The first place I would be looking for trouble is located behind the clutch basket. You'll need to remove the oil filter which requires a special tool that can either be made or purchased.
I'm thinking something is going on with how the gear shift spindle is pushing or pulling on the drum plate. Here is parts fiche diagram of the parts your are gonna need to look at.
Honda Cb350k4 Super Sport 1972 Usa Gear Shift Drum - Spindle - schematic partsfiche

 

Could be the centering pin and spring (#s 16 & 17 in the parts diagram) are loose or bent. The pin can be bent by the shift lever being hit. The shifter shaft has to come back to center after every shift to engage the next gear. Try pushing the lever down a little to see if it will catch the next gear up.

 

+1 on what Mike in Idaho said.

There is a good write up on HondaTwins somewhere about splitting the cases that has some great pics of what the author called "the clockwork" behind the clutch basket.

One thing on my mind since you said the shifter is connected directly to the shift shaft and has no linkage is that I have heard or maybe I made it up that the linkage works best in the vertical position. So, 6 o'clock or 12. Maybe someone will chime in on that.

 

I'm guessing you are talking about this thread: http://www.hondatwins.net/forums/48-engine-discussion/17947-sl-350-engine-rebuild-4.html

Can anyone point out #16 and #17 in this photo? http://www.hondatwins.net/forums/at...7016d1343137817-shifting-problem-1st-gear-neutral-but-nothing-else-dsc05644.jpg

Is the centering spring the same spring that is used by the kick starter? Or is it not shown in that photo? My problem sounds a lot like the one described in this thread: http://www.hondatwins.net/forums/48-engine-discussion/38987-not-shifting-into-3rd-gear.html

Can anyone provide any clues and explain like I'm 5 years old on how I should proceed?

 

I have a single piece shifter and it works fine. I doubt the oil leak is related to shifting problem. A sprocket side oil leak that persists after shaft seals are replaced is often the rubber wiring seal. I fixed mine with a bit of Hondabond.

 

That's the post I was talking about. Center in spring is not the kick start spring.
Nope. Can't point to 16&17 cause they aren't there. If they were they would be toward the top and right of the shift drum (star looking thingy.) The centering spring slides on to a piece that looks like a lowercase h and the spring has a point on it that fits into a hole to the right. The "h" piece is held on with the 10mm bolt and a collar that lets it (the h piece) side back and forth.
Sorry for the lame description. If that is your motor or if your is taken apart to that point you could try shifting through the gears by turning the star shaped deal with a screw driver. You'll need to be able to turn the transmission a bit to get the gears moving. It's sort of confusing when you shift that way because of course 1st is down and the rest is up but just manipulate with assistance of the shifter and that should keep you straight.

Good luck

 

davekiss, IF you haven't already torn things apart, you may want to try the large adjuster (looks like a dome nut) on top the transmission. It has one of those lock washers with the fold-up ears to secure the nut. I had an issue with neutral and someone (unfortunately I don't recall who) on the forum suggested it. Only took a VERY slight twist to correct the problem and no messy disassembly! I would suggest marking the present position with a line from a sharpie across the nut onto the case and gingerly tweak it to see if it helps. If not, return it to the original location and proceed with more in depth repair.:-?

I'm far from "experienced" I'm not even sure your engine has the same feature, but this solved my problem. Thought I'd mention it before more drastic measures are taken.

 

The Pic you asked about #16 & 17 in is from an old post of mine.

The issue we had was the Bearing Caps for the Transmission Shaft had slipped and the alignment PINS that keep them from spinning and SLIDING OUT has gotten out of position during assembly.

(2) Things happened

1st the hardened Steel Bearing End Caps forced the hardened Pins to push thru the Aluminum Case. The fix for this was not complicated but did take some time to find someone willing to do it. The details are in the original post.

2nd the end cap slipped outward away from the Shaft which in turn allowed the shaft to slip outwards. Once that occurred the Shift Fork did not have enough throw to move the gears from 1st to Neutral or 2nd - 3rd etc.

It's not a fun project to have to pull the motor and re-build the bottom end but...

You CAN determine if this is your problem by looking at the area of the case where the Transmission Shaft Bearing End Caps are to see if there is a BUBBLE that should NOT be there. That would indicate the PIN has push up into the case.

 

aaaaand we're back! 7 months later and I'm finally getting around to looking at this again. I missed out on last year's season but am determined to get this thing going this time around.

So I've disassembled and removed the clutch basket and the oil filter to get a good look at the moving parts underneath, and I've gotten a little closer to determining the culprit. I made two videos to showcase my findings:

Video one shows the shift pins. Three of them look like they are in place, but the fourth one seems like it is popping out a bit and is not flush. I cannot push it in any further.

Video two shows the actual shifting process. I can shift with a screwdriver - it is a little clunky, but I am not sure if that is just because the bike is not actually running or if it is because there isn't any oil in the case. But when I try to shift with the lever, I run into the same issue that I did when I was actually riding the bike. It will not catch on the next gear and gets lost somewhere inbetween. I described a "hard stop" earlier that I felt when attempting to shift while riding, and I show what happens in the video that was what I was feeling.

Here is a link to an album with some close-up photos showing the issues: Imgur: The most awesome images on the Internet

Here's a link to the Schematic that I am using: 1973 Honda CB350G Shift Drum / Shift Fork Schematic - Album on Imgur

Does anyone have any ideas on what I should do next based on what is shown in the videos?

Thanks so much for your help!

 

aaaaand we're back! 7 months later and I'm finally getting around to looking at this again. I missed out on last year's season but am determined to get this thing going this time around.

So I've disassembled and removed the clutch basket and the oil filter to get a good look at the moving parts underneath, and I've gotten a little closer to determining the culprit. I made two videos to showcase my findings:

Video one shows the shift pins. Three of them look like they are in place, but the fourth one seems like it is popping out a bit and is not flush. I cannot push it in any further.


Video two shows the actual shifting process. I can shift with a screwdriver - it is a little clunky, but I am not sure if that is just because the bike is not actually running or if it is because there isn't any oil in the case. But when I try to shift with the lever, I run into the same issue that I did when I was actually riding the bike. It will not catch on the next gear and gets lost somewhere inbetween. I described a "hard stop" earlier that I felt when attempting to shift while riding, and I show what happens in the video that was what I was feeling.


Here is a link to an album with some close-up photos showing the issues: Imgur: The most awesome images on the Internet

Here's a link to the Schematic that I am using: Does anyone have any ideas on what I should do next based on what is shown in the videos?

Thanks so much for your help!

I'm not sure about the pins - I seem to remember, although it's been longer since I had a 350 apart - that the star plate is supposed to cover the pins, but not sure of that. Either way, you'll do a lot better by simply turning the mainshaft (sticking out) than turning the rear wheel. Turning the mainshaft accomplishes the same thing as far as getting the gears moving to allow smooth shifting, but the rolling weight of the rear wheel will help here because you really want both shafts to have some movement as there are engagement dogs on gears on both shafts in play depending on which gear is trying to engage in the shift order. So, to test properly, just turn the mainshaft with your hand and then turn the shift drum. You might find that it goes into all gears better, but you'll still need to investigate the pins in the drum end.

 

Thanks for the reply, Tom. On further inspection, it looks like the star plate has a groove on the back of one of the points that seems to fit the one pin that is extruding/not flush, so I placed the star over the pins and I feel confident that it is in the correct place now. The star was loose before because the screw that held it in was not tightened all the way, which I'd imagine could partially be contributing to the shifting issues.

Anyway I have two more videos. The first one shows some shift attempts moving the shaft by hand that result in some difficulty moving between gears and falling into false neutrals..

The second one shows some movement/play in the shift stopper (this is a cb350g so it looks a bit different from previous years)

I removed the shift stopper to see if there was some kind of evidence contributing to this movement, and it appears visually to have a bit of bend in it, but I cannot tell if it was manufactured this way or if it is meant to have this shape:

http://i.imgur.com/2sIx0s7.jpg

It does appear to be bent a bit part #7 in the fiche (http://cdn1.bikebandit-images.com/schematics/schematics/honda/hon005/hj0906w0105042.gif)

Hopefully this is enough information for someone to weigh in and help with the next steps

 

Yeah, I'm not as versed in the 350s as the 450s, so someone else would be better for the finer points. In my experience, if the rear wheel is sitting still and you turn the mainshaft while trying to shift it, you'll feel the dogs line up and it drop into the next gear as they align. If that isn't the case, then you may have something going on with the shift drum or detent mechanism including the detent arm you referenced. Can't recall what the detent arm is supposed to look like but that discussion was had here recently in a different post, I believe

 

Your shift drum stopper is worn out.

replace it with a new one

part 7 in the fiche at the top

 

Well... if @outobie says it, it must be true!

Any clues on where to pick one of these up? The ones on ebay look to be in worse condition than mine. Anyone happen to have an extra shift drum stopper for sale?

 

Quick search on eBay by part number and I found 9 of them NOS in the $20 range

 

That shift pin that is not flush in the second photo fits into a hole on the backside of the star plate ... I had this issue a few months back ... take the star plate off and look at the backside ... you'll see a hole that the pin that is not flush fits into ... should work after that unless there are other issues ...

 

So I ordered a "NOS" stopper (in quotes because upon inspection it had about the same amount of wear as the current one off the bike) and I realized it really wasn't the stopper wear causing the issue after all. There is a rivet on the end of the screw that holds the star plate that needs to go inside of the star plate to ensure the stopper doesn't wiggle off of the roller. The rivet wasn't in the star plate hole so it allowed the stopper to move more than it should. I corrected this and buttoned it back up and it's shifting much better now!

Thanks for the help!