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Aprilia RS125 - Costly Lessons

Discussion in 'Modifications and Projects' started by Disco Spider, Apr 12, 2013.

  1. To anyone who kept tabs on my story, I bought an Aprilia, which turned out to an "Economical Write-Off", well, after riding my bike home FROM the VIV inspection, she seized!

    The only thing different about this ride was the spark-plug, I went from an NGK BR-8EG to an NGK BR-10ES.

    It's the plug everybody recommends, but is it really the best?
    For Melbourne?

    My mechanic was shocked, and in his eyes he definitely believes that the BR-10's would only really help out if you're revving it to it's limits, and holding it there, for a decent amount of time.

    Any way, I'll be posting up picture of my work, and rebuild. Right now I've already got all my spares and am preparing for my big build day tomorrow, fingers crossed it's good weather!

    Also, I'm mounting a TYGA Stainless Steel exhaust with the engine rebuild, do you guys think I should re-jet the carb?
  2. Sell it and buy one that hasnt been ruined by the previous owner. be as unscrupulous as the last guy that you bought it off.
  3. so the ...10 is a colder sparkplug than the ...8 and you seized your motor using it on the road???

    I don't know your history with the bike, but I reckon this problem would involve it's history.
  4. You don't say why it seized...
    • was it over revved,
    • was it a badly adjusted or failed oil pump,
    • Was it poor quality 2 stroke oil
    • was it a new and tight top end which had not yet been properly run in,
    • did you use std 91 unleaded in it instead of 95 or 98

    The standard plug for the Rotax type 122 engine used in the Aprilia is NGK R BR10EG...
    The number is the heat range. Bigger the number, the colder the plug.
    The heat range to use is a fine balance between too hot ( preignition, ie. piston damage) and too cold ( wet fouling ). A fouled plug is easier to deal with, than a hole burnt in the top of the piston.
    ES is a standard type plug

    EG is a racing type plug with thin platinum centre electrode.
    More information....http://www.ngk.com.au/spark-plugs/product-information/part-numbering-system

    Changing the exhaust may require the carb to be adjusted or re jetted. "As a general rule of thumb" at the very least go up 1 size in the main jet.
    ( assuming that you have not modified the intake or airbox ).

    If you don't properly understand 2 stroke tuning, my best advice is to seek the help of a knowledgeable tuner. 'Road going' tuning will always be a compromise between performance and allowing for the full range of atmospheric variables.

    1 last note for you...tuning starts during the rebuild...make sure you set the squish clearance carefully and accurately. ( that's why your gasket kit has a number of different thickness cylinder base gaskets )
  5. Thanks for the replies, and it was completely my fault, I revved it too hard and it seized.

    Mechanic was saying even though it appeared to be hot enough, once I started riding, coolant would be pumped in and rapidly cool the cylinder, but not the piston, and that's my story.

    I bought and am installing a Mitaka Top-End rebuild from PJME, but I found (after bloody putting everything back together first) that the top engine brace (black contoured metal piece with two mounts for a single bolt to go through to hold the motor) doesn't fit on the Mitaka cylinder.

    Does anybody have any experience with this?

    Was actually going to fire it up tonight.. :'(

    @Mike: I have around ~2ml of squish right now, is that fine for this motor?
  6. #6 mike8863, Apr 15, 2013
    Last edited: Apr 15, 2013

    Having recently done a full rebuild on the same type of engine using the same aftermarket parts (Mitaka), I had no such problem with the upper engine mount....trick may be to install the engine with the mounting bolts loose until they are all installed, then torque to spec.

    Did you just replace with standard size or the 150cc big bore kit???

    2mm clearance is a bit larger than spec...

    The engine manual is 11.5mb. If you need it and your email can handle that large a file, PM me and I'll email it to you.
  7. What he said above x 10. I'd make damn sure I was confident of why it seized before rebuilding it and thumbing the starter. A good guess/assumption won't cut it.
  8. #8 Disco Spider, Apr 30, 2013
    Last edited: Apr 30, 2013
    For the record, seizure was entirely my fault (over-revved + too cold)

    The top engine mount must've been poor quality control on mitaka's end, just filed it out a bit and it fitted nicely/filed it out a lot.

    Have finished rebuild and breaking in, looking into getting it jetted properly, it just feels wrong from 8500 rpm and up.. ?
  9. #9 mike8863, Apr 30, 2013
    Last edited: Apr 30, 2013
    a125_hirpm_running_fault. Is the power valve connected and working properly ?
  10. These engines loves it when you rev it hard and rev it hard often :).........