Unfortunately, Bob's experience seems to be common practice among many aircraft cylinder rebuild shops. Instead of core drilling the valve guides so they can be easily removed, they drive them out, wrecking the guide holes in the process, then ream the heads to the next available size. If your head is already at the max oversize, they'll tell you your cylinders are worn beyond repair or that they will have to weld the heads. The most recognized names in aircraft cylinder rebuild and repair all seem to do this to save time.
I don't allow aircraft cylinder shops to remove or install valve guides for me anymore. I take the work to a local machinist who knows aircraft entgines and I can trust to do quality work. Whether it's a Corvair, VW, Continental, or Lycoming, it's worth your time learn about the process and ask how the shop does the work you want them to perform. -Jeff Scott -- "robert glidden" <glid...@ccrtc.com> wrote: Fellow Netters Just to give you a little heads up about your local machine shops.I recently took my crank and heads to a machine shop recommended by a fellow builder here local to have the crank tapped for the safety shaft and the valve guides removed and replaced in the heads.I dropped them off two weeks ago prior to a trip to Michigan.I returned to the shop last Monday to find out they heated the head like they was suppose to and tried to remove the valve guides with a air gun.To make a long story short,the holes for the guides look ugly.And now have to be reamed out for the oversized bronze valve guides.Make sure the shop you take them to knows what they are doing.I've been a tool and die maker for several years and have never seen a first year machinist screw up this bad.I think the worst part is I've become so attached to my engine I felt like somebody had kicked me in the gut,was not sure rather to scream or cry.....Bob
