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Author Topic: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp  (Read 45762 times)


Offline JadusMotorcycleParts

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #351 on: Jul 15, 2019, 06:26:40 »
Interested in performance/operation comparison of front disk on "daily rider" vs front drum brake. I assume its from a Virago (or maybe just a newer SR250 that did not come to the USA)?

The front end is standard on the later model SR's - which were only manufactured in the Spanish Yamaha factory.  This fork and disc brake is on models from '95 onward.

I find the disc marginally better than a well dialed in drum.  That is because I hardly ride hard enough on twisty enough roads to experience fade, which is where the disc would out perform the drum.  Bite is of coarse a little better with the disc as well.  The lackluster performance is also because it is a single pot set up.  This could probably be improved a lot with better pads, a better disc or upgrade to a twin pot set up.

Offline JadusMotorcycleParts

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #352 on: Jul 25, 2019, 07:51:00 »
Bit the bullet and got this done...  Pretty cool!  105g out of the rear axle and 73g out of the front  ;D

Offline crazypj

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #353 on: Jul 25, 2019, 20:34:25 »
Drilling axles is hard work because they are tough and long.  The originals are massively overbuilt. Very long time ago( 1974 maybe?)  I asked an engineer what kind of shear load they would take. Anyway, he did all the calculations and  5/8" axle in my Royal Enfield 'Continental GT' 250 was over 100 tons (Britain's first 100mph 250cc four-stroke)  100g is about 4 ounces?
« Last Edit: Jul 25, 2019, 20:36:03 by crazypj »
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Offline JadusMotorcycleParts

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #354 on: Jul 29, 2019, 03:20:20 »
Exactly.  The machine shop actually had to EDM them, which is very time consuming.  But yepp, 100g is about 3,5 ounces.  These are still well over dimensioned for the job!

Offline Sav0r

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #355 on: Jul 29, 2019, 12:39:35 »
That's awesome! When I center drilled my axles I started with a standard jobber bit and then moved onto a very small boring bar. It was tedious work, especially considering I had already machined the axles by hand, so screwing up was not something I was too keen on. I didn't have the tooling to get all the way through the axle, so the threaded end is still solid, which is fine because it's the small OD. EDM is amazing technology, I wish I had thought of it when I doing my axles. I considered buying some tube and then threading both ends, not sure how that would have worked exactly but it may have been easier than doing what I did in the long run. Then again, paying for some EDM would have been easier too.
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Offline doc_rot

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #356 on: Jul 31, 2019, 11:57:04 »
would it be more cost effective to find a axle from a sport bike and retro fit it to your application? I have done it a couple times with axles and pivots now. Works well and is cheap.

Offline crazypj

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #357 on: Jul 31, 2019, 16:55:52 »
Majority of sport bike axles are much larger diameter. I'm guessing the SR250 has 17mm front axle and 20mm rear? Could probably find a swing arm pivot bolt to fit but it would need cutting and threading. I think Suzuki used 17mm 'gun drilled' on early GSX-R? Not too familiar with other brands so couldn't make a recommendation
'you can take my word for it or argue until you find out I'm right'
Best thing I ever overheard
"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
XS650,  http://www.dotheton.com/forum/index.php?topic=11922.0

Offline JadusMotorcycleParts

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #358 on: Aug 01, 2019, 03:30:32 »
I think if you were to machine these yourself, you would be best to start with chromoly tube first and then thread the ends - like Sav0r suggested.  Drilling these would not really be possible with home equipment.  A bit like the internal engine component I took to a machine shop to 'turn down'.  They couldn't because of it's hardness and had to grind it down instead.  Can you grind drill?  I dunno but I am very familiar with EDM - I have visited many tool making shops and it is standard affair there.  My day job involves designing a lot of injection molded and dies-cast parts - where they machine up an electrode male/plug and 'plunge' that into the metal of the tooling to make the cavities.  Plus they can do EDM drilling in all sorts of materials down to 100th's of a millimeter, amazing stuff.

I think if you have the equipment and the skills (I don't have either), it wouldn't be so hard to adapt sports bike axles - there is plenty of meat in the forks to bore up to a bigger axle.  Same with the swingarm.  Then you would need new bearings and wheel spacers to suit but they must exist.

Offline JadusMotorcycleParts

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #359 on: Aug 01, 2019, 06:30:53 »
I finally got the dent pulling tool in the post this week.  The bracket that holds the support pads was not quite wide enough for the large dent I needed to pull, so I modified it a little to be able to spread them right to the edge.

Long story short, it worked surprisingly well!  I would highly recommend trying something like this if you yourself have a dent in your tank of this nature.  The first pull did the most work, then things were a little uneven - see red circles I marked out.  So I did a few more pulls with different sized pads in different positions.  It only got marginally better and I think this process is limited in terms of how even you can get sheet metal.  I imagine with modern plastic panels in cars for example the panels would just 'pop' back out.  Anyway, I think it is the best it'll get and the most important thing is...  I am satisfied and I get to keep the cool paint job without destroying it's charm  8)

The hardest thing was getting the hot melt glue off afterwards without damaging the paint.  I used a plastic 'spudger' from Ifixit (from my Mac repairing days).  It was brilliant - a hard and stiff enough plastic that you can scrape with, but soft enough not to gouge the paint.