G: Gearbox (Twin) Gearing - Series ‘C’ Black Shadow

Bill Thomas

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By overdrive, I mean it should not be able to pull top gear at 5,800 rev's, Unless the Engine is Tuned.
The Comet is like this also, ie Over Geared.
I have pulled 6,500 rev's on a Road Twin on Standard Gearing, On an Airfield, But lots of Tuning !.
Also I can do 40 in Top Gear with 36mm Dellorto Carb's. Cheers Bill.
 

Chris Launders

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In the 60s there was a Shadow owner lived near me in S. Yorks and he worked in Dagenham I was told during the week, he'd swap to sidecar gearing when he got home, changing it back to solo to go to work. Once saw him in what must have been frustration with a crawling bus give it a fist full in first passing it, and had the front wheel up through 2nd and 3rd !!
 

Bill Thomas

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Hello Tim, I have been having a read up, Not like me !.
With the high first gear, 55 mph = 5,000 rev's.
With the low first gear, 44 mph = 5,000 rev's.
So you can see, If you have the high one 27.5 mph = 2,500 rev's, That's near to your 30 mph ?.
I think a twin should run nice at about 2,000 rev's, or lower ?, Which comes back to I think the Carb's or ign' are not spot on, As Albervin says, A lot of people put a 48 rear sprocket on, Which is cheap and easy to do.
Cheers Bill.
 

TouringGodet

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Even with the lower first gear, when pulling away from a signal, behind a car, I find that the small lurch in speed when the clutch is just fully home seems to coincide with the car in front slowing down because they are already pulling in their clutch to shift into second.
 

deejay499

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Pulling away from Marcus's place with high first gearing was almost like riding a two stroke. On the road though it is just fine. It would be an utter bastard in a hilly town with stop signs and traffic lights though. Agree that the ATD should be checked as it could be sticking or just lazy. You do say it has STOCK sprockets Tim. Are you sure?

Hi Alyn. Imagine what it was like with a high bottom gear, standard on my ‘51 Shadow, with a sidecar, family, plus pulling a trailer at times. It was certainly ‘interesting’ pulling away from the lights! Soon swapped for a standard bottom gear. Sidecar rear sprocket of course.
 
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Kiwi_Tim

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Thanks for the feedback, Not totally sure what the motor spec is and there are some interesting but unsubstantiated rumors about that I hope to have some better insight into soon. It was apparently a detuned race motor prior to the 80's so runs 32mm mk1 amals, 2x front heads, KVFTT magneto. quite likely the race cam, but not hi comp pistons.
It has developed a nasty oil burning problem that is going to necessitate a top end strip shortly.
The back story for the bike that seems quite plausible given a number of parts on the bike... is that the box was ex lightning type (CR perhaps?). While I did mention top being a bit of an overdrive, the gears do all seem quite close and all tall. I do intend to get another club member to give me their opinion once I've resolved my inpromptu smokescreen issue.
 

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Bill Thomas

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Hello Tim, As I have said, My Engines are L/ning spec, So should still be better than your results.
A Standard Engine, Should run much slower at tick over !!, To hear a Comet running So slow, I have always found Amazing !!, Never had it myself because my Comet is Flash Spec'.
An oiled plug = Misfire , Could give your problem ?, Slow running.
Some of us have had trouble with NGK Plugs, I have gone over to Champion N5 or N9y, With about 20 thou gaps.
If redoing the Heads, With (Mk2 Cams), Have a read up on Valve Guides, The book tells us to take a bit off the top of the lower Valve Guides, Because of the higher lift. Good Luck, Bill.
 
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