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-   -   PreviouslyDecked block 1980 Chevy 350 (http://www.hotrodders.com/forum/previouslydecked-block-1980-chevy-350-a-218790.html)

Frosty1956 04-29-2012 04:27 PM

PreviouslyDecked block 1980 Chevy 350
 
recently bought a 1980 corvette with the original 350 but has had the block decked and owner did not know how much was done. How can I tell I want to add after market heads and intake. He did state the springs on the stock heads had been shimmed

DoubleVision 04-29-2012 04:57 PM

What do you mean by how can you tell? Tell what? How much it was decked?
How many performance parts were used? You said the block is original, original according to the owner? If the block has been decked then the suffix code was milled off when the block was decked so there is no way to verify if it's the original engine.
If you plan to add aftermarket heads why are you concerned with the springs on the stock heads?

Frosty1956 04-29-2012 06:01 PM

Well Duh!!!!!!! Yea the its been milled off but the other codes are period correct for a Vette. Since material was removed you would assume that the shims were to get the proper clearance to keep the valves from striking the top of the pistons. I mean I know its been a lot of years since I did a motor but I dont think Ive forgotten everything. He had misplaced the receipts where he had the motor work done. Had a new crank, cam, rods and pistons put in it when it was done and what sounds and feels to be a pretty hefty cam. Im just looking at aftermarket heads and intake and was wondering if anyone could tell me how to measure how much had been removed when it was decked. That much I,ve forgotten..............

Silver Surfer 04-29-2012 06:27 PM

*gets popcorn*
This thread is winning.

DoubleVision 04-29-2012 07:49 PM

Shims were used to keep the valves from kissing a piston? Thanks! I'll be laughing about that one for days. There has to be a thousand blocks produced that year that were "period correct" and carried the same identical markings, corvettes didn't get anything unique that made them one of a kind or special blocks. I could tell you how to tell how much it's been decked but I'm not going to bother since you want to get smart about it. Your placing the duh on me and your the one asking the question genius. You could go to google and get the answers your after.

painted jester 04-30-2012 12:37 PM

When you mentioned shims in one statement did you mean shim head gaskets to get valve clearance, and in the other statement just mentioned spring shims. I might have read that out of context? and thought you mentioned valve spring shims to get valve clearance? :confused:

Any way a lot of machine Shops (the good ones) will stamp the deck ( mark it)!! When you clean the deck look for the marks like .004 or .010 etc if its not marked do like doublevision said and look it up there are a lot of good tech articles that cover this and would save us a lot of typing :eek: I type really slow and hate long answers!!! Theres probably a thread already on hotrodders covering this, do a search!

Jester :thumbup:

oldbogie 04-30-2012 03:23 PM

Quote:

Originally Posted by Frosty1956
recently bought a 1980 corvette with the original 350 but has had the block decked and owner did not know how much was done. How can I tell I want to add after market heads and intake. He did state the springs on the stock heads had been shimmed

Well Duh!!!!!!! Yea the its been milled off but the other codes are period correct for a Vette. Since material was removed you would assume that the shims were to get the proper clearance to keep the valves from striking the top of the pistons. I mean I know its been a lot of years since I did a motor but I dont think Ive forgotten everything. He had misplaced the receipts where he had the motor work done. Had a new crank, cam, rods and pistons put in it when it was done and what sounds and feels to be a pretty hefty cam. Im just looking at aftermarket heads and intake and was wondering if anyone could tell me how to measure how much had been removed when it was decked. That much I,ve forgotten..............

OK, The term Zero Decked relates to how high the block's head deck is above the piston crown in the case of a 350 with a 3.48 inch stroke divided by 2, plus a 5.7 inch long rod center to center of the bearing to pin bore and the compression height of the piston which standard is 1.56 inch from the pin bore center to the top edge of the piston crown. This should be 9 inches. The production standard block from the center-line of the crankshaft to the head deck is 9.025 inches. Zero decking is removing some to all of the .025 inch making the deck surface even with the piston crown edge. Not all factory blocks have all of this clearance either, Blocks and other parts are sometimes damaged in the manufacturing process and is not so badly damaged to the point of being scrapped, they are salvaged with extra boring or milling as is required. So sometimes you find a factory zero decked block or an over-sized bore, sleeved lifter bores etc. However, a factory zero deck block will have the stamped codes where a block re-machined in service would not.

Zero decking would not affect valve springs, however, a valve job that cut new seats into the head and onto the valve makes the valve stem tip sit higher (sinks the valve into the seat and the seat into the pocket) which lengthens the spring's installed height which reduces its installed pressure, to restore this a shim is often used under the spring to return it to the nominal compressed length when the valve is closed. What zero decking does is to change the distance between the cam and lifter to the rocker arm to less than designed which is the pushrod lenght. Though this usually isn't so much of a distance change that the pushrod length needs adjusting to restore proper rocker arm geometry between it and the valve stem. But it's always good practice to check.

In terms of telling how much of the deck has been removed, there would be no way of telling without at least pulling a head and even then it isn't a guarantee.The reason is that there are rebuilder pistons out there that from the pin center to the crown edge are .020 to .025 inch shorter than the the 1.56 OEM production down to 1.54 inch. This restores the factory clearance to the deck and with that the factory compression with the OEM head. So you can find a zero decked block that measures the factory piston to deck clearance because of this.

The downside of your block being decked is that even though the casting codes may be period correct, there is no way to prove that this is a numbers matching situation where the engine is native with the chassis rather than just loosely related to it. The lack of receipts is not a good thing both in that regard and in the fact that you have to take what's been done on faith. Getting more power out of a 1980 350 whether a 'vette or a pick up is hardly difficult, those engines were so anemic from the factory that the simple act of boring and milling with the other standard machine shop restorative procedures will substantially improve their power output by accident of renovation of the dimensions giving more displacement and compression. Add to that a little cam and it feels like you've bought a real race car.

Bogie

cool rockin daddy 04-30-2012 04:11 PM

In addition to what Bogie said, you don't have to worry too much about numbers matching on a '80 Vette. Dime a dozen, poor performers, not a lot of demand. You probably got a great deal on it because of those very factors.

Doesn't matter how much it was decked. I would pull a head and see how far down the hole the pistons are, that's the important dimension. Mount your aftermarket heads but do the math and figure out what gasket thickness to give you a good quench. Follow the head manufacturer's guidelines for how long a push rod to use with their heads and you're golden.

painted jester 05-01-2012 10:27 AM

I see your in good hands with bogie & daddy :D It saves me from typing :thumbup:

Chris


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