Tranny day today! (Pix at 11 PM - tomorrow...)
I've been jealous for years of the easy-to-find Neutral (when hot) of the mid-1973 K3 and later 750. This was due to a 'delta change' Honda did with the shift drum (which I'll show in those pix...) that made the insertion point for the Neutral to be 0.5mm wider, and the opposite side of the fork pin's channel was reshaped from a sharp "U to a more "omega" shape. This allowed the shift pin to accelerate more slowly into and out of the Neutral Zone (yeah, I'm a Space Cadet...the back of my car even shows my Starfleet Academy sticker, still!) and helps the fork idle there. This gives the 1-2 shift a notchy feeling, much slower gear-to-gear than the earlier drums did, but I don't street race anymore, so that's OK with me.
And, I found a K4 shift drum with only 17k miles on it in pristine condition! That was Step 1. Can't wait to try it out with a hot engine.
Step 2 was to find out where the other 3 Neutrals were coming from. Turns out, the inner countershaft bearing has almost .003" clearance, guess it's done. This lets the whole countershaft tilt. To help that tilt, the outer one has .0022" clearance, so between them, it's no wonder it started rounding the dogs on C5. But, I have a better C2 and C5 pair from another K1 tranny, complete with the bronze inner bearings (which went away and became cast iron in the K3, losing HP in the trade), so those went onto the c'shaft.
Next was the mainshaft. The M4 gear also has a bronze bearing, had to find a better one for that, too. It came in the form of an early K3 shaft I have with the bronze inner bearing and the dual thrust washers on either side: this will be an upgrade, if a slight .02mm misalignment away from the clutch, because my C4 was the old K0 style with only a shim washer against the snap ring on the right side, and nothing between it and the M1 gear. This type always makes C4 drag a little near redline speeds, and the M1 shows it on the side nearest this gear. This newer arrangement inserts a grooved thrust washer on both sides of the C4, so the side-load friction should be lower. The M2 was also worn in the bronze ID, my K3 shaft had a good one of those, too.
Overall, I am stunned by how little wear is actually in the box. The only things that show visible wear (i.e., didn't have to use calipers, mic, and ID bore gages to find it) was the grooves in the shift drum. The steep ramps up to the Neutral peak are very shiny and the chamfer at the tops of the groove on the wear side are gone, indicating there is almost .003"+ wear there. In the new K4 drum, these chamfers are almost .008" instead of the older .003" size, which lets more oil slip into the grooves (even if it does reduce the depth of contact about .008" in the process). This is one big reason the later gearboxes shifted so much more smoothly when hot.
So, I hope to now combine the more efficient K0-K2 bronze bearings with the slicker drum and new ball bearings, all to make for a happier ride!
