5 Speed Gearbox

Black Flash

Well Known and Active Forum User
VOC Member
altered gearing

Hello Tom, I feel I have to answer your post concerning the altered gearing.
First off all I fully appreciate your opinion, 5 or even 6 gears is much better than 4 gears, there is nothing to discuss about!
but I also think that comparing a highly tuned Manx Norton raced in eager to a bored and stroked Comet, even with much higher power compared to the standard engine is not appropriate. If I understand Mick alright he is guiding tours of motorcyclists around the countryside at more or less road legal speeds :D. He is now helped by an extremly torquy engine to do so. With much increased torque on a touring bike, there is in my opinion no real need to change to a five speed box. Also there are two other reasons that spring in my mind why to alter the gearing.
1. engine speed. When I was working with Jaguar cars, the safe long time (10 min to 20 min) rev limit for the straight six 4.2 ltr. Engine with 106 mm stroke was ca. 5700 rpm. On german autobahn where you have no speedlimit even this figure was too much and travelling at this speed with an standard engine was calling for trouble (I learned the hard way holing pistons). It was wise not to exceed 4800 rpm on long fast journeys. From this time I know that an average piston speed of 20 m/s is sort of an universal figure in standard piston engines, you should avoid to go beyond that point consistently. On a standard comet with 6000 rpm, your piston speed is already 18m/s, with the stroked engine you already reach this magical 20m/s, so increasing the gearing by 10% makes sense, just for that reason.
2. More than that and even worse, you also have a 5mm shorter rod with the longer stroke, which again adds up to the piston acceleration. This puts even more stress on the piston, rod, bigend… so this is another good reason to alter the gearing beyond the 10%It would be best, if it was possible to change the engine sprocket, therefore speeding up the poor Burman box and reducing the torque in the box to make for easier gearchange, but with the Vincent ESA it is easier to change the gearbox sprocket from 18 to 21 to start with. In my opinion it is the easiest and cheapest and fastest way to have a go and try out.
I will ceratinly certainly try out once my bike is finished, but there are still many things to do before I can put it together.
 
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Black Flash

Well Known and Active Forum User
VOC Member
Spongy brakes

Now there is my waffle about spongy brakes. My new bike has ally brake plates, but I can still feel the sponginess of my brothers Comet brakes. First of all adjusting the brake levers in the aforementioned way is a must. I do it exactly the same way. On my brothers Comet there were other problems too. Standing next to the bike peering down the forkleg toward the brakelever when gradually applying the brake until the lever touches the handlebar, I could see that only 70% of the pull was used to apply the brake (moving the brakearms), the rest was simply lost in bending/flexing the brakeplates and the alloy bridgeplate carrying the balance beam. I have now fitted a balance beam outrigger steady plate, which made this area rocksolid. You can find a drawing with all dimension in “Know thy beast”. Moreover I also strengened the brakeplates by externaly welding two 2,5 mm steelplate wedges approx 3” long on each brake plate against the cam boss. If the cam pinion boss is at 6 o’clock, the strip run to approx 3 and 9 o’clock. I have seen this mod on many bikes and the combination of both did the trick. In “Know Thy Beast “ there is also the description of internal stiffening, but I never tried
 

Tom Gaynor

Well Known and Active Forum User
VOC Member
Gearing again

Somehow i messed up the bookmark to this page, and have only just discovered why nothing was happening: I was looking at the old, abandoned site......

I don't disagree with the arguments in favour of running a taller gear to keep engine speeds down, but adding 3 "or even four" teeth to the gearbox sprocket is a very large gearing increase. I used to alter the gearing on my Seeley-Gold Star depending on what use i put it to, and while 19T was ideal for "short circuit scratching" - i.e. riding in traffic....... it only took 21T to turn it in to a motorway cruiser. I'd be more inclined to try a 2T increase first.
On the Manx, it isn't the top speed one needs to focus on: it's the point at which it starts to pull. Road or track, one doesn't spend a lot of time at peak revs. My one-time sponsor used to say "The owner always wants the gearing dropped, the rider always wants it raised, and the owner is always right."
 

Tom Gaynor

Well Known and Active Forum User
VOC Member
Brakes

Now there is my waffle about spongy brakes. My new bike has ally brake plates, but I can still feel the sponginess of my brothers Comet brakes. First of all adjusting the brake levers in the aforementioned way is a must. I do it exactly the same way. On my brothers Comet there were other problems too. Standing next to the bike peering down the forkleg toward the brakelever when gradually applying the brake until the lever touches the handlebar, I could see that only 70% of the pull was used to apply the brake (moving the brakearms), the rest was simply lost in bending/flexing the brakeplates and the alloy bridgeplate carrying the balance beam. I have now fitted a balance beam outrigger steady plate, which made this area rocksolid. You can find a drawing with all dimension in “Know thy beast”. Moreover I also strengened the brakeplates by externaly welding two 2,5 mm steelplate wedges approx 3” long on each brake plate against the cam boss. If the cam pinion boss is at 6 o’clock, the strip run to approx 3 and 9 o’clock. I have seen this mod on many bikes and the combination of both did the trick. In “Know Thy Beast “ there is also the description of internal stiffening, but I never tried

There are many myths about Vincent brakes. One is that using twin cables is a good / bad thing. It makes no difference. Whatever pull is given to the lever serves two small drum brakes. There really isn't such a thing as a free lunch.
Regardless of what you do to them, and stiffening the plates is always good, they're still 7" single leading shoe brakes, and while they have the width to combat fade, and do that very well, don't have the diameter or design to outgun bigger drums or better designs. Rudges had 8" brakes by 1934.... I didn't want to lose "the look" (or to have to "make my own arrangements" for a speedo gear which ruled out discs or a big four-shoe) so changed my first upgrade from standard, Lightning plates with turned linings, to PV 2ls plates. They transformed the stopping. Two fingers is enough. They still aren't as good as a 9" four-shoe, but more than adequate for road use. What I particularly like is that when I have to grab them in traffic, I get an instant response, something I never managed with the standard 1ls brakes.
 
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