Delrin Arms for '94 YZ10

[ralphee]

Thanks man.....dont even know your name!!!

lee

[stickboy007]

Let me know if you hear back from them about ordering another set. The whole reason I did this (apart from having a cool set of arms) is so that other people would have a source for '94 repro arms.

[stickboy007]

As promised earlier today, I'd post some pictures of how I dealt with the fact that these arms are straight, as opposed to the stock arms which have kick-down.

Let me first point out that these mods that I have performed in no way reflect the build quality of these arms. These are fantastic arms, but tooling limitations meant that they can only be made flat, and so I had to do some post-repro work to make them more suitable.

The inside front part of the rear arm is the first to touch the chassis on downtravel, and so this part needs to be shaved first. I basically flipped the car over and pressed the a-arm toward the chassis, and then took a sharpie and marked a line where the arm was touching the chassis. Then it is a simple matter of using a round sanding bit on a Dremel and grinding away. I did this bit by bit on both the left and right arms. As I did the left arm, I kept the stock arm on the right hand side so that I can directly compare/measure the total downtravel. Likewise for the opposite side.

You really don't need to take away too much material, since a small change on the inside of the arm will result in a large difference in downtravel at the outside of the arm. When I was done, I added somewhere around 1-1.5cm of extra downtravel at the rear. As you can see from the pictures, it still does not quite go down as far as the stock arms, but if you use the upper hingepin hole on the rear hub carrier, you'll push the wheel hub down and so the wheel hub position is almost back to where it was in stock form. Granted, pushing the rear hub carrier down like this will increase the rear roll center and make the rear rotate more, but this is arguably offsetting the smaller rear downtravel which would otherwise give you less turn-in under braking (nevermind the center one-way giving you plenty of rotation anyway). Rear camber gain will also be smaller at full compression, since the outer camber link is lower down and so the hypotenuse length between the inner and outer link positions is smaller (assuming we have an imaginary turnbuckle that can extend/contract dynamically to keep the camber constant). This will also help the rear rotate more. One way around this is to get the Pavidis rear camber link plate and use one of the lower hole positions. Another option is to keep taking more material out of the inside of the rear a-arm to get more droop, so that you do not have to use the upper hinge pin hole on the rear hub carrier. Another option still, if you're brave enough, is to start shaving the chassis so that you don't have to take too much material out of the arms.

Another thing I needed to do, which you can see at the U-joint in IMG485a, is to use a rounded sanding bit to make a little pocket for the U-joint which would otherwise scrape against the arm.

I left the front arms untouched, since as you can see, the downtravel is comparable or larger than in stock form.

[stickboy007]

I finally got to running this thing yesterday at one of my local tracks. Had a real blast with it. Below is a video of me running during open practice after the main (I ran my 870C during the main...which actually ended up winning...that video is also below ).

For electronics, I am using a Hitec HS 7966HB servo, with a Novak GTB2 ESC and a Novak Ballistic 10.5T. 81T spur and I think a 20-ish tooth pinion (can't remember). 2.2" JC Racing rims with Pro-Line Holeshots front and rear with stock foam inserts (full inserts, not cut).

It took me a little time to get used to the one-way center pulley, since I'm not used to my B44 rotating like my B4.1. It's very interesting driving a chassis like that, but once you get accustomed to it, this thing is really awesome! You come into a tight turn thinking you overshot it, but since it rotates more, you end up hitting the apex just right. Very strange...

I don't have the stock wing mount piece in the back (although I recently got one from Jose), so I started by using allen keys to hold the rear wing. I began in the morning with a molded wing, but it was just too heavy for the allen keys and they started bending back after a few landings. Not wanting to fiddle with it too much, I eventually just took one of my beater lexan wings and mounted it on this. That worked just fine, as it was plenty light not to put too much stress on the allen key wing mounts.

I was also quite surprised with how well the 870C was running. It was harder to run consistently fast times with it, but it was indeed quick and my fastest lap time with it was in the 14.7 sec range (by comparison, my fastest lap on this same layout with my B44 was 14.0 sec).

94 YZ10 with delrin arms, open practice -->
[youtube]HXu4k_B2_RI[/youtube]
870C kicking some butt -->
[youtube]Ely_jU5Angg[/youtube]