Sid-I think a ribbed tyre is good idea too.
Comet suspension
- Thread starter redbloke1956
- Start date
Our Vincent steering dampers if their steering head bearings have not been cleaned out and repacked with high temp . Non melting grease , disc brake type bearing grease is this sort , are prone to grease oozing down on to the damper plate surfaces just below the bottom one bearing . Especially if run long and hard in hot weather . The heated oil tank does the deed .
Most are slick and greasy , need a good cleaning and all flat surfaces roughed up to be effective .
The D damper is a nice piece of equipment . Be sure all surfaces are flat and free to fully come together and kiss the discs . Usually needs a bit of TLC to ensure this is the case . Definitely worth the cost and bother to fit .
The only time my dragster went into a wobble , way up in top gear , was that I'd forgot to tighten the damper knob and it got spit off , the rod and plates found bouncing on the front tire . He went all over the track fighting it , the crowd , on their feet were yelling , " He's going down " , ! , but he stayed aboard . Paul said right after that , " If I don't ride it again RIGHT NOW I'll never ride it again ". Double nutted it after that , no knob , set very firm . Paul was happy after that as the knob had often jumped up and clouted him in the mouth !
AMA champion racer Tommy McDermott had it go into a wobble under him , was doing some grass drags . He gripped it so tight with his knees that he broke off the rear plugs porcelain with his knee . Also stayed aboard .
Racing ain't for the faint of heart .
Someone recently asked me what did the bike do . Running worn 4:00 / 4:50 rear tires and spinning out of sight she did right at 140 mph in 10 .8 /. 10 .9 sec . Could be heard to be breaking free right across the finish line .
With an AVON Slick she would have eclipsed that easily , but I didn't have one . Was good enough tho . Sid .
Most are slick and greasy , need a good cleaning and all flat surfaces roughed up to be effective .
The D damper is a nice piece of equipment . Be sure all surfaces are flat and free to fully come together and kiss the discs . Usually needs a bit of TLC to ensure this is the case . Definitely worth the cost and bother to fit .
The only time my dragster went into a wobble , way up in top gear , was that I'd forgot to tighten the damper knob and it got spit off , the rod and plates found bouncing on the front tire . He went all over the track fighting it , the crowd , on their feet were yelling , " He's going down " , ! , but he stayed aboard . Paul said right after that , " If I don't ride it again RIGHT NOW I'll never ride it again ". Double nutted it after that , no knob , set very firm . Paul was happy after that as the knob had often jumped up and clouted him in the mouth !
AMA champion racer Tommy McDermott had it go into a wobble under him , was doing some grass drags . He gripped it so tight with his knees that he broke off the rear plugs porcelain with his knee . Also stayed aboard .
Racing ain't for the faint of heart .
Someone recently asked me what did the bike do . Running worn 4:00 / 4:50 rear tires and spinning out of sight she did right at 140 mph in 10 .8 /. 10 .9 sec . Could be heard to be breaking free right across the finish line .
With an AVON Slick she would have eclipsed that easily , but I didn't have one . Was good enough tho . Sid .
I don't get involved in frame/suspension threads normally, so I'm sure someone must have said this in the past - nomatter what you do with a friction damper it's still the wrong tool for the job. No criticism of Vincent, like the Lucas and Miller electrics, it was probably the best available at the time.
Tighten the damper knob and you'll have a hard job turning the bars when you push the bike, when the damper's acting in static friction, but when you're riding the bike the damping is just right for travelling at speed, because you're still turning the bars slowly in the static friction zone. The big problem comes when a road condition causes the bars to turn quickly breaking the static friction, then dynamic friction takes over, and unfortunately dynamic friction is half static friction, so just when you need damping you lose 50%.
Just my theory from working with industrial friction torque limiters, plus my racing Comet Girdraulics with hydraulic damper were never anything but planted and reliable.
H
Tighten the damper knob and you'll have a hard job turning the bars when you push the bike, when the damper's acting in static friction, but when you're riding the bike the damping is just right for travelling at speed, because you're still turning the bars slowly in the static friction zone. The big problem comes when a road condition causes the bars to turn quickly breaking the static friction, then dynamic friction takes over, and unfortunately dynamic friction is half static friction, so just when you need damping you lose 50%.
Just my theory from working with industrial friction torque limiters, plus my racing Comet Girdraulics with hydraulic damper were never anything but planted and reliable.
H
You made me think of another issue with friction dampers Howard, if a damper was adjusted pretty tight and something (crap on the road or a pothole)caused your wheel to jar the bars in a particular direction and the wheel to bounce at the same time, when your wheel then makes contact again it is pointing askew?
Just a thought, not sure if I would like to ride with a very tight friction damper.
Kevin
One of our older section members came a cropper on a parade run round the IoM. He's ridden Vins for a long time, and still covers more miles than I do. The scrutineer insisted on screwing the damper down tight, and the result was a very painful and embarrassing dismount.
H
H
Girdraulics and tank slappers
I have given this topic much thought lately way before this thread had started, after much thought after reading the various comments made by other members world wide about their experiences with tank slappers, what caused them and how they occured. It appeared to me that this is a common fault with Girdraulic equipped machines rather than their earlier counterparts with Bramptons. Obviously when the Vincent works were trying to come up with a stronger fork design, their preferance was toward the original Brampton patern due to the inherant ridgidity of the design, and the fact that the two Phil's were unhappy about Telescopics due to their Dive characteristics under braking. So what Faults exist about the Girdraulics, that make them behave this way.... The chance of a tank slapper happening amongst Girdraulic equiped machines is about as common as the same machine falling off it's front prop stands during the life of the machine......very high. People with track experience have been through this, and suffered the consequence many times, and mostly at high speed. Whereas people on roadbikes tend to suffer the conditions of a less controlled environment, but being generally more bumpy and unpredictable. People who come off on the road would tend to struggle to even remember "What the hell happened" whereas people on the track tend to be able to study what happened, and also have the benefit (sometimes if their lucky) to have the input of other bystanders who may have seen what happened. Examples of these people include davidd and his good friend Charlton Palmer who have spent much valuable time trying to assertain " what the hell happened" and actually come up with very sensible answers as to.......Why... Why indeed do our beloved Vincents suffer from a condition that if taken lightly, or Ignored, Bites us severely and tosses us and our Prized Vincents on the ground. If a modern bike manufacturer had a bike with a similar common fault, they would recall them for immediate redesign and repair. With our bikes reaching the age that they are, this is something we need to fix ourselves, or else continue to suffer the consequence. I believe the main faults that exist with this design of front end are that by comparison with the Bramptons, the Girdraulics with their standard spring set up is way over sprung, and if used as per standard with the lower link sitting either level (unlaiden) or with the front of the link in a lower position than the rear ( where the eccentric is) then a condition exists where under heavy braking, the rest of the bike( and rider ) tend to roll over the forks, this causing the forks to go to full extension. Once this happens the function of the front suspension becomes nil, and only the flex in the sidewall of the tyre is what you have left. This ridgidity verses the gyroscopics of the wheel and the undulations on the road surface can only act on the weakest link in the equassion......the pivoting handle bars ( and the rider attached to same).....the end result is the violent to and fro action of the handlebars and the rapid increase of you and your bike comming into an unpleasent contact with the road/track surface. This is not a good condition at all, as it seems all too common a fault to simply accept. My experiences with mild / strong tank slappers on My Rapide were not under braking at all. One happened at about 80 MPH overtaking a friend on his B Rapide, when i hit some bad ruts in the road surface, the others were at around 20 MPH going across a bridge with ruts as well. Even at this low speed the bars were still trying to shake left to right. This is what has lead me to believe that the standard springing in my front spring box's was way too stiff..even though upon a thorough inspection afterwards i could not find any other faults with the front end, The links and bushes....fine.. the shocker unit ( an Armstrong ) Fine...The only thing i hadn't been doing was to tighten the steering damper tight enough.....but if you think about it...the steering damper is not the cause of the Tank Slapper, it's only there to try and absorb it....the underlying fault is still there...as Rip said. In summary i would say to anyone concerned about their Girdraulic suspension, then make sure of the following.....check that all the bushes and links are in good condition with minimal play in them, and that they are lubricated properly..not dripping with oil or grease which will end up on the steering damper unit and render it useless. Make sure your shocker unit is in good working condition, and if it is the original type.....not leaking or run out of oil....the better units are the Koni/ Ikon units or the Thornton or similar....remember this..VERY IMPORTANT...the shocker is designed for one purpose......to keep the tyre on the road.....if the shocker is useless then your suspension is not much better.....the front springs in their original form are too stiff, you primarily need to soften the front end and lower it to make the lower link sit in a safer possition so that the forks ( spring box's ) are in their more compressed possition rather than extended, this so as to stop the bike and you " Rolling" over the forks under heavy braking, automatically sending the forks to full extention ( no more suspension = Tank Slapper about to follow). And lastly, then make sure your steering damper ( the last line of defence) weather it be a modern hydraulic unit or an original type is in good serviceable condition, and as Sid said....not covered in oil or grease. All of these items will make your beloved Girdraulic equiped bike far less likely to suffer from front end shudders and behave more like their older and softer brothers.....the "Bramptons"
I have given this topic much thought lately way before this thread had started, after much thought after reading the various comments made by other members world wide about their experiences with tank slappers, what caused them and how they occured. It appeared to me that this is a common fault with Girdraulic equipped machines rather than their earlier counterparts with Bramptons. Obviously when the Vincent works were trying to come up with a stronger fork design, their preferance was toward the original Brampton patern due to the inherant ridgidity of the design, and the fact that the two Phil's were unhappy about Telescopics due to their Dive characteristics under braking. So what Faults exist about the Girdraulics, that make them behave this way.... The chance of a tank slapper happening amongst Girdraulic equiped machines is about as common as the same machine falling off it's front prop stands during the life of the machine......very high. People with track experience have been through this, and suffered the consequence many times, and mostly at high speed. Whereas people on roadbikes tend to suffer the conditions of a less controlled environment, but being generally more bumpy and unpredictable. People who come off on the road would tend to struggle to even remember "What the hell happened" whereas people on the track tend to be able to study what happened, and also have the benefit (sometimes if their lucky) to have the input of other bystanders who may have seen what happened. Examples of these people include davidd and his good friend Charlton Palmer who have spent much valuable time trying to assertain " what the hell happened" and actually come up with very sensible answers as to.......Why... Why indeed do our beloved Vincents suffer from a condition that if taken lightly, or Ignored, Bites us severely and tosses us and our Prized Vincents on the ground. If a modern bike manufacturer had a bike with a similar common fault, they would recall them for immediate redesign and repair. With our bikes reaching the age that they are, this is something we need to fix ourselves, or else continue to suffer the consequence. I believe the main faults that exist with this design of front end are that by comparison with the Bramptons, the Girdraulics with their standard spring set up is way over sprung, and if used as per standard with the lower link sitting either level (unlaiden) or with the front of the link in a lower position than the rear ( where the eccentric is) then a condition exists where under heavy braking, the rest of the bike( and rider ) tend to roll over the forks, this causing the forks to go to full extension. Once this happens the function of the front suspension becomes nil, and only the flex in the sidewall of the tyre is what you have left. This ridgidity verses the gyroscopics of the wheel and the undulations on the road surface can only act on the weakest link in the equassion......the pivoting handle bars ( and the rider attached to same).....the end result is the violent to and fro action of the handlebars and the rapid increase of you and your bike comming into an unpleasent contact with the road/track surface. This is not a good condition at all, as it seems all too common a fault to simply accept. My experiences with mild / strong tank slappers on My Rapide were not under braking at all. One happened at about 80 MPH overtaking a friend on his B Rapide, when i hit some bad ruts in the road surface, the others were at around 20 MPH going across a bridge with ruts as well. Even at this low speed the bars were still trying to shake left to right. This is what has lead me to believe that the standard springing in my front spring box's was way too stiff..even though upon a thorough inspection afterwards i could not find any other faults with the front end, The links and bushes....fine.. the shocker unit ( an Armstrong ) Fine...The only thing i hadn't been doing was to tighten the steering damper tight enough.....but if you think about it...the steering damper is not the cause of the Tank Slapper, it's only there to try and absorb it....the underlying fault is still there...as Rip said. In summary i would say to anyone concerned about their Girdraulic suspension, then make sure of the following.....check that all the bushes and links are in good condition with minimal play in them, and that they are lubricated properly..not dripping with oil or grease which will end up on the steering damper unit and render it useless. Make sure your shocker unit is in good working condition, and if it is the original type.....not leaking or run out of oil....the better units are the Koni/ Ikon units or the Thornton or similar....remember this..VERY IMPORTANT...the shocker is designed for one purpose......to keep the tyre on the road.....if the shocker is useless then your suspension is not much better.....the front springs in their original form are too stiff, you primarily need to soften the front end and lower it to make the lower link sit in a safer possition so that the forks ( spring box's ) are in their more compressed possition rather than extended, this so as to stop the bike and you " Rolling" over the forks under heavy braking, automatically sending the forks to full extention ( no more suspension = Tank Slapper about to follow). And lastly, then make sure your steering damper ( the last line of defence) weather it be a modern hydraulic unit or an original type is in good serviceable condition, and as Sid said....not covered in oil or grease. All of these items will make your beloved Girdraulic equiped bike far less likely to suffer from front end shudders and behave more like their older and softer brothers.....the "Bramptons"
Not only are all Vin's different, But owners also,!! I know of what Davidd tells us, But it has never bothered me, Even when racing I shut off a split second befor braking, So the forks are as David likes them. I think it is the change of trail, OK in the middle, Not enough when the forks are up or down, Then the weight of the forks, So far forward of the axis, Turns into a pendulum. I have had many that I have got away with and one I didn't !! I have a Comet which I Must not ride, Untill I have fitted an hydraulic steering damper. I will say that I road for many years without trouble and my standard Lightning rep' was a delight, Untill one day, Ouch !! Lots of Luck, Bill.
A bit of feedback here might be useful for all of us who have not tried the davidd type springs yet. I think that I understand David's reasoning and it sounds correct to me BUT. Several years ago Dick Sherwin fitted disc brakes to the front of his twin and invited me to take it for a ride up the road, about five miles. Although I have raced in the UK and have also ridden on normal roads in South Africa, all through France and of course all over the UK and have what I consider excellent Vincent brakes, I had never realised that when braking a Vincent the front end rears up above the front forks which then try to drop to their lowest level. It was only the superior braking of the discs, which with very light handlebar lever pressure massively out braked what I was used to, that allowed me to realise just how strong this effect is. It is entirely possible that I am the only Vincent owner who did not realise what was happening under normal breaking but with the discs even I could not miss it. So the question is even if we start off with a lower link in which the front end is higher than the eccentric end what happens when one brakes. If the same thing happens as with the standard set up ( I have always set up my front forks so that the lower link is lower at the front than at the eccentric end) then under heavy braking does the front of the bike still rise up and the lower link revert to the original front down attitude? This might be fully discussed in David's MPH article but I do not have that available as I write this.
I have to admit that this thread has captured my interest even though this has been a subject of discussion, theory, and experimentation for the 48 years I've been involved with the machine.
I am frustrated now because I can no longer ride and I love testing mods.
But, as I brought up earlier in this conversation, does anyone have any thoughts on the long lock to lock travel of the forks themselves??? Shortening this travel would not prevent a slapper but I believe make them less severe. The farther the wheel
travels to the side the more force is put against it. As the angle of the fork to line of travel increases so does the force when the stop is slammed and then the long travel to the other is probably more extreme.... and faster moving bars.
I am just taking a stab at something here and I really would know what y'all think.
I am frustrated now because I can no longer ride and I love testing mods.
But, as I brought up earlier in this conversation, does anyone have any thoughts on the long lock to lock travel of the forks themselves??? Shortening this travel would not prevent a slapper but I believe make them less severe. The farther the wheel
travels to the side the more force is put against it. As the angle of the fork to line of travel increases so does the force when the stop is slammed and then the long travel to the other is probably more extreme.... and faster moving bars.
I am just taking a stab at something here and I really would know what y'all think.