Yamaha XJ600 shifting problems

[Wheaton Jr.]

Hello everybody. Right now I'm trying to fix a problem with my bike and my dad(WheatonFJR) told me to post it here along with my XJ forum to see what you guys thought. So I first started noticing an issue when my dad and I took a trip last summer. When I would downshift and give it 100% throttle to pass a line of cars, the bike would get very jerky as if the gears were slipping or something. The revs would dip a bit but go right back up again until it jerked again. It would do about 3-5 jerks until I just shifted up a gear and they stopped. This would usually happen in 3rd to 4th gear. Then I noticed it also jerked in 2nd gear(50% throttle) when I was taking the corners which made it feel very unsteady when I was leaning over. After the trip, the jerking went away, and I thought it was perhaps because I wasnt giving it 100% throttle when on the streets. Instead a new problem showed up. It no longer jerks when giving it 100% throttle. The new problem is when I shift into 2nd gear and give it even 10% of the throttle, it immidiately shifts into neutral. When I'm in 3rd gear and downshift into 2nd in order to engine break it is fine, but under any throttle amount while in second, it jumps into neutral every time. It no longer jerks while under 100% throttle in any other gear. So now I just ride shifting from 1st all the way into 3rd. Also one last symptom that's been happening more and more as time goes on is that as I'm shifting, sometimes I cant just tap the shift pedal up twice into third. After one tap into second, the shift pedal wont physically move up any more until I let out the clutch while in second. So I just quickly pull in the clutch again then it shifts into 3rd. So people on my XJ forum said it could either be bad transmission gear teeth, bent shift forks, or something wrong with the external shift assembly. So now I have the engine out of the bike and split into two pieces. The gear teeth look brand new and the shift forks arent bent. The external shift mechanism looks ok and isnt bent. Now the next step is to take the trans and shift forks out as well as the shift drum(cam) and check very carefully for any wear. I was just wondering if anybody else here had any thoughts of what it could be based on the symptoms. Thanks for any and all of your guys help. -David Below are some pictures of the suspected bad parts.

Engine upper half

Transmission, shift forks, shift drum(cam)

Another angle

Transmission upper half of engine

Both haves of engine

Engine in one piece

Engine-less bike

 

[HotRodZilla]

Some thoughts:

I'm not sure that jerking was gear/shift related. It sounds carburetor related. Like maybe your pretty lean right now and when you rode somewhere else, it just magnified the problem. Since you have it apart, get the carbs taken apart and thoroughly cleaned as well as having all the rubber parts replaced. Carbs degrade over time and do weird things.

As far as your shifting issue, I agree with the XJ guys. Your problem lies somewhere in your shift mechanism, shift forks, or gears. I'm assuming this bike has gear dogs like the FJR. Wear on those will cause dropping out.

Many bikes with short shift throw are susceptible to shifting problems if the shifter gets gummed up. Clean all the outer stuff well, and get those gears out so you can get a better look. I'm betting something will become obvious.

Lastly; on that first pic, the large dark gear in front of the chain looks crooked. Is that the case or just the light. Worn shafts or bushings could cause what you describe.

 

[rushes]

Best fix? Your dad offers you a good deal on his bike, and he gets that new red one....

I'd guess the shift forks and gear dogs (the parts of the gears that slide sideways to interlock each other) are worn. ($$)

edit:

Here's a pic of worn dogs. The shiny radiused edge should be square

And a pic of a really bad shift fork.

 

[Wheaton Jr.]

Thanks for the replies guys. I'll have the parts taken apart tomorow so I should be able to tell what's going on soon.

 

[Bearly Flying]

Wheaton Jr; I think Rushes has hit it right on. Yamaha had problems with several of their bikes in that era, concerning the shifter dogs. A popular fix back in the day was to have the dogs undercut slightly to help hold the dog into engagement.

Welcome to the Forum, Have fun with the XJ, They are a pretty good old bike.

 

[wfooshee]

Until you get the shafts out and the gears separated you can't tell if the dogs are bad. That's the "teeth" that engage when shifting. Radiused edges will make them behave as you described. You also won't see the fork wear until they come out.

The not-being-able-to-kick-again-to-the-next-gear sounds like the pedal just needs to be cleaned. If it doesn't spring back to center, it won;t engage the next step to ratchet the shift drum. That's probably not a mechanical issue.

 

[Wheaton Jr.]

Well I'm pretty sure I have finally found the culprit. Seems to me I have a bad shift fork, as well as the gear dogs are a bit worn down. Do you also think I should replace the shift cam because of the wear in that one spot? That spot is where the shift fork goes to for second gear. The bad shift fork was also the one for second gear so after a few new parts it should be good as new! ...or at least as new as a 22 year old bike gets. Thanks for all your help guys. -David

Shift cam

Shift cam

Shift fork

Shift fork

Shift fork

 

[RossKean]

Depends on availability and cost for parts. If it were me, I would replace anything that showed any obvious signs of wear while I was in there. On the other hand, I wouldn't drop $500 replacing parts that might be OK. How many times do you want to take it apart?

 

[wheatonFJR]

This was a $1000 bike David got four years ago.

He seems determined to get his edumacation on this one...I salute him for tearing it apart with his auto mechanic friend.

Putting it all back together into working order will be the real education.

 

[Fred W]

Might as well do it right and replace the fork and the drum. Those both look knackered. No piccies of the dogs. They (old gear dogs) could probably be ground under-cut to restore to better than new engagement.

Good Luck and have fun.

 

[HotRodZilla]

+1 to what Fred said. If it's more wear than you can buff out with some really fine sandpaper (500) replace it. If you don't, you may have to take it apart again in a year. Of course this depends on parts cost. If it's more than you want to/can spend, ditch it...

Good luck.

 

[FJRay]

A quick look shows parts ought to be around 300.00 and you can do the dogs your self if needed. If the rest of the bike is OK you should have a good runner until your Dad gives you the FJR.

 

[Wheaton Jr.]

Way back when I thought it might be the transmission, I bought the gear set for 20 bucks, and it's in really good condition. I bought the shift cam for 15, and a set of the 3 shift forks for 30. Overall for the whole fix I spent about 150 but that includes 4 new carb boots, new air filter, and 2 gaskets for the clutch and oil pan, so I think I did pretty good. Just dont tell my dad about the 150...

 

[rushes]

It's refreshing to see a young guy fixin their own bike.

Keep up the good work! :thumbsup:

 

[HotRodZilla]

Way back when I thought it might be the transmission, I bought the gear set for 20 bucks, and it's in really good condition. I bought the shift cam for 15, and a set of the 3 shift forks for 30. Overall for the whole fix I spent about 150 but that includes 4 new carb boots, new air filter, and 2 gaskets for the clutch and oil pan, so I think I did pretty good. Just dont tell my dad about the 150... :grin:

Saweet!! Don't worry about your dad. He's easy to distract!!

 

[Chuck35]

Good to hear you have some replacement gears. The dark ones would concern me.

Great work!

 

[Fred W]

Maybe DAd could learn a few things about trannys (besides the ones on Rush St.) in this endeavor too?

 

[wheatonFJR]

Update-

David has the bike all back together and rode it up and down the street around ice patches before the lastest snowfall we had yesterday. He says the shifting is like butter now.

He had some very good help from an auto mechanic friend of his when he would get into a jam.

Davis is one happy camper.

 

[wheatonFJR]

Maybe DAd could learn a few things about trannys (besides the ones on Rush St.) in this endeavor too?

Nope, no tranny learning during this adventure...I just pointed and said, ooh, look at those dirty oily sprockety looking things...what do those do?