[axman88]

I have a Yamaha VStar that I acquired as a project, with a transmission that behaved correctly for N - 3rd, but refused to shift into 4th.

Now that I've split the cases, I see that the problem is the sliding 3rd Pinion is seized on the splined input shaft.  It's not entirely seized, but it is very stubborn in sliding laterally to engage the 4th or 5th pinion.  I can persuade it to move through its range of motion with a brass drift and a hammer, but it requires way too much force to apply via the shifting mechanism.  The 3rd pinion appears like it was overheated, it's blackened and there is carbon buildup on the associated fork.  I've attached a couple of pictures and there's considerably more info at this thread on the VStar forum:  https://www.starbikeforums.com/threads/2000-xvs650-failing-to-shift-trans-diagram-description.127070/#post-1157364

I'm posting here because this forum has members with considerably more knowledge and experience than I've found elsewhere.  I know I can replace the guts of the transmission relatively inexpensively, but I'd like to have some idea of why this happened, so I can avoid it happening again.

What might cause the 3rd Pinion to overheat and seize to it's splines.

Is it reasonable to think that the same carbon visible on the fork and the outside of the gear is also inside the gear, fouling the sliding surfaces?  Could I expect success with a strong solvent and mechanical means, like filing or stoning to get it sliding again?

Thanks in advance for any insight you can offer.

[AzCal Retred]

You can see that the inside of the shift fork groove is galled. This is where the heat came from. Wear is supposed to be confined to the sides of the fork tips, the shift fork just "floats" in the groove after the shift is completed & all is well mechanically.

Causes could be from:
Shift fork shaft could be bent forcing fork into gear groove.
Actual fork doesn't really fit/wrong part/touching gear groove bottom.
Gear shift groove OD too big/wrong part.

Replace shift fork, shift fork support shaft & 3rd gear.

Reassemble & use dykem blue on fork & groove to test for interference. Should be none, just the side of the fork tips should lightly touch the sides of the gear groove.

Personally I like the bent shift fork support shaft theory. An idiot stomp shifting can introduce huge unintended loads inside a gearbox. Most mechanical problems on riceburners are self inflicted, they are pretty well engineered and tough.
That is the problem with making stuff idiotproof though, they are always coming up with better idiots...

PS - Carb cleaner might touch that baked on oil. Maybe try some Liquid Wrench as well. Shotgun it, right? 

[axman88]

I appreciate your input on the XVS650 trans issue.

Although the inside of the center fork does look galled, I think the rough appearance may actually be the original, unmachined surface.  Compare the surface of the Center Fork to the similar inside surfaces of the Right and Left forks in the first picture.  They are all rough and grooved.  Also there outer circumference of the slot in the sliding 3rd Pinion is quite smooth .

When I tap the 4th pinion to the position it wants to be in for ratios 1rst - 3rd, and assemble the Center Fork and Shifter Drum with the Input Shaft assy, as shown in the 2nd picture, the Input Shaft spins nicely and freely, and the Fork floats nicely in the gear's slot.  I'd estimate about .015 - .020 of lateral motion in the Fork around the circumference of the slot.  The Center Fork doesn't appear to be bent, or worn, except for some wear on the surface facing towards the 4th Pinion.  This is best seen in the 3rd image.  I'm not sure if what I'm looking at is scoring in the metal, or just wear in the carbon coating on the surface.

The channel in the Shifter Drum looks excellent, as does the Button on the Center Fork that rides in it.  There's no visible damage to either.

Placed on the polished piece of granite that passes as a surface plate in my basement shop, the tubular Rail that the Center Fork rides on looks very straight.  My thinnest (.05 mm = .002") feeler gauge can't get in at any point, at any rotation of the Rail, and light barely peaks through.  I'd estimate less than .0005" of crooked, which seems pretty good to me.

I disassembled the Output shaft, and I see that Yamaha puts pinholes under the free rotating gears, and fits them with bronze bushings, but there were no pinholes under the sliding gears.  It did not appear that #3 output gear's oil supply hole was plugged, which would have been a nice conclusive discovery.  I assume that the oil leaks out of the journal under the free rotating gears, runs out radially along the gear, and lubricates the mating sliding gear that way.

At this point, I'm psyched to follow through the process of fixing what I have.  I know I'll get 100 times more satisfaction with the repair than just replacing the guts with purchased take-out parts, so even if it's more expensive as well as more time consuming, I want to take the more educational route.  The bearing splitter I ordered should be waiting for me when I get home this evening.

I'm leaning towards disassembly of the Input Shaft, and cleaning the 3rd pinion of carbon.  I'll fit and stone as needed with the Machinist's Blue, and do the same with the Center Fork.  What do you think?

More background on the situation, as it was related to me:
    The original owner of the bought the bike new, but fathered a child about 2000 miles into ownership.   His wife forbade him from riding, and the XVS650 spent many years waiting patiently for his return.
    After a decade and a half, first owner sold the bike to my buddy, who started actively riding it.
    I think that my friend told me he did NOT change the oil that came in the machine, he figured the bike has 2000 miles, oil change interval is 4000, I'll ride!   My friend is not very "mechanically sympathetic", definitely more of a "if it ain't broke, don't fix it" character.
    About 4500 miles later, he was riding with a group when the incident happened.  They were riding, everything was copacetic.  They stopped for fuel/piss break.  They started riding and the bike refused to enter 4th, instead reaching a false neutral above 3rd. 
    My friend didn't force it, but there was no doubt some period of " repeatedly trying to get it to shift into 4th".  (This could be relevant to "wear in carbon coating on surface of fork")
    My buddy changed the oil,  (Finally??!!!) ... no change in characteristic.
    My buddy pulled off the right side cover and clutch, chasing a possible shifter issue.  He consulted me.  I told him to pull the engine, take it down.  He did not do this, instead started talking about magic "fix it fluid" infusions.
    Another 9 months of sitting in his garage and he had enough.  Swapped it to me, plus some cash, for a well running Honda VT600.   Since the engine was already started towards disassembly, I didn't ride it, didn't run it, ... just took his word at face value.  I got it cheap enough to buy a takeout engine and break even.

[richard211]

Hopefully the splined shaft is not bent or badly distorted. I would try using some lapping compound, to get a perfect fit between the sliding gear and the splined shaft.

[AzCal Retred]

There is metal to metal galling on the side of the fork. The metal is cooked around it. That's where the heat came from to bake the oil under the gear into Bondo. The gear doesn't do anything but push on the splines below it. At the very least I'd toss the fork and verify the fit of the new part. The fork slider shaft passed the bent inspection so it isn't that.

MAYBE your buddy's toe was wedged under the shift lever and caused the rubbing/overheating. MAYBE the bike fell over and bent the shift fork at some point. Somehow those bits suffered a change of OEM fitment.

However, I've NEVER found a mechanical problem yet that money wouldn't fix...

[axman88]

There is metal to metal galling on the side of the fork. The metal is cooked around it. That's where the heat came from to bake the oil under the gear into Bondo. The gear doesn't do anything but push on the splines below it. At the very least I'd toss the fork and verify the fit of the new part. The fork slider shaft passed the bent inspection so it isn't that.

MAYBE your buddy's toe was wedged under the shift lever and caused the rubbing/overheating. MAYBE the bike fell over and bent the shift fork at some point. Somehow those bits suffered a change of OEM fitment.

However, I've NEVER found a mechanical problem yet that money wouldn't fix...

I think you are right, condemn the Center Fork and perhaps the 3rd Pinion.

The irony of the fixing with money situation is that I can Parzilla source just these two parts NEW for $52 + $107 PLUS shipping, OR I can buy everything USED from Ebay, (both Shafts full of Gears, plus the Shifter Drum and both Fork Assys) for around $40.  At 4.3 : 1, this just doesn't feel like a choice to me.  Is it weird that buying all the those parts, to use just one or two, denigrates the whole repair experience for me?
 
At least the scandalously low prices of the take-out trans parts does give me confidence that this particular mechanical failure is a very rare occurrence.

My pet theory is that my friend was in the habit of inadvertently resting his boot on the shifter pedal during long hauls in top gear.  It's all apart so I can't test how much force this would take, but at least in theory, a lazy foot in 5th could result in shoving the Center Fork towards the 4th Pinion side.    I can't prove it, but I'd guess that 5th is the gear most people have their bike in while napping.

 I don't think it hurts my argument, that the Shifter Pedal is an expensive looking, and HEAVY, aftermarket Kuryakn part, or that the rider's Pegs are not pegs, nor floorboards, but a sort of mini floorboard / peg arrangement, with a weird batman style /transformer fold-out highway peg mode, also Kuryakn branded.

[AzCal Retred]

Is it weird that buying all the those parts, to use just one or two, denigrates the whole repair experience for me?

I'm with you, it feels wasteful, like killing a buffalo for just the tongue and hide. HOWEVER, if you don't use those 4.3:1 cost ratio used parts they become landfill material or get tossed into a bucket that'll fill with rainwater in the back of an unheated shed somewhere...   Life isn't fair.

[gizzo]

  Is it weird that buying all the those parts, to use just one or two, denigrates the whole repair experience for me?
 

Not at all. Using good secondhand parts is fiscally smart and environmentally responsible. Use what already exists instead of causing another new part to be made, you know?

Good luck with it. That baked on carbon can be a bitch to remove. Know anyone with a blasting cabinet?