Initially I was planning to have the heads done by a pro machine shop. Unfortunately the shop closed down in the middle of the Covid pandemic and I was happy to get my heads back before they might declare chapter 11 (which luckily did not happen after all). Anyway I needed the heads be ready in order to keep my timeline, so decided to do the job myself. You can find several detailed threads on these type of jobs in this forum. Here a short description of what I did:
Removing the old guides:
Tap a 10mm thread to the spring side, drill the center from the other side (just shy of the threaded area). Screw a bolt to the threaded side and use a suitable drift to hammer out the guide from combustion chamber side to spring side. No big deal just cover the head with a rag in case you miss the drift and risk damaging the head with the hammer. Important: Measure guide holes in the heads to decide if you can use standard size guides or need over-sized ones.
Installing new guides:
I first built a wooden support to hold the heads in place (must be really solid and hard wood to take the beating). Then the heads are heated to ca. 150°C to 200°C (300 to 400°F). Kitchen oven is fine but heads better be clean before). I place the head in the cold oven and heat slowly from room temperature to reduce risk of warping. Wait at least 30 min to allow the heads to heat up all the way. The guides are put into the freezer (as cold as possible, dry ice even better). Then you have to be fast to hammer the cold guides into the hot head (everything prepared and of course you need thick gloves). Be careful to press guides to the right depth. Then I put the heads back to the oven and let them cool down slowly.
Reaming the guides:
You just need a suitable reamer (Size 9H7 should be correct for new valves) to ream the guides to the correct size. Helpful to have a bore measuring tool (bore gauge) but with some experience you can feel when valve stem has just the right play/wiggle and moves up and down just right.
Re-cutting the valve seats:
Probably not always necessary but should be good practice to make sure valves are well centered in guide and seat. I used a manual Neway style cutter and on most valves it only took some minor cutting to do the job. Just one guide had to be redone after I realized the bore was too much off-center (guide had to be exchanged with a new one – learned my lesson to better check guides before you install them).
Grinding valve and seats:
You just need a basic rubber valve grinding tool and fine grinding paste. To check I use a black marker pen to paint the valve seating surface and turn the valve in the seat. You want to see a 360° metallic line on valve and seat not too far from the edge of the valve seat. Once you think its o.k., verify seal by putting water to the inside of the combustion chamber and watch if seat is water tight. If not good, you might have to go back to the cutting procedure and start a new loop.
Rocker shaft holes chamfered for RSR seals:
As advised by others in this forum, you should chamfer the rocker shaft holes to avoid cutting the seals during installation. Just used a small manual chamfer tool (small enough to be squeezed into the cam housings) paired with a set of 3/8“ extensions to reach all rocker holes from on side of the cam housings. Of course you should think ahead from which side you will insert the rocker shafts into the cam housings during final assembly.
As said you will find plenty of detailed information on these jobs in this forum. Special tools required are reamer, Neway cutter and measuring tools but you might borrow them from a friend. However - if you have never used a reamer or cutter - you probably don't want to practice with you valuable 911 heads. Looks easy but still takes some experience and routine to do things right. I recommend to get a set of old VW heads for training purposes.
Chamfer tool:
