Ron_Stoppable

iTrader: (1)

I bought a 5.3 iron block. Basically rebuilt the entire valve train. Stock bottom end. I cleaned the block surface so now its smooth to the touch and also cleaned the heads. Just wanted to know if its imperative that their decked or if i should be fine.? I got the heads as clean as i could and they feel really smooth. :/

SS10Tech

Normally you deck the heads for decreased combustion chamber size in order to increase compression ratio, if the block and/or heads have been warped due to overheating, or you're building an all out effort blueprinted motor and need it done for proper/identical clearance purposes.

The most apparent reason is just general proper head gasket seal. Milling is recommended to return the heads to a square facing and assuring the gasket is perpendicular to the bores. This is also to prevent abnormal gasket wear or improper sealing. If the heads are milled due to concern for overheating or casting imperfections but the block is not also decked to a zero clearance then it defeats the purpose of decking the surfaces to be perfectly flush.

Even though you may feel a smooth surface distinct high and low surfaces from normal high mileage driving can exist.

I would recommend decking the block and heads ~0.005 to clean them up. A blown head gasket down the road can lead to many problems - its not expensive to have done and good assurance should something need decking or milling.

While you have it apart you could also replace bearings if desired or check to see if they are good. It would be a good step to do regardless IMHO.

mark21742

Just like ss10tech said, I'd atleast have them checked and if needed get them milled...the plus side to this is the raised compression which can increase power and economy at the same time

Sales2@Texas-speed

iTrader: (5)

The problem with having a machine shop check to see if they need to be decked is, most of those shops don't actually have the proper tools to check it. Many will use a straight edge that they have and hold it up to the heads to see if they are flat...but who says that straight edge is flat/straight?

wildcamaro

iTrader: (15)

I always use a straight edge, and my last set was ever so slightly imperfect but the MLS head gaskets make up for minor imperfections, so unless they are super wavy you will be fine...

3rdCoastPowerSports

iTrader: (5)

that's how i have always done it. how else do you tell if its flat or not?

JakeFusion

iTrader: (7)

If you're putting them back on a stock block, it's not a huge deal as long as you use GM MLS gaskets. Cometics may not seal well if everything isn't perfectly straight/clean.

Most head porters deck the heads after a port job for cleanup. Usually .005" or so. If they haven't had any work done to them, it's probably a moot point.

Sales2@Texas-speed

iTrader: (5)

We use a CNC machine with digitizing probe to check the deck at numerous points....same as we use to check surfaces on all our blocks.

jridenour31

All you need is a precision straight edge and feeler gauges.

machinistone

Hmm...I would think that the name "straight edge," kinda implies that it is in fact flat and straight. I mean I know that mine is perfectly straight - I touched it up myself on the CNC a couple months ago. But I guess only those of us who have CNC machines are capable of checking if a head is straight right?

Sales2@Texas-speed

iTrader: (5)

The statement that you felt compelled to touch it up on the machine says it all...they are not all straight! The average edge that the DIY'er will buy are very cheap, and not meant for precision like this.

And no, unfortunately, the average machine shop does not have access to the equipment to check it to the tenth of a thou like we do....but they certainly aren't going to tell a customer walking in the front door that there is a better equipped shop down the road, are they?

machinistone

Ok, so a "straight" edge that a DIY'er would buy is cheap and possibly not straight...but you said in your first post

You're not talking about the average guy at home, you're talking about a machine shop that should have precision measuring equipment, a decent straight edge with feeler gauges will tell you if a head is straight enough to reuse(.002" or less), that's something that any machine shop is capable of doing, to say otherwise is being extremely intellectually dishonest. Now if you want to comment about the ability of some machine shops to surface a head to the proper Ra for an MLS gasket I would have no problem with that, its true that many either do not have the proper tooling, or don't use what tooling they have properly in order to get the surface smooth enough. This is not limited to people with manual machines, I have had plenty of heads and blocks come through with improper surface finishes due to too fast of a feed rate or worn out inserts that were done on a CNC machine. Just because a job is done on a CNC does not mean that it's better than a job turned out by a competent machinist on a manual machine, you should see the piles of junked parts that come out of the CNC shop.

So you're implying that you setup each head in the machine and probe the deck to check to see if it's straight rather than just simply giving it a skim cut? Do you do this service for free, or do you just use it as a tool to up-sell the surface job because the head is out by .0004"?

And you guys only recently got your CNC, funny that now all of a sudden it's imperative that it be used, hmmm....

Bilster

iTrader: (21)

A machinist straight edge is not a square from Harbor Freight or a even a machinist scale. It's a designated tool. To be effective, it must reach the span of the entire head surface....not just a portion of the head surface.

Sales2@Texas-speed

iTrader: (5)

Easy there, I get the feeling you are a machinest and have hurt feelings for some reason. I certainly wasn't trying to offend you. Our old machine shop builds some pretty high-end stuff for some BIG names...and no, they cannot check surfaces like we can. And I've seen some surfaces on blocks and head surfaces from "reputable" builders on this forum that were off by a couple thou brand new out of the box, high to low, and the average joe wouldn't know any better.

machinistone

No hurt feelings because I have no dog in this fight, I'm not a vendor here trying to sell something...I just don't like the spread of misinformation, and implying that a CNC machine is necessary to check a head for straightness is simply false.

Sales2@Texas-speed

iTrader: (5)

By no means did I say that it is required! But you are kind of doubling back on yourself and hammering my point home by saying you hit yours with the CNC machine to straighten it too....So even if you use a straight edge, you still needed the machine to ensure it was straight, essentially?

I'm just saying there are different levels and qualities of straight and flat, that many DIY'ers are not aware of.

machinistone

Really? Saying I "touched it up," means that it wasn't straight to begin with?

No, it was perfectly straight, but after 10 years of use I decided to skim the edge to remove surface scratches. Point is that a straight edge that was purchased as such from any reputable manufacturer, which means no harbor freight, is going to be perfectly capable of telling someone if their head is warped. A broom handle does not count as a straight edge.

And yeah, you pretty much did say that a CNC machine is the "right" way.

Any machine shop could sweep the surface of a head in their manual decking machine with a tenths gauge and find out just how straight it is...no CNC machine required, but nobody is going to do that because it's a huge waste of time if you already have it mounted up rather than just simply cutting it. The straight edge is used as a go, no go gauge to determine if decking is necessary and whether you should mount it up in the machine or not.

The simple fact of the matter is that while you may have had the intention of educating people on the varying quality of straight edges, your posts came across as saying that only your CNC machine is capable of completing this most basic of inspection tasks.