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Author Topic: Yamaha SR250 - A clean standard build  (Read 91592 times)

Offline JadusMotorcycleParts

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Yamaha SR250 - A clean standard build
« on: Jun 22, 2015, 05:50:20 »
Hi all,

New to the forum but not so new to building bikes.  I hope to post some projects I have worked on over the years to share some knowledge and experiences - after all I have gained a lot of insight from people posting their own projects on various forums.

This thread will hopefully be mainly focused on a build I am working on now - a 1983 Yamaha SR250.  There are and have been many conversions of this particular bike - I have seen SR250 cafe racers, bobbers, trackers etc, but I am hoping to throw in a couple of original things and am developing parts for sale for it along the way.  The aim/direction is to build a bike that does not conform to any particular style/genre, but rather take cues from many and to create something that looks clean and almost standard in some ways.  I am not a huge fan of extravagant overly worked customs with wacky paint jobs.  Each to his own of coarse!

Hoping to gain and share information and skills working on this bike :)

Offline JadusMotorcycleParts

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Re: Yamaha SR250 - A clean standard
« Reply #1 on: Jun 22, 2015, 05:54:12 »
The original bike was in pretty decent condition.  Almost a shame to cut it up... except for the fact that these bikes are unapologetically ugly in standard trim!

Offline JadusMotorcycleParts

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Re: Yamaha SR250 - A clean standard
« Reply #2 on: Jun 22, 2015, 05:57:22 »
Investigating a possible seat form and seeing what some tear-drop style handle bars would look like (got a 3D printer at home  ;D)

Offline JadusMotorcycleParts

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Re: Yamaha SR250 - A clean standard
« Reply #3 on: Jun 22, 2015, 06:09:43 »
Working on lowering the tank to achieve a better line with the frame rails.  Plus looking at how the seat base could be made without removing the stock mudguards that i like.  To remove the original tank mounts, just punch a hole right in the middle of each of the 3 spot welds and drill until the weld is removed - but don't drill through the entire sheet metal thickness.  The mounts should then just pull off with some pliers or something.

Offline JadusMotorcycleParts

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Re: Yamaha SR250 - A clean standard
« Reply #4 on: Jun 22, 2015, 06:54:40 »
Buying resources of inspiration...  This is a goodn'   ;D

Offline JadusMotorcycleParts

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Re: Yamaha SR250 - A clean standard
« Reply #5 on: Jun 22, 2015, 06:56:57 »
Rear frame loop investigation plus another look at above yoke clip-ons.  Also thinking about designing a fork brace for the flimsy 32mm stanchions... 

Offline JadusMotorcycleParts

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Re: Yamaha SR250 - A clean standard
« Reply #6 on: Jun 22, 2015, 07:10:26 »
Investigating the possibility of running 19" dirt track style tyres for a street tracker style look...  Involves measuring the standard spokes and calculating the percentage increase to get from a 16" rim to a 19" rim.  I also did a quick check to see if the rims/tyres would actually fit using a cardboard rim haha.  Turns out it is too tight for my liking and really exaggerates the flimsiness of the front forks - just look at the contrast from front on with the massive 19" tyre.  Looks goofy.  Yes I could do a front fork conversion - I have done one before with a Yamaha DT400:



But I want this bike to be a slightly easier build in terms of avoiding adapting parts from other bikes.

Offline JadusMotorcycleParts

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Re: Yamaha SR250 - A clean standard
« Reply #7 on: Jun 22, 2015, 07:36:34 »
Btw, if anyone has questions about how or why i did a certain thing, please fire away.  I have received so much help from forums over the years and have not really given anything back.  So I hope this can be my chance to give back to the community. 

I got quite a few views on youtube for a SR250 I built 4 years ago when I was a real newb and many people asked for more photos of certain aspects of the bike and if I had documented it online at any time - which I didn't/hadn't.  But this build will be different!  That old bike (which I sold to a friend) can be seen here:




Offline JadusMotorcycleParts

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Re: Yamaha SR250 - A clean standard
« Reply #8 on: Jun 22, 2015, 07:47:16 »
Feels like this project is all over the show but I want to do everything at once!  Looking at a nicer battery box/tray design that fits the battery and electrics plus maybe a relocated ignition...

Offline JadusMotorcycleParts

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Re: Yamaha SR250 - A clean standard
« Reply #9 on: Jun 22, 2015, 08:09:15 »
Fork brace measurements and first prototype...  Plus considering a 16" front wheel conversion instead of the 19" conversion.  This will give a more bobberish look.  I always liked bikes that had even rim diameters much more than ones with odd diameters.  I just think it looks 'right'.  I would also like to integrate the front fender into the brace design - so I can eventually shave the forks  ;D

Offline JadusMotorcycleParts

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Re: Yamaha SR250 - A clean standard
« Reply #10 on: Jun 22, 2015, 08:12:33 »
Back to the drawing board for the brace.  Its one thing to see a sketch of it, then its another thing to print it out in 3D and 'feel' its size and proportions.  And this one was waaay to big and chunky I thought!

Offline JadusMotorcycleParts

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Re: Yamaha SR250 - A clean standard
« Reply #11 on: Jun 22, 2015, 08:20:28 »
Another attempt at the fork brace - this time much thinner and more in proportion.  Plus another attempt at some above yoke clip-ons.  This time in more of a riser bar style.  I like these a lot more.

Offline JadusMotorcycleParts

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Yamaha SR250 Exhaust header
« Reply #12 on: Jun 23, 2015, 04:08:31 »
Designed and printed (in pieces) an exhaust headers.  I like the style of header with sharper lines and tighter curves rather than the vincent style swooping bends.  So I tried to match the angles of the frame/engine so it looked right.  Has anyone ever used an exhaust header calculator?  I tried a few but ended up liking this one the best:  http://www.mezporting.com/exhaust_length.html

I also bought and tried reading Philip H. Smiths 'Scientific Design of Exhaust and Intake Systems' but it was just too heavy for me.  Most of the principles I understood but I got caught up in all the thousands of possible variables.

Offline JadusMotorcycleParts

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Yamaha SR250 battery tray
« Reply #13 on: Jun 23, 2015, 04:15:51 »
Seeing how the design fits everything in.  Not too sure about the ignition location...

Offline JadusMotorcycleParts

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Yamaha SR250 custom seat
« Reply #14 on: Jun 23, 2015, 04:28:20 »
Thought it was about time I figured out what I will do about the seat - for me the key to success for the SR250.  The real make or break.  No better way than to sketch up some ideas and print them out and test them!  Only had time to test the fit for the base of the seat and the mechanical attachment mechanism.  I decided I don't like the new trend of 'lush' plaid, pleated or diamond pattern seats...  I will go for something cleaner - a bit like Roland Sands seat designs for the modern Triumph Bonnevilles maybe  ;D 8)