Block deck surface roughness, is it too smooth?

[ronstory]

Just got the block back from the machinist and when they surface ground the deck it is smoother than before. This machine shop does not have ability to directly measure the RMS value.

With the head I run my fingernail across surface and I can feel the 'zzzz' of vibration do to the original machining, but it's less than it was before. That said, it's now flat, so a plus.

How smooth is too smooth?

[Dave Neptune]

Ron, to smooth is not good. You want the roughness of the milled surface to give some "BITE" to hold the gasket(s).

The smooth surface can sslip under pressure much easier.

Dave Neptune

[ronstory]

Dave--

That's my fear. It's now like the deck surface I would see on chevy or ford cast iron block. Is it more of a risk because we stack two gaskets?

[Dave Neptune]

If it looks like a machined block, your fine!

Are you assembling wet or dry?

One or 2 gaskets, works both ways.

Dave Neptune

[lat 64]

Feelin' grooovy

If it was cut by a broach cutter, It should have marks like the grooves in an old lp record but perhaps a less pronounced. It's groovy!
This is best IMHO
The grooves should be across the surface like in the drawing, not straight down the length of it. A belt grinder surfacer will leave lines straight down the length. That will still work, just not as desirable as a broach cutter.

Russ

[ronstory]

Dave--

There are still machining marks that are 'less hard to see' but you can easily feel with the finger nail test... but before they were visible. That said, when I looked at the surfaces of "surprise" box-o-build I purchased... I thought, "hmmm... it looks like a Monday build, they forgot that final light flycut for surfacing". As an old school Chevy/Ford person, I would have gone... WTH?

Lat64--

The good news that you can still feel the ridge between the cylinder that you have artfully reproduced/delivered. If you go 'vertically' between the cylinders its seem smooth. But when you go side-to-side through the area between the cylinders you can still fill the ridges with your finger nail.

All--

Now the $64K question (unadjusted for inflation )

What should the minimum surface look like for a good gasket seal?

[ronstory]

Here are pics of the block deck... area between the cylinders is where I'm concerned it's too smooth.

The lower picture is where the surfacing procedure removed less material.

[ronstory]

Example image from YT

I think what it should be like from a decking machine... see the image at 5:45 of this video.

[YOUTUBE]https://www.youtube.com/watch?v=tBMwpOHNvnk[/YOUTUBE]

[Dave Neptune]

Ron, if it doesn't shine your probably fine. On many big HP aluminum engines and some CI ones I would take a center punch and put many punch marks on the surfaces (block & head) this gave a bit more bight. It worked especially well on valve cover gaskets on overhead engines. If the head gaskets slipped again it was time to "O-ring" the block.

Dave Neptune

[ronstory]

Crisis adverted. I took the block back to the machine shop and just had them surface it. It now looks correct (per Lat64's image) and ready for assembly.

Thanks you all for the help and feedback.