Front Spring Box Compressor Tool

[timetraveller]

One thing to remember now from all Chis' testing is the change which occurred when we went from Oilite bushes at the rear of the lower link to bearings. Chris used needle rollers and Greg Brillus uses two ball races each side, which is what I supply with the kits. The bike front end became so much livelier that it was assumed that the AVO damper had failed. The reduction in friction was so great that the AVO was having to work harder. What I had not understood is that the damper is trying to control the weight of the centre of the bike, i.e. engine /gearbox, UFM. petrol tank and rider etc, which is pivoting around the rear wheel. Instinctively one assumes that it is the front forks etc. which are being controlled but it is the centre of the bike which is being controlled. With Chris' weight on a twin we had to go from 36 lbs/inch springs and a standard AVO to 45 lbs/inch springs and a stiffer than standard AVO. I did try supplying the stronger springs for all twins for a while but most medium weight riders found them much too firm. Nowadays, I try to persuade everyone who wants to use the new front end to go for the bearing modification. That way the ride is being controlled by a hydraulic damper, not by friction at the rear of the lower link.

 

[greg brillus]

On the JE stem kit the upper spring case attachment is further forward, thus a weeker sping rate is needed as the triangulation is less almost level with the fork blades themselves.......best senario is no spring cases at all, and have a coilover where the shock absorber is.......this really transforms the forks.......but not easily done, well for most Vincent owners bikes anyway.

 

[timetraveller]

Just to fill everyone else in on this; cyborg has fitted a DD steering head and is using an eccentric at the rear of the lower link. That was his choice, The problem for me is that I have not actually seen a DD steering head but clearly using an eccentric is going to place the top of the spring box further back than would be the case with the JE design. This means that Greg's comment above is relevant. The best that I can do is to offer cyborg a pair of 33 and a pair of 36 lbs/inch springs so that he can mix and match to see what works. Also a Lightning replica is going to be lighter than a normal twin, hence the suggestion that 33s (normally used on Comets) might be suitable for his bike. Or one 33 and one 36. I do have 30 lbs/inch springs as well but they would normally only be used on a stripped down racing single.

 

[Cyborg]

I was aware that JE stem doesn’t use the eccentrics and that puts the spring box upper pivot farther forward, but it’s only about 0.750”, so I wouldn’t have thought it would make much difference. It also looks as though moving the pivot point forward might create a little bit more preload because of the way the eccentrics sit?

Chris, that’s a good suggestion to use the mill bed, I’ll do that. I’ll also test the strength of the tempered glass surface of the bathroom scale. These springs were purchased from Coventry, so I have no idea if they were made by the same supplier used by VOC Spares. May as well find out what I’m starting with.
The front end is solid enough that it seems like there might be something else going on. If D springs give a softer ride, then I wouldn’t think that my extra 0.5” of preload would make things so stiff. As previously mentioned, the forks (without springs and damper) would fall under their own weight. Something going on with the eccentrics when the spring boxes are installed? I did notice that one of the spring boxes is touching the eccentric where it shouldn’t be. That needs to be addressed, but I don’t think it’s contributing to the problem.

 

[powella]

Used this for years - simple and effective.

 

[Chris Launders]

Don't risk the tempered glass, it's too smooth to be a reliable base anyway, use a bit of wood between the glass and spring box.

It may be your damper, try it with and without.

Remember the standard set up IS very stiff.

Have you seen the video of my forks in action.

 

[timetraveller]

You don't have to risk the glass on top of the scales. Put a piece of wood or metal on first and just reset the zero.

 

[Cyborg]

I removed one springbox, stuffed it between the scale and mill knee with just a touch of tension.…. basically enough to hold it in place. Lowered the knee 1” and got a reading of 66 lbs. Yesterday and this morning, I checked out a couple of the local twins with girdraulics. My set, now with just one springbox acts about the same. Jim, who is our very gracious section organize (and who started this thread) lent me a bin of springs. I will measure them as well and see if I can figure out what works. I’ll also recheck my spring to make sure 66 is reasonably accurate.

 

[Chris Launders]

I've not been able to find figures for the standard springs in my stuff, I said 57lb , but it was going on for 6 years ago now so I'm almost certainly wrong.

 

[timetraveller]

Don't do just one measurement. Try three more at 2. 3 and 4 inches if you can move the mill knee that much. Then plot a graph and put a straight line through it. Excel can do that or I can use excel to do it if you send me the measurements. The gradient of the straight line is the rate. 66 sounds very high compared with what I supply, 45, 36, 33 and 30. Is it possible that you have one of DD's early experiments?