F: Frame AVO COIL OVER WANTED HELP PLEASE

[greg brillus]

Kerry, the Ikon's you mention are new ones actually made here in Australia ( that almost seems too hard to believe) I had some specially made for me that were re valved to behave not dissimilar to the Thornton front shocks that have been un available for some time now........Their shock design is different to the Thornton, the stock ones they supply are fine for the rear of the "B" and "C" bikes but way too stiff for the front. They will not supply my altered version to anyone but myself.......after the batch of 10 were sold off or used by myself, I have nil stock now.......i have tried many and all available shocks on my bike.......Ideally one with adjustable rebound is the best, but with such limited space, it is difficult to find one that will fit without hitting something.......It is something i am going to pursue more as my next 2 Vincent projects will both have coil over shocks front and rear.......The ones i used on the race bike in my picture were a Fastace brand of Pitbike shock.......these with 270 mm centers......i used about a 170 Lb spring on the front and a 300 Lb on the rear using a fully sprung seat.......This was a striped down race bike and quite light weight at about 155 kg's........That with many other upgrades but nothing outrageous, was by far the best handling Vincent I have ever riden.

 

[kerry]

Update, Thank you for the brilliant help.
I have now sent for a 300 spring as well and will show photos etc soon of how we created similar to Avo for a rear coil over to fit on D Series.
Thanks
Kerry.

 

[timetraveller]

This is why these forums are such a useful way of exchanging ideas and information quickly. Just one comment about the above. Because of the geometry of the Vincent rear suspension any load measured at the rear wheel is increased by 50% on whatever spring is used. The 'D's get away with the fully sprung rear end because a much larger space was made available for the coil over damper unit than on the 'B's and 'C's. If one wants more rear wheel movement to improve rider comfort by installing, say, Pettiford springs then really one has to go for a fully sprung seat as without that the extra movement is transmitted directly to the rear end of any pillion passenger. The person on the front of the dual seat is not subjected to the same amount of movement. So, if you carry a pillion passenger at times and want more comfort then one should go fully sprung and that creates some additional problems. This limited distance causes problems with what can be done in the space available for the springs and dampers. AVO used an ingenious design by offsetting the lower mounting to the side of the coil over damper unit to make most of the travel available but what Chris and I found is that the AVO uses an 8" long spring which will become coil bound at 4" of compression, This means that any preload of the rear springing, say 2", reduces the potential travel to 2" on the coil over, i.e. 3" at the rear wheel. Please note that this restriction is much less on the 'D's because of the extra length available for the coil over.
About a year ago one gentleman wanted the full conversion to the JE system on the front end but did not want to go for the AVO coil over at the at the rear, possibly because of the danger of bending the upper support for the coil over at the rear of the oil tank. I looked into off the shelf coil overs as supplied to the rear of many bikes. As a criterion I used the hole centre to hole centre distance of the normal spring boxes fitted with Pettiford springs which is 10"/250mm. There are lots available and most have adjustable spring pre-loading but I did not find any low priced ones which had adjustable damping but they possibly exist. The mounting of such units is the same as the original Vincent system in that the forces are taken right next to both the upper and lower supports and will not cause any over loading or bending of the supports.
So it seems to me that the problem at the moment is confined to finding something for the front end. Just at the moment I am somewhat over loaded with trying to build three car alternator systems, getting ten new steering heads machined and organising the machining of 35 of the new Girdraulic lower links so if anyone wants to do any background research, or offer advice, on front suspension units then I will be happy to accept such advice. Discussions on here offer a world wide perspective so that has to be an advantage.

 

[vibrac]

If someone could give me the series C lengths open and shut front and rear ( rear as a coil over) and choice of general poundages I think I may have a manufacturer who already do units.
Later perhaps a rear damper only and series D but the above is my starting point after having a coil over on the Goodwood Racer and my Comet I would not revert to the original

 

[timetraveller]

Tim, I make the fully open length of a standard Vincent damper to be 10.0", hole centre to hole centre. Fully closed 7.25", The rear spring boxes are more problematic as the eyes at each end screw in and out to alter the overall length. The only one I can find off a bike so it is neither compressed or stretched is about 10". That would make sense and it matches the damper centres. AVO rear coil over, fully extended and hole centre to hole centre is also 10". Fully compressed is a problem as four inches of movement would result in coil binding of the spring and the free movement of the damper rod is about two and a quarter inches but beyond that is a compressible bump stop which will allow at least another half inch of movement. Rear poundages range from 275 lbs/inch on the AVO up to at least 400 lbs/inch.

 

[Peter Holmes]

Water under the bridge now, but when I spoke directly to AVO regarding springs for the Series D short version, the maximum poundage they could supply was 400lbs

 

[oexing]

Greg, I cannot see how you can put up with all that money and time wasted in your hunt for acceptable shocks like from Koni/Ikon and all. Sure, coil overs got their limitations from coil binding, so travel is less than wanted. And the AVO offcenter lower bracket welded on for extending range is a no-go for me from start, even as it may last quite a while. But this will not help the seals and the minimum of bushes inside in tolerating side loads on the piston rod. At the rear two shocks in standard place got a few benefits, well, do not lower costs, but look a bit more durable and end caps can be had with spherical or rubber bushes in them - standard in all other shocks - well, Fournales on Max´s Ducati got their IGUS spherical bushes already. So I had , without knowing , come to same idea years later when working on the B Raps.
What type of Koni did you try to fit, a coilover I guess? Are these the dial-a-ride type with knurled dial at top cap? Anyway, in your place I´d have someone make you a tool for opening the damper and do all mods myself. This is no rocket science and quite simple - nothing like engine work on Vincents - on which you appear to be very competent. So what´s not to like, you can do various mods, like having less spring preload, get PU real seals for less friction, do some more holes for less damping, on compression or extension, whatever. Could be restored to standard any day.
Next time I get into a Koni I will look into the bottom valve for maybe additional modding
Reading this never ending story I ´d be itching to ask people for sending their shocks to me for mods that companies seem to be unwilling - wonder, why on earth . . .

Vic

photos from the old Vincent Koni from Spares Co:

piston drillings and valves:

wave washer (compression) left, spiral spring extension setting right:

bottom valve cap with damper setting key:

all old components, for round slotted nut a tool is required:

blue and brown seals plus adapters are new hydraulic PU types:

 

[greg brillus]

Hi there Vic, No sorry I was only advising on currently available shocks that bolt straight on, more for owners who are looking for something to install on their bikes that look correct and work ok. You have to experiment with what else is available that will fit and work within the confined space........The options for owners is getting less, so an alternative is needed.......using something that is readily available is better option than building something from scratch.......The suspension/comfort issue is probably the biggest bind to owning a Vincent, as owners get older and their backs/hips suffer the impact of bumps on the road.......in some cases they prefer to park the Vincent and ride a more modern bike with electric start and soft suspension.......They don't actually want to do that but their body is telling them to go this way.......Its a world wide thing now.

 

[Chris Launders]

It would be useful if someone developed new internals for the standard damper, this would keep the "keep it original" sector happy as well.
I mean we know they fit reasonably and wouldn't need building from scratch.

 

[A Nut]

I had a D shock absorber made for my Victor replica (Comet version of a Black Prince) by Protech Shocks, Lysander Road, Bower Hill Trading Estate, Melksham, Wiltshire. Initially it would not fit as the geometry of the Comet is different to a twin but they were very helpful and sustituted a shorter rod and now it fits fine. It has 14 damping positions operated by a knurled knob.They can supply a variety of different springs which are adjustable for ride height. This was several years ago and I assume that they are still in business but try them on 07860541474 and ask for Kevin. You can email me direct on b.werrett10@hotmail.co.uk.
Brian Werrett