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Safe Decking of head and cylinder?

Nessism

Nessism

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Dropped off my 1000S cylinder and head at a machine shop today and asked them to clean up the sealing surfaces. Head has some corrosion etching and the cylinder has some dings in the sealing surface. The machinist asked me how much is safe to remove and I had to shrug. We wound up deciding .010 max on the head and he said there was one particular dent on the cylinder that needs to come out - about .005 - .010" or so I estimate.

So do these numbers seem okay, or do I call this guy back and tell him to stop?
 
those are good numbers that we use with the stock cars........but we also have the ability to get thicker head gaskets. I would assume that as long as it doesn't interfere with clearance you'll be ok. However, it may change your combustion a little......
 
Those are WAY SAFE numbers, we use to take .020 off the head and that was still considered safe.:)
 
progas said:
Those are WAY SAFE numbers, we use to take .020 off the head and that was still considered safe.:)
Click to expand...

So should I call the guy back and tell him to just cut the head until it comes out clean and not worry about going past 10 thou.? Using stock everything in the engine.
 
Nessism said:
So should I call the guy back and tell him to just cut the head until it comes out clean and not worry about going past 10 thou.? Using stock everything in the engine.
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I have a block I sent to Ray to be prepped for some Cosworths. Before sending it out I had a cylinder liner replaced and found the block had already been decked about .030" Another .006 was taken off to get that and a slight warp straightened out. The .030 had already been run with Cosworths previously. If it's too much I'll just use a thicker base gasket. If you happen to find too much has been taken off you should be able to do the same. I doubt you'll need to though.
 
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.010-.020 should be fine, but the cam timing will change so you may want to degree the cams or get a thicker base gasket
I did a V8 one time smog motor. Decked .050 offf the block & .020 off the heads
 
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First off, you have to take at LEAST .040 off the head to start to effect the compression to any degree. Take as much off the head as needed for cleanup. Second, .010-.020 off the block deck has MINIMAL effect on the cam timing. Ed, mock the motor up with the 1 & 4 pistons on the rods with NO rings & just the pins in, NO clips. Drop the block down over them with NO base gasket & use spacers on the studs to clamp the block down to 20 lbs. Measure to see if the piston is down IN the hole, at ZERO, or up OUT of the hole. If it is Down or at ZERO you can use any stock base gasket you want. If it is OUT you need to add however much it is OUT to .010 & order a custom base gasket in that thickness. Or you can stack 2 base gaskets to get to a .020 thickness. After figuring all this, assemble as normal & degree the cams to manufacturer's specs. Ray.
 
Many times on air cooled heads and blocks, there will be surface flaws in areas that don't matter. Surfacing to remove them, only makes it pretty.

Jay
 
Big Jay

Big Jay

Many times on air cooled heads and blocks, there will be surface flaws in areas that don't matter. Surfacing to remove them, only makes it pretty.
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Could you explain what "just makes it pretty" means?

Could you also explain what typical depth cut is made to achieve such "prettiness".

Is the prettiness confirmed by abundance or lack of blow head gaskets?

What tolerance do you typically try to achieve for a stock engine?

What surface tolerance do you typically try and achieve for 10.25:1

What surface tolerance do you typically try and achieve for 12:1

TIA

Jim
 
Jay and the guy that did my head think alike; he did a clean up cut on the head and cylinder and focused on the area around the sealing points - around the combustion chamber and outer studs where the oil moves up. I was a little alarmed to see some pitting remaining in the head but he said it's just cosmetic. Started to think about it and I'm sure he's right. Modern vehicles use small margins around the combustion chamber, I think to increase the clamp pressure in that area by reducing the area supporting the clamp load.

As an aside, during this engine build process I've played around three different heads and cylinders and most were warped to some extent, or had imperfections in the sealing surfaces in important places. I'm starting to think that this may be why so many people have problems with head and base gaskets failing. I know that it's important to not cut too much on a warped GS head or the cam bore alignment will be messed up, but that said, I think having flat gasket surfaces are critical. Find a good machinist and make sure everything is as it should be.

IMG_1039.jpg

IMG_1040.jpg
 
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I have .090 taken off of my head and .020 off of my cylinder.

Now remember if you take ANY measurable material off of either surface the geometry of the valve and piston valve pockets are going to be off.

you WILL NEED to enlarge the piston valve pockets to avoid unwanted valve to piston contact.

I use prussian blue to verify the valve is INSIDE the pocket area and not tapping the outer edge of the piston.

test fit test fit test fit UGH hot rod engines test fit again and again.
 
posplayr said:
Could you explain what "just makes it pretty" means?

Could you also explain what typical depth cut is made to achieve such "prettiness".

Is the prettiness confirmed by abundance or lack of blow head gaskets?

What tolerance do you typically try to achieve for a stock engine?

What surface tolerance do you typically try and achieve for 10.25:1

What surface tolerance do you typically try and achieve for 12:1

TIA

Jim
Click to expand...

When you machine aluminum, many of us believe the finish is "pretty"
 
Jay

Jay

When you machine aluminum, many of us believe the finish is "pretty"
Click to expand...

I was looking for a little more substantive comment specifically related to decking tolerances.

Wiesco Is now selling piston kits with MLS gaskets that appear to be rebranded Cometic.

Here is a picture of one....

picture.php


http://www.cometic.com/faq.aspx#q4

The Cometic website recommends a 50 RA surface finish, but doesn't specify any particular level of brilliance (i.e. shininess).

Do you want to comment on this and how you might ascertain what RA is on a particular surface.

A surface finish of 50 RA (roughness average) or finer, is recommended for a proper gasket seal. Anything rougher may conflict with the gasket design.
Click to expand...
 
There are measuring tools for surface finish - hand held gauge. Looks expensive.
I suppose an experienced machinist could judge the finish pretty accurately with their eye.
 
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