Block Question

[utahseries]

This one goes out to the historical geniuses on the forum.. What differences, if any, are there between a series 2 block and a 2a block?
Thanks

[Sputnicker]

I just finished a complete mechanical restoration on my 1960 Series II and found several differences from the later IIA block. Many of these differences are not identified in parts lists from various suppliers, so knowing in advance should save you some grief. Here's the list:

1) The front timing cover on the SII is a different casting (cast iron)
2) The water pump is smaller and has 8 holes instead of 9. These pumps aren't readily available, but they are rebuildable with the same kit for the IIA (same bearings impeller, seal and flange). The gasket is NLA, so I used silicone.
3) The crankshaft has smaller rod bearing journals and uses different connecting rods and bearings, which may not be available. The later IIA crank is interchangeable, but you'll have to get connecting rods as well.
4) The main bearings are exactly the same dimensionally, but the tabs that keep the bearings from spinning are reversed. I had to grind slots in the block and main bearing journals to use the IIA bearings. It wasn't that difficult, but requires a die grinder and a steady hand.
5) If you are planning to use a Delco alternator with Pangolin brackets, you will use a 48" belt instead of the 49.5" belt used on the SIIA (if you keep the original timing cover/water pump).
6) The cylinder head on a IIA uses a different 2-piece rocker shaft. The rocker pedestals are also different and so is the valve cover. So if you want to use an 8:1 head (which I recommend), you will need to use the later style one-piece shaft, all 5 pedestals and rocker cover.
7) The SII has an earlier style timing chain tensioner and doesn't use the rubbing block. All of the parts for the earlier tensioner were available.
8) The flywheel has different spacing for the clutch pressure plate locating dowel pins. The SII used a 9" clutch and the SIIA used a 9.5" clutch. Fortunately, the bolt holes are all the same. I converted to the 9.5" clutch by filing down one of the dowels to clear the pressure plate.
9) The SII used a one-piece thermostat housing and a "bellows" thermostat, which is no longer available (and probably less reliable). I converted to the later two-piece style housing and thermostat.

I think that's all. My SII motor was the original and had never been apart. It's highly likely that some or all of the above-mentioned differences have already been changed/updated on most of the SIIs during the last half century. If you are not committed to keeping everything original to the SII, it may be easier and less costly to start with a later motor that uses all the parts that are still available. If you are committed to maintaining originality, you may find it difficult to source everything.