Odd shifting issue on recently rebuilt '74 TX650A

[nhsteve]

I just finished a rebuild on a '74. Bought not running, no compression on RH cylinder. Pull motor, rebuild top end (long story in there, not pertinent to my 'issue'), reassemble. No major headaches during rebuild. As I had suspicions of 'stuff' in the base (none found), I split the cases and vapor blasted cases, cylinder, head, cam cover, etc. (had to remove shift drum assembly to do this).

Reassembly of all this held no drama. Continue on with rebuild. Lots of new bits (it is to be my son's bike, so I want it solid).

My issue: bike shifts fine between first 3 gears, any way, all day, as long as I stay in those 3. If I shift up to 4th or 5th, also no problem. Shift 5th to 4th, no problem. Shift 4th to 3rd, no problem. At this point, the shifter will not go from 3rd to 2nd. At all. Period. I had to get to the side of the road, shut it off, play with the shifter by hand, get it back into 2nd, then neutral, and I was off again. Shift distances "A" and "AA" shown in the manual are equal, things are tight.

I can duplicate this on the lift/centerstand by moving the back wheel (1" chain slack) and shifting between the first 3 gears fine. Shifting up never seems to be a problem. It is only from 3rd to 2nd that seems to be an issue. Suspecting a bent 3rd gear shift fork I have replaced it, but the original barely seems marked at all. Any damage is certainly not obvious.

Moving the shift drum assembly with no gearshafts in place I can shift the first 3 positions ok. When I push and go further, something binds so bad that I need to disassemble things again to free them up.

Sorry for the long explanation. This is really kicking me at the moment. Anyone seen this? Bent shift drum? Shift rod?

I have a later motor for parts I intend to disassemble and compare.

 

[nhsteve]

Just as a clarification question: should I be able to shift the drum in place, with the clutch off (spinning the input/output shafts to ease things) easily into all 5 gears. I removed the clutch completely at one point, and again I can shift between the first 3 gears ok, up into 4th & 5th at that point not so much.

 

[TwoManyXS1Bs]

Just as a clarification question: should I be able to shift the drum in place, with the clutch off (spinning the input/output shafts to ease things) easily into all 5 gears.

Yes, that's a typical test.

Some things to double-check and examine:

Neutral detent plunger and spring. Normally only affects the 1st-N-2nd range, but who knows.

Guide bar for the shift forks. Burrs, nicks, straightness, properly aligned and held by its notch.
Aluminum plug still fitted in its end (oil flows thru that thing).

Possible interference of shift fork cotter pins.

Possible missing roller dowel, at tip of shift fork pin (if yours has that feature).
Check parts manuals to see if yours applies...

 

[nhsteve]

Thanks for the response and input, I do appreciate it.

I can say for sure that the rollers at the end of the pins holding the shift forks in place are in fact there. I replaced the 3rd gear fork yesterday, so I had to take the assembly completely apart to do so. I have used just a smear of grease to make sure they don't slip out of place when I reassemble.

Good point on the cotter pins. I think I have them bent over enough that they do not interfere with anything, but quite hard to see if one has the gears in place.

Neutral detent seems ok. No burrs, and spring is not misshaped.

Alloy plug is in place, but I will make sure the oil passage is clean. I am currently suspicious of the shift guide bar. Not that it actually looks bent to my eyes. Need to find a piece of glass to roll it across to check it, and maybe the shift drum also.

Of note to me at this point, is that if I assemble it all up, with the guide bar in place and properly locked down by the plate, with the detent wheel and springs all in place, I absolutely can NOT shift up past 3rd gear using either my hand or a screwdriver on the end of the drum. This is with OR without the neutral detent. Have not tried it putting the lower case back on and with the shift lever. That will be a task for today.

I have a feeling that I will be into the other set of cases eventually, if only to do some comparisons, especially if that one seems to shift ok.

Will report back. And again, I do appreciate the comments and questions. It's that kind of thing that makes these forums so valuable to us.

 

[TwoManyXS1Bs]

Sounds like your problem may be localized to just the 2-3 shift fork, the one closest to the drive sprocket. That fork slides the 5th driven gear left-right-center, full travel during the 2-3-4 shift. A very busy shift fork.



I personally don't like this particular guide bar design. Too much opportunity for fork binding on the bar, kinda like the way the basket jitters down in that "mousetrap" game. Toyed with thoughts of making a hardened/polished version, with better (reduced binding, maybe bushed) fitment to the shift forks. That guide bar is the first thing I'd closely inspect, straightness, diameter, gouging, ...etc.

Second thing to check is the slider gear itself, to see if you may have a possible gear/shaft mismatch. There was a change to the transmission around '77, changing the polished sliding contact areas of the slider gears from the root of the shaft splines to the tops. See if this service bulletin makes sense.

 

[nhsteve]

2M,

I think you had it at 'cotter pin'. Cannot say definitively just yet, but I did have the 3rd gear fork roll pin/guide cotter pin installed in the direction opposite the photo in my Haynes manual. Will try to load up photos I took before and after.

One of the symptoms I experienced during my checks was a difficulty shifting just the forks through all 5 'gears' and neutral. It would bind up going beyond 3rd, and then I would actually have to disassemble to continue. Not correct.

Taking your suggestions of possible sources of the problem point by point, when I inspected the cotter pin and moved the shift drum I could see just how close together those forks get. Then I went to the manual and in the one photo it provided I could see that their cotter pin was going the opposite direction.

That cotter pin 'head' was preventing the forks going to their correct positions, I believe.

So I reversed mine. I was then able to shift through the 5 gears ok, so I dry assembled the cases with the gears in place and shifted through them 'sort-of-ok'. Installed the partial motor back in the frame, installed the clutch, sprocket and chain, etc. (didn't go overboard as I just wanted to see if there was any improvement). I was then able to shift up and down without my problem (I did my 'test procedure', which was to shift up and down, spinning the rear wheel, up and down through all gears, for 10 cycles. This procedure failed on me 7 times out of 10 before).

Feeling it was a success, I have pulled the motor back out so I can properly seal it and torque the base back down. It is re-installed and back in the frame, but I have yet to finish that process. That is today's project, but I am pretty hopeful, and will report back, hopefully with photos.

Thanks for your help, I do appreciate it!

 

[TwoManyXS1Bs]

Hey, Steve, we appreciate your detailed report of your findings.
Very helpful for future readers.

Also appreciate the "meeting of the minds". Seems you've a good grip on this...

 

[TwoManyXS1Bs]

Here's a pic from hard_y_rd's thread, showing a better view of the cotter pins:

View attachment 20510

 

[nhsteve]

2M-

This was my problem exactly. I had installed the cotter pin holding the 3rd gear shift fork guide pin/roller from right-to-left instead of left-to-right as this photo showed. When downshifting (more than upshifting, which was never the problem), I believe the two shift forks would clash and not allow the gears to slide. I could always shut the motor off and eventually ease the shifter into 2nd, but that is not correct operation.

I have corrected my mistake, and yesterday took a short shake down ride and was able to shift up and down ok. Bike does not shift as easily as my '77 though, which is a disappointment. Double checked clutch adjustment but have yet to go out again. Main irritation there is refusal to shift 1-2 or 2-1 when stopped or going very slow.

As I had no clutch cable at all on the bike when I got it, I ordered the stronger one from 650 Central, and also replaced the clutch release worm gear assembly from Mike'sXS, which has the longer release arm feature. So hoping I can fiddle with that and gain something there.

Thanks for posting the photo, which shows the correct orientation.

 

[TwoManyXS1Bs]

...This was my problem exactly.

Great! Glad you got that licked.

... As I had no clutch cable at all on the bike when I got it, I ordered the stronger one from 650 Central, and also replaced the clutch release worm gear assembly from Mike'sXS, which has the longer release arm feature. So hoping I can fiddle with that and gain something there...

If you carefully read thru the "Clutch worm experiment" and "Clutch cable experiment" threads, and survive the ordeal, you will find that the MikesXS replacement worm produces less pushrod travel, and the EZ-Pull cable produces less worm lever travel. The combination of the two could get you a very short pushrod travel, bordering on marginal clutch disengagement. To double check this, you could measure the angular movement of the clutch worm actuator, and multiply the angle by 7/8, which is the ratio change of the MikesXS worm thread pitch.

Clutch worm actuator experiment and tidbits
Clutch cable experiment and tidbits
Clutch worm rotation gauge

Clutch worm depth dialgauge-post90
Clutch worm depth dialgauge-post91
Clutch worm depth dialgauge-post92

 

[nhsteve]

Thanks 2M, I do have still more issues to sort though on the bike, which I kind of expected. Will read through the threads as I can, looks to be way more info on that subject than I would have thought

Interesting comment on the mike'sXS clutch release, as the info on their website seems to indicate it was an upgrade. I do have another left cover with the release in it, so that one may be coming out and get put into this one! Same deal with the cable.

Going to try and attach some photos I took of the shift forks & cotter pins. The first two show how I had the pins in WRONG, and just how close together the forks actually get when in use, and the third should show the CORRECT cotter pin orientation. This should agree with the photo you provided.

Here goes............