* . . . Installation of the Top End

4 steps to head identification just from site plus head bolt spacing: ¹⁾

1a. If these fins are present, your looking at 900 heads for sure. In later 71 these fins disappeared. That means:2)	1b. There are some 900 heads that didnt have those fins and no 1000 heads have these fins. If no fins go to step 2.3)	2a. Decide if the heads are later 71 (900) or 1000. Do that by looking at oil drain size Note the size of drain compared to head bolt holes.4)
1957-71 bolt pattern ( inside of hole to inside of hole, diagonally ) is 3.440“. 57-mid 73,threads for head bolts, come all the way up to the head gasket surface on the cylinders.5)
2b. 1000 uses 3/16” oil drains. Now you know if your looking at late 1971 900 (big drains) or 1000 (small drains). If heads have small drains go to step 3 to determine if heads are E1000 (72-E73) or L1000 (L73-78). 6) When the change to 1000 happened in 72 the cylinders casting size was increased but for augments sake the head casting was not. Consider the cylinders: The bore was opened .094“ radius. That pushed to the oil holes in cylinder to a larger pattern. To get the matching larger pattern in the old heads, the holes needed to be reduced in size so they still fit in the 900 size casting.7)	3a. E1000 (72-E73) On 900 heads (smallest bolt circle), the bolt holes bulls-eye the casting boss. Looking close at the 72 heads you can see the bolt circle was slightly enlarged while the casting boss stayed at the original position. 8)	3b. L1000 (L73-78). In later 73 the 1000 heads change to bigger bolt pattern.9) The L73+ heads have the spot facing further out on the casting boss. In other words, the PCD of the spot facing is greater than on the 72/e73 heads. 10) In L73 the bolt circle was really enlarged. Again the boss stayed at the 900 position. There is added meat around the bolt holes between the fins but that's a moot point in identifying what year heads your gawking at. 11)
	72-mid 73 1000 bolt pattern ( inside of hole to inside of hole, diagonally ) is 3.540”.12)	L73 - 85 bolt pattern ( inside of hole to inside of hole, diagonally ) is 3.640“. Late 73-85 threads for head bolts are recessed in the cylinders by 1/2''13)
4. In 79 a boss was added for a/c mounting. This is a 79 only head. 1980-1983 is same as 1979 but doesn't have the intake o-ring lip. 84-85 had no intake o-ring lip either. The air cleaner boss was still present but it wasn't drilled or tapped.14)	84-85 heads also had the shoulder-less valve guides and took a small washer for the inner valve spring instead of the full size lower spring collar the previous heads used. The valve guides do require machining if you want to use a seal the top spring collar will contact them. 15) While this info is accurate, don't let missing guides or incorrect vintage guide installation influence you in identifying what heads you are looking at. 16)

• From a Service Bulletin in October of 1981, all standard sized pistons are graded for size in .00025” increments. This is done for production purposes on­ly and does not apply to oversized (.010“-.070”) pistons. ¹⁸⁾
• The grade number is stamped on the dome of all standard pistons. In the case of a grade 10 piston, the number 10 is stamped on the dome. This is a standard sized piston and should not be confused with a .010“ oversized piston which also has a number 10 stamped on the dome. If there is any doubt about a piston's size, it's largest diameter should be measured.
• In the future, all grade 10 standard pistons will be marked “G10” for ease of identification. All oversized pistons used in oversized cylinder bores (.010”-.070“) will continue to be stamped in the usual manner.
• Example:
  • Standard Grade 10 piston range: 3.18725”-3.18700“ stamped with “10” or the new G10 stamping (old style).
  • Oversized .010” piston range: 3.197“-3.196”

* . . . Three angle valve seats - 1980 and up FLT/FL/FX/XL models