Head resurfacing question

[Bill R.]

want in the 60 or so ra range for most cylinder heads.. its a case of not too smooth and not too rough. Most engine shops here are using a head resurfacing machine with a great big flycutting head that has many tool bits mounted on it that turns at a fairly slow rpm but pretty high surface feet per min...because of the size of the cutting head...When you're using one of these in good shape with freshly sharpened carbides you can get a 60 or even lower ra . There's newer equipment now that does a better job but very few shops are going to have them. I go to about a half dozen auto machine shops here regularly and they all still use the same stuff that i used in the 70's. For most general purpose work it will be fine. You actually want to see the surface of a head that was just done on the machine at whatever machine shop you go to to get an idea of how sharp their cutting bits are and how good a job it it do. An old machine can still do a fine job if its used with sharp tool bits and kept in good shape. Here's a link to the most common type of head resurfacer that i see around here

Don't let them resurface it on one of the big belt sander looking head resurfacers, And yes the older machines are adequate if someone who's fairly skilled is operating it. Here's the specs on your m20 head, you can only machine off .3mm total or .012 thousands of an inch

Haven't had the head tested yet but have been doing some research into various methods of resurfacing of the head if necessary. Just a couple of questions :

If resurfacing is necessary, what sort of process should I be looking for - are CBN (cubic boron nitride) or PCD (poly crystalline diamond) machines necessary.

In other words what roughness average (Ra) should I be aiming for ?

Or are the older machines and techniques adequate ?

(Was part of another thread but was getting lost).

[Zeuk in Oz]

Thanks Bill, just the info I needed !