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Author Topic: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp  (Read 45768 times)

Offline crazypj

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #380 on: Aug 20, 2019, 03:14:59 »
I use moly / graphite grease on fork seal 'insides 'You can also get Teflon based greases very easily today .  I wouldn't attempt running without seals, stiction is minimal until you use air pressure in forks instead of springs. Forks will have to be compressed a bit to develop any air pressure which then causes seals to 'grip ' I remember test  riding a Goldwing with S&W air suspension. Almost crashed watching the front and rear pressure gauges moving around between 35 ~ 110 psi as suspension was moving. Worked well though as road didn't fel at all undulating. You could look at mid~late 90's mountain bike forks for air shock idea's, there was a LOT of engineering, information and speculation going on back then plus, they had to be light as possible. If you really wanted to go nuts, a set of modern downhill forks would most likely work but they are very very expensive for good ones, all alloy / titanium construction
« Last Edit: Aug 20, 2019, 03:17:04 by crazypj »
'you can take my word for it or argue until you find out I'm right'
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"yep, PJ's my boss, he taught me everything I know, just didn't teach me everything he knows"
Brian Morgan, 1982

CB360's,  http://www.dotheton.com/forum/index.php?topic=11736.0
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Offline JadusMotorcycleParts

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #381 on: Aug 21, 2019, 12:42:17 »
Good point about the seals crazy.

Fork decision was made a while ago so no air forks and no swaps - this fork is already getting a whole lot of trick treatment.  I was just curious how the Minton mod would work in this case - as it obviously worked very well in the case of the XS650 using larger seals.

Offline JadusMotorcycleParts

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #382 on: Aug 21, 2019, 12:49:49 »
Jumping around here a bit again but I try to tackle jobs that I can complete in the time I know I will have in the workshop - to be as effective with my little time as possible.

So I really wanted to get the engine halves back together with the rebuilt crank.  I cleaned everything up (a lot of crud), cleaned all the mating surfaces, used the suggested Three Bond, which seems to be awesome, then screwed the halves together with the Ti bolts I ordered.

The engine also had a bent gear lever shaft which I swapped out for a spare one I had.  I needed to screw a bracket into the crankcase half to keep it in place while I put the halves back together - frustrating having it all in place then falling out when turning the assembly over (which happened twice haha).

Stoked to have the engine rebuild underway and even the kickstarter installed.  Woohoo!

Offline JadusMotorcycleParts

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #383 on: Aug 27, 2019, 15:43:24 »
While the engine is underway I had a neat idea to make an adapter for the chosen blinkers - so I don't need to fabricate another bracket or drill more holes into the headlight ears.  It will also make for tidy electrics - no visible blinker wires because they go right into the headlight!

After making this first prototype I decided to ditch the hex drive entirely and just have a small spacer type thing instead, so there will be a much cleaner transition from blinker to adapter to headlight ear.

These have now been ordered in aluminium  8)

Offline zap2504

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #384 on: Aug 27, 2019, 16:40:27 »
I guess I'm missing the point of the turn signal adapters. Are they not threaded, hollow mounts? Then they should be able to be used with either a washer on the inside and outside of the headlight bucket (but you need to "play" with the alignment), or a short (just enough material for the ear/headlight bucket) aluminum tube with an ID appropriate for the turn signal stalk and an OD that fits within the ear/headlight bucket hole.

Offline SONIC.

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #385 on: Aug 27, 2019, 17:10:13 »
Yep you lost me there too, just a spacer to get the OD of the stalk on the turn signal up to the size of the hole in the headlight would work fine? Unless it's too short?

Offline irk miller

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #386 on: Aug 27, 2019, 20:50:57 »
Sort of like Sonic suggested, I like to do this on my bikes when I have a bigger hole to fill.  This is for an allen screw, but the concept is basically the same.  In this example, I'm making a mounting screw for a BMW R100/7 headlight.  The hole is much bigger than the head of the screw because BMW uses this location for the keyswitch on one side and then just a bigger flanged washer deal on the other.  I machine the piece to be flanged so that it locks into the headlight ear hole, then allows the allen screw head to be countersunk for a cleaner look.  I could see a similar deal on your bike, but with the blinker stem inset instead of an allen screw.  Unless your signals are weak plastic, there's no reason why they can't double as your headlight mounting screw.  Is that why you're doing the double screw thing?


Offline JadusMotorcycleParts

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #387 on: Aug 28, 2019, 03:20:37 »
That looks great irk!

Sorry I was not clearer but you're all off track  ;D

The blinkers have a super tiny and weak M6 thread.  Weak because the threaded section is thin because it has the wires running through it.  The threaded section is also too short to extend all the way inside the headlight :( So the spacer is both to increase diameter through the headlight (yes, could have used a spacer tube instead), but also to increase length, but most importantly, to relieve any fixing/mounting stress from that particular thread.  I didn't trust it to hold the whole headlight assembly together.  So now this bolt is internally threaded M6 and externally M8, with neither of the threads overlapping internally - so the is plenty of meat in the adapter where load by the fastening nut is applied - see attached.

Offline JadusMotorcycleParts

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #388 on: Aug 29, 2019, 04:28:47 »
Some photos from Chris today saying the porting is done!  Awesome.

Offline JadusMotorcycleParts

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #389 on: Sep 02, 2019, 06:16:06 »
And here are the beehive springs along with the Ti retainers he has machined up!