Vintage Rear engine kart Steering Geometry?

[Denny Graham]

Just finished up a my Alley Kat copy last month and.....well, it's really twitchy!!!! As ya'll know, once the
welds are made on one of these, you're pretty limited as far as front end alignment goes. I set it up with
7° KPI and 7° Caster, toe in is the only thing that's adjustable on these old style karts, and that's about
1/16" to 1/8". I've got about 60-70 yards of straight drive before I have to shut it down and from a dead
stop I'm getting it up to 48-50 km/h (that's around 30mph) before I have to brake. At that speed it really
is quite....twitchy..... is the best way I can describe it.
There us no slop in the steering set up, has brass bushings, i.e., in the steering shaft
and king pins. New brgs in the front wheels with new vintage 4.10x3.5-5 slicks.
Using the typical pitman arm set up with tie rods swinging on a 2 1/2" arc.
This kart has the tie rods out in the front porch so Ackermann is not possible. (wish it were),
and that has me wondering if that might be the problem
Next one will have the tie rods behind the axle so I can build in Ackerman!!!!
Any ideas, examples or similar experience with this type of kart and this type of steering set up???
Denny G
Sandwich, IL

 

[anderkart]

I'd try more toe in.

Cool kart

 

[Denny Graham]

Think I had that first time out, that is a bunch of toe in. First run I just
eye balled the toe in just to give the kart it's first run after working on
it for two months.
It was super bad if I remember correctly, that's when I immediately shut
her down and put a ruler on it adjusting it correctly.
Still think it might be those damn steering arms/tie rods in front of the axle
that's causing the problem.
I've been working with Cyclekarts for the last 7 years and they're more
like a real car and respond to standard wheel alignment much better.
This is the first time I've messed with a go kart since I was a young teen
and that was 65 years ago. Both the karts I built back in the late 50's &
early 60's had the steering behind the axle and I can't remember ever having
a problem with poor handling due to wheel alignment. The were copies of the
early Bug karts. And I raced them at a local track for a few years.
dg

 

[madprofessor]

I started my big kart with spindle arms leading too, not to mention those spindle assemblies from MFG were factory welded at 90 degree angle so I couldn't set for any Ackermann either. Because the extreme angles and very long travel of the front end suspension that I set up with Monroe Max-Air MA-775 airshocks was binding the tierods, I had to weld on and reinforce some tabs to the spindles at a compound angle to make things able to move throughout the entire turning radius. (Had to custom make my own tierods too.) That also allowed me the bonus of making a radius so tight that it would almost go sideways.
My answer to not having any Ackermann was to mount those double-thick tabs well above the kingpins, with something of a flat Z-shape that allowed drilling the holes for bolting the rod ends down where the axle center/kingpin line would intersect the rod ends for correct Ackermann. No pics to explain it, but I'll attach a pic from much earlier where I tried to make my own rack-and-pinion with a sprocket and piece of chain, all of which the whole front end got cut off and remade with a pitman arm driven by a sprockets-and-chain reduction.
You can see some black tubing between the rod ends and spindle arms (that I twisted to give an outward angle for Ackermann) that raised the tierods to more closely parallel the homebuilt A-arms. That upward/outward angle sort of represents how the super-strong "Z-tabs" ended up relocating where the tierods mount.
No matter where you have to make the mounting holes for the rod ends to achieve enough room for Ackermann, even if it were a foot above the kingpins, as long as your tierods are parallel to the A-arms it'll work. If it's a rigid kart, the tierods only need to be parallel with the floorpan.
Including a pic of current but unpainted front end sans the outer rod ends.

 

[Denny]

Everyone is kind of avoiding the turd in the punch bowl and scooping out the punch around it. The tire centerline should be closer to the kinking pin. Having the wheels so far out on the spindle like they are just aggravates the movement. The wheel turning responds faster to less steering input. I’m not that eloquent with words, I hope you can understand what I’m saying.
picture your tire on the end of a phone pole. Now you push on the pole on the eng closest to the ground. It seems like it doesn’t move. But the end with the tire on it in the air sways a foot or more. Get it? What I would do for a quick fix is cut the top of the pitman arms free of the barrel and widen the notch. Then bend in the pitman arms to give more clearance to the tires and wheels to move them more inboard. And then reweld the pitman arms up.

 

[madprofessor]

D.Graham, I hadn't even looked closely at your kart pic when I started typing my previous post. Just clicked the magnification on your pitman arm, and I'm really confused now.
You've got those nice tierods mounted standard style on the same bolt on the pitman arm, and with the welded spindles you can't set for Ackermann like you said. Thing is, aren't I seeing a multi-mount "plate" as a pitman arm, with 3 holes down each side in addition to the center hole you're bolted up to currently?
Somebody here will likely tell me it's a bad idea, but far as I know, tierods can be mounted in such a way that they pass by each other as a way to achieve Ackermann angle just by changing the spot you bolt the tierods to on the plate. Imagine bolting the left tierod's rod end to the right side of the plate, and vice-versa for the left tierod to the right side of the plate.
That creates what the Ackermann setup is trying to accomplish, turning the inside wheel more sharply than the outside wheel. I've seen pics of several karts that get their Ackermann that way. Note that mounting the rod ends in mirror image as you should, it could make the bolts/rods/rod ends bind against each other in full turn. The cure is washering a standoff position for the rod ends so everything can pass each other smoothly.
Okay y'all, you can pile on and beat me up now, I'm a full-grown boy, I can take it.

 

[madprofessor]

bend in the pitman arms

reweld the pitman arms

I believe Denny meant to say the plural of "spindle arms". There's 2 of them (R&L), and only 1 "pitman arm". Though in your case I'm tempted to say "pitman plate".

 

[Denny Graham]

Yep, nothing or no one anywhere around me to go by so I've had to reverse engineer the whole kart.
Haven't messed with them since the very early 60's.
Yes, the pitman arm has multiple holes, for to experiment with. Set up a wooden bench test dummy and
the cross over steering attachment at the pitman arm was the first thing I tried. That would be the only
way other then locating your steering arms splayed out at the front to achieve Ackermann. It din't work
on the actual kart because the angles just simply, well....won't work unless there is lots of room for spacing
of the tie rod ends. And again, Locating the steering arms at the proper angle for true Ackermann, not enough
clearance with the front tire for that.
dg