Thunderbird Sport Gearing.

Discussion in 'Thunderbird' started by Godders, Jun 21, 2019.

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  1. Godders

    Godders Well-Known Member

    Apr 29, 2019
    118
    83
    Keith
    I don’t know if a previous owner altered the sprockets on my bike and made it low geared but I don’t particularly like a bike revving it’s nuts off on cruise.
    Mine is at 4250 rpm at 60mph and 7000 rpm at around a 100 mph, with only Bout a 1000 revs to go. I’d be happier if the revs were down to 3000 for 60 mph to give a less revvy 80 mph cruising speed. Is my bikes present gearing normal? Has anyone gone up a tooth at the gearbox? My wheel sprocket looks about as small as I could go, so I’m thinking a dodge might be trying to get away with changing the smaller sprocket with one a tooth bigger while retaining the present chain and wheel sprocket.
    Anyone else done this?
     
  2. freck

    freck Noble Member
    Subscriber

    May 4, 2017
    856
    450
    Preston, Lancs, UK
    • Like Like x 1
  3. Godders

    Godders Well-Known Member

    Apr 29, 2019
    118
    83
    Keith
    Cheers. Just looked on eBay for the front sprockets and see they range from 16 teeth to 20. Mine is probably a 16 tooth one, so I’ll be going for a 18 or 19.
     
  4. freck

    freck Noble Member
    Subscriber

    May 4, 2017
    856
    450
    Preston, Lancs, UK
    Just be careful, if you go up too many teeth you’ll be needing a new chain too :confused:
     
  5. Godders

    Godders Well-Known Member

    Apr 29, 2019
    118
    83
    Keith
    Yes understood. It looks like there's a good inch of rearward rear wheel movement on the adjusters, and the chain and sprockets are all good. So for a £20 counter sprocket it looks like a possibility even I need to rivet in some additional chain.

    It is also quite hungry on fuel so this might not only save on the buzziness but save a bit at the pumps.
     
  6. Godders

    Godders Well-Known Member

    Apr 29, 2019
    118
    83
    Keith
    Well that’s a crap design! After carefully removing the 8 mm headed bolts and gear change, and seeing engine/gear oil leaking out, it obviously involves changing the oil again. Just done that 200 miles ago so won’t be bothering with that for a few thousand miles.
    A bit of a bugger just to confirm how many teeth are on the counter sprocket in order to buy one with a tooth or two extra.
     
  7. Godders

    Godders Well-Known Member

    Apr 29, 2019
    118
    83
    Keith
    B295DE15-8B7F-4032-9805-D4B3DADCCEC2.jpeg
    Well I got sick of the bike buzzing away almost flat out at 100 and at over 4000rpm at 60 mph so I laid the machine over on a post to save my new oil pissing out and changed it.
    It was a 17 toothed counter sprocket and I’ve changed it for a 19 toothed one.
    Haven’t had it out on the road since the change but even going down the driveway it doesn’t need an up change. Perfect!
    I can see why the gear change rod needs the support of a needle roller bearing as it comes from the R/H/S of the bike, but to need to lubricate it with engine oil seems a little excessive, when greasing it occasionally would have been more than adequate
     
    • Like Like x 1
  8. Godders

    Godders Well-Known Member

    Apr 29, 2019
    118
    83
    Keith
    Done a couple of hundred miles now and what an improvement. 1000 rpm less for the same speed as previously. I can only assume the previous owner rode and lived in town and didn't bother with going any distance on it.
     
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