Engine Decking???
Le Mans Master
Joined: Oct 2010
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From: melbourne florida
2023 C3 of the Year Finalist - Modified
Melting Slicks
Joined: Apr 2007
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From: Tolland CT
A NOM is much less hassle.... no need to prove anything.
Race Director
Joined: Apr 2000
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
I had a brand new race block decked, heights were different from side to side and corner to corner. If you really want to build a good motor deck height must be measured properly then you would "deck" each side to the same height that you want.
I doubt 99% of those rebuilding their motors know the true deck height, just what is given to them in the literature. Hey it's supposed to 9.025" so knock .025" and I have a zero deck, that is usually the way it's done when in fact the deck height can be all over the place from 9.010 to 9.040.
One of the biggest aftermarket race block companies says 9.025" deck height +- .005" so you can get one with 9.020" to 9.030" and that doesn't mean they are the same on both banks either you could have 9.020" on one side and 9.030"
I doubt 99% of those rebuilding their motors know the true deck height, just what is given to them in the literature. Hey it's supposed to 9.025" so knock .025" and I have a zero deck, that is usually the way it's done when in fact the deck height can be all over the place from 9.010 to 9.040.
One of the biggest aftermarket race block companies says 9.025" deck height +- .005" so you can get one with 9.020" to 9.030" and that doesn't mean they are the same on both banks either you could have 9.020" on one side and 9.030"
Last edited by MotorHead; Jan 3, 2011 at 04:43 PM.
Melting Slicks
Joined: Mar 2002
Posts: 2,164
Likes: 7
From: Beringen
I had a brand new race block decked, heights were different from side to side and corner to corner. If you really want to build a good motor deck height must be measured properly then you would "deck" each side to the same height that you want.
I doubt 99% of those rebuilding their motors know the true deck height, just what is given to them in the literature. Hey it's supposed to 9.025" so knock .025" and I have a zero deck, that is usually the way it's done when in fact the deck height can be all over the place from 9.010 to 9.040.
One of the biggest aftermarket race block companies says 9.025" deck height +- .005" so you can get one with 9.020" to 9.030" and that doesn't mean they are the same on both banks either you could have 9.020" on one side and 9.030"
I doubt 99% of those rebuilding their motors know the true deck height, just what is given to them in the literature. Hey it's supposed to 9.025" so knock .025" and I have a zero deck, that is usually the way it's done when in fact the deck height can be all over the place from 9.010 to 9.040.
One of the biggest aftermarket race block companies says 9.025" deck height +- .005" so you can get one with 9.020" to 9.030" and that doesn't mean they are the same on both banks either you could have 9.020" on one side and 9.030"
Race Director
Joined: Apr 2000
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
Burning Brakes
Joined: Oct 2007
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From: Crystal Lake IL
St. Jude Donor '12-'13
My engine got rebuilt a couple yrs ago, and when I was asked whether I wanted the engine decked, I said ok. Now the shop was aware the engine was from my matching numbers corvette and they were careful to not wipe any numbers.
But with some of the horror stories I've read here, I'm not sure decking is such a good idea unless you trust the shop.
But with some of the horror stories I've read here, I'm not sure decking is such a good idea unless you trust the shop.
Drifting
Joined: Dec 2005
Posts: 1,360
Likes: 3
From: NORTHEAST
The worst GM block I have seen was 9.006 on one side and 9.036 on the other. Now cyonder location the worst one was .032 out of blue print location.
No block should be bored of the decks with out being squared first as I have seen few blocks ruined over the years because they were not squared first.
Remeber GM bores of the pan rails not the decks and it a good thing!!
We can deck the blocks with out removing the VIN numbers
Race Director
Joined: Jul 2001
Posts: 15,892
Likes: 42
I can tell you have never had a chance to check a GM block for squareness and flatness as we have never seen one yet that the decks were flat and square and we have probed out a lot of GM blocks in CNC machine to check the deck heights and cylinder bore locations and so far have never seen a GM block that was zero.
The worst GM block I have seen was 9.006 on one side and 9.036 on the other. Now cyonder location the worst one was .032 out of blue print location.
No block should be bored of the decks with out being squared first as I have seen few blocks ruined over the years because they were not squared first.
Remeber GM bores of the pan rails not the decks and it a good thing!!
We can deck the blocks with out removing the VIN numbers
The worst GM block I have seen was 9.006 on one side and 9.036 on the other. Now cyonder location the worst one was .032 out of blue print location.
No block should be bored of the decks with out being squared first as I have seen few blocks ruined over the years because they were not squared first.
Remeber GM bores of the pan rails not the decks and it a good thing!!
We can deck the blocks with out removing the VIN numbers
This is a classic justification of inspecting a piece until a 'defect' is found then convincing the customer that it's fortunate that you found it and it needs to be fixed. If your operation needs to deck the block to suit the boring operation, that's your problem, not the engine.
Not picking on you as all machine shops tell the same story, but the belief that decking is necessary is just not true.
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Safety Car
Joined: Oct 2005
Posts: 3,570
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From: Algonac Michigan
My opinion is that for most applications, decking is not nessasary. However, for a engine that will be used under the most extreme conditions, I think it would be prudent to have the machined surfaces as square and true as possible.
Considering the amount of money some may invest in a high output engine, I would think the cost of decking the block would be a "Drop in the Bucket".
But no, I did not have mine decked, or even checked for that matter, and it is fine.
My .02!
Considering the amount of money some may invest in a high output engine, I would think the cost of decking the block would be a "Drop in the Bucket".
But no, I did not have mine decked, or even checked for that matter, and it is fine.
My .02!
Advanced
Joined: Jun 2010
Posts: 86
Likes: 0
From: Pulaski Wisconsin
I can tell you have never had a chance to check a GM block for squareness and flatness as we have never seen one yet that the decks were flat and square and we have probed out a lot of GM blocks in CNC machine to check the deck heights and cylinder bore locations and so far have never seen a GM block that was zero.
The worst GM block I have seen was 9.006 on one side and 9.036 on the other. Now cyonder location the worst one was .032 out of blue print location.
No block should be bored of the decks with out being squared first as I have seen few blocks ruined over the years because they were not squared first.
Remeber GM bores of the pan rails not the decks and it a good thing!!
We can deck the blocks with out removing the VIN numbers
The worst GM block I have seen was 9.006 on one side and 9.036 on the other. Now cyonder location the worst one was .032 out of blue print location.
No block should be bored of the decks with out being squared first as I have seen few blocks ruined over the years because they were not squared first.
Remeber GM bores of the pan rails not the decks and it a good thing!!
We can deck the blocks with out removing the VIN numbers
.030 taller then the other bank. Would that not mean I would have 12.5 to 1 compression on one bank and 13.5 to 1 on the other? I think all the rebuilds engines that we put back in our cars should be Decked/Squared and make mine zero please.
Drifting
Joined: Dec 2005
Posts: 1,360
Likes: 3
From: NORTHEAST
I would not sleep if I knew that one bank of my new rebuilt engine was
.030 taller then the other bank. Would that not mean I would have 12.5 to 1 compression on one bank and 13.5 to 1 on the other? I think all the rebuilds engines that we put back in our cars should be Decked/Squared and make mine zero please.
.030 taller then the other bank. Would that not mean I would have 12.5 to 1 compression on one bank and 13.5 to 1 on the other? I think all the rebuilds engines that we put back in our cars should be Decked/Squared and make mine zero please.
Thats why we deck all our blocks just to square them if any so all the pistons are the same height from the deck down to the piston.
And you've done an excellent job of documenting exactly how the blocks were machined by GM in the first place. No great revelation there. If they last 100,000-200,000 miles between overhauls without issue in spite of the 'horrible machining', why does it need to be fixed now?
This is a classic justification of inspecting a piece until a 'defect' is found then convincing the customer that it's fortunate that you found it and it needs to be fixed. If your operation needs to deck the block to suit the boring operation, that's your problem, not the engine.
Not picking on you as all machine shops tell the same story, but the belief that decking is necessary is just not true.
This is a classic justification of inspecting a piece until a 'defect' is found then convincing the customer that it's fortunate that you found it and it needs to be fixed. If your operation needs to deck the block to suit the boring operation, that's your problem, not the engine.
Not picking on you as all machine shops tell the same story, but the belief that decking is necessary is just not true.
I can tell Mike has never built a performance engine and he does not care what the deck heights are from side to side and from front to rear this guy really sounds like a hack to me.
We tend to shoot for a .040 quench for our applications and having different deck heights is not the hot set up.
Boring of the decks of an unsquared block is certainly a hack job and I have seen to many of them over the years, GM bores and decks of the pan rails, We deck and bore of the GM blue print which is off the crank center line and the 45 on the decks referances off the cam and crank center lines.
Take and draw file a deck on a SBC and tell me how flat they are???
Most guys building an engine are looking for a certain deck height as they are tring to acheive a certain compression ratio for their build.
Most performance pistons for 350 and 5.7 rod have a 1.550 and if a GM deck was at 9.025 the piston would be .035 in hole not very good when you are looking for a .040 quench.
Drifting
Joined: Dec 2005
Posts: 1,360
Likes: 3
From: NORTHEAST
I doubt the thread will be ruined.
I deal with alot of performance shops and I have not seen an OEM block come out of their shop that was not decked to a certain demension for quench and a known compression.
Maybe not a stock rebuild where you don't care what you compression is or your not concernd about quench.
I deal with alot of performance shops and I have not seen an OEM block come out of their shop that was not decked to a certain demension for quench and a known compression.
Maybe not a stock rebuild where you don't care what you compression is or your not concernd about quench.
Race Director
Joined: Jul 2001
Posts: 15,892
Likes: 42
I'm not interested in a game of epenis.
I'm simply stating fact- the engines were manufactured by the millions with all sorts of machining variations. These were known about and accepted by GM and deemed as acceptable for production. They ran 100K to 200K miles without problems. This infers that the decision was correct. Comes time for a rebuild 20-40 years later and these original variations are 'discovered'.
Why do they now 'need' to be corrected? Yes, I know they 'can' be corrected but there's a big difference between 'can' and 'need'.
Are you inferring that if they are not corrected, the motor is not reliable? Durable? Impotent? I suppose then that any fully overhauled engine running around that has not been decked and therefore sports it's original pad must be a 'hack' job? So the much adored 'matching numbers' engines are really a badge of dishonour?
Sorry, but I spent 31 years in the engine OEM business and am very familiar with aftermarket shops trying to upsell 'repairs' that are of dubious value. You're not doing your own shop much good by carrying on the tradition.
Drifting
Joined: Dec 2005
Posts: 1,360
Likes: 3
From: NORTHEAST
Let's not start name-calling please.
I'm not interested in a game of epenis.
I'm simply stating fact- the engines were manufactured by the millions with all sorts of machining variations. These were known about and accepted by GM and deemed as acceptable for production. They ran 100K to 200K miles without problems. This infers that the decision was correct. Comes time for a rebuild 20-40 years later and these original variations are 'discovered'.
Why do they now 'need' to be corrected? Yes, I know they 'can' be corrected but there's a big difference between 'can' and 'need'.
Are you inferring that if they are not corrected, the motor is not reliable? Durable? Impotent? I suppose then that any fully overhauled engine running around that has not been decked and therefore sports it's original pad must be a 'hack' job? So the much adored 'matching numbers' engines are really a badge of dishonour?
Sorry, but I spent 31 years in the engine OEM business and am very familiar with aftermarket shops trying to upsell 'repairs' that are of dubious value. You're not doing your own shop much good by carrying on the tradition.
I'm not interested in a game of epenis.
I'm simply stating fact- the engines were manufactured by the millions with all sorts of machining variations. These were known about and accepted by GM and deemed as acceptable for production. They ran 100K to 200K miles without problems. This infers that the decision was correct. Comes time for a rebuild 20-40 years later and these original variations are 'discovered'.
Why do they now 'need' to be corrected? Yes, I know they 'can' be corrected but there's a big difference between 'can' and 'need'.
Are you inferring that if they are not corrected, the motor is not reliable? Durable? Impotent? I suppose then that any fully overhauled engine running around that has not been decked and therefore sports it's original pad must be a 'hack' job? So the much adored 'matching numbers' engines are really a badge of dishonour?
Sorry, but I spent 31 years in the engine OEM business and am very familiar with aftermarket shops trying to upsell 'repairs' that are of dubious value. You're not doing your own shop much good by carrying on the tradition.
Using a block that is not at least sqaured and decked for perfornance use is a waste of time in feild of building engines.
95% of the guys building performance engines are looking for a desired compression but first you have to know what you have to start out with.
If a boring bar is setting on the deck it should be at least squared deck it sits on at least from front to rear off the main line and the 45 is important when bothing the heads and intake on for alignment perposes.
If I did the things OEM builder do I don"t think I would be in business long as the OEM stuff I have seen is not quality thas for sure!!!
Anyone that does not beleive in square decking useally does not have the ability to deck block same with line honing if they can't do it they will always its not needed.
Le Mans Master
Joined: Jan 2006
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From: Butler Pa
Race Director
Joined: Jul 2001
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It's unfortunate that so many people place great financial importance on having the original block with untouched stamp pad in a car, but that's the way the car hobby has gone. It's unfortunate also that engine overhaul shops knowingly or unknowingly destroy this perceived value of the car by performing a machining act in the name of 'quality'.
Most likely the engine in the car you were/are looking at was decked for the above reasons. If the seller was unaware of the ramifications, too late now. He's not the first and not the last. Good luck in your search.