Numbers matching or Milling the deck

[Alex McDaniel]

Thanks in advance to all those who can help. I'm really in a desperate situation.
I'm having my numbers matching 1970 454 engine rebuilt, (balanced, blue printed the works) and the the machinist recommended re-decking the block, but then the numbers would be gone. The deck on the block has some small pitting in certain areas, the deepest ones are maybe 1/32 deep and across if even that. By my layman's eye not very bad.
Are there any other alternatives to re-decking, perhaps a very hi-temp filler or maybe nothing at all and let the gasket do what it can?
If it definitely needs it are there places to have the block re-stamped and have it look -exactly- like it does now, from the factory? There are two different sized dies used, one for the code and a smaller one for the VIN.

Thanks Alex

[Joe L.]

Re: Numbers matching or Milling the deck

Alex----

Have the block deck surfaces checked with a precision straight edge for FLATNESS. If the block checks out ok, then it does NOT need to be decked. If it does not check out ok, the you must have it decked if your head gasket seal is to be reliable. The "pits" that you described should present no problem, UNLESS they are in sealing-critical areas.

[Chuck G.]

Re: Numbers matching or Milling the deck

BIG mistake to deck the block. I can't think of many, if any instance that you would need to do it for a street motor. I would explain the importance of those "numbers" to the machinist. If he disagrees, find another shop. You'll do major damage to the value of your car with the original stampings gone. Chuck

[George D.]

Re: Numbers matching or Milling the deck

I had my matching numbers block decked and kept the numbers. What needs to be done and it ca be is that when the machinist is using the cutter they can come us just short of the numbers. The heads will fit ok. The only trhing you can notice is the radius of the cutter which is probably 8 or 10 inches in diameter. As previously mention mmake sure the machinist under stamd the importance of the numbers.

[Bill Lloyd #33481]

Re: Numbers matching or Milling the deck

Have your machinist Check the block for flatness and for slope front to rear. The problem with the original GM milling process (called broaching) was that it was not very precise front to back. Based on tool wear the front can be as much as 0.025 different (Higher/Lower) than the rear. This affects the cylinder volume. You would like to have all of the cylinders within 1 CC (0.002) of each other. This makes for the most balanced rotating assembly. Decking also effects the static compression ratio. This should be calculated prior to decking based on combustion chamber volume, piston type and head gasket thickness. Your machinist should have this done for you.

With all that said, it will not be worth the decking operation if they remove the numbers. Tell your machinist to save them by stopping the raidal decking operation just prior to the pad area. In this way, you can even the cylinder volume and save the pad. Good Luck.

Bill

[John H.]

Re: Numbers matching or Milling the deck

Maybe I'm missing something here, but I'd like to see a rotary mill cutting head that can be stopped with its forward edge just short of the pad and not leave un-milled sealing surface above and below the circumference line of the cutter.

[Jack H.]

Hah!

I remember seeing one car on the Flight Judging field that had done (attempted) this feat (stop the machinest's circular mill machine just short of the stamp pad). The owner was proud & tickled to death that he'd done a 'correct' restoration and saved the original stamp pad!!!!!

THEN, the car came to it's Operation Check.... Oil was blowing/spurting in rather regular 'dribbles' out the front side of the RH cylinder head!

Maybe these machine shop 'heroics' DID save the correct/original factory stamp pad marks, but would you want to buy/own/drive this car? I'd sure rather have seen before + after shots in a scrap book of how the owner did due diligence to capture the engine's original pad surface silhouette and how it was professionally 'restored' to duplicate its factory original condition after the lid was decked....

[Joe L.]

Re: Numbers matching or Milling the deck

John-----

I agree. I don't see how it can be done.

[George D.]

Re: Numbers matching or Milling the deck

I hate to be a spoil sport, but I had it done and retained the original numbers on the stamp pad.I do not have a digial camera, otherwise,I would post a picture of the pad. As I stated in my previous e-mail there will be a radius showing on the pad from the cutter. The headsfit fine and there are no oil or antifreeze leaks.

[Bill Clippinger]

Re: Numbers matching or Milling the deck

Well, I'm not a machinist, but could a block be decked using a standard milling machine or one of those neato CNC computerized thingys? I'd like to think that a competent machinist with an imagination could come up with something other than using the "normal" block decking machine with the large diameter cutter. If such a machine could be adapted, and used let's say, a two or three inch diameter cutter that moved in both directions ("north/south and east/west" on a flat surface) then the block should be able to be milled while staying away from the pad. I guess the hard part would be finding a machine big enough to work with an engine block.