Thread: Deck flatness specification?

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This is a continuation of my thread regarding "White Smoke". Engine is an L98 that I ran hot for a short distance due to being close to home.
Well the heads are off to the shop for a pressure test. Cylinder bores look good with the exception of #5 which has a pit near the top of stroke about 1/8" x 3/8". It can be felt by touch which if memory serves means it's at least .002" deep. This cylinder registered 140 PSI before pulling the heads. #3 read 145 & #7 138. Running a straight edge along the left deck checked pretty good. Couldn't get a .0015" gauge under anywhere however the right bank deck is a different story. Most of the deformation of the right deck in the top front of #2 cylinder. So the question arises: just how flat does the deck need to be? Additionally is one gasket manufacturer better at accommodating out of flatness. In another world I'd be fixing the block but money is really tight and since we're in AZ I want to get back on the road.

Thanks DennyW for your quick response. As I mentioned in my post I exceed that .0015" upper limit for out of flatness spec only at the upper front area of #2 cylinder. Do I need a new block, since the existing block has already been milled some years back?

I'm in CA right now and the car is in AZ and the only picture I have with me is of the whole right bank. I'm uncertain as to how to upload a photo to this post. If you would text me you email address or phone number via my phone I'll send it directly to you Denny. If I can figure out how to do that.

On page 75 of his book, Gaskets and Gasketed Joints, author John Bickford has a table showing the “maximum out-of-flat amounts” for internal combustion engines. For V8 engines he recommends .004” in the length and .002” in the width of the gasketed surface. (This is a well-known 20 year old college level text book typically used by mechanical engineering students – Sells in the $250-$300 range on line!) He also has this note;

“This is the sum of the values of the cylinder head plus block combined. Since cylinder blocks usually do not display major out-of-flat conditions, out-of-flat conditions are usually associated with the cylinder head; but the sum of the two must be kept in mind and must not exceed the recommended specification.”

That said, I have seen factory GM blocks that measure 9.020” - 9.027” with as much as a .003” variance corner-to-corner. I still use a carpenter’s framing square and feelers (like the long one below) but have used a deck bridge with a dial caliper from time-to-time if I think there’s an issue. I’ve put a lot of engines together with Fel-Pro 1010 (.039) and 1003 (.041) gaskets that were .002” - .003” off corner-to-corner and never had problems. To Denny’s point, the 60 to 120 micro inches Ra is important and too smooth for Chevy small block can be a problem. It might be ok for aluminum Japanese engines, but cast iron should be a bit rough.

I have a lot of measuring tools – but I have consistently used these guys a lot. Inside and outside calipers, straight edges, feelers from .001” to .025”, a manual caliper (I have a digital one as well – but like this one), a lighted 10X loupe (great as the eyes age!) and my prize position the 1” micrometer that was my fathers and is more than 70 years old – still smooth as butter and dead accurate.

Keep us posted!
Glenn

Wow, thanks Glenn for all the detailed information. I'll spend more time measuring when I get back home and post again. Hopefully I'll have a reading from the shop as to the condition of my head by that time too.

Originally Posted by mr-natural

Thanks DennyW for your quick response. As I mentioned in my post I exceed that .0015" upper limit for out of flatness spec only at the upper front area of #2 cylinder. Do I need a new block, since the existing block has already been milled some years back?

You will need to measure the block deck height (distance from the centerline of the main bearing bore to the flat surface of the block where the heads bolt on). Design deck height of a small block Chevy is 9.025", but I have found them to be off by 0.020" from one end on one side of the block to the other end on the other side of the block. I would never, ever build a motor without decking the block to square it up. Normally, the "stack" of parts that go into the block measure out to 9.000", leaving 0.025" piston deck height above the piston.

So, it depends how much the block has been decked and what the block originally measured when released by the factory. Measure your block.
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that the right or left side??????

I apologize for the confusion. I sent that picture from my very old phone and didn't look closely enough to see that I was sending a picture of the left bank head gasket and not the right bank. I don't have a right bank picture with me but when I get home I'll post one.

techinspector1 from my understanding of the methodology of metrology I would need to pull a piston which of course involves lots of work i don't want to do at this time. Plus I don't have the instruments to make the measurement. All I have is several micrometers, a 1" depth micrometer and some calipers. Is there a simple way to make this measurement?

those machining marks look like ahighly loaded cutting tool/grinding wheel to surface the block---as the surface machine moves down the block it is grinding across more/less surface area and of course the material removal varies-this is why you have to run machine until it "SPARKS OUT"

Quick and simple....finding piston deck height....
http://bbhp.bigboyzheadporting.com/a...tachmentid=202

Add together the piston deck height, piston compression height, rod length and half of the stroke. That will equal your block deck height. Push your feeler gauge under the steel rule somewhere along the wrist pin axis to prevent the piston cocking in the bore and giving you an erroneous reading.

Denny beat me to the piston deck height, although he didn't include the rest of the procedure to find block deck height.
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Watched some of those U tube thingies--------------ughhhhhhhhhhhhhhh
I'll look to see if I can find some of the stuff I photographed but never got on here because of the stupid specs for pics

I understand all about piston deck height, but I was after block deck height.
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So here's the latest. Heads checked out clean regarding any leaks. However my engine guy "Automotive Machine of Scottsdale" did find that five of my intake valve stem seals were destroyed. He called and asked the lift of my cam. I didn't have that information since it was a Chevy experimental cam recommended by my first engine builder - who has an excellent reputation by the way. Having a dial indicator and magnetic base I went ahead and found that my intake lift is .510" and the exhaust .504" - too much for the stock valve stem bosses. So he cut the bosses and the spring seats and I'm not reassembling the whole mess using Fel-Pro 1003 head gaskets. I'm anxious to see the results. By the way, TPI's are one pain in the arse to assemble - why did I want to put a computer engine in this car I'll never be able to explain properly. One more thing, the heads were out of flat by .004" & .005" so he did a clean up of .005" which didn't affect the match to the intake.