Cylinder Head Resurfacing

How to resurface cylinder heads – At Home! This article probably falls into the category of “Doing the right thing the wrong way.” for some people. This process can also be used to renew and plane other gasket surfaces, such as the exhaust manifold flange, water pump face, intake manifold gasket surface, carb bodies and more. It can also be used for aluminum and cast iron. It’s recomended to do this procedure last, after porting and polishing for example, so the gasket surface is free of any accidental scratches, dents, dirt etc.

This process is not just a “cheapskate shortcut”. Many modern MLS type or specialty head gaskets require precise surface roughness and finishes, and the reality is many machine shops are not equipped to do this properly, or not knowledgeable enough to know the specifics of your application. Most resurfaced cylinder head surfaces I’ve seen returned from the machine shop have had a rough ~100-120 Micro-inches, or average roughness (Ra), while some MLS gaskets require surfaces as smooth as 20 to 40 Ra. The reality is that most machine shops won’t measure the surface roughness after they finish, or ask what type of head gasket you are using. Here’s one possible solution, short of shipping your cylinder heads out of state for $$$. This is also a better way to remove old stuck-on gasket material, versus a wire wheel etc (which is NOT recommended! But commonly used)

Work Time: Approximately 2 hours, depending on gasket surface condition and your endurance.

What You’ll Need

Very flat and level table or work bench.
A sheet of thick glass, ideally at least 1/4″ OR A machinists metal table as long as it has a very flat surface.
80ish grit, 120, 200, and 400 grit sandpaper sheets. Grit selection depends on cylinder head material and head gasket selection.
Spray adhesive. Ideally, temporary adhesive. I used batting adhesive for sewing, since it’s designed to be washable. Headliner adhesive would make changing sandpaper very difficult.
A machinists straight edge, or make one (explained later)
Feeler gauges.
Masking Tape
Dykem blue/Machinists blue (Optional)

Some of you may be thinking, but who has all of that laying around! The reality is that most people who do serious automotive work should have the majority of the above. If you don’t have feeler gauges for example, it’s time to buy some.

Regarding the surface, it must be 100% flat. If it’s not, your cylinder heads won’t be either and you will sand them unevenly. This is why a THICK sheet of glass works well. You can buy a cheap sheet of glass from a local glass shop for about 20 dollars, and most cities do have a glass shop within 30 miles or so. I used a glass shelf from a display cabinet, and as long as you are careful you shouldn’t damage it, but this is your call.

Regarding the glass surface:

It must be level
Longer than the cylinder heads. You don’t want your head to move past an edge that might cause more aggressive wear.
Wider than the width of the cylinder heads
Supported by a flat and even surface, such as a nice work bench or perhaps table saw surface etc.
At least 1/4″ thick.

Procedure

The tolerance you are working to depends on your head’s material and gasket choice. On most pushrod engines with cast iron heads, up to 0.003″ out-of-flat lengthwise in V6 heads, 0.004″ for V8 heads, and up to 0.006″ for straight six cylinder heads is acceptable. The maximum allowable limit for out-of-flat sideways in any head is 0.002″ — with no sudden irregularities that exceed 0.001″ in any direction. These tolerances might be more tight depending on your head gasket choice as well, and if you have a DOHC cylinder head design.

Grit choice also depends on gasket choice and head material. Use a less aggressive grit for aluminum versus iron or steel. You might start with 80 – 100 grit for iron, while you may start with 120 or 150 grit for aluminum. Aluminum cylinder heads also often use a more modern head gasket choice that requires a specific surface roughness, or Ra. Going too smooth, or too rough can both cause problems with head gasket sealing for your application.

General Surface Roughness guidelines BUT VERIFY WITH YOUR GASKET MAKER

Ra (µ in.) vs US Sandpaper Grit:

US Grit   UK Grit   Ra    Ra 
ref       Ref.      µm    µ inch
          120       3     125
          180       2      85
80                  1.65   70
          240       1.50   50
          320       0.75   30
180                 0.62   25
240                 0.45   18
          500       0.40   15
320                 0.25   10

OEM compression ring type (Permatourque) – Iron head and block – 55 to 110 Ra (60-125 Root Mean Square (RMS).

60 – 100 Ra preferred.

OEM compression ring type (Permatourque) – Aluminum head on iron block

30 – 60 Ra. 50-60 Ra preferred.

MLS (Multi-layered Steel)

30 or smoother Ra.

Begin by cleaning the table and glass so there is not grit or trash that could cause an uneven surface. Clean the cylinder head’s gasket surface AND chamber as well. You don’t want oil, grease, or carbon to bind up the sandpaper and cause uneven abrasive action. If desired, apply machinist’s blue to your gasket surface to aid in low/high spot detection as you work.

Tape the glass to the table top around the perimeter to prevent it from moving. Start with coarse sandpaper and glue the sandpaper to the glass with spray adhesive. Note that you should not tape the sandpaper to the glass, as this would cause high spots where the tape is present. The idea here is the sandpaper must be completely flat or the heads will wear unevenly.

Lay your cylinder head gently onto the sandpaper. I like to work in a “cross hatch” pattern, similar to a cylinder wall. I apply 50 strokes at a slight diagonal one direction, and then switch and apply 50 the other direction. Each stroke slides the cylinder head across the sandpaper surface, and I stop just shy of overlapping the edge of the glass (this depends on your glass or surface size). After each direction change, I sweep the sandpaper clean with a broom and check the head surface. I continue with coarse grit until high spots are removed to my satisfaction (for example, no dykem blue remaining). I like to count strokes so I remove a similar amount of material on each cylinder head, at each grit.

Before Resurfacing. Includes some nicks from porting and polishing.

After 50 passes with 80 grit. Cast Iron.

Remove the coarse grit and apply the next level finer (example, moving from 100 to 150 grit). Repeat the steps above working in a cross hatch pattern at the finer grit. Continue until the surface’s average roughness seems consistent. Repeat with finer grits until you reach your desired Ra for your material and head gasket spec.

If you don’t have a perfectly straight edge, why not make one? If your glass is good enough for your cylinder heads, it should be good enough to make a straight edge. For small defects, such as a pit, you can use a razor blade as a straight edge and a a flashlight to gauge depth and severity. Shine the light behind the straight edge/razorblade and look for gaps.