Featured Speedmaster 865 Carb-new Hc Pistons And 790 Cams

Discussion in 'Builds & Projects' started by Wishbone, May 5, 2019.

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  1. Wishbone

    Wishbone Senior Member

    Nov 4, 2018
    322
    113
    Essex UK
    Sorry for the long post but it all needs to read to get the gist of how my Speedmaster Gained more than a few extra horses.

    Finally got round to getting this Build done and completed.

    For strip and build I used a combination of Pat's Big Bore saga
    http://www.bonnevilleamerica.com/dinqua/Triumph/BigBore/bb1.html
    Triumph service manual and Haynes manual.

    Firstly bought a set of Arias High Compression (10.8:1) 90mm pistons from eBay 6 weeks ago, decided to wait till Easter break to start as my bike is used for commuting.

    While waiting I saw a pair of 790 cams for sale on eBay from a German breaker. So nabbed them also.

    And lastly managed to get an OEM Top End gasket kit off eBay for £20

    So started the strip on first weekend of Easter fortnight, strip went OK other than a tight header pipe.


    Got it all apart cleaned up the main components and set about installing the pistons!

    And that's when the fun started put new rings on the Arias pistons set the ring gaps at the recommended angles, put Pin clips in the inside of each gudgeon pin bore then put pistons in through the bottom of bores ( there is a good taper lead at this end), with piston ring compressor and set them just so there was enough room to slide in the pins and outside clip.

    Or that's what I thought? No amount of pushing swearing and sweating would get the pins in far enough to get the clips in their undercut bore I could barely even see it.
    Took them back out and it was clear there was something not right about either the gudgeon pin length and/or the clip diameter (1.5mm).
    Fired off an email to the eBay seller and to Arias pistons UK explaining my dilemma!!
    Ebay Guy responded next day and essentially told me I was a "tard" and didn't know what I was doing?
    I explained I have been an engineer since the 70's and had worked on 2/4 strokes diesels, V6/V8 Jag engines.
    It went quiet.
    4 days later got a reply from Arias stating that the piston clips I had were too big and should be 1.2mm diameter.
    Long story short I bought some 19mmx1.2mm piston clips and shaved 0.4mm off the gudgeon pin length and re-cut the chamfers at each end.
    Rebuild went smoothly other than dropping a cam cap dowel down the spark plug hole, used all my rags plugging the spaces round the cam chain, didn't think that little spark plug hole could be an issue! but fished it out with a 4mm diameter Laser flexible magnet.

    So buttoned everything up last night filled with mineral oil, left it over night to check for leaks and took it out this morning for a Ring break-in session.

    She started up third prod and left her idling around 2-2.5k for 3-4 mins with an occasional blip to 4k and then jumped aboard and went for a spin.
    I followed the Motoman method of break in, warm up and the ride it like you stole it for 20-30miles took it home after about an hour and it sits on drive with a piece of cardboard underneath to see f she is oil tight.

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  2. Wishbone

    Wishbone Senior Member

    Nov 4, 2018
    322
    113
    Essex UK
    Just remembered the New 790 cams I think from a 2004 had an extra 2mm lift on inlet side and only 0.5mm extra on the Exhaust side.
    Also took the measurements from all shims and positions to make re-shim easier and there were some big gaps when the 790 cams were installed.

    I hope to get her on a dyno once it is all dialled in Carb wise and will update.
     
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  3. capt

    capt Senior Member

    May 8, 2016
    1,343
    250
    western Australia
    Hi Wishbone,
    I did big bore kit with high compression pistons, went from 8.5 to 9.8 on my 2009 America. I kept std camsc as I liked the torque (towing was planned) going for 790 cam's will give you more HP for sure ! I did clean up and port polish, most of the work was inlet side. Kept valves std size too. I had to put up rated heavier clutch springs in, std good for 70ish HP, my clutch started slipping on occasion when towing, so I'm thinking 75/80 HP achieved aftra dyno work.
     
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  4. Wishbone

    Wishbone Senior Member

    Nov 4, 2018
    322
    113
    Essex UK
    Hi capt, good to know;
    I was not bothered about cams until that set cam up for £150 delivered so jumped on them at that price, likewise the pistons at £250 delivered didn't see the sense in big bore if most of the gain on an 865 is in the HC pistons.
    It definately felt spritely when I took her out this morning and expect it to get better over coming weeks as the rings bed in fully.

    I take the better half out couple times a month and the extra hp will help pull us along.
     
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  5. capt

    capt Senior Member

    May 8, 2016
    1,343
    250
    western Australia
    Hi Wishbone,
    The 790 and 865 motor's in std trim put out the same/similar horse power, but the 790 does it at higher rpm's. I've ridden a friend's 790 about 8 years ago now but from memory - mine pulled a little better mid range but not much, the higher compression should improve torque and the cams will give better top end ! So two gains ?? Is your bike EFI ? If so try my mapping posted in "tuneecu" site ! It was for std 865 motor with short pipe's and totally opened intake ( hi flow filter &baffles removed) had it tuned for 'Torque' so smidgen rich (safer) . I rode Northam WA to Bundaberg in QLD, over 7 days ! Towing a 150kg camper trailer , fuel economy was around 17/18 klms/ltr. Solo was 20/21 !!
    Will watch this thread to see where and how you go..

    Cheers capt
     
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  6. Wishbone

    Wishbone Senior Member

    Nov 4, 2018
    322
    113
    Essex UK
    Hi Capt,
    Before engine upgrade was getting 150 ish to a tank before reserve, will monitor in next few weeks once my throttle hand settles
    My speedmaster is last of the Carb ones, I had already added short TOR's, DNA filter, original airbox but opened top and bottom with baffle removed, Stage 1 Igniter and rejet.
    I can feel the difference across the whole range and only done a hundred or so miles, at around 500mls will look to do carb optimisation and sync possibly at dyno.
    Just curious to see what its pulling?

    Joe
     
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