2020 - Bonneville T120 - Zero Inlet Valve Clearances!!

Discussion in 'Technical Help' started by Steve T., Nov 27, 2021.

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  1. Steve T.

    Steve T. Active Member

    Dec 6, 2020
    188
    33
    Northern British Columbia
    #1 Steve T., Nov 27, 2021
    Last edited: Nov 27, 2021
    Winter is here so I decided to check the valve clearances etc.. The bike is just over one year old and has 16,600 kms. After the major battle to get the valve cover off I could finally measure the clearances.
    The Exhaust Valve clearances are all in the mid-spec range - so OK.
    However, measuring the Inlet Valves, all four were "tight". So much so, that I couldn't get the skinniest feeler gauges in there! Sure, I rocked the camshaft etc. to ensure the valve was fully closed (i.e. max gap).
    The rocker arm is 100% in contact with the shim - there is zero gap.
    Next, I slowly loosened the rocker arms to try & observe any further movement / extension of the valve spring. It did not appear move any more. Also, when I rplaced the rocker arm and torqued it down it did not appear to move.
    Apart from checking the clearances I also wanted to identify the original shim sizes that were installed.

    Over the (many) years I've done valve shims etc. on many different bikes (new & old) but this is the first time I've ever seen the Inlet Valves with Zero Clearance.
    As many of us know, the inlet clearances tend to be stable and it's usually the Exhaust clearances that change the most.

    My questions:
    1. When calculating the New Shim Size should I use the measured clearance as Zero and also aim for a slightly higher new clearance than the usual mid-point (Inlet Specs are 0.05 to 0.13 mid-point is 0.09mm)
    I attached a new copy of my Calculation Sheet using increased target clearances for the Inlet Valves (can't upload Excel file)

    2. Has anyone else ever seen this issue?

    3. Are Triumph shims the same physical size as, say, Honda or are they uniquely Triumph specific? There is no local Triumph dealer in Northern B.C.

    Bit of a long post but I'd appreciate comments, suggestions....
    Steve T.

    T120 Valves.jpg

    T120 Valves.jpg
     
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  2. Linx

    Linx Well-Known Member

    Mar 14, 2020
    190
    93
    Stratford Upon Avon, UK
    #2 Linx, Nov 27, 2021
    Last edited: Dec 8, 2021
    Hi Steve, Personally I'd use the new shims to adjust the gap to 0.13 on the inlets, presuming the gap is 0 wouldn't worry about the lack of gap. Especially as they didn't seem to be held open. Probably just bedding in. Just as well you checked them though.
     
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  3. Steve T.

    Steve T. Active Member

    Dec 6, 2020
    188
    33
    Northern British Columbia
    New shims arrived today... I'll fit them tomorrow and see what happens!
    BTW - the Triumph shim diameter is 9.5mm and Made in Japan.
    Unfortunately, I cant find my old Honda shims anywhere to a comparison...
     
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  4. Steve T.

    Steve T. Active Member

    Dec 6, 2020
    188
    33
    Northern British Columbia
    New shims (5) are in and clearances are now towards the upper spec.
    The rocker arms are a real pleasure to work with - great design.
    Shame about all the crap that has to be removed and disconnected to get the valve cover off and then put it all back together - nothing difficult, just tedious but far easier than my Honda Africa Twin or Honda Varadero (V-twin DOHC shim under bucket).

    Here's a couple of pics.
    Everything between the frame/spine to the valve cover and radiator cap has to be removed.
    Two bolts allow the rocker arm to be removed and the shims are easily removed with a magnet.

    P.S. She fired up a treat :cool:

    Valves 1.jpg

    Valves 2.jpg

    Valves 3.jpg
     
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  5. Linx

    Linx Well-Known Member

    Mar 14, 2020
    190
    93
    Stratford Upon Avon, UK
    Well done. That looks a nice easy engine to work on once the cover is off. Are you going to check the clearances again next year?
     
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  6. Steve T.

    Steve T. Active Member

    Dec 6, 2020
    188
    33
    Northern British Columbia
    Thanks
    The first time pulling it apart is always the hardest. For sure I'll be in there again next year and it'll be a quick afternoon's work :D.
    Also managed to tidy up some wires for my GPS and running lights (but still a rats nest under the seat :confused:)

    P.S. The shims can be seen sitting on top of the valve springs in the last photo above
     
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