is it necessary to have heads decked?
is it necessary to have heads decked? 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. :/
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Joined: May 2012
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From: NC
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.
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.
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?
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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...
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?
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.
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.
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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.
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Joined: Aug 2006
Posts: 326
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From: North Bay, CA
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?
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?
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?
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Joined: Aug 2006
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From: North Bay, CA
Originally Posted by Matt@Texas-Speed
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?
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?
And you guys only recently got your CNC, funny that now all of a sudden it's imperative that it be used, hmmm....
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.
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.
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Joined: Aug 2006
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From: North Bay, CA
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.
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.
I'm just saying there are different levels and qualities of straight and flat, that many DIY'ers are not aware of.
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Banned
Joined: Aug 2006
Posts: 326
Likes: 0
From: North Bay, CA
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.
I'm just saying there are different levels and qualities of straight and flat, that many DIY'ers are not aware of.
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.
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?
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.
