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Yammy XS250 Breat Style Project

Discussion in 'Modifications and Projects' started by jayray, Nov 23, 2010.

  1. I have been wanting to post my progress on my bike project for some time, so im going to summarise what has been accomplished thus far and then document its progress until completion……

    I have always wanted to start a project bike, both out of a love for customised café racers and the new breed of Jap brat style bikes. I would also like to ride South America for 3-6 months and a reasonable knowledge of bike maintenance will be necessary. But having absolutely no knowledge about mechanics it remained a dream for many years. But a chance meeting with a fellow Fitzroy local 12 months ago has made this dream a reality.

    Enter Big Chris, a 6ft 6 Scotsman who has been working on bikes for 20 years. He was prepared to devote time to impart his knowledge of bike mechanics and rebuilding. And lets face it, two blokes having a few beers in the mancave working on and talking bikes is time well spent.

    We bought this little baby on eBay, a 1981 Yamaha XS250. While requiring a bit of work to get it registered and roadworthy, it was in reasonable running order and the perfect platform to build a little inner city Jap Brat style runabout…


    And this is our inspiration….

  2. All it needed was a basic service and new battery, brake pads and brake fluid. A RWC and Vicroads inspection later and it was street legal!

    Next on the agenda was to replace the clutch plates and springs as it was slipping at high revs. There was also a fine mist of oil coming from the head that would need to be looked at.

    I ordered the clutch plates and springs from http://www.wemoto.com/ in the UK.
  3. here's mine.

    i still need to get rid of the hidious seat and fix the rear end, basically wanted a brat/rat commuter. engines a bit ****ed atm, but for around town its fine.

  4. my old man got me 1 in 1980 ? loved it rode it every where
  5. LoL I had one.. 10 years ago... I think I have some pics.. I made a cafe racer out of it...
  6. Nice one shady_knife, ive also got some black wrap ready for the exhaust. A new seat and a tidy rear end will make a huge difference. Let me know how you go.
  7. The replacement of the clutch plates and springs was a relatively straight forward process and made a huge difference to the drive of the bike. It now pulls away strongly in every gear.

    This was my first real mechanical work on the bike. I was surprised at how easy this task was and that working on a bike isnt exactly "brain surgery". That said many lessons were learnt, such as the importance of a clear workspace and ensuring that all parts removed are put into plasstic containers and labeled if necessary.

    A copy of the Haynes XS250 manual whch clearly steps though the procedure.

    The fitted clutch plates.

    Big Chris gets artistic and creates a template to store all of the bolts from the clutch cover. This ensures the bolts are all returned tio their original holes. Its this kind of methoical approach to dismantling the bike that I have found invaluable.
  8. Next job was to remove the cover and head.

    The rocker cover off, exposing the valves, cam shaft and chain.

    cover off.

    We inspected the pistons for wear and sideways movement, all looked to be in good order so we covered the bottom end in plastic to keep it free of dust ready for reasembly.

    cover on bottom end.

    Attached Files:

  9. Next job was to remove the valve springs so that we could re-seat the valves and replace the valve stem oil seals. After two failed attempts with crappy valve spring compressors, one even bought back from the UK that failed to do the job, Big Chris found a nice heavy duty MADE IN ENGLAND compressor at Modak Motorcycles in the Melbourne CBD which did the job beautifully. Careful not to lose the split collets, we had one fly across the room that took 30mins to find!

    Nice bit of kit, a spark plug welded to a metal tube allowing the head to be held securely in a vice. Talk about making the job a whole lot easier!!

  10. By using grinding paste and a piece of glass we gave the gasket face a new flat surface. Unfortunately there was a small nick in the gasket face that could cause us problems retaining good comprssion so Big Chris advised that we have a copper gasket fabricated. I found a metal works who were happy to do this small job.

    nick in head.

  11. So when is a XS250 not a 250? When its a 400.. WTF??!!

    We fitted the copper gasket on the cylinder block to ensure it was accurately cut to size. It slipped perfectly over the dowel pins and lay to rest, but something wasnt right. The bore holes in the gasket were not big enough, and considering that all of the measurements were taken from a new Yammy 250 gasket we couldnt have got it wrong.

    We looked at each other dumbfounded. The bike had been previously bored out to a 400 but refitted with a 250 head!!! Needless to say we high fived and celebrated over a few beers!!! The 250 project had suddenly taken a whole new direction. God damn we had spent a lot of time refurbishing that 250 head but it doesnt matter, we are damn excited about our 400!!

    So we are now looking for a 400 head and cover...can anyone help???

  12. Nice man, looks good btw, ebay or look for wreckers for the head, good luck!
  13. Your manual covers the 250, 360 and 400, does it list different valve sizes for the diffferent size engines?
    If it ran OK before with the 250 head, why not keep it?
    I pretty sure they all use the same stroke and only differ in bore size. Its likely someone replaced the original cylinders with 400 ones rather than bored the originals. If the heads are different, its likely the 250 head would have smaller valves, and would probably give a slightly higher compression ratio than a 400 head. If so, your performance with the current set-up would be between the 250 and 400 (probably closer to the 400). The higher compression may mean you need to use premium fuel to prevent detonation.
    Good luck with it!
  14. The manual doesnt list different valve sizes, but ive been told that the 400 has bigger valves and a bigger combustion chamber. The manual does however state that the valve timing is different for the 400 and keeps the valves open longer. To me this all adds up to more horses, so why not maximise the engines potential?!
    That said if I cant find a 400 head soon ill just put the 250 back on and get the bike up and running again.

    Cheers for the premium fuel tip!
  15. well I found a 400 head! There was an XS250 engine being sold on Ebay and at the end of the description it stated the sale included a box of 400 parts. And yep, it included a complete 400 head! What a rare find, 6 months of daily searches on ebay in Australia not a 400 head in sight. There are plenty on Ebay USA but their 400 freatured rounded fins that wouldnt match my 400 cylinder block.
    I have since found NOS 400 valves on Ebay USA and seated them into the 400 head.
  16. If the manual tells you the valves are open longer on the 400 it means the camshaft is different as well..
  17. It's unusual to buy a new head and not get the camshaft with it. Looks good by the way.
  18. Yep, good point, ive got the 400 camshaft to suit the different valve timing.....
  19. Good news! The only downside is that the 400 and 250 are in the same price bracket for rego now, so you won't have cheap rego on a more powerful bike!
    Given that, it might be worth changing the rego to show that its a 400, to avoid any insurance hassles should it be involved in an accident, although if the engine cases are the original 250 ones its very unlikely to be discovered.
    Downside of making the change official is that the RTA might want an engineers certificate as you're fitting a larger engine (even though we know the 250 and 400 used the same cycle parts).