Overdrive 5th gear

cheers skull... you know everything :D:thumbsup:

i'll have to make a cuppa and chew that lot over a bit cos my head is hurting.

right !.....changing from a 16" rear wheel to a 18" rear wheel with standard 17T /34T sprockets gives a reduction of

approx 132 RPM @ 50Mph
and 165 RPM @ 60Mph
not a lot !.....

Whereas just changing the primary sprocket from 17T to 18T with standard 16" rear wheel gives a reduction of
approx 190 RPM @ 50Mph
and 228 RPM @ 60Mph

so definitely not worth changing the rear wheel to reduce revs .

Changing the rear sprocket from 34T standard to 30T with standard 16" rear wheel and standard 17T front sprocket gives a reduction of
approx 402 RPM at 50 Mph
and 483 RPM @ 60 Mph

So changing the rear sprocket only from standard 34T to a 30T is easiest and gives almost double the reduction in revs that changing to a 18T primary gear would give ! (bugga wish i'd done this study yesterday before i ordered a 18T sprocket )

changing both the front and rear sprockets to 18T and 30T would give a reduction in revs of

approx 570 RPM @ 50 Mph
and 684 PRM @ 60 Mph

However these changes according to XSJohn would require some changes to the bikes ignition timing and mixture etc or it would be undrivable.
I just thought that this might help some other owners ,like me, visualize the various options and rev reductions at typical highway cruising speeds without fitting overdrive gears. Hope I've got it correct ?
 
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I have read about 3rd and 5th gear being weak... can someone provide more info about this? Those gears the two gears that I use most. 3rd is great around town, and 5th is obviously the highway gear.

Is it really a problem? I can't imagine that 5th gear is so weak that you cant cruise in 5th...

What causes them to break? Beating on the bike, revved up clutch dumps, or just normal cruising?

For what its worth, I have a 1979 with a 16'' rear wheel. I have the stock 17 tooth front sprocket, and a 32 tooth rear. At 75 mph (cruising highway speed) my bike is turning exactly 5,000 rpm in 5th gear (stock 5th). It might be different on every bike, but 5,000 feels like a 'sweet spot' to me. Its very smooth and comfortable that that rpm. 3,000-3,500 is another 'sweet spot' where the vibes magically disappear. I have literally cruised for hours at 5,000 rpm in 5th with NO problems. Whats the obsession with reducing engine RPM? As long as you aren't near red-line and the vibes aren't killing you, the bike should be fine.

I get the most vibration between about 4,200-4,600. I had a 30 tooth rear sprocket for a bit, but it made the bike sluggish off the line and put me too close to the 4,200-4,600 horrible vibration zone at 75 mph. Because of this, I went back to the 32 tooth rear, which raised my cruising RPM's and actually made the bike more comfortable...
 
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That's kinda what I have been saying. The 17/32 is a good combo. Those and proper tuning and the vibes are a non issue.
Leo
 
Im having great luck with the 17/34 on the stock 5th gear.

Ive gotten about 40 hours on my bike after removing the "junk" Mikes OD 5th gear and the problem is gone.....
 
Im having great luck with the 17/34 on the stock 5th gear.

Ive gotten about 40 hours on my bike after removing the "junk" Mikes OD 5th gear and the problem is gone.....

well thats good to hear but strewth thats a lot of extra work and expense and wasted time. I hope you gave mikesxs some feedback :laugh::wink2:
 
Hi I am running a 18' rear wheel,17/30 gear combo and mikes 5th gear od, Night and day to a stock set up.THanks
 
This is an update to the overdrive 5th gear bore size issue.

Found a new part listing for another overdrive 5th gear, and a slightly confusing clarification (using 'mm' instead of inch) on the MikesXS transmission parts page:

http://www.mikesxs.net/products-22.html

The bore size issue thread: http://www.xs650.com/forum/showthread.php?t=33019

It appears that:
The early 73-77 trans shaft is 0.979", fifth gear bore is 0.984", use part# 05-0869
The later 78-84 trans shaft is 0.975", fifth gear bore is 0.979", use part# 05-0870

5th. Overdrive Gear for Yamaha XS650(73-77), Prefix # 256 Engine,
Main shaft 0.979 mm ONLY 0.984 inches or 25 mm (Hole diameter)
http://www.mikesxs.net/product/05-0869.html

5th. Overdrive Gear for Yamaha XS650(78-84), Prefix # 447 Engine,
Main shaft 0.975 mm ONLY 0.979 inches or 24.82 mm (Hole diameter)
http://www.mikesxs.net/product/05-0870.html

Hope this helps...:thumbsup:
 
i will be splitting cases to fix my chipped kickstart gear and will be installing the 5th gear overdrive. you dont have to change the main gear also right ?
 
No, the gear faces themselves are identical, pre midway 1977 gear sets have different splines on the shafts. Easy way to see is the raised part of the new splines is polished. On the old ones the polished surface is the valley. Now that i have seen both splines in my hand, it is easy to see the difference. You just cant use new style gears on the old style shaft.

My new engine has 78 main gear set and a 74 pinion set. The trans works fine with mixed sets, but no mixing new gears on old style splines and vice versa. Yams tsb actually makes sense to me now. Hahaha.

The 5th gear od only fits the new style shaft. If you have doubt of what tranny you have post a pic of the splines and ill tell you.
Posted via Mobile
 
also the newer gears have lines cut into every tooth. Worst case for some reason my bike has older gears in it, i have a trani from an 81 i purchased soley for the purpose of stealing the kickstart gear from it.

thank CDNTX650 that was my only fear that the 5th main had to be changed also
 
Ok so the conclusion on the 5th gear OD is that it's pretty good if you get the right sized gear? And it's a pretty easy swap once you split the cases? If people had issues from the 5th gear OD what were they?
 
ToomanyXS1Bs said,

5th. Overdrive Gear for Yamaha XS650(73-77), Prefix # 256 Engine,
Main shaft 0.979 mm ONLY 0.984 inches or 25 mm (Hole diameter)
http://www.mikesxs.net/product/05-0869.html

5th. Overdrive Gear for Yamaha XS650(78-84), Prefix # 447 Engine,
Main shaft 0.975 mm ONLY 0.979 inches or 24.82 mm (Hole diameter)
http://www.mikesxs.net/product/05-0870.html


I have an '83Heritage special that I added 5thOD to. The pinion for that year was way too small to fit the shaft, well maybe with a Hydraulic press...But the alternate larger holed size for older bikes slipped right on. A little looser than I would prefer, but altogether it seems within tolerance. Now, understand that I bought this bike new in 1985 so it was made close to the end of production for the USA in 1983. I have to wonder if Yamaha had started using up old stock parts to finish the run. I have no clue.
Moral of the story is even if you are your own previous owner, with bikes this old you can't tell what is inside until you open it up and MEASURE it first. Clutches are a good example of this. Well, I've talked enough about that.
Cheers
 
OK then,
perhaps I spent too many years as a machinery designer but HTF can that overdrive gear possibly work?
It's a 24T gear that replaces a 23T gear.
It still has to mesh with the same gear as the original.
But it's got one more tooth so it must have a bigger pitch diameter so how can it run on the same centers?
Someone please enlighten me?
 
Hello All,
I just bought the overdrive 5th gear. I purchased a used 81 trans also just last month. It fits in my 72 cases perfectly. No problems at all.

Now, Mikes says, as 2 many has quoted above, that a 73-77 uses the .984" ID gear, and that the 78-83 use the .979" ID gear.

OK, ready? I carefully measured both shafts and I came up with a .979" shaft on both 72 and 81 trans'. So I bought the .984" ID gear and it fits perfectly.

Mikes, is confused. (You may notice by the misprint of .979MM., that's smaller than a 63 model motoring rear axle). It's obviously inches.

The moral of the story is............. MEASURE IT!. The shaft and the ID of your original gear. If u r unsure about ur measurements, bring it to a bike or machine shop.

MY sweetheart should be running next week. The cases go together tomorrow. Oh, I also bought used shift forks and all that goes wit it for like $35. One of my forks was bent. Well, somebody out there knows that I can't shift. Can't wait to try it out.
 
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Good info, guys.

Mikes, is confused.
The moral of the story is............. MEASURE IT!. The shaft and the ID of your original gear. If u r unsure about ur measurements, bring it to a bike or machine shop...

Yes, this should be the battle cry when pursuing this mod!

Just a theory.
Knowing the potential foibles of the manufacturing processes, I can easily imagine a supplier or machining mistake of 0.1mm (0.004") in the supply chain, followed by frantic/internal shuffling in the factory, with little to no notices to the field. (Rather embarrassing)

Fred: I'm still trying to chase down that old posting on gearteeth geometry change to accommodate that extra tooth.

Here's the ancillary threads:

http://www.xs650.com/forum/showthread.php?t=31092&highlight=involute
http://www.xs650.com/forum/showthread.php?t=40233&highlight=involute
 
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I think the problem is the gear doesnt come with the ID he says it will. Doing this mod, I think you will have to assume that you will pay for machining. I know I did. ($30)
 
Hi guys, I have a '77 xs D, 447 unit. Gears are early cuts with single grooves.
I find myself looking into this 5th gear upgrade again as I get ready for rebuild.

Can someone clear up my confusion over what I need to buy or what my best course of action is?
Should I get a later set of gears and 5th O/D to match or stick with what I have and just get a 5th to match that? Have people had issues with the new 5th sizing either way?
 
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