FF: Forks Modified Steering Stem

[macvette]

Going to ride it before I try anything else

 

[Chris Launders]

Yes of course but they need shortening to allow full travel without the possibility of them hitting.

 

[BigEd]

While we are talking about shortening springs, shorten carefully and take off small amounts until you get the required length. You can't put it back on. Shortening a spring increases the spring rate i.e. it will take more force to move the same distance. In this instance, we are removing relatively small amounts so the rate will not increase much. If you shorten a spring too much you may be able to correct the height with spacers but bear in mind that removing coils limits the amount a spring can compress before it becomes coil bound. As a rough check, measure the gap between two coils and multiply by the number of gaps to get a ballpark figure for how much the spring can compress. May not be a problem here but maybe worth checking.

 

[vibrac]

I have to agree with Greg on the AVO damper, I run mine on a twin with the damping on the lowest setting, and I'm 130kg, the problem is the AVO for the bushed front end is too soft for the ball bearing front end and the AVO for the bearing front end cannot be softened without an expensive complete re-design, they are totally different dampers internally.
As almost all the testing was done on twins might I suggest perhaps someone will volunteer to try the Bush type damper on a single with the bearing mod and see how it performs.

Mine is a bearing front end with an avo damper as supplied with it and I consider it far too stiff on a comet but I am going to revisit but not now I have missed enough riding weather playing with it

 

[davidd]

While we are talking about shortening springs, shorten carefully and take off small amounts until you get the required length. You can't put it back on. Shortening a spring increases the spring rate i.e. it will take more force to move the same distance. In this instance, we are removing relatively small amounts so the rate will not increase much. If you shorten a spring too much you may be able to correct the height with spacers but bear in mind that removing coils limits the amount a spring can compress before it becomes coil bound. As a rough check, measure the gap between two coils and multiply by the number of gaps to get a ballpark figure for how much the spring can compress. May not be a problem here but maybe worth checking

Very nice summary Eddy. When I was shortening Thornton springs which were 17" long and had a wire diameter of .177" they tended to rise 5 lbs. for every inch of spring I cut off. It was a 50 lbs. rate spring. When cut to 14 " they went up to 63 lbs. At 13' they were 67.25 lbs and at 12 they were about 75 lbs. It is difficult to cut much off before you stiffen things up a lot.

The white 130 sidecar springs coil bound at 9.3" out of the total of 14". The lighter 14" springs would coil bind at a lower height. Your results will probably vary a lot. I am surprised that anyone would have to cut down the spring boxes. The Works Performance damper has 2.85" of free movement and is supposed to get another .25" of movement into the rubber snubber for a total of 3.10". Having said all this I would follow Norman's advice as he is much closer to what is going on.

The Koni dampers were always wildly stiff. Bill's 30 year old konis should be perfect in just a few years and I know he will be enjoying them!

David

 

[macvette]

I checked the spring rate before cutting the spring. It came out at 44lbs/ins close enough to the nominal 45 lbs/ins. By calculation, taking off the 22mm has increased the spring rate to near enough 48lbs/ins so let's just say 50 lbs/ins. It has also reduced the preload on that spring to 1 ins. The total preload on both springs previously would have been 180lbs now with one spring modded and one as was, it is 140 lbs.
Just to be clear, when I refitted the shortened spring, the bike was on its centre stand with the other spring fitted i.e. some weight on the wheel but no damper so when I said I fitted the modded spring by hand it does not mean there is no preload on that spring. The 22mm is measured from the flat on the spring which is inactive so it effectively removes 2 coils
Regards Mac

 

[greg brillus]

The spring set up is entirely experimental and depends a lot on rider weight and other factors. I have had bikes where I have used one of David's red 75 lb springs on one side and a weaker one on the other. You need to be able to push down on the bars of else the set up is over sprung (or the shocker is too stiff) remember to that the front end will settle some amount, this is why you need to careful not to chop too much off the springs. This is the fine tuning that each machine needs..........The mod was done to improve the behavior and safety of the forks, the springs and shocker are more for rider comfort.

 

[macvette]

The spring set up is entirely experimental and depends a lot on rider weight and other factors. I have had bikes where I have used one of David's red 75 lb springs on one side and a weaker one on the other. You need to be able to push down on the bars of else the set up is over sprung (or the shocker is too stiff) remember to that the front end will settle some amount, this is why you need to careful not to chop too much off the springs. This is the fine tuning that each machine needs..........The mod was done to improve the behavior and safety of the forks, the springs and shocker are more for rider comfort.

I agree

 

[Chris Launders]

Spoke to a friend today with a Comet who tried the original bush type AVO with the bearing conversion, as with the twin it was far too soft, virtually ineffective even on full.
Chris.

 

[greg brillus]

Its not the shocker then its the springs too weak.