[RisingSun]

I was burning my brain cells thinking of what could I stuff into the TW without going crazy.....In Japan Yamaha makes a SR500 bike and yes 500cc that pretty much bolts up to the TW frame. It looks almost exactly like it too.

http://i1216.photobucket.com/albums/dd369/ryukyustriker/449x600-cimg1959.jpg





What do you think?

 

[RodneyReed]

No more struggling up hills and in headwinds. The Harley guys would be left way behind at the stoplight. Definitely need to go with a bigger tank.

 

[lizrdbrth]

It needs almost 1 1/2" of offset to the left, as does nearly every engine out there. That big tire has a cost.



All Yamaha engines, whether 125's or 1000's all have their output shafts ending in roughly the same location because they all have narrow tires and rims.

 

[RisingSun]

It needs almost 1 1/2" of offset to the left, as does nearly every engine out there. That big tire has a cost.



All Yamaha engines, whether 125's or 1000's all have their output shafts ending in roughly the same location because they all have narrow tires and rims.

I heard ya. So now either look for a jack shaft or make one.

 

[RisingSun]

No more struggling up hills and in headwinds. The Harley guys would be left way behind at the stoplight. Definitely need to go with a bigger tank.

could go with a sportster tank fabbed up. The stock Yamaha SR500 probably would work as well.

 

[Wheelie Nelson]

i have a sr500 in pieces right now i'm building a custom bike out of. if you have any questions about measurements, i can answer them.



i have some pictures of it here. i'm waiting on a few things to get rolling on it again.



My link

 

[RisingSun]

i have a sr500 in pieces right now i'm building a custom bike out of. if you have any questions about measurements, i can answer them.



i have some pictures of it here. i'm waiting on a few things to get rolling on it again.



My link

What the hell those bikes in your shop are awesome. I hope your build comes out good.

 

[lizrdbrth]

I heard ya. So now either look for a jack shaft or make one.

I've finally acheived Motorcycling Nirvana. Which occurs when you've finally thrown enough time and money at similar projects to know well in advance what a worthless item a TW500 will be.



But good luck on your own journey, pilgrim.

 

[lorddaftbiker]

A TW 500 would make significantly more power, which would require a new suspension to handle that power, which would...might as well just buy another bike for the effort involved and money required. Unless of course, you want to make a stupid and futile gesture, in which case, you can't be blamed

.



-Lorddaftbiker

 

[lorddaftbiker]

A TW 500 would make significantly more power, which would require a new suspension to handle that power, which would...might as well just buy another bike for the effort involved and money required. Unless of course, you want to make a stupid and futile gesture, in which case, you can't be blamed

.



-Lorddaftbiker

 

[pgilles]

I heard ya. So now either look for a jack shaft or make one.

I say rig up a driveshaft extension with the tip of it supported with a sealed (spherical?) bearing. Use existing points on the cases for the support.

 

[lizrdbrth]

I think my previous post was a bit harsh, which isn't constructive.



Let's start all over, since Wheelie has provided us with such great pics.



The SR500, TT500 and XT500 motors are essentially the same. The 600's are the same, only larger, with two exhaust pipes and two carbs. None of these engines carry any oil to speak of in their crank cases. The oil is pumped into a storage tank via the hoses seen looped in RisingSun's pics.



If you look carefully at Wheelie's pics you'll notice that the top frame tube also serves as an oil tank. IIRC it holds 3 quarts and is about 3 1/2" in diameter. The TW's backbone is about 1 1/2" diameter and 15" long. It holds 486 cc's, or about half a quart.



So you'd need an oil tank. Which would pretty much eliminate any chance of an air box or a room for a battery. A 3 quart oil remote tank would have to be roughly 6" in diameter and take up most of the available space for these things. Or you could re-engineer the top tube of a TW frame to look like the SR frame, which is longer, so you'd need to up the TW top tube to 4-5" diameter to get the same capacity, then try to find a gas tank to fit over it, and so on.



Oh, by the way, the 500 is long enough fore-and-aft that your front tire will now hit it. That'll need some creativity. You've also lost about 2" of ground clearance because your front sprocket has to maintain the same geometry relative to the swingarm as your original motor, but your 500 has a deeper crank case. Speaking of sprockets, which end do you want to have a custom sprocket made for? A 428 for the front, or a 520 for the rear? How's it goin', so far?



A TW motor weighs 75 pounds, 4 oz. ready-to-run. Care to hazard a guess what a longer, wider, taller 500 weighs with all its plumbing, oil tank and 3 quarts of oil?



Those are just a few of the engineering issues involved. I'm quite confident that once all the height, width, offset, exhaust, carb clearance and other unseen issues were overcome and you began addressing the real world issues such as braking and suspension you'd quickly realize that your new toy outweighed an XT500 and was zero fun to ride.(Don't axe me how I know this

The path to Nirvana has had a fork or two)



I have examples of almost every Yamaha thumper ever made sitting either in a bike or under or my bench. Trust me, if any of them were suitable candidates one of them would be in a TW by now.

.



If you wanna play with a project that has a reasonable chance for success I'd recomend the XT/SR 250 or 350 motors. Both have been done, both involve major surgery and compromises, but either stands a better chance of being rideable within the TW platform.



Or pop a light weight, compact. air-cooled, old school big bore 2 smoker in there, shove it all the way to the left and go out and kill sumpin'.

 

[qwerty]

The only Japanese single 4-stroke I've found that may have enough countershaft sprocket offset is the Suzuki S40. It has much of the TW200 goodness in the form of a mile-wide powerband (31hp, 40ft/lb), mechanical simplicity, and rock solid dependability. I expect a custom frame would be easier than modifying the TW frame. I expect the TW swingarm and rear wheel assembly would be adequate, if the stock TW front disc was adapted to the back, and the drive chain and sprockets sized 520 or 525. Everything else would be up for grabs.



The only problem I see is the transmission gear spread. The S40 ratios are



1st gear 2.333 15/35 24

2nd gear 1.578 32% rpm drop 19/30 37

3rd gear 1.142 28% rpm drop 21/24 52

4th gear 0.956 16% rpm drop 23/22 ideal new ratio 0.868 68 22/19 0.864

5th gear 0.884 11% rpm drop 26/23 ideal new ratio 0.652 90 26/17 0.654



This progressive narrowing of gear spread is exactly the opposite of what you want for a dirt bike. My one ride on a 5-speed S40 I really couldn't tell much difference between 4th and 5th. If an S40 was given sprockets for a 90mph top speed at redline (about the stock gearing for an S40), 1st gear would wind out to 34mph, which would make idle speed work in the technical stuff tricky. For reference, a stock TW runs about 15mph at 6500rpm. I expect the idle speed is slower for a 650, though. Maybe make new gears for 4th and 5th with 24% or 25% spreads? That should put redline in 1st about 25mph, redline in 5th about 90mph. That would be about perfect. Okay, the numbers are crunched--it can be done.

By my measuring, wheelbase and seat height would both need to be increased by about 2 inches. I'd go with a double downtube diamond frame of chromemoly tube to simplify mounting footpegs and skidplate. I'd like to have a stronger front fork assembly, but there are plenty of old dirt bikes with good forks with about 7 inches of suspension travel. I had a Ceriani fork set on an XL500 flattracker that would be perfect. I think with careful attention to detail wet weight would not go up but about 45-50 pounds.

 

[lizrdbrth]

Subliminal message:



(Pssst....You could jackshaft nearly any Yamaha (XT

) 250, 350, 500 or 600 product (frame and all) using existing parts ( BW200 or BW350 swingarm ) it would go (it would even stop. Sorta..) the motor could stay where it is in the frame (it would be rideable in a week given good building skills, preplanning, careful measuring, etc.) It would have a Wall of Tire. You'll eventually get used to carrying a grease gun in your back pocket, but the giggles should offset that. Don't listen to that mean old Lizrdbrth. Don't listen to that mean old Lizrdbrth.....)

 

[RodneyReed]

I like the idea about the old two smoker. A good old YZ490 engine would be perfect. Get hit with a ton of power right off idle. If you could just attach the seat to the top of the handlebar so it wouldn't be so wheelie-prone.

 

[lizrdbrth]

The old Suzuki TS and Yamaha Enduro 400's etc. had an alternator, of sorts.



Going mostly by memory, even these could be a handful if you twisted on them.



A 490 would definitely be an "E" ticket ride.

 

[ronnydog]

[quote name='lizrdbrth' date='07 July 2011 - 06:53 AM' timestamp='1310050400' post='21734']





I think the idea is to end up with a TW.........!

 

[lizrdbrth]

Well, there ya go. Buzzkiller.

 

[ronnydog]

Well, there ya go. Buzzkiller.

TW buzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz