Made a pilgrimage to the local rubber and gasket industrial supply house. They only had US standard o-rings. So, I bought 2 each 011 and 2 each 012 to try. I also asked them about P80 lubricant and they had some. The counter guy pulled out a small container and gave me some. Since the o-rings were $1.30 each, I really did not get anything for free.
Since M&S, the local Brit shop is right around the corner I went there and got 4 correct E3253 o-rings from Steve. All four were $1.00. Talked to Steve at length about installing the o-rings and he said that you always shave a bit off. He said his trick is to smear a little Threebond or black RTV on the cap inboard of the o-ring and then tap it in place using the factory tool. This way, the sealant takes over if you snip the o-ring. He said he's never had one leak using that procedure.
So, from M&S, went home and tried a few experiments first.
First was the 012 o-ring. The CS on that ring is .062, which is larger than the width of my groove. But since the o-ring ID is smaller than required, it is stretched a bit which seems to reduce the CS. It fit. But when I put it into the tool, there was too much interference. I tapped it into the tool, but it sheared off a fair size piece of the o-ring OD.
So I tried the 011, which is what ed-h said he used. It was a bigger stretch, but same result going into the tool. I think the difference is ed's cap groove diameter was 0.490 and mine is 0.550. So he has much less ring compression than I do. Actually a stock o-ring will not seal with ed's spindle caps. There would be zero ring compression. So I suspect ed's spindle caps were machined at some point to take larger CS o-rings.
By the way, in both experiments above, I tried the P80 and was not impressed. I went back to STP.
I tried one of the new correct o-rings and did my best to nurse that ring and spindle into my tool. I won't bore you with the details and number of methods tried. Bottom line is as the ring compresses that last tiny bit, it gets caught by the sharp edge at the outboard side of the groove and shears an extremely thin slice from the back OD of the ring.
Since Steve said he's never had one not slice a ring and since others have had the same results, and given the schmoozing I did to coerce that ring into my tool and then the rockerbox, I'm convinced that Meriden was knee-deep in 0.0005 buna-n o-ring peelings in one station along the assembly line.
There is another piece of the puzzle that makes a perfect ring installation nearly impossible. It is the chamfer at the entry to the spindle cap hole. Even if you could get it into the tool without shearing, when it jumps across the gap made by the chamfer, it's going to bulge out and get snipped there, anyway. I tried to counter that by machining a matching taper on the nose of the tool. And the chamfer is a 60 deg chamfer not 45 deg as reported by others. It's actually 30 deg from the axis of the spindle which is a 60 deg included angle. This is a typical chamfer angle in machine shops. Even with a tool that matches that chamfer and eliminates the gap, it still sheared an extremely small amount off the o-ring.
So, the rockerboxes are assembled. If the spindles leak, I'll try Steve's suggestion of Threebond or black RTV.
Here are some pics for reference.
Here are the three o-ring sizes I tried.
Here's the tool that compresses the o-ring. The view shows the taper I machined on the end to match the chamfer in the rockerbox spindle hole. It's a little beat up on the end from installing the two o-rings. That' a knife edge.
Here is an assembled box and the mandrel I used to align the thackeray and flat washers. Manual recommends making this tool and I second that recommendation.
Here is a close-up of the nose of the mandrel. Note that I rounded the corners to allow it to smoothly engage and position the flat and thackeray washers.
Here's the assembled rockerboxes.
Here are close-up showing the correct positioning of thackeray and flat washers for a '66 big twin rockerbox.
UPDATE: John Healy replied to a similar thread to what I have in the general forum here, regarding these stinkin' o-rings. He says it is possible to get them installed properly and that the factory tool is useless. Here's a link to that thread.