1968 Yamaha YG5T 80cc Trailmaster timing problem

^^ what he said.

 

Correct. That pin contacts the trapezoidal boss (at 12:00 in the photo) on both ends of it's travel. First question, though was whether that pin is sometimes contacting the slightly raised round piece (at 5:30). You can see a few striations on the upper left of that "button." After further examination, I don't think so.

Yesterday I took apart the shifter to see if I could see why I was feeling a little drag while turning through part of its range. There was some corrosion on one side of one of the fork's bores. The body of the shifter was quite clean, but I polished the bore on both shifter forks and the shifter body a little with some 600 paper and penetrating oil. It felt smoother after that.

Partially reassembled the motor (shifter, transmission, and clutch without the pressure plate) to test again. Here's what I can tell you.

NEUTRAL (all the way up - 4 down shifting pattern)
The motor turns freely, meaning that the drive axle and clutch are spinning without resistance.

1st GEAR
The drive axle will move back and forth about 3mm.

2nd GEAR
Almost impossible to shift cleanly from 1st to 2nd. Shifter hangs midway, then I have to turn the drive axle with a pliers while gently coaxing the end of the shifter that has the pins with a channel locks. Once it drops in, the drive axle will move back and forth about 8mm.

3rd GEAR
Same difficulty shifting from 2nd to 3rd. Once it's in position, the drive axle will will turn maybe 8 or 10mm.

4th GEAR (all the way down)
The drive axle and clutch again will turn freely.


I can certainly post more photos of anything that might be helpful to see. Thanks.

 

A motorcycle transmission won't typically shift unless the shafts are turning. That's because it can't drop into gear until the gear dogs align with the slots on their mates.

So long as it shifts with a shaft turning it's probably just fine.

 

Thanks for responding, MiCarl. I'm still concerned, though, because the problem I've been trying to troubleshoot was the motor locking up when I shift (while the motor was running). Long time back in this thread, I know. But I don't feel like I've actually diagnosed that problem. Do I dare put it back together just hoping that I've accidentally fixed something?

 

baytonemus,
These things are very difficult to diagnose from your description - even though your description is rather thorough.

To answer question #1, the raised 'button at 5:30' should never be touched by your shifting assembly. The fact it is touching suggests that either something is missing or in the incorrect location. Perhaps

Assuming you have a correct understanding about what MiCarl said, and you are attempting to shift through the gears with the clutch gear spinning, then Something is obviously wrong.

Here is an image of the shifter.

Does it look like you have all the parts, especially the washers/spacers that fit to the end of the shift drum?

-Steve

 

Yes. The shifter is properly positioned and the shifter arm interfaces with the pins on the shifter as it should. When it does shift cleanly - at the bottom and top of the range - it feels as I would expect it to.

I've also very meticulously inspected the transmission parts diagram to make sure everything is there and installed correctly.

 

Hi guys. sorry to resurrect an old thread. Just picked up one of these bikes. Seems a lot of parts are no longer available. Baytonemus (or anyone) where did you source parts from? The fork gaiters I cannot find anywhere.
Thanks

Mark

 

Hi Mark-

Congrats on your acquisition. Hope you have better luck than I've had. This is actually still an active thread (I posted 2 days ago), so I'd like to keep it focused on my bike for the time being. I'll just say that I've sourced parts mostly from eBay and through my local Yamaha dealer. Here's a pair of aftermarket fork boots on eBay. If you've got other questions, please send me a PM.

Thanks.

 

Hi Mark. I also you encourage you to seek out some vintage 2-stroke forums. I recommend www.2strokeworld.com. They are a friendly group that primarily focuses on the older Yamaha 2-strokes.

I recently restored a similar 1968 Yamaha, a YCS1c, and the most difficult part was sourcing parts. I found them one at a time, shipped from all over the world.

...and now back to Baytonemus' machine.

 

thanks for the info guys. I had started another thread which I will post any more questions to. Sorry for the hijack. Thanks a lot.

Mark

 

I wouldn't, not just yet. Carls' right, it shouldn't shift through the pattern without turning the input (or output) shaft a bit to get it to shift.

I'd revisit whatever you polished with 600 and re-polish it with 1200-grit and oil. Followed by Scotchbrite and a good flush with contact cleaner to ensure all traces of sand gone.

If there was rust/corrosion/whatever keeping the "previous" gear from disengaging freely, it might cause the "two gears at once" lockup condition.

And I hate to ask this, but are we 110% certain the gearbox and not the motor itself was doing the locking up? Did it FOR SURE correspond to shifting gears?

 

Not sure why I never got an email notification for these Monday responses. A belated "thank you," however.

OK, I have not been clear as to the requirements for "turning" the motor. How fast, etc? I've been turning the drive shaft with my fingers (CCW) while shifting, but like I said, it doesn't actually turn except in the top (neutral) and bottom (4th gear, theoretically) positions. I can only pivot it back and forth a few MMs.

My measurement for the shifter being in the proper position each time is when the stopper lever assembly (#17) drops into its detent position between the pins.

Back on the shifter parts diagram again, I polished the bore of #3 & #4. I can certainly hit them again, but I'm doubtful that will help, to be honest. They're definitely smooth enough to slide back and forth and I have them oiled up. Maybe, though. I'm also a little concerned about taking away too much material such that they become out-of-round or just enlarged enough to bind as they slide over the body of the shift drum.

Well, when the bike was running, yes, I was able to shift through the gears a few times. Also, what would be the evidence of the motor itself locking up? I've rebuilt the top end and got the crank moving smoothly. I didn't replace the needle bearing where the rod connects to the crank, but the guy at the machine shop thought it was fine.

And for what it's worth, the crank shaft has not been installed while I've been bench testing the shifter/transmission.

 

You should be able to turn the input shaft in all gears, not just N and 4.

If you can't turn it something must be binding up.

 

Thanks, MiCarl. I must not have made that very clear in my post last weekend. Sorry.

It doesn't feel like "binding" really. It seems like the tranny has "dropped in" once I get the shifter to turn all the way. The drive shaft pivots freely but only those few MMs, then comes to a hard stop/click in both directions.

 

It sounds like it's engaging two gears at once, somehow. Is something maybe backwards/flipped over on the shaft(s?)

 

Hey, Fitz. I actually just came back in from the garage where I took the case apart again and carefully re-inspected each shaft and the shifter. I'm confident that I have everything in place according to the parts diagrams. I suppose it's possible that the fiche illustrations could contain errors.

I can't say for sure if the gears that are pressed on the shafts are exactly in the right place.

I wondered if I might have reassembled the shifter incorrectly, but I think that's just about impossible to do.

Should I take more pictures? Make a video?

 

A video is probably worthless. It's likely going to require someone who understands how it works having it in his hands to mess with.

Your problem isn't with the shifter. There are either gears in the wrong places on the shafts, bent shifter fork(s), or wear at the shift drum/shift fork interface.

Hey Fitz! How do you feel about ice fishing?

 

I just went and looked through some of the previous posts. You have a scan of figure 3-15-1 from page 43 of your manual. From that figure I see that gears 1-2 are on one shift fork and gears 3-4 are on the other. So it's entirely possible that 2 & 3 could be simultaneously engaged if there is something bent or out of place.

Do you understand figure 3-15-1? It shows exactly how the transmission is supposed to work.

One thing that occurs to me: Will the shift forks rotate clear around the shift drum (with the assembly removed, of course)? If they do, it could be that your shift drum needs to be rotated 1/2 turn.

 

Thanks again, MiCarl. Since you posted last evening I have spent some time analyzing figure 3-15-1. Although I can't really say that I can confidently picture in my minds eye how the transmission gears are specifically moving in each position, I believe I do understand the concept. The shifter forks are moving a gear/pinion on each shaft such that it becomes disengaged with its current gear and then engages a different one. Power is thereby transferred from the main axle to the drive axle at varying degrees of power(?).

I opened the case again and reinstalled the shifter after turning the drum 180°. No change. On a positive note, I can really break this motor down and reassemble it quickly at this point.

I think I might be on to something, however. Referencing both figure 3-15-2 from the manual and the online parts diagrams (which unfortunately are shown from opposite angles), there is one gear on each shaft that doesn't spin freely.





Part #10 on the drive axle is called the "4th wheel gear" on the fiche. On fig. 3-15-2 is simple shown as an integral part of the drive axle. I believe this is pressed on and should not spin on the axle.

Part #6 on the main axle is called the "4th pinion gear" on the fiche ("top pinion" on fig. 3-15-2). It is held in place by a washer and circlip. This gear also will not spin on the axle, but I'm thinking that it maybe it should?

 

Gear #6 should freewheel. It connects to the shaft via gear 5 when the shift fork engages gear 5 dogs into it.

The gears either side of 5 and 14 should freewheel on the shafts until gear 5 or 14 slides over to engage it.

 

FINALLY! I was able to remove that gear with a 3-jaw puller. Here's how things look:





What do you think? Is it worth trying to clean those up? I would guess there are pretty fine tolerances for how much play is acceptable.

 

Is that the "pressed on" gear (#10) or the "should be free-wheeling" gear #6?

 

#6.

 

That is your problem. That gear being welded to the shaft has the effect of 4th gear always being engaged. Putting it in 1, 2, or 3 will cause the transmission to lock up.

That gear should ride on a film of oil between it and the shaft (there should be at least one oil hole in the shaft). Apparently there was an oil delivery problem - which will need to be addressed.

I'd worry that just cleaning it up wouldn't work. In the pictures it looks like most of the damage is to the shaft, the gear seems to just have some shaft welded to it. If that's the case, a welder can fill the shaft and a machinist can turn the shaft and ream the hole in the gear.

 

I actually don't see any oil ports in the shaft. On the parts fiche it appears to show some holes, at least on the smooth part of the shaft away from the end where #6 lives. Maybe they improved the design when they made the replacement parts? Either way, these axles are not easy to find.

I don't quite understand how holes in the shaft would deliver oil, though. Isn't the whole tranny constantly spinning in an oil bath and throwing it all over the inside of the case?

 

It also occurs to me that the end of that shaft, just beyond where #6 rides, fits down into the receiver where that plug has been epoxied into place. This is going back quite a ways in this thread, but could that be related at all to this oil issue? Seems implausible, I guess, but it just caught my attention.

Thanks.

 

You might be correct about them living in oil. I'd forgotten that this was a 2 stroke....... If the shafts aren't hollow they aren't meant to deliver oil.

 

No, they're not hollow. I'll take it to my machinist on Monday and see what he thinks. The shaft actually looks worse than it feels. There are still a couple of places I can buy that gear, so that's an option, at least.

A HUGE thank you, MiCarl!

 

8O

But Carl already beat me to it, there's the problem.

I wouldn't "clean up" the shaft, I'd get it welded and re-machined. If you can get a new gear, do so, and take it to the machine shop with the shaft.

Mysterious lockups solved. And the gear probably would turn on the shaft occasionally, so it would work until it locked to the shaft then bang.

Wow.

 

100% in agreement. I'd assumed you couldn't get a gear.

I'll add that you need to use a welder that knows what he is doing. Getting this done right is beyond the abilities of your "average" welder. Machining shouldn't be that difficult.

I'd suggest you check around for someone that refurbishes or builds crankshafts and camshafts.

 

Got it. My machinist will know where I should take it or send it. He does a lot of cycle work. Thanks.

 

On the other hand, I just figured out that both that axle and gear are also used on the YL2 and YL2C. I can actually buy a complete used transmission for $60 with free shipping, so that would probably be cheaper. I'll see what the rebuild will cost first, though, before I decide.

 

Here's an update...

The machinist I usually use said the axle was too small for his lathe and sent me to another independent shop. That guy said that welding on such small abrasions probably wouldn't hold and that, because the axle is hardened, he couldn't lathe it anyway. He did say that he'd be willing to try and clean it and the gear up a little. When he was done there was just a little bit of wobble.

I then took it to one of the cycle shops to have a mechanic look at it. He said that, because it was a collectible bike that probably wouldn't have very many hard miles put on it, plus the fact that it will be swimming in oil, it would probably be OK.

I reassembled the motor to test the shifting again. All gears now engage as expected and the drive axle turns as it should. I still can't say that the shifter performs great through the middle range. It doesn't quite want to go from 2nd into 3rd real smoothly. However, when I'm spinning the clutch faster it works much better.

I believe I can hear a little rattle from that 4th gear when I'm spinning the clutch. There's no oil in the motor at this point, of course, so that would make some difference. Let me know what you think.

Thanks!

 

There is some play in the gear dogs. Unless you put some load on it and/or turn very smoothly they will rattle a bit.

 

That makes sense.

I might actually be catching on...

Thanks again.

 

Sorry to keep this simmering but, because I have no real experience with shifters and transmissions, I'm really struggling with whether or not I should do a final reassembly of this motor. I still can't get the thing to consistently shift all the way from one gear to another. It wants to hang up between gears.

Will the release of the clutch fix this, that is, force the transmission to fully engage the gear? I'm just not sure what to expect. Thanks.

 

I'm not sure exactly what you're asking, but I can tell you this:

It absolutely will not shift from one gear to the next unless all the gear dogs are lined up. AND they don't line up.

The only way it'll consistently shift properly is if all the pieces are moving relative to each other. This means spinning the input shaft vigorously with some drag (but not a lot) on the output shaft.

 

OK, now I'm confused. In the second sentence above, are you saying, "AND (your gears) aren't lining up"?

And how do I create that drag? Should I just grab the output shaft with my hand after I've got the clutch spinning?

 

do you have a socket that fits the nut on the input shaft (clutch basket)? adapt that down to something that will fit in a variable speed drill. spin the input shaft in the normal direction, slowly. hold back the output shaft with your hand (don't hurt yourself). now shift thru the gears, you shouldn't need a clutch. but you might need three hands or a helper

 

OK, but that input shaft spins CCW. Got a suggestion for how to keep that nut from spinning off? Not sure where I would find a big nut and a small nut in that thread pitch (to lock nut it).

 

loc-tite, super glue, paint, fingernail polish, elmers wood glue, tighten it real tight. take your pick. i'd go for fingernail polish, tighten it up then paint some on the threads, dries fast and easy to take off
it shouldn't be hard to spin so it wouldn't take much to hold it on

 

Any recommendation on color?


(Just kidding.) Thanks.

 

before you go much farther i have to rain on your parade a little.
that gear and shaft, thats what's called a plain bearing, the OD and ID are made to a certain fit depending on the size of the shaft. the closer the OD and ID are to each other the more bearing surface there is and slop on the gear/shaft fit means there is more more slop on the teeth to the next gears teeth.
all that might not mean anything but then again......

 

I hear what you're saying. However, the shifter has been acting like this the whole way along, even when that gear was seized on the shaft.

It won't take much doing to test the shifter using the three-hand/fingernail polish/power drill method. If it still doesn't feel right, then I'll need to make some decisions about a replacement shaft, gear, and possibly shifter fork(s).

 

I finally was able to test the shifter with an assistant holding a power drill on the clutch basket nut while I held the output shaft and operated the shifter. The bad news is that the shifter still wants to hang up between gears, especially while downshifting. The motor no longer locks up, though, because of having freed that 4th pinion gear.

Not sure if I should be looking for a whole used transmission, a shift drum, forks, or all of the above. MAN, I wanted to be able to put this thing away for the winter!