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Thread: 851/926 race mongrel

  1. #1
    Join Date
    Apr 2013
    Location
    Perth, Australia
    Posts
    95

    Default 851/926 race mongrel

    I'm a bit iffy about doing this, my project is very much "girl next door" compared to most of the "super models" that seem to grace these pages, but it has been a big week for my slow burn project: she lives!

    It was most unexpected to tell the truth, kinda like that girl next door you've always quietly fancied sneaking up and giving you a kiss before you've realised what's happening.

    I'd bought the ol' girl as a virtually bog stock 851 Strada with the aim of giving it a quick tickle up for some classic racing.....of course the gods had other plans contrary to my mere mortal wishes with a relocation from New Zealand to Oz, an old orchard property to rehabilitate, my 749R shitting itself and ongoing associated dramas.....and before you know it 4 years have gone by since I'd last heard the lazy throb from the stock exhaust.

    Not to mention somewhere along the way I took a wrong turn and went from just cutting the top off the airbox lid and looking to lop off a bit of weight to....to....aaah, I dunno what you call it, or how I got here! But a few bits and bobs are:

    Corsa crank cases
    Corsa copy carbon intake and 1 piece airbox
    96mm Pistal pistons/SP barrels (926cc)
    Balanced 851 crank
    H-beam Pankl Ti rods
    Nichol's lightweight flywheel
    748R heads, inc cams, unshrouded valves*
    748R CR gearbox
    Alloy subframe
    Mag marchesini's
    P8 ecu
    FG9051 front end
    FBF slipper clutch
    Braced frame a la Bob Brown's carb'd 851 from back in the day
    "Aesthetically challenged" 45mm single exhaust system **
    etc

    I'd filled it with fluids a few weeks ago, turned it over with the plugs out to prime the oil system, oil pressure light goes out, so all good. The forks were away for some Racetech valves and new seals at the time so she didn't really look in great shape. But I got the forks back last week, fitted them, faffed around with a few other little jobs and all of a sudden it looked like a proper bike again.

    Hmmm, I wonder if she's got some spark? After "racefying" the loom, struggling to make sense of the pic's I took during disassembly when reinstalling the loom, I was already thinking about the fault finding process.....when the old Iridium plug I'd chucked in threw a nice fat fire-lighter. Hmmm, that was unexpected!

    A mate in NZ was after some pic's of the bike so I thought it would be a good time to put the tank on and take an up to date snap. Might as well connect it up rather than just sit it there, eh? Then I remembered the fuel pump hadn't primed when I first installed the P8 a few years ago. With so much work ahead I hadn't really worried about it at the time, but now I gave the switch a tentative flick and bugger me if it didn't whine away quite merrily.

    At that point I realised if we have spark...and fuel...and the suck/squeeze of turning over, theoretically it could run....I mean, purely theoretically speaking. Suddenly I found myself scrambling about for some gas and putting the plugs in, then with a deep breathe....hit the button again.....

    ......but the new found compression of 96mm HC pistons, small chamber 748R heads, were too much for the Shorai lithium battery which barely turned it over.

    A bit more scrambling about and I'd pinched the (new) battery I'd just put in our lil' tow behind self powered slasher for a few more CCA's. Bracing for more disappointment I pressed the button.......

    ....rrrr rrrr rrrr BOOM! she burst into life and settled straight into an idle Brad Black would be proud of. The chip in the ECU is (I think) an old 916SP chip that has been lying around my various sheds for the last 10 years. Surely it'll pop and fart with a bit of throttle though eh? Nup, it just sounds angry! The exhaust won't win any beauty contests but it sure sounds good, lol. With a heap of rotating mass removed gone is the lazy slow to rev 851-ness (if that makes sense) and it has a quick bark much more like my 749R.

    If you don't mind looking at the grubby arse of my overalls, and listening to the crap sound from my phone, I couldn't resist taking a quick vid and posted it here: https://youtu.be/TTKEIgTVN_w

    Sorry, the phone has done a crap job of capturing the sound, it sounds pretty wimpy here, when it actually sounded great in the shed (converted cool room, hence the cave like look)

    There were a couple of issues though: the temperature gauge has gone AWOL, now sitting at 3 o'clock even with the ignition off, and I came back the next day to find a small pool of fuel on the floor from a pin hole leak in the alloy tank. The leak was an easy repair but in handling the tank the fuel sender/pump wiring has given up the ghost and snapped off at the base of the sender unit. Not such an easy fix but fingers crossed it's do-able without forking out for a new sender unit which seem to be pretty salty in price.

    Oh yeah, you'll have to excuse the drip "tray", the horizontal cylinder exhaust valve inspection cover has a tiny crack that seeps oil, a replacement is on its way.

    * why the asterix at the 748R heads listed above? By the class rules all major castings are supposed to be from the era (1 Jan '83 to 31 Dec '90), which the 748R heads clearly aren't. BUT, I think I have pretty legitimate claim to them being Corsa replica heads (replica parts are allowed) as all desmoquattro heads with the small stud spacing pre-996 are much the same save for valve sizes and combustion chamber which are allowed to be modified. I mean I could fit the 748R cams/valves etc to the 851 heads, skim them, and achieve exactly the same thing, it would just cost more money, so my intent is not to gain any advantage or go outside the book....but time will tell I guess.

    ** this exhaust isn't ideal but it is cost effective at this point until I can find something better at a reasonable price. All the same I'm interested in seeing how it performs on the dyno.
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    Last edited by seven4nineR; 07-20-2017 at 01:48 PM.

  2. #2
    Join Date
    Oct 2013
    Location
    Belgium
    Posts
    679

    Default

    You,ve got some nice parts on that project. Keep the photos and the news coming. HP at the back wheel ????.

  3. #3
    Join Date
    Aug 2007
    Location
    Cornwall S.W. England
    Posts
    5,067

    Default

    I'm following this thread with great interest, it's somewhat similar to my ever ongoing project.
    Far more interesting than reading about slotting in a 1098 etc into a 851/888.
    Can't wait to find out how much power it kicks outs.

    On another note I think you need a bigger bore header system to realise the full potential of your motor.
    IME a 50mm header system really unleashes the power from a tuned Desmoquatro motor.

    Steve R

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