Head Turning 101 By Sainty

First off is mounting the spindle, if you are turning an existing head, not making new 
inserts like I do lots of, you need to get the spindle fairly accurately centred first. Using 
a centre to get it roughly in place before tightening the chuck fully is always a good idea.

Next up is mounting the head and checking the run out with a dial guage

Max run out is less than 0.001” if you want to do it properly. You will be surprised 
just how far stock heads can be out from the spark plug thread, this CR250 head 
was 0.020” in total run out measured at the outer edge. A few well placed taps with 
a soft hammer had the run out down to 0.001”

When you have calculated all the head shapes that you want, you start by machining 
the gasket face to get the depth of head you need.
I tend to use diamond tips for turning aluminium at high speed. The finish is much better
 than using tool steel for the job, but a specific insert for ally would be just as good



Next up comes the squish band machining. From the gasket face you should know 
what the undercut depth is, if its an “o” ringed head this will be the squish clearance, 
if a gasket head it will be the squish clearance minus the gasket thickness
.
Set the cross slide to the angle required, its 10 degrees here and you can machine 
the squish band directly from the depth you need.

Finaly, if you need to set the spindle dead square before machining ( ie. If you 
are doing new heads) The easiest way is to use a strip of feeler gauge resting 
on the thread. You can not run the dial gauge directly on the thread so you make a follower. 


Next instalment soon,
Mart. 
Stealth-Engineering