-
Enjoy XS650.com? Consider making a donation to help support the site.
XS650.com receives a small share of sales from some links on this page, but direct donations have a much greater impact on keeping this site going.
5th overdrive gear grooves/mod?
- Thread starter desmodromic
- Start date
-
- Tags
- engine
bloglos
XS650
1974jh5
Curmudgeon.
Dang, looks like I was way wrong about the grooves, they do have a meaning.
After engine no 271 262 on the 77D. Meaning some 77D's had the upgraded gearbox......not just 78 and later...................Confused about what your last sentence, (highlighted), means
Now you are in the realms of Yamaha and unless someone knows for sure then it is work it out time.
Reading the bulletin it states that some sets of gears already have one grove on them and where they do then a second set of groves are added.
I have 2 old sets of main gears and one has the single grove and the second has the 2 groves.
No camera so can't take pics.
Ok looking at the 2 sets closely....... one is similar to your main gear shaft in the pics with the one grove on some of the gears........the other set has 2 groves on three of the main gears and 1 grove on one of the others.
I take this to mean..........the earlier gears had some groves cut into the gears.............and the later 77D's with the different upgraded splines on the gear shaft had 2 groves set into any gears that already had one grove in them and 1 grove where there wasn't a grove before........Not yelling, just highlighting main points.
My conclusions are based on what i have before me, (2 sets of main gears), comparing your pics and Engine no, and relating to the bulletin.
The gears sets are rusted up so i can't take them apart to compare the shaft splines against the different gears
According to your engine no it is about 4900 engines before the change over
Last edited:
bloglos
XS650
Ahhh and I went and got my hopes up. Crap.
desmodromic
XS650 Addict
To make it less confusing. If your 5th main gear (the one that meshes with the 5th overdrive gear) is in good shape, then the only gear that you have to replace in the transmission (78'+) to do the 5th overdrive mod is the OEM 5th gear (23T) for the 5th overdrive gear (24T).
If I miss understood something please correct me so I don't confuse people.
Some people have done this mod on early trannsmissions without any trouble. I guess the wear on the shaft is enough so the new gear works.
Leo
Leo
Tim of DO THE TON
XS650 Junkie
Maybe I'm daft today (as I am most days), but sitting here staring at the 2 stock 5th gears I've replaced with the taller ones, I don't understand what the change to the splined shaft has to do with these gears?
These don't mate with the shaft - they're smooth bores. They interface with the gear next to them with the pins (clearly not my technical forte so forgive the layman language).
Anyhow - the two gears I pulled have 2 sets of grooves on the teeth, so I'm assuming for the moment that I'm OK
Mine were a 1978 and a 1984 engine, but of course, anyone could have swapped in an earlier transmission set at any time since then.
Behooves everyone to confirm what transmission is in your bike when doing this change, regardless of the year you think the engine is.
These don't mate with the shaft - they're smooth bores. They interface with the gear next to them with the pins (clearly not my technical forte so forgive the layman language).
Anyhow - the two gears I pulled have 2 sets of grooves on the teeth, so I'm assuming for the moment that I'm OK
Mine were a 1978 and a 1984 engine, but of course, anyone could have swapped in an earlier transmission set at any time since then.Behooves everyone to confirm what transmission is in your bike when doing this change, regardless of the year you think the engine is.
Tim of DO THE TON
XS650 Junkie
Street Tracker
Dirt Track Mentality
I think that may be what the TB is trying to clarify. They never would good at writing these TB's still are not today I know with my Harley, but I think tho is it when you read the TB and close your eyes to the pictures.
On the shafts they changed the way the gears rode on the shafts. The earlier gears splines rode in the bottom between the shafts splines. The later the shafts splines rode in the bottom between the gears splines.
I think they made the splines on the shafts larger diameter on the later. So the hole in the new fifth gear is larger to fit the larger shaft. Being larger it won't fit the older shaft. Or it's just the other way round. I have a pic showing the differences some where just can't find it.
Either way the new fifth gear is made to fit the later but the earlier with the wear of many miles the new gear can fit .
The only way to be sure is to try one on your early shaft.
If it won't work, get a 78 or later tranny. It will fit in all of the 74 up cases. The earlier cases may not work with the later trannies because of a change with bearing diameter.
Leo
I think they made the splines on the shafts larger diameter on the later. So the hole in the new fifth gear is larger to fit the larger shaft. Being larger it won't fit the older shaft. Or it's just the other way round. I have a pic showing the differences some where just can't find it.
Either way the new fifth gear is made to fit the later but the earlier with the wear of many miles the new gear can fit .
The only way to be sure is to try one on your early shaft.
If it won't work, get a 78 or later tranny. It will fit in all of the 74 up cases. The earlier cases may not work with the later trannies because of a change with bearing diameter.
Leo
I've read this thread through a couple of times and studied both the Haynes manual schematic and my open transmission and I still don't understand this at all?
The Haynes manual schematic Fig 1.4 has
cog 6 as 5th Gear pinion (23T) input shaft
cog 17 as 5th Gear pinion (22T) output shaft
Although the diagram is rather confusing I have counted the teeth on the 2x cogs and I have 23 T and 22T respectively
Now if I fit a 24T overdrive gear to the input shaft surely I will need to fit a smaller opposing gear to the output shaft because the 24T gear will have a larger diameter won't it ? Is the thickness of the gear teeth changed to retain the same diameter but increase the number of teeth?
sorry if I'm being dim here but it doesn't make sense not to change the pair ? perhaps some kind soul can explain it to me please
http://www.donkersdesigns.com/gear%20calculation.html
Edit
ok I think I've worked out how it is done. The teeth of the overdrive 5th gear have a contoured profile so the contact point of the 2x cogs remains in the same place as the original 23T/22T cogs, so that when the new overdrive cog with 24T replaces the original 23T cog the mesh point of contact remains the same as does the overdrive cog diameter .phew
The Haynes manual schematic Fig 1.4 has
cog 6 as 5th Gear pinion (23T) input shaft
cog 17 as 5th Gear pinion (22T) output shaft
Although the diagram is rather confusing I have counted the teeth on the 2x cogs and I have 23 T and 22T respectively
Now if I fit a 24T overdrive gear to the input shaft surely I will need to fit a smaller opposing gear to the output shaft because the 24T gear will have a larger diameter won't it ?
Is the thickness of the gear teeth changed to retain the same diameter but increase the number of teeth?sorry if I'm being dim here but it doesn't make sense not to change the pair ? perhaps some kind soul can explain it to me please
http://www.donkersdesigns.com/gear%20calculation.html
Edit
ok I think I've worked out how it is done. The teeth of the overdrive 5th gear have a contoured profile so the contact point of the 2x cogs remains in the same place as the original 23T/22T cogs, so that when the new overdrive cog with 24T replaces the original 23T cog the mesh point of contact remains the same as does the overdrive cog diameter .phew
Last edited:
Yes, the teeth are cut different so they could add an extra tooth, without changing the diameter.
I like this idea. I would like it expanded to include more gears. Four 5th gear it should be two teeth different, 4th gear one tooth, 3rd can stay the same, 2nd one tooith, first two teeth.
With the lower 1st and 2nd, higher 4th and 5th we could use the higher ratio sprockets for better cruising rpms without losing the quick acceleration of the lower gears. These with the high ratio primary gears would give us even more room to play with sprocket ratios.
Leo
I like this idea. I would like it expanded to include more gears. Four 5th gear it should be two teeth different, 4th gear one tooth, 3rd can stay the same, 2nd one tooith, first two teeth.
With the lower 1st and 2nd, higher 4th and 5th we could use the higher ratio sprockets for better cruising rpms without losing the quick acceleration of the lower gears. These with the high ratio primary gears would give us even more room to play with sprocket ratios.
Leo
sounds like a dream come true leo.
Why did Yamaha choose those ratios I wonder . They probably chose them to match the high reving engine to give better acceleration that the triumph Bonneville and other brit bikes of the era .Clever marketing maybe ?
Why did Yamaha choose those ratios I wonder . They probably chose them to match the high reving engine to give better acceleration that the triumph Bonneville and other brit bikes of the era .Clever marketing maybe ?
The XS650 was Yamaha's first 4 stroke bike. They call this transmission a wide range tranmission. It may be a wide range for a two stroke that has a some what narrow power band, but on a four stroke with a wider power band these gears are too close. Well maybe for racing they are fine but on the road they are too close.
Leo
Leo
Well maybe if enough people contact Mikes he will have a wider range of gears produced. I think the 5th gear he sells now has been a pretty good seller. I had a friend that had an old Panhead that need a gear replaced and he knew a good machinist that made him the gear and he said the end result was a work of art and worked fine.
jefft
jefft
Heiden Tuning have some other racing gears a 22T 5th if I remember correctly.
Wonder where they get their gears from ?
Has anyone ever checked all the other contempoary Yamaha gears ffitted to other models to see if any would fit an XS650 ?
Wonder where they get their gears from ?
Has anyone ever checked all the other contempoary Yamaha gears ffitted to other models to see if any would fit an XS650 ?
jdizon
XS650 Guru
On a 78+ Trans to confirm.. All I need is Part #05-0870 and Part #05-0857 is not necessary to upgrade?
Correct, I used to think they had too be installed together until it was brought to my attention that 0857 is just a direct replacement for the oem 5th gear. All you need is 0870.
