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5 Speed Gearbox

mick the vin

Well Known and Active Website User
Non-VOC Member
#1
WE HAVE A HOTEL UP HERE IN WHITLEY BAY - THIS WEEKEND AND LAST WEEKEND WE HAVE HAD TWO BIG HARLEY CLUBS ; ONE FROM LONDON AND ONE FROM MANCHESTER. PART OF MY ONEROUS DUTIES AS MEIN HOST IS TO TAKE THE LADS AND LASSES ON A RIDE OUT OR TWO OVER THE WEEKEND
I HAVE BEEN LEADING BOTH GROUPS ON MY COMET WITH AN AVERAGE OF 300 MILES EACH WEEKEND. I WON'T TALK ABOUT SOME HARLEY RIDERS ON
1600cc MACHINE THAT CAN'T KEEP UP WITH A 55YR. OLD BIKE WITHME AND MY WIFE ON - AND I'M NOT THE LIGHTEST PERSON IN THE WORLD.

THE BIKE WAS JUST STUNNING - THE ENGINE IS A BORED AND STROKED BOB DUNN SPECIAL. THE ONLY ISSUE I HAD WAS ONCE WE GOT UP TO 70/75 I WAS LOOKING FOR ANOTHER GEAR
DOES ANYBODY KNOW OF A GEARBOX THAT WOULD GO ON AN OTHERWISE STANDARD COMET WITHOUT ANY MAJOR ENGINEERING ISSUES.
ALSO IS THERE WRITTEN ANYWHERE AN IDIOTS GUIDE TO SETTING UP THE FRONT BRAKE

LOOK FORWARD TO HEARING

MICK
 

captain vincent

Website User
Non-VOC Member
#2
Mick,

Give me aring on 01506 416774,and I will tell you a very simple method for setting up the front brake that works with no tecno vinny bull****e.

Captain Vincent (ex North East,banished ti Scotland for 15yrs!)
 

dave g6xnc

Well Known and Active Website User
Non-VOC Member
#3
Kapitain

Glad to hear that the comet (best bike vincentents made) is going strong and that it showed the posers the way home!. Front brakes, this is poorly described in nrichardsons bible, but the way is; Lie on the ground in front of the bike(if you havent a lift) and look at the cam arms on (the brake operating arms) get someone to apply the front brake. Now, you are looking at the brakes in the applied position and the arms must be paralell looking at them from the front. Now look at the arms from the side the angle should still be less than 90 degrees, if not, the arms must be slackend off and adjusted
unit till THEY ARE PARALELL IN THE APPLIED POSITION. Dosent matter if their out of line in the "off" position but they MUST be paralelell when applied. If you cannot get them to align correctley remove the arms and also the serrated disc that the arm bolts against turn this 90 degrees and try again.
This is abit fiddly but belive me you will notice the difference if you've done it
correctly, I only figured it out after quite a lot of experinting and have always reckond this to be a good way of determining someones knowledge of vincents. If the lever comes back to the bars or twin pulls are installed they've missed the boat, so, try it and be carefull when testing, 'cos vincent brakes DO WORK. ( better than BMW's). Gear box, have you tried altering the overaul gearing?, I fitted an amc norton box to my comet for racing
This is not a five minute jod an e ntails machining away the inner chain case behind the clutch (to take an amc unit) all very good as you could then possibly get a Rod quafe five peed conversion for it. I appreciate this is the ravings of an old fart regarding gear boxes but this would seem to be the right direction as moxt (all?) Jap gear boxs are unit contruction with common
oil supply (no chopping jobs) The brake adjusting will work but you must take tyour time , remember Vincents are engineers machines. ( thats why I love my BMW tractor (1150GS) it aint!), lights are crap so are the brakes!.
Good luck withit.
dave gs.
 

Tom Gaynor

Well Known and Active Website User
VOC Member
#4
Five speed box for Comet

I have a five-speed cluster which I used in my Manx that I no longer need (having replaced it with a six-speed). It will fit straight in to an AMC casing - which is what it came out of! I also have the correct Newby clutch centre for it. If you are interested, contact me directly via
sunbeam42@tiscali.co.uk or 07767 328 615.
(I've inserted what amounts to "an ad" here since it is relevant to the thread, rather than in flogger's corner.)
 

Piston Pete

Well Known and Active Website User
VOC Member
#7
Hmm.I too would like some "guidance" on the front brake set up routine. My comet's brake lever comes back to the bar ,but the brakes seem to work well enough,although the "feel" would lead you to think that the lever isnt actually connected to anything.

Re the lads on the Harleys and keeping up, I am just back from a 2200mile tour of Spain and my companions on a sports bike,big traillie and mega scooter found the twisty mountain roads a bit difficult to handle (i.e. keep up with me),but on the motorways they were happy to blast past with gay abandon.

Peter Redmond

Dublin
 

Black Flash

Well Known and Active Website User
VOC Member
#8
Hello Mick, I have just received my engine back from Bob Dunn. It had the same treament as yours, bored stroked, 36 mm carb, MKII cam and so on. When I spoke to him about the gearing, he told me that I have to increase the size of the g/box sprocket by 3 teeth for a start or maybe 4. He told me that the engine has so much torque that increasing the overall gearing by 20% will have no effect on acceleration as the engine doesn't built up speed fast anyway due to the long stroke of 100 mm. His words really make sense to me and with a gearing about 20-25% higher you should get enough terminal speed without the need of a 5 speeder. You should also keep in mind that the engine should rev a bit when cruising to dampen the power pulses of this big bang engine in the poor old Burman gearbox. I am just building another Comet special with a Terry Prince 600 cc topend and use an AMC commando gearbox with special machined lugs, possibly the strongest of all the english gearboxes. If you fit one of these Commando boxes, there is no need to machine the primary chaincase as the mainshaft is longer than on the earlier AMC boxes(ie. Atlas). as much as I know there are drawings for Converta engine plates in 40 years on or some other publication, I am sure they were in MPH yaers ago, but you can certainly ask Ben Fietje, cause he is using this conversion on his racing Comet.
Hope I could help you a bit
Bernd Schmitz "Black Flash"
 

BlackLightning998

Well Known and Active Website User
VOC Member
#9
Hello Mick, I have just received my engine back from Bob Dunn. It had the same treament as yours, bored stroked, 36 mm carb, MKII cam and so on. When I spoke to him about the gearing, he told me that I have to increase the size of the g/box sprocket by 3 teeth for a start or maybe 4. He told me that the engine has so much torque that increasing the overall gearing by 20% will have no effect on acceleration as the engine doesn't built up speed fast anyway due to the long stroke of 100 mm. His words really make sense to me and with a gearing about 20-25% higher you should get enough terminal speed without the need of a 5 speeder. You should also keep in mind that the engine should rev a bit when cruising to dampen the power pulses of this big bang engine in the poor old Burman gearbox. I am just building another Comet special with a Terry Prince 600 cc topend and use an AMC commando gearbox with special machined lugs, possibly the strongest of all the english gearboxes. If you fit one of these Commando boxes, there is no need to machine the primary chaincase as the mainshaft is longer than on the earlier AMC boxes(ie. Atlas). as much as I know there are drawings for Converta engine plates in 40 years on or some other publication, I am sure they were in MPH yaers ago, but you can certainly ask Ben Fietje, cause he is using this conversion on his racing Comet.
Hope I could help you a bit
Bernd Schmitz "Black Flash"
Hi, I'd love some more detail on how to tune the brakes on the front as well - soounds like there are a few of us that would like to benefit from the advice of more experienced owners - mine work fine, impressed the MOT chap - but the lever comes back to the bars.

I'll watch the thread with interest - perhaps we should start a new one on front brakes?
 

Tom Gaynor

Well Known and Active Website User
VOC Member
#10
Altered gearing

That's a HUGE increase in gearing. I race the Manx with 19 and 20 tooth gearbox sprockets (Newby belt drive). 19 is for Cadwell and East Fortune, 20 is for Chimay and the Ulster (both with long 130 mph+ sections). Of course you must try it out first, but the problem with a four-speed box is that, say you were getting 25, 50, 75 and 100 at peak revs, with higher gearing there is an even BIGGER gap between ratios, so to "knock it back one" without locking the back wheel and knotting the valves, you would have to drop the speed from (say) 120 to 90. Generally the concensus on five and particularly six-speed boxes is that "they have a gear for every corner", and while no doubt Lea Gourlay would perform well with a three speed box in a manx, five and six-speed clusters have virtually taken over.
The only circuit I can think of that a four speed works well on is Knockhill (there are doubtless others) where series of corners can be taken at similar speed in the same gear, and going up and down the box is largely confined to straight line stuff.
As you can probably discern, I'm a complete convert. Everything about it is better: the ratios, the closeness of the ratios, the ease of changing - and the reliability thus far, fingers crossed........
 

Black Flash

Well Known and Active Website User
VOC Member
#11
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 Website User
VOC Member
#12
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 Website User
VOC Member
#13
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 Website User
VOC Member
#14
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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