How To CC Cylinder Heads
Compiled by Mark Booker (Boatnik)
A performance boat enthusiast is always looking for ways to tweak just a bit more power from his outboard. We know the story all too well. Whether it be the meager in-line 6 on the family fish and ski, or the mighty V-6 on the screamer ride, the pursuit of this mechanical madness is a performance journey that never ends.
One of the ways to improve performance is to mil the cylinder heads. Before we can mil cylinder heads, we have to first find out what size combustion chambers we have. This article will discuss the process for cc-ing cylinder heads. It WILL NOT tell how much to mill the head. That information will come in a future tech article. The cylinder head used for this article is from a mid-1980's Merc 175 V-6.
To begin, we'll assemble our Needed Items (see picture). The list is as follows:
a) One cylinder head off our engine;
b) One tube of all-purpose white lithium grease (WalMart, for about $3.00);
c) One bottle of 70% isopropyl rubbing alcohol (WalMart, for about $1.00);
d) One small bottle of food coloring (Kroger, for about $2.00);
e) One chemistry burette, 50cc size (chemistry or school supply shop);
f) One small piece of 1/4" thick Plexiglas (Home Depot or Lowe's, check the scrap bin so you don't have to buy a whole sheet);
The Plexiglas must be sized so that it covers the entire perimeter of the chamber we're going to cc. The best way I've found to easily cut Plexiglas is to use a variable speed jig saw with a 16 tooth per inch saw blade. Run the saw on the slowest speed so the blade doesn't melt the Plexiglas as it cuts. Try cutting on a practice piece first to get the feel of it. Next, drill a 1/4" hole in the Plexiglas toward the outer edge of the chamber. This hole is both our fill and vent hole. Drill the hole using the same process as cutting the Plexiglas. Run the drill as slow as possible so the bit doesn't melt the Plexiglas when cutting. Incidentally, notice my piece of Plexiglas has two holes. The hole closest to the center was used for cc-ing a Briggs and Stratton head. There's no need to drill a center hole in your Plexiglas.
The only Needed Item I've found hard to get is the chemistry burette. Check your local Yellow Pages for chemistry supply stores and call. I bought a used glass burette with a chipped end for $15. A new one is $75-$125. If you can't find a used one, go to a local school supply store and ask for a burette marked off in milliliters. One milliliter equals one cc. A school supply house by me had a plastic 100 ml burette for less than $10. You'll have to pour the fluid though, instead of controlling it with a small valve. It's a trade-off. If you're doing a lot of heads, spend the money and buy a good burette. I've had mine for ten years and used it at least 100 times.
Let's get started…
1) Add 2-3 drops of food coloring to the alcohol. This will color it enough so it can be seen it when it's in the combustion chamber. The type of fluid used is a matter of personal preference. I like alcohol because it's easy clean up (it evaporates). Other gearheads I know have used water, transmission fluid, and antifreeze, just to name a few.
2) Put the cylinder head in a holding fixture (6" vice works good, or jig made for holding heads) so that it will be held stationary. Mount the head so that it has a slight tilt in any direction. This will help push air out of the chamber as fluid is added.
3) Place a small (about 1/16" thick) bead of white grease around the perimeter of the chamber you're going to cc (see picture). Don't forget to put the spark plug in the head.
4) Take the Plexiglas and place it on top of the chamber. Gently push on the Plexiglas until it's flush with the head. This action will squeeze the grease out and form a seal for the fluid in the chamber (see picture).
Notice that the inside perimeter of the grease seal is pretty close to being even with the inside perimeter edge of the chamber. Get the grease seal as close as possible to the chamber perimeter edge so that the fluid stays inside the chamber and doesn't seep out above the chamber edge. This will insure the fluid gives an accurate cc measure. Also notice that the Plexiglas fill hole is at the top of the chamber in the picture because the head is tilted downward slightly (the tilt can't be seen in the picture).
5) Now the fun part…Fill the burette with the alcohol and food coloring solution we mixed up earlier and drain the burette so that the alcohol level is right at the zero starting point marker on the burette. The below picture shows what the alcohol looks like in the burette (the picture is horizontal instead of vertical). I used three drops of green food coloring in one whole bottle of alcohol.
6) Finally, gently lower the tip of the burette into the hole of the Plexiglas, open the valve, and let the fluid flow into the chamber. Don't seal the hole off with the tip of the burette because no air will escape as the chamber is filled. Fill the chamber until the fluid comes to the bottom of the fill hole. Note how much fluid was used from the markings on the burette. If you get air bubbles in the chamber, a slight tap on the Plexiglas will usually move the air bubbles enough to get them vented through the fill hole.
Special thanks to Ron Pratt (Alaska Streamin') for providing the cylinder heads used in this article.
Hope this helps!
Disclaimer: This article was compiled from the author's many years of performance boating experience and test-and-tune sessions. I'm not a machinist, nor do I own or operate a boat or performance dealership. There are many ways to cc cylinder heads, this is just one I have found which worked for me. The purpose of this article is to share information with other boat gearheads so that we may scream down the River together a little bit faster…nose to nose, cleat to cleat. It's not who wins, it's how much fun we have flying the bow!
Source: Boatnik's archived testing notes