Many questions about different parts

[81xsproject]

Okay so I have some future projects in mind and wanted to get the specifics on some model/differences. I am sure I could spend 3 hrs doing searches and reading through 50 different threads. But, I know many of you know the answers right off the tops of your heads.

First, I want to go to a standard front fork assembly. I know that the wheel mounts are not rear set like my special, that the speedo gear/cable and calipers are different. Are the forks the same length? Do the triple trees hold the forks at different steeper angles?

Second, does the 4R0 ignition have a built in advance 'CURVE' or does it just have one set advance that the vacuum retard unit adjusts creating a 'curve'.

I am also curious what would be involved in converting back to a mechanical advance unit so folks would have a way around trying to find the more rare 4R0 units.

[fredintoon]

More trail if you ain't careful

"First, I want to go to a standard front fork assembly. I know that the wheel mounts are not rear set like my special, that the speedo gear/cable and calipers are different. Are the forks the same length? Do the triple trees hold the forks at different steeper angles?"
Hi 81XS,
the Standard and Special front axles are in exactly the same place although it don't look so. Mix'n'match can change the trail so be careful.
What I did was install the 'trees from a Standard on my Special. This moved my front wheel forward by ~ 1-1/2" to give me the reduced trail to lighten the bike steering for sidecar use. Do you propose fitting Standard fork legs into your Special 'trees? If you do you will get ~ 1-1/2" MORE trail and very stable very heavy steering as a result. You have to swap the entire fork assembly. If you do that the front wheel stays exactly where it was.
Yes, the Special's fork tubes are longer but the axle is stuck on the front while the Standard's axle is underneath.

[Renegade]

Re: Many questions about different part

Originally posted by 81xsproject
[B]First, I want to go to a standard front fork assembly. I know that the wheel mounts are not rear set like my special, that the speedo gear/cable and calipers are different. Are the forks the same length? Do the triple trees hold the forks at different steeper angles? /B]

Triple trees are different between Special and Standard because of the axle location. The different trees give both models the same steering geometry. If you swap the forks and trees as an assembly, there is no change in geometry. But Standard trees with Special forks, or Special trees with Standard forks will change the trail. I forget which is which now, but one combination increases the trail while the other way reduces trail. I believe that this was discussed in another thread in regard to sidecars some time ago.

[81xsproject]

What I am going for is to decrease the rake by using both the standard tree and forks. I also plan on letting the tubes sit about 1" out of the top of the tree. I would like to quicken the steering a bit. I might also get about and inch taller rear shocks. This down in the front/up in the rear combo was said to really improve the handling by xs650mike.

[Dennyz]

Using Standard trees and forks will not change the trail or rake (steering angle). As, stated above, the Special and Standard have the exact same steering geometry.

[Dennyz]

There might be some confusion between fork angle and steering angle. The steering angle can only be changed by moving the steering head.

Since trail is the distance from where the steering angle is projected to the ground to a point projected straight down from the axle, moving the tire forward (increasing fork angle) moves the axle towards the steering angle projection point. This reduces trail.

[TopCatGr58]

Hey Jessie,

What Fred said is that you need to swap ONLY the TT's to change the geometry to quicken the steering. IF you swap both the standard TT's and the front forks, then you won't change a thing!

The 4RO TCI does have the cent. adv. curve built into it's programming, it just uses the vacuum advance/retard unit to change that aspect of that curve. If you haven't seen or read the Ignition Module thread, doing a search will reveal some information and graphs about that very thing!

That'll be very nice of you to offer your soon to be spare 4RO box once you get your new Ebay MSD system running!
T.C.

[81xsproject]

So, with that plan shot what about the timing curve. Does the 4R0 ignition have a built in curve? The reason that I ask is because of the MSD ignition I am planning on trying out. I think it will requires removal of the unit and addition of a mechanical advance pick-ups.

[fredintoon]

Got the parts?

Hi Jessie,
if you fit Standard 'trees to your Special fork tubes you will for sure quicken the steering. I'd say try it. Very carefully, it may be too quick for solo work. Swap in the Standard fork ears too so you won't have to cut down the Special's; that way you can swap back no problem if the quickened steering is not as you wanted it to be. On either model just lifting the fork tubes through the 'trees will quicken the steering a little. ALSO, fitting the complete Standard fork will swap those daft ATE style front brakes for the Standard's normal ones.

[TopCatGr58]

Hey Jessie,

I didn't re-reply to your last post because the answer was in my last one, think you might not have seen it before you posted your last reply???

IF you are wanting to use the standard brakes, I'm pretty sure you can swap the upper tubes from the special into the standard's lower sliders, and use the standards TT's, that way you have more upper tube to slide up thru the TT's for adjustment and mounting clip on bars as well.

As for this mod being too quick, Fred, I don't think he'll have any problem. IIRC the trail gets reduced by about 1 to 1.5 inches with this TT swap, which will give him abotu 4 to 3.5 inches of trail vs. the stock 5. Due to my frame RAKE adjustment, I've been set at 2.5" of trail, and it still behaves fairly well, so I think he'll like it!
T.C.