Suspension - please explain.

[Howard]

David, Look at photo of Howard in post 19,
He was years ahead of us, I thought it was 70s, But I have lost the plot !!.
But I knew the Bike before Howard had it. Cheers Bill.

I had it from 1980 to late 90s - sold it and bought a Fireblade, still got the Fireblade, and bought my current Comet from the guy I sold the racer to. Funny old world.

 

[Bill Thomas]

You sold a Vincent !, I don't know what to say .
1980 I cheated and built the L/ning rep'.

 

[Vincent Brake]

But it wi

Howard, if you want to keep the standard geometry and just replace the Oilites with a freer type of bearing then you have to consider why this type of mod was developed. Both John Emmanuel and Dave Dunfey came to the same conclusion in that the front wheel path with the standard Vincent set up could cause trouble. They independently arrived at different methods of changing this path. The suspicion is that the problem was known to Vincents early on as when one looks at photographs of work racing bikes from the early 1950s they all have the bottom link horizontal. That limits which part of the original wheel spindle track is used. It should also be noted that George Brown was also not happy with the front end and when he built Nero he changed to telescopic forks. David's first attempt at a cure was to use shorter, stiffer springs at the front which put the wheel path back to what the works racers were using. John's efforts were more adventurous in that he realised that he wanted a different wheel path and he then set up a jig to replace the lower support for the steering head and rear pivot point for the lower link and then moved the pivot point about until he had the wheel movement that he thought would be better. He wanted to, as nearly as possible, make the front wheel movement similar to that given by telescopic forks, i.e. upwards and backwards. To understand fully what is wrong with the original system one needs to study the wheel path, which is like a distorted 's'. To finally drive it home borrow an enclosed 'D' and then brake hard, or use a disc brake, and see what happens. The whole of the 'dashboard' rises up to meet one as the brake is applied. This means that the front suspension has dropped to its lowest level, the wheel has moved backwards and the trail has increased to about 5". One has to release the front brake before the wheel can move forwards again and the suspension starts to work.
Just replacing the Oilites with, say, ball races, will reduce the friction but will do nothing to change the wheel path. Indeed, I would expect that one might run into serious trouble as one would then have the original wheel path and much freer movement. The original dampers would not be up to controlling that movement in my opinion. Please remember that when Chris Launders changed his Oilites for needle rollers there was so much movement that we thought that the new AVO damper had failed.

So, by all means replace the Oilites with bearings and all the other bushes with needle rollers if you wish but do not blame me if you and the bike end up in a ditch somewhere.

The use of a hydraulic steering damper is not because the new system is more likely to cause a speed wobble than the original one. Quite the contrary in fact. However, it is worth asking a question and please understand that I am not 'getting at' anyone who prefers to stay with friction damping. The question is why do you not see any modern bikes or cars using friction dampers on their suspension or steering? It is clearly not a matter of cost but of function. We all know, and have known since we were children that friction damping gives lots of 'sticktion' and very little damping. You will also not find many/any modern machines which use the same amount of damping in compression as extension. There is a reason for that. When I decided to design a hydraulic steering damper system to fit to either the modified or original systems it was because I have been in a speed wobble at 100 mph and it is not a good experience. I landed on my face and my goggles went through their backing and took a piece of from my cheek bone right down to near my jaw line. I was not beautiful before but sure as h**l I was less beautiful afterwards.

Now to Bill's comments. Replacing the eccentrics with concentrics will not do the job. I have tied to explain that it is not the use of concentrics which is important but the centre of rotation of the rear of the lower link. This is moved by far more than the difference between an eccentric and a concentric and you could well end up making things worse rather than better. Please do not do it.

Here endeth the lesson.

But it will if one puts it in the center and than 2 mm down...

Well the mod from Norm or Davidd does a better job.
Most nice now ive got it in.

And with the new softer spings in even the girls sitting on the tank says its an easy ride out.

 

[vibrac]

Howard,



As far as I know, the best front suspension set-up is the coil-over. When Carleton Palmer installed his he said that the "harshness went away." I suspect this is due to the differing motion ratios of the spring box vs. the coil-over, but I am not certain. David Tompkins noted the improvement to the handling of his racer at Laguna Seca with the coil-over and the Reg Bolton type modification.

Just for information, Ertalyte TX is a good bearing plastic that is oil-impregnated

David

Interesting David but as far as I know there is no comercially available coil over for Girdraulics I know there was some activity in UK with AVO but I dont know how far it has progressed. Something like the spring and damper rate adjustable Coil over I have on my Bramptons would be ideal for our racing twin, I know thats what Ben wants, but since the lockdown we still havent had chance to try out the JE forks as they stand. Stationary the link looks horizontal but the action seems stiff so we are into that messy AVO damper stiffness/spring poundage morass which only a track day will sort. Of course then there is the strict scrutineer waiting to pounce if we went that way ,heck, he may still kick up about the coil over on the rear.

 

[Howard]

Interesting David but as far as I know there is no comercially available coil over for Girdraulics I know there was some activity in UK with AVO but I dont know how far it has progressed. Something like the spring and damper rate adjustable Coil over I have on my Bramptons would be ideal for our racing twin, I know thats what Ben wants, but since the lockdown we still havent had chance to try out the JE forks as they stand. Stationary the link looks horizontal but the action seems stiff so we are into that messy AVO damper stiffness/spring poundage morass which only a track day will sort. Of course then there is the strict scrutineer waiting to pounce if we went that way ,heck, he may still kick up about the coil over on the rear.

Can you put a gaiter over it, and add a couple of empty spring boxes?

 

[davidd]

Can you put a gaiter over it, and add a couple of empty spring boxes?

I used an empty spring box on the Grey Flash when I raced it because one stock spring was enough for the entire front end. So, it does work.

I also threaded the Works Performance damper body and added collars and springs...but, I thought DIY was OK?

I spoke with Patrick about Works Performance going out of business before he died and he said that he was going to build them in France. I spoke with Francios at the end of last year and sent him all the info and drawings I had for Works Performance and he got the coil-overs into production. So, they are commercially available, but I have not tried to purchase any as I had purchased a number of dampers from Works Performance before they went out of business.

David

 

[Oldhaven]

Worx Shocks

Worx Shocks - #1 in Replacement Shocks for ATV & Motorcycles

www.worxshocks.com

I’m not sure how they are doing after the shutdown here, but they were trying to keep the business going under another name.

 

[highbury731]

What is the Greg Brillus mod to the oilite bushes>?
The mod consists of removing the Oilite bushes totally and boring both rear eyes of the lower link by a few thou to take a 32 mm O.D. ball race, two ball races each side so four in total. Some other people have replaced the Oilite bushes with needle roller bearings. If I supply the whole kit which I think gives the best ride, performance etc. then stainless steel concentrics are supplied to replace the original eccentrics which went through the Oilite bushes.

Ah, in other words the mod you already made for me....

Thanks!

Paul

 

[Howard]

Update.
I've done a few more miles, and a bit of adjustment and the rear suspension is much more comfortable. I fitted an hydraulic steering damper (just in case) and overhauled the front damper. The Girdraulics are still quite harsh now, compared to the rear but I can't see a simple way to improve the travel, and suspect increasing the travel would create other problems - all the pivots and bushes seem to be working well. The front end was pogoing a lot when I set off, but after a mile they settled down, I can only think the damper needed to charge itself, or maybe the ball valve I fitted had stuck.
Howard

 

[timetraveller]

Howard, something is wrong. Two videos were posted in the thread on Modified Suspension, one by Chris Launders and the other by Chris and Tracy Tilley, showing the front end working as it should. Both were on twins but the lighter weight of a Comet should not make much difference if the correct springs are used. So the question that occurs to me is what is the front damper that you are using? If you have serviced it yourself then almost certainly it is not an AVO. A lot of the old dampers had the same rate of damping in both compression and extension. That is not a good idea. Please let us know what damper is being used and then we can work from there.