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 . 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.
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 . 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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