[groundrail]

I have a general question about flycut piston valve reliefs.

Starting with flat top postions, I can find where valve relief cuts should be made using plasticine (modeling clay) on top of the pistons.

I read that closest proximity between valves and a piston with some cams is NOT tdc but might be anywhere between 10-20 deg after tdc on the intake.

I read that some people use the Isky flycutting tool and some people take the pistons to the machine shop. If I calculate the required distance using the clay, how do I tell the machine shop what angle to cut the valve reliefs?

 

[Max Keith]

valve angle

To get the proper flycut angle will require knowing what the angle is in relation to the deck of the piston and the valve itself. You will notice that there are aftermarket head that are called 13 degree, 18 degree etc. What this means is that the valve stem is that many degrees off of the perpendicular centerline of the piston deck, or block deck. A good competent machine shop that deals with building performance engines will know what you need and can deal with it accordingly.
Unless you have the jigging equipment, I dont recommend doing this in your garage. This isnt something you can just chuck into a drill and start cutting.

I got involved in this at one time and used a section of head and an engine block. The flycutter I used was designed for just such an application.

I had the block bored for different sized pistons (overbores), and with an old crank in the block, I would put the piston and rod assembly in the cylinder with the crank turned to TDC, then with a collar stop in the stem of the cutter, would actually use a half inch drill to make the fly cuts.

It worked pretty well. However, unless you expect to have to do this quite often, or are doing it for other people as well, I dont recommend spending your money and time on such a project, as doing it yourself.