Overdrive 5th gear - Dropping/Slipping Out to Neutral

[dps650rider]

No, they were definitely not undercut. Best I could tell with a caliper they were tapered a thousandth or 2 the other way. I tried cutting them back with a dremel but wasn't satisfied with the results so I ended up reassembling it with the stock 5th gear. The riding season is short and I didn't want to miss any more of it.

Right now I checking out possible gearing changes at the final drive. I converted to a belt drive with the stock ratio a couple years ago, changes with the belt drive are more limited and difficult.

 

[glennpm]

Thanks!

Yeah, I would have, should have, stayed with the original 5th. I'll be putting it back next Winter.

 

[TwoManyXS1Bs]

No, they were definitely not undercut. Best I could tell with a caliper they were tapered a thousandth or 2 the other way...

Well, THAT can't be good.

This is definitely a heads up for anybody inspecting a newly acquired OD 5th...

 

[dps650rider]

The thing is, other than the problems with it the OD 5th is a really good thing especially with a modified engine. As I recall with the OD gear my 700cc engine pulled in 5th about the same as a stock engine with stock gearing.

Maybe over the winter if I'm ambitious...

 

[glennpm]

With the other thread discussing gear changes, I decided to check into it as an alternative to Mike's OD 5th. It looks like a 17T front and 32T rear set yield about the same thing.

This would give me 3874 RPM with the stock 5th gear versus 3945 with the bad Mike's OD 5th gear. Looks like a good change.

Best place to get the gears is from 650Central who sells a good set with a "spacer"for the front gear.
http://www.650central.com/ under "Chains & Sprockets"
520 Conversion kit w/ O-RING Chain

Front steel sprocket, 17 or 18T
Steel rear sprocket, 32T or 34T
17/32 #GCEN52-0T17/32.... $112.50 ea.
With Case Hardened American countershaft sprocket
17/32 #GCEN52-0A17/32.... $117.00 ea.

 

[dps650rider]

I ended up going to 40T front and 75T rear (was 80T rear) with my belt drive which is very close to 17T front and 32T rear with a chain. Spent Saturday machining the 75 to fit and got my first real ride on it today. Definitely lost a bit in 1st but 5th is very close to what I had before with the OD gear and stock ratio on the final drive.

One more thing, with this final drive ratio 4th gear is more useful on back roads and will likely get used quite a bit more.

 

[glennpm]

Good feedback, thanks dps650rider

 

[glennpm]

Well its winter and I've pulled my engine, made a stand to hold it upside down and split the cases late this afternoon.

I can't see anything obviously wrong and it shifts up and down fine with complete engagement with the dogs into 5th. The only thing I've noted is that the "main shaft" not the drive shaft, can be moved a little over a 1/16" longitudinally. Of course with the clutch mounted there would be no movement. Looking at the parts diagram, there doesn't seem to be a thrust washer on the opposite end to the clutch basket. Just wondering ...

 

[TwoManyXS1Bs]

Hey, Glenn. That's right, the mainshaft's first gear and the clutch clamp the double-row bearing, and it controls the lateral position of the mainshaft. It also receives the lateral force of clutch actuation, like a throwout bearing. So, you want to ensure that double-row bearing has no lateral play.

Not sure if you have it, so here's the 4-page Service Bulletin on "Gearbox Spacing":

 

[glennpm]

Thanks, I didn't have it!

I'm going to check the drum too. Something is causing the dogs to move out if the 5th gear slots.

 

[glennpm]

Hi,

Last night I noticed that I have a small shiny contact point inside EACH of the 5th gear dog pockets on the overdrive gear. This is telling me that the dog to pocket contact is not spread out well. The stock gear with 7K miles on it, does not have these small contact wear points as you can see from my pics below. The pockets for the stock gear are also shaped differently and appear to be undercut, although very hard to see. You can however see how the end mill cut on each side of the pockets is not perpendicular to the gear, orientated to undercut, which is a good thing!. This is not the way the OD 5th is machined. Looks to me to be a square to gear, end mill pocket.

I also attached some pics showing 5th gear position, false neutral and real neutral positions. All shift forks and gear spacing look good to me. I have not measured them against the bulletin that TwoMany attached above. The selector wheel on the end of the shift drum is also sitting firmly on the two adjacent pins. This is true for all gear selections.

See the bottom left corner of each picture for a description.

Anyone see something that I don't?

Thanks

 

[TwoManyXS1Bs]

Excellent pics there, Glenn. Yes, the differences in the 5th gear dog pockets are quite obvious.

An annotated version of your 1st pic:


1 - Check for any excess wear/scraping/galling/clearance and bending of:
--- Both sides of middle shift fork.
--- The groove sides of the 3rd slider.

2 - While in 5th, see how much shuttle/slop movement you can get from the 3rd slider by nudging (shuttling) it in/out of the 5th's pockets. Gently apply prying pressure to move it to that false neutral, while observing the shiftdrum, noting any tendancy of the drum to want to rotate. Also, try this with the shiftdrum stopper wheel removed (or its spring removed). Drum rotation could reveal a rounding of the final part of the ramp in the shiftdrum's middle fork slot.

Otherwise, your pics of the wearmarks of the 3rd's dogs' endcorners inside the OD 5th's pockets are excellent evidence of missing undercutting. The Dremel Hobbyist in me wants to use those marks as a guide to hand-grind some undercutting in there. It's interesting that those marks seem to be only halfway deep into the pockets. Wondering if that 3rd slider is supposed to enter any deeper...

 

[glennpm]

Thanks TwoMany will do .... !

 

[glennpm]

Okay the results:

1 - Check for any excess wear/scraping/galling/clearance and bending of:
--- Both sides of middle shift fork.

Little wear but minimal I think. See pics below of both sides

--- The groove sides of the 3rd slider.

Looks good around the 360 degrees

2 - While in 5th, see how much shuttle/slop movement you can get from the 3rd slider by nudging (shuttling) it in/out of the 5th's pockets.

None

Gently apply prying pressure to move it to that false neutral, while observing the shiftdrum, noting any tendancy of the drum to want to rotate.

No shiftdrum movement

Also, try this with the shiftdrum stopper wheel removed (or its spring removed). Drum rotation could reveal a rounding of the final part of the ramp in the shiftdrum's middle fork slot.

Pulled spring and also no shift drum movement

Thanks,
Glenn

 

[TwoManyXS1Bs]

I can see the scuff / burn mark on the shiftfork pad in pic #2, and strange checker marks.
The stringent standard we had in the shop would call for replacement.
On this forum, it's your judgment call.

In pic #3 you can see the shim washer between the OD 5th and it's circlip.
The freewheeling 5th is straddled by 2 of those shim washers.
My manual shows 2 thicknesses available for those straddling shims, 1.0mm and 1.2mm.
Those can be used to adjust gear position, engagement depth and dog clearance.
Curious to know what thicknesses yours are, and if your manual shows the same offerings...

 

[glennpm]

I'm going to keep the fork. The surfaces seem okay to me and don't feel rough to my fingers.

Okay, I put the old 5th back in but took it apart to measure the shims ;-)

The one most inboard, on the other side of 5th and not visible in pic #3, is 0.95 mm. The one on the other side that you can see, measures at 1.15 mm. There is also another shim at the end of the shaft to the right between the last gear and the needle bearing. It measures at 0.60 mm. All measured with Vernier calipers re-set to zero.

Thanks for your input on this!!

 

[TwoManyXS1Bs]

I'm going to keep the fork. The surfaces seem okay to me and don't feel rough to my fingers.

Like I said, your call.
The sides of the 3rd's slider's slot and the contact pads of the shiftfork are supposed to be parallel.
Having wear/burn marks concentrated to an edge/corner of a shiftfork raises an eyebrow.
Hopefully it's just from miniscule flexing of the fork during gear ejection.

...took it apart to measure the shims ;-)

...The one ... on the other side of 5th and not visible in pic #3, is 0.95 mm.
...The one on the other side that you can see, measures at 1.15 mm.

Well, that's interesting. Swapping those two would increase engagement depth.
But, would also reduce dog/gear clearance while in neutral.
Thoughts?

 

[glennpm]

Hi,

In person, the forks I think look better than the pictures but if I could get a new one reasonably, I'd probably do it.

I think I'll switch the shims and see how the neutral clearance is. Better to check stuff now rather than go through this tear apart again!

 

[TwoManyXS1Bs]

You DO realize, the student is becoming the teacher?

Welcome to another dark and mysterious world, tranny tuning...

 

[xstra]

We've been undercutting those pockets for some time now. 3° works good. VHM cuttter followed by polishing. Dremel doesn't provide the necessary accuracy.