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Yes, it's the detent wheel (or more accurately the riveted head of its pivot pin) that may hang up on the edge of the plate or screw. The drum itsellf turns freely whichever way up you bolt the plate on. The hole pattern and the plate are symmetriical.
Because the loads on the plate are axial it would be tempting to make a two piece plate that can be inserted from both sides with the two halves locking together once inserted....
Just another of those "because I can" sort of solutions..... :-)
It reminds me of the Simca car we had where the oil filter was mounted on the engine before the body was lowered in place. Aftermarket filters were an inch shorter, and you had to smash or cut the original to get it out..... :-(
G
Trans Prob Solved -Shift drum bracket installed upside down
gents, thank you all for your explanations and input!
Being the curious little bastard I am, I took LM's explanation and fiddled with the trans to see if i could spot it in action. its not that i didn't believe you by any means, i just love seeing how stuff works. I had a go with the trans with the plate off and with the plate on (installed wrong). sure enough it shifts through all gears with the plate off. whats odd is i dont really see any visible wear marks from the roller/roller-arm. im not so sure that's the hang-up although it sure looks that way. as LM was describing, the bracket appears to incorrectly hold the drum when installed upside down. As he said, the bracket only shows wear on the corners, and not around the whole radius. Things must not be as symmetrical as they seem or im overlooking some contact areas. either way, it clearly does not work upside down. so i dove in on splitting the case! ...but forgot to ask the do's and dont's first. I have the bill Silver CD's and have browsed the forum but never found good disassembly instructions. I figured id just try to take it apart upside down and leave the top end in tact. I didn't know if this was possible but figured worst case you guys would tell me im an idiot and I'd throw a few bolts back in and do it right side up. I got the case split but the crank assembly wants to go with the half im trying to remove. i forgot my stator remover bolt thing so i wasnt sure if there is a retainer back there holding things or im just doing this plain wrong and have to disassemble to top end in order to put this silly plate in correctly. Admittedly i have no clue what im doing, but im having fun figuring it out! thanks everyone! Wrong way?  Steve
CA78 65? CB77 65? The cam chain should hold the crankshaft down and that lower case half should come right off as long as you took the two nuts off the studs that protrude through the upper case half. You can leave the dynamo on and the crank, main, and countershafts should all stay "down" in the upper half. Then lift the main and countershafts out to get to the shift drum.
Should be nothing holding the crank to the case half you are trying to remove except maybe the oil seal is stuck to it but that should break free relatively easily. I'd put a popsicle stick or two between the cases near that location and tap on the rotor with a rubber mallet... Above all don't damage the mating surfaces.
The hole pattern and the plate are symmetriical.
This is not true. The holes are not centered to the drum. They are actually more down from the top case That is why only the outside corners are in contact not the entire circle. When the part is from the bottom and only the corners of the part touch the drum it drags drags and doesn't move smoothly making gear changes more tough than when part is installed correctly. ..................lm.
Dead right LM, My mistake. Holes are below the centreline.
 Putting it in upside down reduces the contact with the drum.  Though I couldn't feel any tightness when I tried this old drum and plate in a NOS case.  [url=https://flic.kr/p/xci6ng] 
'60 C77 '60 C72 '62 C72 Dream '63 CL72
'61 CB72 '64 CB77 '65 CB160 '66 Matchless 350 '67 CL77 '67 S90 '77 CB400F
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