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Thread: 851 SP3 replica project.

  1. #21
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    And this is the frame before...



    ...during (sandblasted)...



    ...and after



    It's been really a perfect job and I like the look after having removed the helmet lug.

  2. #22
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    Cool, keep up the good work

  3. #23
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    Love it when the bits start coming back all shiny and better then new!
    Ducati's 851, 888, Bimota's Db2, Db5, Honda blades 93 /96, Triumph speed triple, Zxr 750K1, Zx7rr

  4. #24
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    And now it's time to start with the engine!!!



    This is a 996 from a ST4s. I've removed heads, cylinders and pistons and I've checked that almost everything inside is in perfect condition.

    Once everything has been checked, I clean soot in the pistons and get them in the barrels to start assembly.


    Piston in the barrel...


    ...ready to fit on the engine.

    Once this has been done, I take the squish measurement to get it in a more suitable 0,9-1,0 mm to get a bit more of power out of the engine.


    I need 0,2 mm cylinder base gaskets.

    Next step are heads. I'm going to overhaul them in order to get that nice bit more from them with the small details than make the difference.

    The "Testabassa" heads from the engine are going to be replaced by regular 996 heads for something most of you know, which are exhaust ports of the first one.


    "Testabassa" (left) and 996 regular head (right). The exhaust port is not really good in "Testabassas". This design was no evolution but simply a front wheel clearance issue when the ST4s was designed.

    No I take my superb "made in china rotary tool, adapter and steel brushes (the last one the really good dremel originals) and remove soot from the combustion chamber.


    I got the head like this.
    Last edited by BARONROJO; 03-15-2014 at 04:43 PM.

  5. #25
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    But with a little patience...


    ...it starts improving.


    Exhaust valve as extracted...




    ...and once having been cleaned.


    It takes a while but gets a good result.

    And now a little cute detail: grinding of the valve seat edges in contact with the ports.


    This part is really sharp.


    I grind them...


    And them a proper finish with emery paper and a final smoothing with the rotary tool steel brush.

    And finally valve grinding a a slight milling @ 75º of the inner side of the valve seats as I had 0,2 mm of space to do so.


    Valve grinding.

    By the way: I still need a 996 head. I bought one but it's beyond reparation and I'll use just for some spares. If someone has one on the shelf I'd be please to get it...

  6. #26
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    great post, great to see your work.
    thanks
    Ian
    1988 851 tricolore strada, 1981 Mike Hailwood Replica, 1996 Bimota DB2 tricolore, 1988 Bimota YB4e.i, 1968 Gitan Grillo sport, 1992 Yamaha GTS1000, 2006 Honda Deauville, 1990 Honda GB500 Clubman
    http://thecrankcase.com/

  7. #27
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    skane, Sweden
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    Nice too see and read about your project, serves too inspire the rest of us
    /Jimmi

    Skickat från min MT15i via Tapatalk 2

  8. #28
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    DePere, WI
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    Wow - I wish I had half your skill.....very impressive! I'm chicken to jump into the motor that much!, Frame, wheels, etc. no problem...motor that deep problem

  9. #29
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    Nice pic's and work so far chap. Please keep them coming.
    You can really see the difference in the exhaust ports there, the dropped cam ST4/4S heads must strangle the performance.
    At the moment I've got a pairs of NOS 888 Corse, 916SP and a standard 916 head on the bench, the exhaust valve guides on all of them don't protrude into the ports as far the standard 996 head in your pic'.
    The 916SP exhaust ports are the same shape/bore as the 916/996SPS heads I recently worked on, (which would make them the same size shape as the 996 Bip' heads) but the Corse ones are huge in comparison. Probably too big in fact for the standard '91 Corse 34/30mm items so I've fitted 37/32mm valves, as these heads are for my 955cc motor.
    It's probably got to do with things moving on as the Corse heads were made in '91, back then head tuners were going as BIG as they could get, these days it's been proved that smaller well shaped ports will actually flow more gas.
    With the benefit of hindsight I'd should have had my 916SP (cast in '94) heads modified and fitted with the 37/32 valves, the exhaust ports are a far better shape as standard.
    Or start with a blank canvas using some standard Strada/Bip' 888 or 916 heads.

    When you ground back the seats to match the inlets ports, did you go for a nice radius on the bottom of the port?

    Steve R
    Last edited by Mr.R; 03-16-2014 at 08:37 AM. Reason: added question...

  10. #30
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    Yes, I got a very smooth and pleasant rounded surface in that area. I didn't go too far as there's not much room for removing material and I didn't want to weaken the valve seat for later heating in use.

    I also angle milled the seats as far as the contact patch allowed it. I'm not planning to get a race engine but a good working street one, slightly optimized here and there.

    Thank you for your encouragement, pals!!!

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