Different Types of Heads
All standard head springs are the same, 70lb seat pressure. Bigports got slightly stronger 77lb springs.
Valve Retainers
The other major difference in the heads is the valve retainers used. The earlier retainers are easily identified by an upside down "cup" on top of the valve spring, sometimes they have an O-ring seal at the top of the retainer, which is taller. These valves have two grooves, the retainer collet fits into the lower groove. Later retainers have none of that, just a valve stem seal which clips onto the valve guide, which in turn is shorter. These valves have only one groove. The later model stuff is the best to use, as you can run higher lift due to the lower valve stem, and the clip on seal provides alot better oil consumption. The newer valves and retainers will change over onto older heads, however the spring height will remain the same. I'm using all newer 4K retainer gear on my originally-early-retainer 3K bigport head.
Spark Plug Tubes
For some stupid reason, probably cheaper casting process, these motors have a removeable alloy tube that the spark plug goes into. Every time you tighten the plugs (such as when cleaning or changing), the bottom of the tube deforms and squishes in to thread onto the spark plug, disrupting the way the plug seats, eventually the o-ring seal at the top of the tube won't seal, and you'll get oil all over the place. Whenever the plugs are out, Brad came up with the idea of flipping them upside down on the bench, putting a block of wood on top, and giving them a tap with the hammer. I had success with some tubes that had threaded on, by filing out the inside and just putting new o-rings on them. If all else is lost, new tubes and o-rings are available from Toyota, I paid $72 trade for two full sets.
Bolt Pattern
The head bolt pattern is the same across all K motors except 7K, which has its own unique pattern of three more bolts around the pushrods, where there are none on the older heads. This means you can put a K head on a 5K if you want, a 3K head on a 4K, etc etc.
Torque order is as such, pushrod side on top, manifold side on bottom
8 6 1 3 9 10 4 2 5 7
It's recommended to do the head bolts up in several passes in order, to prevent head warpage. Durapro gaskest recommend first pass 29ft-lb, second pass 41ft-lb, last pass 49ft-lb.
Casting Numbers
Each head has a number cast into it, usually at the back between plugs 3 and 4. Here are some recorded casting numbers:
Mildport K: 45 Unknown, smaller deck height, mild ports: 4 Standard 3K: 5, 19 Smallport 3K: 25 Standard 4K: 3, 10, 57, 20 Mildport 4K - 11 4K-E: 8 5K: 24 3K Bigport without water jackets: 24010-190, 24010-141, 24010-200, 24010-217, 24010-195, 24010-155
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