SP: Spring Boxes (Rear) Rear suspension springs

[Damien McGouran]

I am sure this subject has been done to death, but please help me..

I am not the tallest person in the world and therefore I am having trouble reaching the ground on my Series C Rapide. I have no issue reaching the ground on the Series B's that I have sat on, so there must be a difference in saddle height between the two models.

Chatting with one of the club members (Andy) he explained that I should in the first instance focus on the rear springs. Therefore armed with his advice, the quest to get rear suspension lowered on my bike starts with the springs.

Referring to the Harpers Engines Limited parts listing for Series B & C models, it shows three different springs to suit rear suspension. It quotes part numbers
F84/0 (.324") for the Rapide Sidecar,
F84/1 (.300") for a solo Rapide
F84/2 (.276") for the Comet and Meteor.

To unravel and understand the above part numbers, please let me know, can the different springs be identified? perhaps by measuring the section diameter of the material which was used during manufacturing?

On the assumption that all the springs are all the same length, has anyone fitted Comet/Meteor springs on a Rapide? or since the rear springs use the same pivot mounting points, has anyone tried one Comet/Meteor spring and one Rapide solo spring?

I am not precious about using standard Vincent parts so I would be just as happy to use a modern fix should it exist

Many thanks in advance

 

[b'knighted]

I recalled some previous comments so used the search function with AVO coilover and seat height which brought up a short thread
“New AVO rear coilover for lower saddle height –any takers?” which you may wish to revive.

 

[timetraveller]

It's all a bit more complicated than you would wish. The standard Vincent rear springs, which I guess is what the part numbers refer to, are not suitable for shortening and if you used Comet springs on a twin you would almost certainly bottom out frequently. For years people have fitted longer springs, originally developed by Ken Pettiford. These are known as 'Pettiford springs'. You can very quickly tell by just looking as to which springs you have. If about one and a half inches of inner protrude out at the bottom of each spring box you probably have standard springs. If you have two and a half inches of spring then probably the Pettiford. This is with the bike on its wheels, not on a centre stand. If you have the longer springs then you can change them for the shorter original springs. Some adjustment can be obtained by slackening the lock nuts on the top and bottom eyebolts and screwing the eyebolts in as far as they will go. If that doesn't do it then the next thing is to reduce the thickness of the front part of the rubber pad within the seat. You might be able to gain and inch there but you will need some skill to make the seat look reasonable again.

Let us have details of the length of the spring boxes and possibly a photo and we might be able to help more.

 

[Garth Robinson]

It's all a bit more complicated than you would wish. The standard Vincent rear springs, which I guess is what the part numbers refer to, are not suitable for shortening and if you used Comet springs on a twin you would almost certainly bottom out frequently. For years people have fitted longer springs, originally developed by Ken Pettiford. These are known as 'Pettiford springs'. You can very quickly tell by just looking as to which springs you have. If about one and a half inches of inner protrude out at the bottom of each spring box you probably have standard springs. If you have two and a half inches of spring then probably the Pettiford. This is with the bike on its wheels, not on a centre stand. If you have the longer springs then you can change them for the shorter original springs. Some adjustment can be obtained by slackening the lock nuts on the top and bottom eyebolts and screwing the eyebolts in as far as they will go. If that doesn't do it then the next thing is to reduce the thickness of the front part of the rubber pad within the seat. You might be able to gain and inch there but you will need some skill to make the seat look reasonable again.

Let us have details of the length of the spring boxes and possibly a photo and we might be able to help more.

Some seats have shorter mounting ears at the front,if you can reduce the length of these you can lower the front of the seat.Not too much or the tool tray fouls the springboxes.

 

[Bill Thomas]

Look at where the pivot bolts go into the springs,
They can often be wound in more to make the bike lower ?.
Cheers Bill.

 

[erik]

I lowered the seat by making the articulation to the UFM on the seatbase in an insert. You could have trouble with the tooltray.Erik

 

[Bill Thomas]

I did a cheap way of doing that ,
And also moving the seat back away from the tank a bit.

 

[Damien McGouran]

Fantastic advice. It would appear that I might just have the longer springs on the machine. That being the case, two shorter springs will certainly help. I did intend to lower the seat height but wanted to start with the suspension as I have a Dave Hills stand to fit (and maybe adjust).

 

[erik]

my conversion lowered the seatbase more than an inch and together with the thinner upholstery it is more than two inch lower than standard.

 

[Bill Thomas]

Fantastic advice. It would appear that I might just have the longer springs on the machine. That being the case, two shorter springs will certainly help. I did intend to lower the seat height but wanted to start with the suspension as I have a Dave Hills stand to fit (and maybe adjust).

Yes looks like the long petteford rear springs ?,
Also the front springs look a bit too high,
What front shocker do you have and do you have the right eyebolts for that shocker ?.
Cheers Bill.
Does the front mudguard clear the mag' cowl ?, And the exhaust on a lock,
looks a bit too close ?.