Clearing Out Your (Cylinder) Head
Discover what must be done to get your cylinder head cleaned and prepped for the season.
From the February, 2009 issue of Circle Track
By Glen Wilkinson
Photography by Glen Wilkinson
The first step, obviously,...
The first step, obviously, is to disassemble the head from the motor. Notice here Mike has tagged the head to keep track of it. Pletcher Racing gets a ton of business and the shop is loaded with all sorts of parts for a variety of jobs, so keeping tabs on which head belongs to which customer is paramount.
Now begins the actual cleaning....
Now begins the actual cleaning. Mike will first put the head(s) in a jet washer or "hot tank." The process, which lasts around 10 minutes, involves simply placing the head on the grating (shown), closing the door, and pushing "start." The jet washer cleans all the oils, rust, and other gunk stuck to the head with a caustic solution that would actually burn your skin. Some heads may require more than one run through the jet washer depending on how much dirt is caked on.
Hopefully your race head will...
Hopefully your race head will never look this bad!
An optional step is to put...
An optional step is to put the head in the shot-peening machine. If a head comes out of the jet washer and is not quite clean enough it would require the shot peener. "A lot of times," Mike says, "a cylinder head will come in the shop real clean and require nothing more than the jet washer. But other times the jet washer will not clean all the junk off a head so I would have to go to the shot peener." Race-only heads typically do not require any shot peening because they are usually fairly clean. One note: only cast-iron heads can be shot peened aluminum heads can not.
Notice the gunk on this head...
Notice the gunk on this head that the jet washer did not remove thus this head is about to get run through the shot peener to make sure the entire surface is nice and clean.
Next, the head travels to...
Next, the head travels to the glass beader. This machine is primarily used to clean the combustion chambers so the chambers can be Magnafluxed to check for cracks. Notice here how well the glass beader performs - the head is clean, shiny, and ready for the Magnaflux test.
Yet, even with all his high-tech...
Yet, even with all his high-tech cleaning machines sometime Mike has to remove the heavily caked-on gunk by hand.
Here, and below, a shop mechanic...
Here, and below, a shop mechanic works the glass beader on a valve.
Mike (shown here holding the...
Mike (shown here holding the Magnaflux magnet) then uses the Magnaflux test to check for any cracks in the combustion chamber.
A Magnaflux test is pretty...
A Magnaflux test is pretty simple. First, very-fine metal shavings, or Magnaflux dust/powder, (shown, and notice the high-tech gravy baster head used to hold the shavings) are just dusted over the combustion chamber. The magnet causes the shavings to adhere to the combustion chamber walls thereby revealing any cracks. Remember, however, that only a cast iron head can be Mangafluxed an aluminum head can not because the metal shavings will not stick to aluminum.
As one can see, performing...
As one can see, performing a Magnaflux test is not too difficult, but the information gained is invaluable.
Here (arrow) a crack can seen...
Here (arrow) a crack can seen in the combustion chamber wall. The crack is "up too far on the seat" and a new seat that Mike could install would not cover this particular damage. The crack could be welded, but in the case of this stock head, the repair would cost more than the head itself - so this head is garbage.
After the Magnaflux test,...
After the Magnaflux test, Mike continues on by checking the valve guides. This is done on all heads - cast iron or aluminum. Again, this is a simple process. Mike usually just takes customer's valves, places them in the valve guides (shown) and rocks them back and forth (typically in a north-to-south motion instead of east-to-west, because, as Mike notes, more of the normal valve guide wear is noticeable in this direction) to check for any abnormal degree of looseness. Mike says valves are very rarely too tight. And how does Mike know if there is too much wear? His own sense of feel from his years of experience - that's why he's the pro.
If the valve guide is too...
If the valve guide is too loose, Mike can fix the problem by installing a bronze liner (shown) in the guide without replacing the whole valve guide itself. Installing a liner is not too difficult, as Mike states, and is cheaper than replacing the head. The liner is placed in the chamber, a diamond honer (not shown) is used to get the proper clearance, and then the top of the liner is snipped off.
Or, Mike can replace the whole...
Or, Mike can replace the whole valve guide, which, obviously, takes more work. First Mike would have to cut out the entire valve guide, install the guide, then cut the excess off at the top (at the location Mike is pointing to in the photo) down to the correct height to ensure a proper seal. This job is pricey but some customers still may opt to have it performed to keep the original head. Installing a liner is much more cost effective, but sometimes there is no alternative.
To be absolutely thorough,...
To be absolutely thorough, Mike also checks the valve stems. Using a micrometer (shown), Mike checks the entire valve stem travel (the space illustrated between Mike's fingers in the next photo below) for taper from top to bottom. Proper taper (the predetermined variance in the thickness of the valve stem from top to bottom) is essential for reliable engine performance. "A basic rule," Mike notes, "is that you can't have any more than about one-half a thousandths taper from top to bottom. Much more than that and the valve goes in the trash."
Lastly, Mike finishes the...
Lastly, Mike finishes the valve service by performing either 3- or 5-angle valve job. Now the head is ready for assembly.
Racing is dirty business. Grit and grime, wear and tear, wreck and repair are all part of goin' racin'. All this mess has to be cleaned up, serviced, and returned to near perfect condition in order to continue being competitive. Unfortunately, not all that grime is immediately visible from the outside. Inside your engine, heat and dirt can turn vital parts into scrap metal, but there is a way to combat this breakdown it's called maintenance.
One part of every racers' maintenance schedule must involve cleaning and freshening the cylinder heads. We visited Mike McGann, an expert machinist at Pletcher Racing, Inc., in Pinellas Park, Florida, to learn exactly what goes into getting a cylinder head ready for a season of racing.
Note: The heads shown in this story are cast iron heads off of restoration projects not a race car but we used these to show just how bad heads can be corroded if this cleaning process is not performed every time you do a rebuild or a refresh.
Pletcher Racing, Inc.
4470 63rd Circle North