DustersVette

Can someone explain the term "engine decking" to me. I am looking at a Vette which has an engine that has been decked and the owner cannot tell me if it is numbers matching or not!?

ED69ray

thats my freshly decked 360ci above. Notice how the stamp pad is wiped clean.

The entire deck surface is trued by machining - it cleans up the head mating surface and allows you to tighten up quench. Removing material from the deck surface allows you to get the piston closer to 0 deck

My 360 above is .005 below 0

BryanB75

The engine has been rebuilt. To deck the block they basically shave the area the heads bolt to to make sure it is level. Sometime when they do this the numbers on the front pad of block can be shaved off. Would be hard to tell if it was the original motor if they were gone

BryanB75

Damn..too slow :-)

CF6873

You can check the casting date on the block and get a good idea if it was the original motor although you probably cant' ever prove it.

Jeff_Keryk

Those little numbers on my L36 engine pad are pretty light...
What's done is done.

Indiancreek

If they are gone it makes no difference if it's the original engine or not. It would never pass as a numbers matching.
Some shops can restamp the pad, they have a multi number stamp.
If the casting dates on the block, heads and build date of the car are with in reason, It may be, but the folks who are interested in numbers matching won't accept it in that condition.
Decking with a rotery broach a guy can deck and save the numbers. May have to finish it up with a vertical mill

Belgian1979vette

FWIW If it was the original block, they should have used a rebuildable core instead of the original block. This just make poor economic sense IMO

Mike Ward

The shame of it all is that 99.9% of blocks don't actually need to be decked- most machine shops do it for the same reason dogs lick themselves.

bashcraft

Dogs lick themself to make money?

Mike Ward

Just about anything goes on the inte weeb these days so why not?

Mike Ward

I re-read your question. If the numbers are gone, how could there be any faint possibility that they would 'match'. This takes the much abused and meaningless phrase to a new low level.

Belgian1979vette

Belgian1979vette

Actually decking a block is done to keep detonation under control, but imo it's only worth the effort on higher CR engines with a thight cam, that run close to detonation or if you're aiming for a high CR on a small ci engine.

BBCorv70

Maybe try the acid test? Take a photo of what appears if anything?

Sorry, have to disagree. I think the 'numbers matching' engine with no car, not even a frame (actually a truck engine) has been the most extreme case so far...

How many numbers need to match to be 'numbers matching'? Seems it's rarely all four...

7t9l82

i was going to say acid test. try wiping it with paint if its faintly there then take a picture

DustersVette

Acid test....?? Please explain! Thanks.

Mike Ward

But then you'd only have a matching numbers photograph

Once the numbers fade from the surface, how do you prove that the engine is the same one in the photograph? And around and around we go.....

7t9l82

then restamp that way you have to a degree established the authenticity of the block and made it readable.

l88rocket

if the motor blew a head gasket or gasket leaked etc decking it is a good idea to make sure its not warpped. if looking for a few easy hp zero deck the block will had some compression and make a few hp.