Ton up SR250: 100mph, 100kg, 30hp

Somewhat but not entirely related... Have spent a lot of time the last couple of weeks filming my wheel building process and editing it together as an instructional video. Now that wee project is complete work will continue with the this build!

To build wheels I came up with this taping method. Perhaps others do this too? Anyway, I find it makes a headache of a process into a pleasantly therapeutic one.

https://www.youtube.com/watch?v=Mj_JUgpImB4&t=337s

I also wrote a blog post about spoked wheels. They are rad! https://www.jadusmotorcycleparts.com/single-post/2018/12/30/Spoked-Motorcycle-Wheels---The-Best-Motorcycle-Wheels
 

Attachments

  • WheelBuilding_Process.JPG
    WheelBuilding_Process.JPG
    548.4 KB · Views: 275
  • WheelBuilding_ColouredTape.JPG
    WheelBuilding_ColouredTape.JPG
    442.6 KB · Views: 269
  • SR250_RearWheels.JPG
    SR250_RearWheels.JPG
    401.3 KB · Views: 273
Both sets of fork springs finally arrived this week and both fit!

Now I can work out the spring rates of both sets and draw up some spacers to make them work.

I am however having second thoughts. After seeing these, I am actually thinking it might be better to use cut stock SR250 springs, calculate the necessary length for the necessary/desired rate, then make some spacers for that and use the spring end adapter I designed. Then I can get testing the performance of these and if it's good, it could be something to offer customers - a much cheaper solution to buying springs from other bikes and saves shipping hassle as well.
 

Attachments

  • SR250_AlternativeForkSprings.JPG
    SR250_AlternativeForkSprings.JPG
    292.7 KB · Views: 264
Not so much to post for a while but things are ticking along. I developed a simpler fork preload and cap kit to see if I could bring down the cost of production for customers - more on that later. Plus I checked a lot more things with cutting the stock springs - worked out lengths, rates, preloads and suggestions for rider weights. I also checked how the spring would be at full compression at it most extreme cut length - see attached. The adapter I designed works a treat to spread the load of a cut spring end.

I ordered a magnetic angle finder as well that works off of level - so you can place it on the fork stanchion and work out rake and therefor trail as well. I need to do this because the current set up I have with an experimental rear shock length of 350mm ends up with 23 degrees rake and only 85mm trail. I want 100mm of trail minimum for this slightly higher speed SR and certainly more rake than that. So I will therefor work with rear shock length and front fork lowering to achieve this. Rake will land between 26 and 28 degrees.
 

Attachments

  • SR250_CutSpringRatesLengths.jpg
    SR250_CutSpringRatesLengths.jpg
    298.4 KB · Views: 240
  • SR250_CutSpring.jpg
    SR250_CutSpring.jpg
    243 KB · Views: 223
  • AngleFinder.jpg
    AngleFinder.jpg
    29.5 KB · Views: 692
So the angle finder came and is awesome. What a great way to measure these things with pretty good accuracy. Anyway, I worked for some time with rear shock height and lowering the front forks until I got something acceptable. One problem is that I am still a little driven by the look and proportions of the build - so I wanted to achieve this flat line of the seat and tank still. This meant a slight compromise for these figures. But I ended up with a rake angle of 25.5 degrees and trail of 95mm. Which is a little border line but still within the acceptable realms of sport bike specs. When I get the bike running I will be careful when coming up to speed at first and if it feels necessary I can install a steering damper as well.

The final rear shock height is 340mm and the front forks are lowered 40mm. I double checked these physical measurements with a quick CAD sketch and they are almost spot on - meaning they are reliable figures/measurements.

Now I just need to find a rear shock that is in that length and is soft enough for a 100-110kg bike... There are plenty of rear shock options for that length with the correct 14mm diameter eyelets, but they are all for much heavier bikes. This would mean a very stiff spring and almost non-functioning rear suspension. I have written to a few companies inquiring about custom set up YSS shocks. Anyone got any other suggestions? I would consider Hagons if their shocks didn't look so damn vintage! And I haven't heard very good things about RFY shocks (shame because they look cool).
 

Attachments

  • SR250_RakeTrail.PNG
    SR250_RakeTrail.PNG
    19.2 KB · Views: 215
  • SR250_Trail.JPG
    SR250_Trail.JPG
    528.6 KB · Views: 213
  • SR250_ForkAngle.JPG
    SR250_ForkAngle.JPG
    376.2 KB · Views: 209
  • SR250_Rake.JPG
    SR250_Rake.JPG
    374.3 KB · Views: 229
And here's how those dims/set up looks. You can see that the rear frame rails are parallel to the ground - one of the visual goals I couldn't let go of.
 

Attachments

  • SR250_FrameGeometry_Stance.JPG
    SR250_FrameGeometry_Stance.JPG
    255.2 KB · Views: 232
I wouldn't worry as much about coming up to speed as backing off from speed. The front dives, rear lifts, and both decrease trail.
 
pidjones said:
I wouldn't worry as much about coming up to speed as backing off from speed. The front dives, rear lifts, and both decrease trail.

Very true. Unfortunately I can't see another way to increase trail without compromise. There is one option left and that is to design some custom triple tree clamps with less offset to increase trail. Because the rake/caster is actually pretty good. But then if I am designing custom triples, I may as well install a modern fork. And I really don't want to do that! Maybe I should look into an anti-dive system ;D
 
And now for something completely different... I was/am not planning on spending much time on styling/finishes on this build as I did with the last build. But that doesn't mean it won't look cool, just a little more function over looks.

Anyway, I was going to go for a completely raw, materialistic look - all aluminium parts bare aluminium, all metal parts rattle canned black and then I was going to strip the tank, brush it and have it clear coated for a nice raw look - see attached. However I recently got inspired by a customers bike in Poland (the SR was a Police bike there for many years ;D ). His bike had the original tank in white and it had gained some really nice patina - the typical collection of grime around the filler cap, a few scratches and dings, then this really nice yellowish brown in some places where fuel had been spilled on it and it had weathered differently there. This gave me the idea that perhaps I want to keep the original paint - it is kinda cool after all, in brilliant orange. Plus it has a really stylish 'SR' on the sides. Then I would reuse the stock headlight too, which also has some nice patina. I then looked at one of my favorite bike books for some inspiration and yes, I really like the rough, old bike look - check out the cool Nougier Four. Yes, I will need to 'cheat' in some places for some parts that are new, but I won't do anything special with them, just leave them uncleaned and unpolished and let time do it's work. What are people thoughts on this idea?

It also leaves me with a dilemma of how to remove the one massive dent in the middle of the tank while retaining the paint... Anyone tried one of these kits?...

https://www.youtube.com/watch?v=NGT5Q7j4xnY
 

Attachments

  • SR250_Patina2.JPG
    SR250_Patina2.JPG
    372.9 KB · Views: 237
  • SR250_Patina3.JPG
    SR250_Patina3.JPG
    381.6 KB · Views: 235
  • SR250_Patina7.JPG
    SR250_Patina7.JPG
    447.1 KB · Views: 230
  • SR250_Patina6.JPG
    SR250_Patina6.JPG
    371.5 KB · Views: 226
  • SR250_Patina4.JPG
    SR250_Patina4.JPG
    410 KB · Views: 238
  • OldBikePatina2.JPG
    OldBikePatina2.JPG
    385.4 KB · Views: 228
  • OldBikePatina1.JPG
    OldBikePatina1.JPG
    308.4 KB · Views: 565
  • OldBikePatina3.JPG
    OldBikePatina3.JPG
    316.3 KB · Views: 243
  • HolidayCustomsXS.jpg
    HolidayCustomsXS.jpg
    85.9 KB · Views: 246
The dent puller should work since its not bad and really no hard creases. You can also try a blood pressure gauge from the inside, inflate it to pop out the dent.
 
The cheaper kits dont really work on fuel tanks as the metals a little to thick...have tried and failed....
 
You can also try getting a lever in there and pushing it out from behind. If you try this be sure to put a cushion on the end so you don't put a fresh crease in the metal from the back side.
 
I tried a very similar hot-glue-gun-bridge device (Ding King brand) and it was so-so. Am following a guy on YouTube (Sweet Project Cars) and he had a couple episodes on using a slide hammer with hot-glue plastic pads. Was so impressed I got a set, but have not gotten around to using it. Many of the kits on ebay include hand or bridge pullers, but the slide hammer and plastic pads looks to be the best option.
I ended up doing the Virago 750 headlight mod to the OEM SR250 headlight ring to get a H4 replaceable bulb (we only got the weak sealed beam headlights in the USA). I think that had I to do it over, I would go with a 5 1/2" LED light assembly (think Daymaker).
 
Brodie said:
Crusty but trusty. I have quite a few bikes like that.

Haha I love it. Exactly.

Thanks for all the tips and info! I'll give the slide hammer version that zap mentioned a go. Makes good sense!
 
I posted something on Instagram a couple of days ago about a header extension kit I am thinking of producing. It lifts the silencer up to a 20 degree angle (matching the pillion peg bracket angle) to get more ground clearance and give a bit of a more sportier appearance. It will clamp onto the existing Jadus header (or possible even the stock header).

For this build, I plan on using this extension to weld in a vacuum pick up for a PCV system. On the third photo you see where the battery is positioned under the swing arm (the Jadus triangle tidy kit puts it there). But for this build, with the elimination of the electric starter, the wire harness can be much simpler and therefor the battery too - so I have bought a 4 cell Antigravity instead of the 8 cell and the small battery will now sit under the seat in the electrics tray. This then leaves space on the Jadus battery bracket for an oil catch can for the PCV system.

I have read a bit about this in Graham Bell's 'Four Stroke Performance' book and have a pretty good idea about how I will do it. I have also read a bit online where people have had success with this system with thumpers - to combat the huge pumping losses.

Here is a great bit of info from zap a while ago in this very build thread:

'One thing to suggest to your list of engine mods is thinking about pumping losses. There was an article by Dave Searle in Motorcycle Consumer News about this a couple months ago. Thumpers are notorious here because they don't have other cylinders working together to offset the crankcase pumping action. Many builders just vent their crankcases to look "cool" but it really doesn't do anything to decrease pumping loss (just keeps oily junk out of the carb like an oil catch can would); I got a Krank Vent off evilbay to experiment with creating a partial vacuum in the crankcase instead of trying to get all that air in/out of that skinny hose outlet (still planning). Krank Vents are a 1-way check valve and seem to be very popular with the H-D crowd as they reduce crankcase pressure and keep gaskets from blowing. My thoughts are that the engine will pump through the Krank Vent a couple times until the partial vacuum is created, then no more pumping.'

Does anyone have a link to that dudes build thread where he made a similar system for an LS650? (must be huge pumping losses in a 650 thumper!).
 

Attachments

  • SR250_CatchCan.JPG
    SR250_CatchCan.JPG
    248.5 KB · Views: 251
  • SR_PCVSystem.JPG
    SR_PCVSystem.JPG
    324.5 KB · Views: 252
  • SR_UpsweptExhaust.JPG
    SR_UpsweptExhaust.JPG
    334.1 KB · Views: 246
Since I sorted the frame geometry/suspension set up (rear shocks ordered, more on that later), it was time to sort out the riding position. The clip ons are not sitting 100% correct but pretty close. They will drop about 20mm once I trim the top triple clamp. But I will leave them there above the triple clamp rather than moving it down to between them.

So with the bars relatively set, the biggest task was to get the footpeg position right. Which sounds pretty straight forward, but with not wanting to use the stock position (too low, too little ground clearance cornering) or the stock rear passenger peg position (too far back, too high, just awkward), I need to draw up a custom bracket. But where to start? I made a simple plywood template with a bunch or known/measured hole positions relative to the stock footpeg bolt positions. After a a lot of playing around and 3 prototypes later (third proto printing now), I am pretty sure I got it right. You can see the development in the images. I wanted to get a comfortable position when crouched (and also aerodynamic-ish) plus a decent leg position when stopped at traffic lights etc. This also worked out nice for a visual position with my knee right on the side of the tank where it should be. To test all this I set the camera up on a tripod with a timer and took a bunch of shots with all the different positions - so I could study them and compare. Don't laugh, I felt as ridiculous doing it as it looks haha ;D

You can also see how much ground clearance there is at full lean (yeah right!!! haha). The exhaust silencer will most likely be the bigger problem now, rather than the footpegs/my feet.
 

Attachments

  • SR250_RearSetBrackets12.JPG
    SR250_RearSetBrackets12.JPG
    279.2 KB · Views: 227
  • SR250_RearSetBrackets11.JPG
    SR250_RearSetBrackets11.JPG
    355.8 KB · Views: 232
  • SR250_RearSetBrackets10.JPG
    SR250_RearSetBrackets10.JPG
    295.7 KB · Views: 228
  • SR250_RearSetBrackets9.JPG
    SR250_RearSetBrackets9.JPG
    434.9 KB · Views: 231
  • SR250_RearSetBrackets8.JPG
    SR250_RearSetBrackets8.JPG
    440.8 KB · Views: 224
  • SR250_RearSetBrackets7.JPG
    SR250_RearSetBrackets7.JPG
    397.7 KB · Views: 218
  • SR250_RearSetBrackets6.JPG
    SR250_RearSetBrackets6.JPG
    423.2 KB · Views: 214
  • SR250_RearSetBrackets5.JPG
    SR250_RearSetBrackets5.JPG
    442.5 KB · Views: 227
  • SR250_RearSetBrackets4.JPG
    SR250_RearSetBrackets4.JPG
    452.5 KB · Views: 219
  • SR250_RearSetBrackets3.JPG
    SR250_RearSetBrackets3.JPG
    456.2 KB · Views: 218
  • SR250_RearSetBrackets2.JPG
    SR250_RearSetBrackets2.JPG
    492.2 KB · Views: 221
  • SR250_RearSetBrackets1.JPG
    SR250_RearSetBrackets1.JPG
    333.8 KB · Views: 226
  • SR250_RearSetBrackets13.JPG
    SR250_RearSetBrackets13.JPG
    368.8 KB · Views: 219
Back
Top Bottom