Part 2:
This is what I use to flatten my heads. It is simply a 1/4" thick sheet of tempered glass that used to be a shelf for something. Don't use an old, swirly-finish pane from an old house or barn; it won't work. Modern glass that is made by pouring molten glass on a bed of molten metal is needed. I attached it to a piece of particle board with a couple wooden clamps. I used similar wooden clamps to attach the sheet of sandpaper. Use 180 grit wet/dry sandpaper to start, and finish with 220. If only 220 is used, it'll take 4 or 5 sheets. Wet sand to make the sandpaper last longer. Use a circular motion, and occasionally rotate the head.
After awhile, the head will start to look like this:
Notice that some areas have been touched by the sandpaper, and others have not. This process must be continued until the entire gasket surface is of a uniform finish. (Aside: Others may recommend the use of a flat file instead, but this takes some practice, and I feel that my method is a bit more foolproof for those of us with less finesse handling a flat file) When the gasket surface looks like this, it should be essentially perfectly flat:
Recheck the head with the sheet of glass and feeler gauge if you like-- I have never been able to slide a 0.001" feeler gauge under any of mine after completing this process.
Next, a short lesson on head gaskets. I typically buy aftermarket gasket sets because they are significantly cheaper than the OEM gasket sets, except for one problem: The included head gasket is often a POS. Below are two nearly identical head gaskets for K241-K321 engines. On the left is the aftermarket gasket, and on the right is the OEM Kohler gasket.
They look very similar, but have a significant difference. Below is a close-up of the inside edge of the aftermarket gasket. Note the exposed three layers of material:
Here is the Kohler gasket. Notice the 'fire ring' around the inside edge:
The 'fire ring' gasket was recommended to me long ago, and now when I buy a gasket set I buy an OEM head gasket. I think these are a much better design. The K161 and K181 head gaskets do not appear to be available in this style anymore, so this only applies to the larger engines.
Some people replace head bolts when a head gasket is changed; others do not, and for various reasons. If I twist one off, I replace all of them; otherwise, I wire-wheel and re-use them. Some people also use Kohler head bolts; others (myself included) use ordinary grade 8 bolts. I have never had a problem with the grade 8 bolts, and this is what I find in half the engines I come across anyway.
It is a good idea to chase the threads in the block to allow the bolts to be torqued accurately. Oil the threads of the bolts, and then put them all in finger-tight. Tighten in the appropriate sequence in steps, i.e. 10, 20, and finally 30 ft.-lbs. The proper sequence and torque values are important, and a torque wrench is required. Below is the sequence for the K-series singles:
After reassembling all of the sheetmetal, run the engine for 20-30 minutes at 1/2-3/4 throttle and then retorque. I have heard of others retorquing after the first hard pull with good results, as well. There are two schools of thought on head retorquing: One, to retorque when hot, and the second, to retorque when cold. Retorquing when hot doesn't make sense to me because the aluminum has a greater thermal expansion rate than the steel head bolts, so retorquing it hot will result in a looser head after it cools and shrinks than if it was torqued cold, so I always retorque cold. I've done at least a dozen heads and never re-blown a head gasket with this method.
