PDA

View Full Version : Cylinder head resurfacing.



Virgil Johnson
02-18-2008, 07:37 PM
I have a friend who needs the gasket surface of a cylinder head off an old Sears 250cc single cylinder motorcycle flattened. He tried to do it on a belt sander but got it off .006-.010. What surface finish do I need on this? Fly cut on the mill , surface grind or 60 grit on a flat surface and elbow grease? Thanks.

lane
02-18-2008, 07:48 PM
Fly cut would be fine

Oldbrock
02-19-2008, 12:45 AM
If the plug hole is centrally located just use a plug in the lathe and screw on the head and machine. first drill and tap a 14 mm thread in a piece of stock in the lathe, screw in the plug and machine off the hex so you have a dia. true to the thread. Chuck up the plug and screw on the head and check with dial indicator. Take light cuts and you're done. All of the sled heads I've done have been done this way. Peter

Carld
02-19-2008, 08:52 AM
Spark plug holes are seldom perpendicular to the head surface on motorcyles. You could clamp it to a face plate to do it in a lathe.

The best way is on a mill and flycut it but holding such things as heads, intake manifolds and exhaust manifolds requires considerable creativity. Every time the boss started walking towards me with one of the affore mentioned pieces I went the other direction hoping he would find someone else. Most the time I found the part laying on my table with a note telling me what he wanted done. I finally gave up and took the crappy jobs along with the rest.

I have extremely fast reflexes that have saved my butt several times when stuff comes loose and chases me. I also learned how to do chancy dangerous setups and live to tell about it.

Virgil Johnson
02-19-2008, 06:15 PM
This things has two spark plug holes and neither are of any use holding wise. There are cooling fins with lots of draft that are too thin to clamp in a 4 jaw. Most likely I'll build a fixture with 4 piloted pins to support the head using the bolt holes in the head.

lane
02-19-2008, 08:30 PM
You just described the cylinder head for a Sears Allstate Punch 1962 are earley

Virgil Johnson
02-19-2008, 10:03 PM
I think my friend mentioned that these were called a "twingle" ? Anyway it took 45 minutes to get it setup and cut. No fixture just 123 blocks , shims, and three toe clamps. It will take another 15-20 minutes to clean up and get the vise back on the mill. Slow compared to the rest of the crowd here but who is counting. Should be worth a burger at lunch.

Sparky_NY
02-19-2008, 11:06 PM
Just a comment you may already know.

When you flycut or otherwise mill a cylinder head you are going to increase the compression. Its commonly done as a hot-rod technique. Problem is if its too much it can cause engine problems due to detonation. (like breaking a rod!) If the increased compression is not desired, the common method is to use a thicker head gasket to make up for the material removed.