shift from the foundry, or serious warp-age I do not think it would be needed.

Are they also recommending hardened valve seats? If so, I'd run not walk from this shop.

Just my $02

[Joe R.]

Re: Decking a block - OK to do?

Greg,

I'm in the process of restoring the engine (numbers matching 66 big block). My machinist was recommended by Pete Rizos (Saint Louis Corvette restorer). Pete mentioned that I didn't want to deck the block because that would wipe out the numbers on the pad. The machinist said that he would take a light cut when decking the block and would not disturb the numbers. He kept his word, the numbers are intact after getting the short block done.

Joe

[Michael W.]

Re: Decking a block - OK to do?

The machinist said that he would take a light cut when decking the block and would not disturb the numbers. He kept his word, the numbers are intact after getting the short block done.

Joe

How about the broach marks?

[John H.]

Re: Decking a block - OK to do?

Decking (if absolutely necessary) can be done without disturbing the pad at all, but it requires a 3-axis mill; most average machine shops only have 2-axis mills, and can't make a straight perpendicular-to-centerline cut short of the pad surface.

[William C.]

Re: Decking a block - OK to do?

using a modern head gasket, it is very unusual that it is "necessary" to deck a block.

[Clem Z.]

Re: Decking a block - OK to do?

Some shops can do this but I would recommend against it. Too much room for error. Plus most blocks do not need this, and it will only raise your compression (if only marginally), which I doubt you want.

What makes your shop thing it is needed? Unless there was a core shift from the foundry, or serious warp-age I do not think it would be needed.

Are they also recommending hardened valve seats? If so, I'd run not walk from this shop.

Just my $02

you need to "deck" the block parallel to the crank center line if the shop uses a deck mounted boring bar. if not the bores will not be perpendicular to the crank center line. there are boring bar setups out there that work off of a plate mounted above the blocks deck and these types can do the boring without decking the block

[Mark P.]

Re: Decking a block - OK to do?

William - does a modern head gasket mean a composition head gasket ? They are about .040 thick I believe. If I used a gasket that thick would a judge deduct because I didn't use a steel shim type gasket which is like .016 thick.



Thanks,

Mark

[Joel F.]

Re: Decking a block - OK to do?

I am sure Bill is referring to a composition gasket, available from any number of manufacturers.

To your second question: your results may vary. Sometimes it will be detected, most of the time not. I think it is worth the minor hit for the piece of mind that a good gasket would give me.

[Jerry J.]

Re: Decking a block - OK to do?

I had mine done... HIS Recommendation...

Problem ended up being -- the bolt holes from intake to the head ended up off
JUST Enough to cause a problem.......

[Michael H.]

Re: Decking a block - OK to do?

Some shops can do this but I would recommend against it. Too much room for error. Plus most blocks do not need this, and it will only raise your compression (if only marginally), which I doubt you want.

What makes your shop thing it is needed? Unless there was a core shift from the foundry, or serious warp-age I do not think it would be needed.

Are they also recommending hardened valve seats? If so, I'd run not walk from this shop.

Just my $02

I'm with Joel, and many others here. I definitely wouldn't try to deck the block unless it was ABSOLUTELY POSITIVELY NECESSARY.
Most machine shops automatically include this in their usual block prep but unless there is some clear cut reason for it, it just isn't necessary.
If the machinist can't show you the reason the deck needs to be machined, look for another shop.

Same for line boring/honing. Unless there is some reason to suspect a problem, the block probably doesn't need that either.
If a straight crankshaft will spin freely in new main bearings with .025" to .030" clearance, the block does NOT need align boring/honing.

I also agree 100% on NOT installing hardened valve seats. More money out the window and another great opportunity to screw up a perfectly good cyl head.

Many of these guys are just trying to pay for a lot of expensive machinery that they're making payments on.

[Jamie F.]

Re: Decking a block - OK to do?

I'm having my '69 3964290 heads done right now, and the machinist said he always put new seats on the exhaust side only.
What is wrong with this?

[Michael W.]

Re: Decking a block - OK to do?

What is wrong with this?

The practice is completely unnecessary on a Corvette- the risk of valve recession is about zero on regular seats. Perhaps more important is the possibility of damaging the heads while having them machined.

[Ridge K.]

Re: Decking a block - OK to do?

First let me make the following disclaimer: I am not an expert on engine rebuilding, simply a mid-fifties guy who has been rebuilding Chevys since he bought his first one at age 15.

I can tell you one thing, in five years of daily seeing engines rebuilt, I can count on one hand how many blocks I witnessed being decked. The same with cylinder wall boring. After hot tanking, and the block checked for cracks, unless the cylinders were way out, they were simply honed, and the pistons put back in with new rings.
The same with cylinder heads. They were hot tanked, magnafluxed for examination, valves cleaned (except for any valve with a burnt edge, which was replaced), valves seated by in with a honing device (once again, unless there was a seat problem), and then put back together.
I witnessed, or assisted in hundreds of these Chevrolet engines being rebuilt in the manner I am describing, and never saw one single engine with a problem. Some of the cars these engines were installed in, I would see traded back in 3 or 4 years later, with another 60,000 miles on the and still be running flawlessly.

[Duke W.]

Re: Decking a block - OK to do?

you need to "deck" the block parallel to the crank center line if the shop uses a deck mounted boring bar. if not the bores will not be perpendicular to the crank center line. there are boring bar setups out there that work off of a plate mounted above the blocks deck and these types can do the boring without decking the block

If you measure the deck clearance of all eight cylinders before you disassemble the block and see no "slope" in the data, then the deck is reasonably parallel to the crankshaft and common boring equipment that indexes off the deck is okay IMO for a restoration engine.

Better machine shops have boring equipment that indexes off the crankshaft axis. If there is any doubt about the parallelism of the decks, find a shop with this more sophisticated equipment to do the boring.

Duke