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Discussion Starter #41
Good info, Here in Utah, we have freeway speeds of 70,75 and now 80 on quite a few stretches. At 80 I was surprised to see the RPMs close to 6k.
Thanks for the info. I may follow your lead on this. Although I do mostly city driving around town in lower Michigan, when I do get on the expressway I fell like I need one more gear. 70 MPH is at about 5000 RPM.
I just returned from an out of town trip and my 16T sprocket was among my delivery items :) Today I focused on doing the majority of the first service, but I hope to try the sprocket installation within the next day or so. I'll update once I attempt the install...
 

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Close fitting sprockets on other bikes I changed gearing on would sometimes get the sprocket pretty close to the engine cases. The chain has a tendency to lift off the sprocket on the bottom side at higher speeds. In one case it slightly grooved the alloy case from the link plates. No harm done, just two slight grooves. That might occur with the 16T. I'd install the 16T when I get my bike just to lower the RPMs at speed (75 here in KS). No canyons or forest service roads here. And I'm not taking this bike on our off road racing tracks. Going over the handlebars and letting the bike bounce off terra firma is not a good idea. I leave that for my KTM 300 XC.

Stu
 

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Discussion Starter #43
Close fitting sprockets on other bikes I changed gearing on would sometimes get the sprocket pretty close to the engine cases. The chain has a tendency to lift off the sprocket on the bottom side at higher speeds. In one case it slightly grooved the alloy case from the link plates. No harm done, just two slight grooves. That might occur with the 16T. I'd install the 16T when I get my bike just to lower the RPMs at speed (75 here in KS). No canyons or forest service roads here. And I'm not taking this bike on our off road racing tracks. Going over the handlebars and letting the bike bounce off terra firma is not a good idea. I leave that for my KTM 300 XC.

Stu
That's a very good point regarding the 'chain lift' at speed. Even if I don't have to file material away for a good 'static' fit, I'll be inspecting after some hard riding to check on that issue. And as the chain wears and stretches/loosens up the clearance from the case might tighten even further. I like that the sprocket cover is easy to remove for inspection purposes :)
 

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Discussion Starter #44
I finally managed to get the 16T sprocket installed today. I installed the sprocket without breaking the chain, but I feel the job would have been much easier by breaking the chain or removing the passenger left foot peg support. I didn't have what I needed for the other approaches and I wanted the bike up for a ride tomorrow. The sprocket barely fit - I'll provide pictures and more details later.

I took it for a short shakedown run and I'm very happy with the results so far. I've noticed no difference in acceleration but the engine is more relaxed at highway speeds. I'll be doing an extended run tomorrow morning and will report my findings ;)
 

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I finally managed to get the 16T sprocket installed today. I installed the sprocket without breaking the chain, but I feel the job would have been much easier by breaking the chain or removing the passenger left foot peg support. I didn't have what I needed for the other approaches and I wanted the bike up for a ride tomorrow. The sprocket barely fit - I'll provide pictures and more details later.

I took it for a short shakedown run and I'm very happy with the results so far. I've noticed no difference in acceleration but the engine is more relaxed at highway speeds. I'll be doing an extended run tomorrow morning and will report my findings ;)
Thanks for leading the way on a search for taller gears. As someone who has on more than one occasion found myself hunting for a '7th gear' that never comes while passing in the lane of oncoming traffic, I am watching your efforts with great interest.
 

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Discussion Starter #46
Thanks for leading the way on a search for taller gears. As someone who has on more than one occasion found myself hunting for a '7th gear' that never comes while passing in the lane of oncoming traffic, I am watching your efforts with great interest.
I only did a 6 mile loop but I'm happy with the way the bike 'feels' with the change so far, it's like I have that extra gear you mentioned. In my opinion this is the gearing the Scrambler should have 'stock'. Tomorrow I'll ride at least 80 miles and possibly quite a bit more. I"ll navigate a mixture of surface streets and expressway/secondary roads. Gauging a fuel economy improvement is going to be tough because our peak temperatures are climbing and are now at 100F or more, which improves overall fuel economy for various reasons. I also have a fresh oil change after the first service which might have an effect. And of course I'm still transitioning through break-in ;)

I'm attaching photos showing the clearance between the new sprocket and the 2 closest engine castings. As you can see it's pretty tight... With the chain pulled away from the sprocket I measured about 0.010" clearance and 0.003" clearance respectively. The 0.003" clearance was against the 'unused' clutch slave cylinder through hole at the 10 o'clock position (covered by a plastic plug not shown in this set of photos). While I can't justify my feeling right now I'm not particularly concerned about these clearances, but I'll be watching close ;)
 

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I only did a 6 mile loop but I'm happy with the way the bike 'feels' with the change so far, it's like I have that extra gear you mentioned. In my opinion this is the gearing the Scrambler should have 'stock'. Tomorrow I'll ride at least 80 miles and possibly quite a bit more. I"ll navigate a mixture of surface streets and expressway/secondary roads. Gauging a fuel economy improvement is going to be tough because our peak temperatures are climbing and are now at 100F or more, which improves overall fuel economy for various reasons. I also have a fresh oil change after the first service which might have an effect. And of course I'm still transitioning through break-in ;)

I'm attaching photos showing the clearance between the new sprocket and the 2 closest engine castings. As you can see it's pretty tight... With the chain pulled away from the sprocket I measured about 0.010" clearance and 0.003" clearance respectively. The 0.003" clearance was against the 'unused' clutch slave cylinder through hole at the 10 o'clock position (covered by a plastic plug not shown in this set of photos). While I can't justify my feeling right now I'm not particularly concerned about these clearances, but I'll be watching close ;)
WOW that is super close, what were the gaps on the original sprocket do you know??

Looks a bit to close for comfort that top clearance.

You obviously took them gaps with feeler gauges no???
 

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16 tooth counter install

Did you remove the back wheel? Did you have help? My 16 tooth comes Wednesday. I am always reaching for 7th gear.
 

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Discussion Starter #49
WOW that is super close, what were the gaps on the original sprocket do you know??

Looks a bit to close for comfort that top clearance.

You obviously took them gaps with feeler gauges no???

I measured the tightened up gaps with a feeler gauge. The original measurement on the top clearance was 0.110". I knew it was going to be close with the larger sprocket, but decided not to grind that area ahead of time. I'll be taking a tool tomorrow to remove the sprocket cover so I can inspect during the run and decide if grinding is warranted. My recommendation to anyone else is to grind down that area but I'm not sure yet how much. The cast aluminum is fairly soft and a small file will do the job easily.

Did you remove the back wheel? Did you have help? My 16 tooth comes Wednesday. I am always reaching for 7th gear.


I had no help but a second set of hands would be beneficial. I loosened the back wheel and pulled the chain off the rear sprocket which gave plenty of slack to pull the chain off with the front sprocket. BUT, it was very difficult to clear them both off the spline because the passenger peg strut interferes with removal. I'd strongly recommend either breaking the chain or getting the tools necessary to remove that footpeg bracket/strut. Getting the new sprocket on without either of those approaches was almost impossible - it took me a half hour of fussing to pull it off.
 

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Thanks again for taking the time to post up the details, such a help for other folks coming along.


Sarah
 

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Discussion Starter #51
Thanks again for taking the time to post up the details, such a help for other folks coming along.


Sarah
You're welcome Sarah. I've had further thoughts about this mod ahead of my ride this morning, and it might be a case of 'Don't do this at home'. From my perspective this is NOT a 'plug & play'. I'm recommending that owners DON'T perform the swap unless you're comfortable with removing a SMALL amount of material at the locations that are close to the sprocket/chain as indicated in the photos. There may be enough variation in engine castings and/or aftermarket sprocket diameters to cause an interference fit on other Scramblers, either immediately or down the road. I'll get experienced opinions this morning with my ride group, and report back here after I do a post ride inspection.
 

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And appreciate you sharing your thoughts as you go, too. I've been thinking might be best to swap out the rear and leave the front alone. Don't know till you try, though. Good luck, and enjoy your ride today.


Sarah
 

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Discussion Starter #53
And appreciate you sharing your thoughts as you go, too. I've been thinking might be best to swap out the rear and leave the front alone. Don't know till you try, though. Good luck, and enjoy your ride today.


Sarah
I had a great ride and a good test of the 16T sprocket :) Summarizing:
1. The engine feels less hurried at freeway speeds but the bike is just as 'frisky' - no apparent change in acceleration. In the lower gears the change is imperceptible to me. Some numbers as indicated on the speedometer:
4000 RPM - 15T sprocket~56 mph; 16T sprocket~60 mph
5000 RPM - 15T sprocket~70 mph; 16T sprocket~75 mph
2. No change in speedometer/odometer error. Speedo is still ~5% optimistic and Odo is still ~0.8% optimistic. This suggests that the sensor is either at the front or rear wheel, not at the transmission.
3. Fuel economy for the run was 54 mpg - no dramatic change from what the past couple of tanks have netted. Each outing has different wind & speed conditions and this run was only 85 miles, making it tough to be accurate.
4. My friends and I inspected the Scrambler sprocket area at the meetup point - no indication of the chain/sprocket contacting the engine. We all agreed that anyone doing the install 'from scratch' would be wise to remove some material from the engine casting at the closest point I've shown in photos - the capped unused 'slave cylinder' area at 10 o'clock. We also agreed that 'watchful waiting' for my particular installation was OK to catch changes as the chain wears. It's easy to remove the cover and inspect from time to time.

Other notes:
1. After installing the 16T sprocket the chain adjustment required one notch of movement to place the rear axle closer to the engine. This arguably now gives more adjustment range for chain stretch. But if I now remove a tooth or two at the rear it will compensate in the other direction and I'll likely be able to still use the stock chain length.
2. I'm happy with the result if for no other reason than reducing engine wear and tear and having the bike feel less frantic at highway speeds. I may leave it this way for now and consider a rear sprocket change when it's time to replace the rear tire.

I'll post more info as I learn more, but so far so good...:)
 

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Discussion Starter #55
Glad that's working out; that gas mileage sounds good, too.


Sarah
I'm only at 663 miles so far but I believe/hope the fuel mileage will improve as the engine continues to break-in.

I didn't buy the Scrambler for high speed capabilities - it's the light weight and agility that has me hooked. But I'm curious about the effect on top speed with the new sprocket. Currently the rev limiter should kick in around 116 mph, and with 16T that should bump up to around 124 mph. Perhaps in a couple of weeks I'll have a chance to check that for a few seconds on a safe section of road after my friend's ZX1400 starts sucking me into his aerodynamic wake while he squeezes the throttle ;)
 

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Currently the rev limiter should kick in around 116 mph, and with 16T that should bump up to around 124 mph.
I don't think 75 hp is going to get you there - regardless of the gearing. Wind resistance would be difficult to overcome.
 

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Discussion Starter #57
I don't think 75 hp is going to get you there - regardless of the gearing. Wind resistance would be difficult to overcome.
Estimation of top speed is pretty tough as there are so many variables, and aerodynamics is a major one. I think there's a discussion thread on top speed elsewhere on the forum and I might post there once I have some personal data. I've had some experience with a few of my bikes and here's what I've reached, tucked in really tight:
1977 BMW R100S - 65 HP & 125 MPH
2001 Triumph Bonneville - 60 HP & 112 MPH
2009 BMW F800ST - 85 HP & 135 MPH (GPS verified)

My BMWs had better aerodynamics than my Bonnie, and that really helps with top speed. If the Scrambler has close to 75 HP then it might reach ~125 mph with the right gearing. This assumes the rider is tucked in, has aerodynamic help from a small bubble/dart screen, etc.

With the 15T front sprocket the engine power peaks at roughly 116 mph and declines from that point onward. So it would be difficult to reach 125 mph unless you had one heck of a tail wind ;) A 16T front sprocket provides the possibility of ~125 mph with engine power peaking at that point.

To me it seems the stock gearing on the Scrambler is setup for acceleration, not maximum engine life, economy, or top speed. It's interesting that taller gearing can either improve engine life and economy, or provide a potentially higher top speed. With different sprocket ratios an owner can tweak the Scrambler to their particular taste :)
 

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Going to give it a try

Got my 16 tooth today from Dennis Kirk - tomorrow I will attempt the installation. I have a dremel tool at the ready should I need it.
 

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Discussion Starter #59
Got my 16 tooth today from Dennis Kirk - tomorrow I will attempt the installation. I have a dremel tool at the ready should I need it.
Good luck with the install! Hopefully if you choose to you'll be able to mount it as I did without breaking the chain or removing the passenger peg support. It was fussy enough that I'd probably do one of the latter if starting from new. About the time I had given up I somehow got it on the shaft with the chain on the sprocket. I managed to gently tap it the rest of the way using the plastic handle of a screwdriver, but it was tough going.

I'll be taking my second excursion with the 16T sprocket installed tomorrow morning so I'll get more of a feel for how it's working :)
 
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