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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: murphsprin on April 21, 2015, 10:59:20 AM
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I have an 85 k100rt. And the hyw rpms are to high for my liking. I was considering getting a rs final drive. But I am not sure if it will help the much. Has anyone made this change? How much did your RPMs drop at hyw speeds. Or is there someone making gear sets I can swap
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What kind of RPM are you running? How fast are you running? Someone on here said they have run theirs all day long at 7k rpm and the bike doesn't seem to mind. My k75 is only turning 5-6k at near 90mph. How fast are you running?
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The K engines really will last forever at high RPMs...these were built for the Autobahn...full throttle for hours on end
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Before I got my tach working I thought I was revving the shit out of the engine... turns out I was short shifting by almost 4k rpm lol.
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Drake's page says he has a K75 transmission that "According to the documentation that came with this bike, gears 1-4 are 4% higher than stock and 5th gear is 9%. (The donor bike was a turbo'd K75 which is probably why this was done.)"
http://www.kbikeparts.com/
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Its running about 6000rpm at 75 indicated pretty sure the spedo is inaccurate at higher speeds. I'll take my GPS with for a ride today and report back with accurate numbers. By the way I'm not worried about hurting the engine at those rpms more after better fuel economie and smoother ride it starts to get buzzie at higher rpms
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I flog the shit out of mine, mostly around town and get 36 mpg. Most ppl report low 40's. I haven't noticed a buzzy sensation at higher speeds... wonder if the tires need to be balanced or... ?
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75's have a counterbalancer. 100's don't.
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Ahhh, that's right.
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just got back from a ride at 75mph it is right at 5000, also checked the FD its a 32/11 does anyone know what my rpms would be if I swaped to the RS unit its a 31/11. I like the downspeed trans option, that along with the 31/11 FD would get my rpms down. but the price is getting a little high at that point.
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anyone herd heard of doing this http://www.k100-forum.com/t3746-gearing-up-an-rt (http://www.k100-forum.com/t3746-gearing-up-an-rt) I found a R1200C FD on ebay but I'm not sure if it matters what year to use
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If I do the math correctly you'll gave 500 rpm.
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Check Anton's page on final drive ratios to get a good idea of the different RPMs you'll encounter for various combinations of transmissions and final drives.
http://www.largiader.com/articles/gearing/
The LT FDs are geared taller than the RT & RS. You'll find from the graph that going to a LT FD (32/11) will lower your RPMs than going to a RS FD (33/11). You'll give up torque at low RPMs for the swap, requiring higher RPMs to start off.
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I think I've decided on going for the r1200c gears. They are 33/13 or 2.53. Going to these from my 32/11 (2.91) should yield about 700 rpm drop. I found a used FD on ebayhttp://pages.ebay.com/link/?nav=item.view&id=181721405516&alt=web (http://pages.ebay.com/link/?nav=item.view&id=181721405516&alt=web) do you think I'll run into any problems.
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If you can obtain the gears cheap enough and they're not bad to DIY this would make for an interesting development
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i prefer tire spinn off the line... between gears...
this final drive may require a red line hole shott... and dropping 2 or 3 gears to pass at speed...
im willing to give it go...
j o
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It is a mind game knowing you engine is spinning at 5-6000rpm at cruising speed. You have to forget that at the same speed your car is only spinning 2500rpm or your old VTwin is at 3500rpm. The K bike was engineered to run within these parameters and loves to do so. My 1100LT has a sweet spot around 5500-5700, so that's my cruising speed when on the freeway. It is also nice that South Dakota just raised its limit to 80mph.
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used to look for 6th... now i ride the slabb in 4th... cause its wants to be tached up...
i acquiesce...
j o
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I think I've decided on going for the r1200c gears. They are 33/13 or 2.53. Going to these from my 32/11 (2.91) should yield about 700 rpm drop. I found a used FD on ebayhttp://pages.ebay.com/link/?nav=item.view&id=181721405516&alt=web (http://pages.ebay.com/link/?nav=item.view&id=181721405516&alt=web) do you think I'll run into any problems.
Do the mounting holes line up (can't tell from the pictures)? Since your bike is pre-86, have you verified whether you have the older 16 tooth drive shaft or newer 20 tooth drive shaft? If you have the 16 tooth, you may have to send the unit out to Bruno's to replace the splines.
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No the housing is different. I will just be using the gears. And yes I have a 16t shaft so I am also looking for a 20t driveshaft if anyone's got one
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Just did a second 700 mile day on the slab across Illinois, Iowa, and a major chunk of Nebraska today. 9 hours at 5500 to 6000 rpm heading into a 35-40mph headwind. Ilsa, my 75RT, is loving it. As for me, I'm really digging on how you can be going 80 mph and you just roll on 5 more to blow past a couple semi's without having to downshift.
I hear ya Johnny on running in 4th and 3rd around town. This is my first major trip on the brick, and I'm really learning how much these engines like to rev. Didn't look for 6th(or 4th) once today.
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illinoguns iower nebrasker are 3 of my favorite places to ride... throw in kansass and oklahomer and there aints no reason to ride anywhere else...
j o
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Swapping FD gears is not what I would call a DIY project. Everything needs to be shimmed properly for correct gear engagement, and special tools are needed. It is a pain to do at the dealer with the tools...I am also pretty sure you will need a custom made driveshaft since the splines will be different, unless you have changed to paralever.
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If you must have the gears, I'd see about having Bruno or one of the final drive shops do it for you. The gears are very particular with regard to shimming and bearings. Also, is yours a paralever or monolever? The R12C is a paralever type pinion, so you would need to upgrade the swingarm. Fairly easy to do though.
The K100 is a bit buzzy, unlike the k75 (which doesn't vibrate, for all intents and purposes). The K engines are built like aircraft engines (the blue and white roundel is a spinning propeller on a blue sky), meant for high RPM, high throttle all day long. Autobahn use after all. I rented a triumph thruxton when I was in Germany, it did not like the long autobahn runs (90 miles/45 minutes between fillups, 24mpg). Could smell the blowby, even at speed.
I wouldn't worry about the gearing. The extra gas you save likely won't make the swap worth it. I considered going with an RS FD on the K75, it probably isn't worth it.
The 32:10 gearing is exactly 80mph (calibrated, not stock speedometer reading) at 6000rpm.
You might find that you overgear the K100/K75 with the 2.54 gearing. There's a big frontal area, and 90mph at 5000 rpm might be too much. Would definitely need to downshift often.
I think the K75 would do fine with the RS gearing (2.91), but that's about it. If I replaced my FD for other reasons (not likely to happen anytime soon, it's a bruno's rebuilt unit), I would probably go for the 2.91. That would turn 5200 at 80mph. Probably bump my fuel mileage a little. But otherwise, I'll just run it fast, it doesn't care. German vehicles are built such that engine operation is permitted at any point up to the redline (or a soft redline, usually 500 under true redline), for sustained periods. Also keep in mind, peak torque on a K75 is at 6500 rpm, and for a k100, 6000. That is where it is designed to cruise, due to peak volumetric efficiency.
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Swapping FD gears is not what I would call a DIY project. Everything needs to be shimmed properly for correct gear engagement, and special tools are needed. It is a pain to do at the dealer with the tools...I am also pretty sure you will need a custom made driveshaft since the splines will be different, unless you have changed to paralever.
Actually the r1200c's were all monolever.
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That is true, but the spline for the driveshaft on the pinion gear should be the same as on the paralever final drives used in everything from the 4 valve K100 through the R1150 and K1200 lines.