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

XS750AU said:
So how are you going to measure success?
I have bought a few bikes, the Husaberg in particular, where the PO had wound up the preload, compression dampening and rebound to a point the bike was unsafe. It would spit you off at the first bump, no wonder he sold it so cheap! Backed it all off so the wheels could actually react and now it is beautiful bike to ride! It is much softer, but it does not bottom out and the wheels stay engaged with the track (except when airborne) ;D.

I would say that not so many people would completely understand what they are adjusting when they adjust things on their suspension. Most would just expect harder/softer rather than different damping settings. Glad you got a good bike out of it though!
 
Here's the first (well actually third after a couple failed attempts) prototype for the stock fork cap replacement. This makes it a one man job to rebuild the forks and a much easier process - push the cap down with one hand with a tool guided in a pocket/recess in the cap (for this purpose - so the tool doesn't slip out), then once it is in the correct position, the other hand can clamp the circlip and let it sit into it's groove.

Then once it is in position, the cap lifts up and actually holds the circlip in its relaxed state - by the shape of the top machined detail. So to release the circlip again, the cap needs to be pushed down a little to pass this detail - an extra safety/security feature (think I got this idea from one of you guys in an earlier response?).

I will experiment with the length of it now and see what I can do with interchangeable spacers.

Oh yeah, the cap will also have a machined top, held in place with an oring - to keep the whole assembly water tight.
 

Attachments

  • SR250_ForkCap1.JPG
    SR250_ForkCap1.JPG
    244.3 KB · Views: 253
  • SR250_ForkCap8.JPG
    SR250_ForkCap8.JPG
    279.1 KB · Views: 256
  • SR250_ForkCap7.JPG
    SR250_ForkCap7.JPG
    406.3 KB · Views: 272
  • SR250_ForkCap6.JPG
    SR250_ForkCap6.JPG
    384.8 KB · Views: 263
  • SR250_ForkCap5.JPG
    SR250_ForkCap5.JPG
    346.8 KB · Views: 262
  • SR250_ForkCap4.JPG
    SR250_ForkCap4.JPG
    384.9 KB · Views: 256
  • SR250_ForkCap3.JPG
    SR250_ForkCap3.JPG
    268.1 KB · Views: 270
  • SR250_ForkCap2.JPG
    SR250_ForkCap2.JPG
    238.9 KB · Views: 253
YES! I just battled mine. Had to be the first time the forks have been apart. I slipped off the plug when putting it back together. Glad the piece didn't hit me. You're doing gods work Jadus
 
Thanks guys.

The plastic is PLA and the method is FDM from a Printrbot printer. It is not the best printer but it works very well for my purposes :)
 
I finally got my custom copper head gaskets for this project as well. 0.5mm thick (and with a larger opening to fit the 77mm piston) giving 10.2:1 compression ratio. I also took the chance to order another version for a boosted stock engine (with standard bore) at 1.5mm thick, giving 8.3:1 compression - good for 6-8psi of boost.

Yes, on the side I am working on a supercharged SR250 project... It is going very slowly though and taking a back seat to this project. Although I am finding there is a lot of nice cross over research and design work.
 

Attachments

  • SR250_1.5mmHeadGasket.JPG
    SR250_1.5mmHeadGasket.JPG
    163.3 KB · Views: 242
  • SR250_0.5mmHeadGasket.JPG
    SR250_0.5mmHeadGasket.JPG
    159.9 KB · Views: 255
  • SR250_CustomHeadGasket.JPG
    SR250_CustomHeadGasket.JPG
    217.5 KB · Views: 255
  • SR250_CopperHeadGasket2.JPG
    SR250_CopperHeadGasket2.JPG
    183.8 KB · Views: 257
  • SR250_CopperHeadGasket1.JPG
    SR250_CopperHeadGasket1.JPG
    236.8 KB · Views: 261
Despite the fact that I haven't found an SR250 yet, I enjoy watching your prototyping and product design processes. Keep up the good work!
 
JadusMotorcycleParts said:
Thanks guys.

The plastic is PLA and the method is FDM from a Printrbot printer. It is not the best printer but it works very well for my purposes :)

Question im going to be re gearing my exciter. Have you messed with different set ups?
 
JadusMotorcycleParts said:
I finally got my custom copper head gaskets for this project as well. 0.5mm thick (and with a larger opening to fit the 77mm piston) giving 10.2:1 compression ratio. I also took the chance to order another version for a boosted stock engine (with standard bore) at 1.5mm thick, giving 8.3:1 compression - good for 6-8psi of boost.

Yes, on the side I am working on a supercharged SR250 project... It is going very slowly though and taking a back seat to this project. Although I am finding there is a lot of nice cross over research and design work.
Who made them for you?
 
2Planks said:
Question im going to be re gearing my exciter. Have you messed with different set ups?

I have done in the past, I think I ended up with 17-40. But I will look more into it when the time comes. I know there are online calculators that help you work out rpm at certain speeds with different gearing ratios. I will be looking for max power output at around 170kph so I have the tip of the torque curve around the 100mph mark so this gearing will be very different to stock bikes. I will also be hoping to have power to 10,000rpm as well.

While on this topic, I have studied the parts diagrams for both the SR250 and the XS250 gearbox's - the latter because it is a 6 speed! From the diagrams I could tell they weren't compatible but I found a good deal on a whole set up on ebay so I bought it anyway, in the hopes of learning something or maybe even swapping some ratios. I learned something for sure, but this idea is a dead end - just look at the differences in the photo - SR250 gearbox at top (most of it), XS250 gearbox at bottom (all of it). Very different beasts!
 

Attachments

  • SR250_XS250_GearBox.JPG
    SR250_XS250_GearBox.JPG
    448.1 KB · Views: 286
der_nanno said:
As a turbo-bike-builder... which s/c are you thinking about? AMR300 or have you found something even smaller?

Nope, you got it! I managed to source a refurbished AMR300 from alibaba. It seems in pretty good shape. I will draw up custom billet intake and outlet ports for it to bolt up to the SR carb and then the engine on the other side (with a plenum-ish thing).
 
If you go draw through, you want as little plenum between engine and supercharger as possible... AMR300s are nice. In your case run it at roughly 1:1 and you should see about 3psi + a bit for the inefficiencies of the engine, so just about enough to make you lust for more and then go completely bananas on the boost level. 8)
 
After being at the motorcycle workshop FOREVER (seems like vintage bikes here get very low prio) the tyres have finally been mounted on the wheels - and they look great. These Avons can be mounted front or back and have a mounting/direction arrow to indicate which direction for which wheel (front or back). Somehow, despite me writing in large text in permanent marker on the rim, the workshop managed to fudge this as well. They were embarrassed and fixed it onsite for me while I waited. So they should.

Anyway, next stop, rolling chassis!
 

Attachments

  • SR250_CafeRacerWheels.JPG
    SR250_CafeRacerWheels.JPG
    400.6 KB · Views: 291
Awesome tires - nothing like a set of fresh wheels all ready and waiting.
 
Before I put the wheels back on I really want to sort out the suspension. The rear will be relatively straight forward after the front is sorted.

For the front I have been investigating what can be done with the stock springs and cutting them. I managed to work out what the stock spring rate is with the dual windings, it is a really low 3.3N/mm, which according to some literature, is suitable for riders weighing less than 50kg! Haha. Now I don't know if I am exactly right with all this stuff but it makes pretty good sense to me - see that attached equation plus the weight/spring rate charts from various manufacturers. Many replacement springs for classic bikes are however much higher ratings - up towards 7-10N/mm for riders ranging from 75-105kg. I'll do some of my own experimenting. The second rate on the spring is a lot more in the ball park at 4.5N/mm.

I started out investigating cutting the spring in three locations, one to separate the dual rate, then another two cuts to shorten each spring based on a percentage increase in spring rate - see attached how I thought a spacer could be made to connect the two and keep their compression separate, plus a chart of some calculations I made. This way, the dual rate could be retained.

Once I did the calculations and did a test cut of the spring, I realised this is not a good idea. The tightly wound part of the spring becomes coil bound quite quickly (did a test compression) and becomes useless (this is the purpose/intended behavior), plus cutting in a few places is a pain. I figured after reading a lot, especially racetechs literature, that straight rate springs with correct rate, preload and damping are much easier to control, adjust and ultimately will behave as intended = predictability and hopefully a well performing fork.

One good thing that came of the exercise though is the spacer I designed to be able to receive the cut end of the spring and provide a flat landing at the other side of it. The spacer matches the angle of the spring in its relaxed state and collects the end of the cut spring perpendicular to its winding. This gives the whole first coil and the end support. I will use this moving forward.

Now I will start experimenting with cutting out the tight windings completely and work out some suitable spring rates by cutting out a certain amount of coils (and calculate for a suitable amount of initial preload as well).
 

Attachments

  • SR_ForkSpring2.JPG
    SR_ForkSpring2.JPG
    292.4 KB · Views: 277
  • SR_ForkSpring3.JPG
    SR_ForkSpring3.JPG
    346.1 KB · Views: 244
  • SR_ForkSpring4.JPG
    SR_ForkSpring4.JPG
    268 KB · Views: 240
  • SR_ForkSpring5.JPG
    SR_ForkSpring5.JPG
    277.9 KB · Views: 247
  • SR250_CutForkSpring.JPG
    SR250_CutForkSpring.JPG
    230 KB · Views: 251
  • SR_ForkSpring1.JPG
    SR_ForkSpring1.JPG
    252.4 KB · Views: 259
  • SR_CutForkSpringLengths.JPG
    SR_CutForkSpringLengths.JPG
    273.4 KB · Views: 243
  • SR250_DualSpringGuide.PNG
    SR250_DualSpringGuide.PNG
    93.7 KB · Views: 453
  • DualSpringRateCalc.PNG
    DualSpringRateCalc.PNG
    143.9 KB · Views: 257
  • 44x470-Spring-Rates.png
    44x470-Spring-Rates.png
    210.4 KB · Views: 247
  • Beta Ohlins Fork Spring Chart.jpg
    Beta Ohlins Fork Spring Chart.jpg
    275.4 KB · Views: 628
  • sxf_450.jpg
    sxf_450.jpg
    120.3 KB · Views: 227
And a prototype of this spacer. Works well.
 

Attachments

  • SR_CutSpringGuide1.JPG
    SR_CutSpringGuide1.JPG
    458.4 KB · Views: 238
  • SR_CutSpringGuide2.JPG
    SR_CutSpringGuide2.JPG
    460.4 KB · Views: 245
  • SR_CutSpringGuide3.JPG
    SR_CutSpringGuide3.JPG
    463.8 KB · Views: 242
  • SR250_CutSpringEnd.JPG
    SR250_CutSpringEnd.JPG
    248 KB · Views: 233
  • SR250_CutSpringGuide.JPG
    SR250_CutSpringGuide.JPG
    242.8 KB · Views: 244
Back
Top Bottom