FF: Forks Modified Steering Stem

[vibrac]

As I have mentioned my cooking comet (now in pieces) had 18" tyres mainly because of its Trials use and I must admit it was more skittish in side winds (on road tyres) than any other properly shod Vincent I have ridden, especially for some reason when I had a solo seat.(I had fleetingly thought it was due to the "hole" in the frame being blocked by the walkernator) but indeed perhaps its the wheel size However although I often espoused the larger diameter tyres especially at the front on Bramptons and they certainly look better I have not experienced any other steering or road holding problems and will retain 18" for the 2020 machine Ben, of course, would race with nothing else than 18"

 

[roy the mechanic]

Maybe I should have said smaller profile, it looks like the mudguard is too big. On the rear it's a 130/??/18 some folks reckon it's too big but I like it.

 

[davidd]

The narrow tires seem to need less drastic angles for cornering, which can make for more responsive cornering Also, I believe the resistance to turning goes up by the 4th power as the diameter of the tire increases. This is why the 18" tires on the racers appear to wake up the handling so much. But, it is a system with many mix and match components and a subjective one at that.

David

 

[Bill Thomas]

I knew Roy had a 90/90 front, And I thought mine was a bit heavy on the l/ning with a 100/90, But after riding a Standard bike with new old type tyres, Mine now feels like a 250cc, I was going to change to 90/90, Like my Comet, But I think I will leave well alone !. Cheers Bill.

 

[hadronuk]

the avo has a build in fault... i have seen them with an broken end. sorry

I discussed this with Vincent Brake and he said:
"I only saw a rider once with only the damper, said he hit a sleeping policeman on the road really hard, and than the sliding axle broke where it screwed in the take up. Only thing I saw."

So it sounds like the the damper rod broke where it screwed into the top eye.
The first AVO rear dampers were sold bare. The damper rod end is threaded 5/16 BSF, exactly the same as the original Vincent damper, so the risk of failure at this point is no greater than for the standard item. The buyer was responsible for assembling it to his own top eye. If this was not done securely and the rod came unscrewed, that might lead to breakage.
Another possibility was that the top eye was not free to move, either due to corrosion or misassembly. This could eventually cause a fatigue failure of the rod.
Regarding fitting, is very important that the AVO rear dampers are fitted with the supplied extra long steel bush fitted in the top eye. This bush allows the damper eye to move freely independent of the spring eyes. (This is only applicable to the AVO rear dampers. AVO front dampers and rear coilovers use a standard length (3/8") bush.)

Although I think this sort of failure is rare, I do know of one case of an original Vincent damper that snapped, probably for one of the reasons discussed, and one case of a Thornton damper that came unscrewed, both without serious consequences.
A failure at this point is is arguably a weakness of the original Vincent design.
The damper eye is only 3/8" wide were it slots into the frame, so 5/16" is the maximum possible size for the thread.

We paid a lot of attention to safety when we developed the coilover., and this is one area we changed.
As the top eye carries both the spring and damping loads, the 0.5 inch damper rod is both screwed and welded to the top eye when fitted to coilover units.. In addition, the first two units were road tested for 3000 miles, then stripped and fully inspected. Both were perfect. I doubt any other unit available is as strongly made.

Rob

 

[Robert Watson]

On my sets of works coil overs for the Bramptons, I made most of the mounts. I had one "customer" wanting to make his own, so let him. About 3 months later the bottom mount snapped off at the rod and my name was shouted from the rooftops. I went to inspect and pointed out that although the shock appears to travel in a straight line it does actually rotate on both mounts and that is why I had been very specific about the lower mount being made in such a way that it could rotate through a few degrees. He had ignored this advice and decided he knew better, but that is a common trait with older brothers. He did have to beat rather large dents from his nice Bermabright front mudguard.

 

[Peter Holmes]

The original Vincent damper top eye was screwed onto the damper rod and then secured with a drift pin of some type, maybe a mills pin into a previously drilled hole through the eye and damper rod, I note the pin is shown on drawing M063 as a 966 but not listed as a part, perhaps that snippet of information could form part of a Vincent knowledge quiz at some point in the future. When I fitted my Avo dampers I used a locktite product purchased from my local hardware shop, don't think it was the permanent type though, seems OK at the moment.

 

[greg brillus]

That small pin was just a simple locking device that actually weakens the thread. A lot of early forms of thread locking were very destructive and really only for single use. The threaded end of the shock absorber shaft is in itself a very weak design, and in fact the shocker is very small for such a hard working area on the suspension...........It's all a compromise.

 

[Peter Holmes]

The small pin is only there to stop the damper rod from unscrewing from the eye, I would imagine the rotational forces on the damper rod, if there are any at all are very small, as for pulling and pushing forces, I think there is quite a few threads engaged into the steel eye before the thread is drilled for the pin, and the pin does not have to resist those forces at all, I doubt that it significantly weakens anything in a functional way.

 

[hadronuk]

The small pin is only there to stop the damper rod from unscrewing from the eye, I would imagine the rotational forces on the damper rod, if there are any at all are very small, as for pulling and pushing forces, I think there is quite a few threads engaged into the steel eye before the thread is drilled for the pin, and the pin does not have to resist those forces at all, I doubt that it significantly weakens anything in a functional way.

The first part of the original eye is counterbored a fair bit (1/8"?), at least mine are. So there are only a very few threads engaged between where the counterbore stops and the cross drill hole! Having said that, in the process of testing many different dampers, bump stops etc I have removed and refitted top eyes an inordinate number of times, but I never found the eye to be loose. Quite the reverse in fact, as I always use thread lock, sometimes too much, so that the damper rod has to be clamped extremely hard in a soft-jawed vice before the eye would loosen. At my recommendation the top eyes that AVO make for their units don't have this counterboring or the cross drill hole.