I've gotten the 261 torn down to the bare block. On the way I've discovered 1 burnt piston, milk-can style lifters worn concave, 10-1/2" pushrods, a cam no longer usable (with "GM" aluminum gear attached), crank ground -0.010 (rods and mains), neoprene rear main seal (didn't appear to be leaking).
Five pistons have "854" cast by the pin boss and one piston has CSxx something I don't remember. I weighed the burnt piston with rings and pin at 835 grams, so I'm guessing 854 is the nominal weight. The rest of the pistons don't appear to be scuffed but do show minor wear.
Questions:
1) Did GM identify their pistons with "GM" or some other mark?
After breaking the glaze with a 200 hone, the pistons have a couple pound drag on a 0.004 feeler. That's more than I would like for quietness and oil control and way over factory spec for original pistons. Could these not be factory pistons and require greater clearance? The bores are 3.752 now I honed them. Had I measured the clearance first I'd have stopped honing sooner but now the bores are straight anyway. Near as I can tell, the pistons are 3.748 and cam ground so they measure way less over by the pin boss. Maybe I can get them knurled.
2) Did GM go back to the milk-can style lifters on the late production? After '60? This is theoretically a '62 engine and the '60 manual specifically shows the short style lifter and shows the milk-can with an X through it and the short one as being OK. I'm guessing that someone replaced the lifters with what they had around at some point. They have 1 groove around the upper third that I presume is an ID mark.
3) There is a special hollow head bolt for rocker oil; and the '60 cut-away drawing shows this being fed from the cam bearing. My engine however, has the old-style tube running from the rear cam bearing to the center head bolt boss. Is this a belt-and-suspenders deal? I ran a piece of welding rod down the bolt hole and it goes to the cam bearing shell. It seems that it should go all the way to the bottom of the cam bore. Maybe somebody put the wrong bearing in that position and one with an additional hole should be there.
I found 2 ea. std. "Sealed Power" pistons, new, for sale cheap and bought them both so I'll have a spare. I hope the weights are reasonably close or a little heavy, in which case I can grind the pins shorter to make the weight proper. The alternative is a $300 set of pistons of unknown brand and a bore job. What do shops charge per hole for running a boring bar?
261 pistons and rings are rare in my usual supplier catalogues. Lots of 235 stuff.
New cast-iron ring gaps are about 0.026" mid way down the bores. That seems like a lot. My rule of thumb has been 0.0035 per inch of bore, which would give ~0.014" gap; and the manual says lots less. Ring-land side-gap seems OK at 0.002." The old rings are out to about 0.050." It wasn't my intention to do a complete rebuild but more of a thorough overhaul since it doesn't seem to need any machine work, so far.
This may be more than some of you want to know but maybe it can serve as a bit of a guide to someone else doing similar work. I keep reminding myself, "It's expensive but it's even more expensive if you don't do it right the first time."
