77 replies to this topic

[dc-65x]

My new project is to build one of my personal favorite cars... yup... a Cheetah.

 

I found a cool web article by Keith Charvonia and Sean Klingelhoefer on the SPEEDHUNTERS website (link below):

 

Fast Cat: The Bill Thomas Cheetah

 

The web article is mainly dealing with a continuation Cheetah project but they did a nice brief history of the original Cheetah I'm quoting below:

 

I think we all have a pretty good idea of what Ford was up to in the early ’60s on the GT race circuit – building Cobras with Carroll Shelby of course. With the undisputed prominence of the Cobra, have you ever stopped to wonder what Chevy was doing around this time? Of course there were the Grand Sport Corvettes, but for a brief moment Chevrolet was also working on a top secret back-door racing effort – something all new that had the potential to be even lighter and faster than the Corvettes. You’re looking at it; the Bill Thomas Cheetah, a Chevy-backed GT racing program designed to be a Cobra killer.

 

In the early ’60s Bill Thomas caught Chevrolet executives’ attention by building some very quick Corvairs, Chevy IIs and Corvettes. When Chevy saw the success of the Cobra race program, they quietly commissioned Bill to build 100 cars to meet FIA homologation requirements. These would be ultra-light 1500 lb, mid-engine, V-8 powered racers designed to do one thing – dominate the Shelby Cobra.

 

It’s fair to say these cars never even really got out of prototype phase though. Development began in 1963 but a fire in Bill Thomas’ shop took out most of the parts, several cars and even the original plywood buck used to form the first two aluminum bodies. On top of that there was an automakers’ racing ban in effect, so GM couldn’t be seen sneaking engines out the back door for Bill Thomas’ Cheetahs. The final nail in the coffin came when Chevy realized just how competitive the Cheetahs could be, not just to Cobras, but to their own flagship Corvette. With all of these combined pressures, Chevy pulled the plug on the Cheetah project in mid-1964.

 

Below are some period pictures of the original prototype which is my favorite version and the one I'll be building. It's devoid of all the later versions lumps, bumps, scoops, vents, fender flares and carburetors sticking up above the hood:

 

 

 

 

I love those period pictures of the prototype possibly during an early test session.  

 

Thankfully Lancer made the early version with their No. 81 Cheetah:

 

 

 

 

I'm working on gathering up the parts for the car. I want to keep the build around the 1965 time period so that's too early for a "jail door" style chassis.

 

I'm still deciding on wheels and tires but I have a very special motor I'm restoring for the project which will be up next.

 

Onward!

 

[don.siegel]

Now, this is exciting! 

 

Looking forward to this one Rick, like all the others. 

 

If you give us a hint, can we guess at the motor? 

 

Hmm, 1965, eh? Special, eh? 

 

Don 

[Alchemist]

Exciting project Rick!

 

I always look forward to the progress pictures as well as the completed project in all its sartorial splendor!

 

Ernie

[dc-65x]

The motor for this car is from the Dave Lenz (brother of Bob Lenz) slot car box he gifted me:
 

The last Dave Lenz car is this Lancer Bat Ray that I need to restore:
 

 

 

 
An early Lenz motor:
 

 
A few more motors and chassis to come........

 

Here's the link to the Dave Lenz Thingies thread:

 

Dave Lenz Thingies

 

This motor is a super early Lenz rewind. Taking it apart for restoration is a real history lesson of how the whole rewound Mabuchi thing started.

 

Disassembly and photos to come.

[Bill from NH]

I like the simplicity of the above Lenz chassis.

[Pablo]

Nice BB fronts

[dc-65x]

The Lenz Bat Ray was gifted to Rodney, less the motor, and was built up to live again. The early Lenz motor gets disassembled for restoration today.

 

In the mean time, here is a 1963 track test of the then new Cheetah from Sports Car Graphic magazine.

 

Click on the picture to enlarge for easy reading:

 

 

 

 

 

 

[Pablo]

Awesome 

[dc-65x]

The motor for the Cheetah ready for restoration:

 

 

 

Here it is in pieces:

 

 

I'll get things cleaned up. I especially want to check out the armature, brush springs and magnets.

[dc-65x]

The armature looks to have been dipped in armature insulating varnish rather than epoxied. I followed PdL's lead on cleaning up the armature and used mineral spirits instead of anything harsher.

 

The first thing after cleaning was the commutator's "valley of the comm".  Here's the divot after coating the comm with black marker and making one light cut:

 

 

Mabuchi comms are pretty thin and I got most of the divot out before I chickened out and stop cutting. 

 

Lenz put some clockwise advance to the comm:

 

 

Here's a comparison with a Russkit 23 arm on the left. The Lenz is wound with a heavier gauge wire and has a 1.2 ohm reading compared to the Russkit's 2.2 ohms.

 

I hadn't realized there were 2 different versions of the Mabuchi "green comm". The Russkit 23 comm on the left is also used on the later 1968 ball bearing version Mabuchi:

 

 

So this early Lenz arm got rewound with heavier gauge wire, the comm advance a bit, a soaking in armature insulating varnish and balanced by some means. 

 

 

 

[dc-65x]

The motor uses stock Mabuchi magnets with no shims............no "masking tape shims" shown in some of the old slot car magazines either.

 

I checked the gauss reading and they weren't very evenly "matched" with one reading in the 480's and the other in the 520's.

 

All the vintage Mabuchi magnets are anisotropic and can't be remagnetized like vintage Champion (ARCO, Super ARCO, DZ, Blue and White Dots), Versatec and Mura Super B's.

 

I chose a pair with a low gauss reading to zap and show this.

 

BEFORE:

 

 

ZAPPING:

 

 

AFTER:

 

 

Here's the reading of a matched up pair of good Mabuchi magnets for this motor:

 

 

The Lenz can and magnets ready for paint and assembly. The dreaded Mura style pin tabs are replaced with 0-80 stainless steel pan head machine screws:

 

[don.siegel]

Thanks for Rezapping 101 Rick! 

 

I've read that before too, but it's kind of sobering to see the real evidence. Can you remind us how these gauss readings compare to the hotter magnets - something around 500 seems higher than I had remembered and not that far from the Arcos. 

 

Maybe no masking tape, but are you using steel shims? 

 

Don 

[dc-65x]

Hi Don,

 

I went through over 20 pair of Mabuchi magnets. Most were in the 480 range and only a few pair were over 500. 

 

I want to just refresh the motor and see how it would have performed back in the day. I did replace the lower gauss magnet in the Lenz with one that more closely match the higher reading magnet. But I've decided not to modify it by adding shims to the magnets. 

 

Here are a couple of later vintage magnets for comparison with the Mabuchi's.

 

Champion Super ARCOs:

 

 

 

Super B magnets for the Mura B motor:

 

 

[don.siegel]

Thanks Rick, I see what you're doing. 

 

Not as big a difference as I would have thought with the Arcos! 

 

Don 

[Bill from NH]

You can also match magnet strength to a track's power source. You don't always want to use the highest gauss possible. A track with plenty amps you would, but a track with a moderate power supply might be better with less.

[don.siegel]

Bill, 

 

Isn't that more in relation to the wind, and not so much to the track power? 

 

Don 

[Bill from NH]

It can be both according to Monty Ohren's old OWH forum. Some classes run the same "spec" arms regardless of track layout or powering. Open class wings & Eurosports are about the only contemporary classes where the arm winds are not specked. Vintage racing may use some unlimited arms too.

[dc-65x]

I have been working on this project but I haven't brought myself to post anything for weeks. My writing is constantly edited and is apparently not up to the standards of this slot car forum. I am edited even after I have my post preapproved before posting it.  

 

I will now try to limit myself to just posting pictures with as few words as possible.

 

Vintage K&B front tires:

 

 

Front wheels are Electric Dreams repop Russkit standard width rear wheels on the left. They are a bit narrower than the vintage Russkit wheel on the right and fit the K&B front tires perfectly.

 

 

This front wheel is set up to "free wheel". The other wheel is locked on the axle:

 

 

Rear wheels are our repop Russkit standard width rear wheels. The wheel on the right had its flanges chamfered and the tire mounting surface roughed up:

 

 

Paul Gage urethane K&B rear tires:

 

 

Wheel inserts are made from Cox accessory tapped wheels. These are not the wheels used in the Cox Cheetah kit:

 

 

Cox wheels machined into wheel inserts:

 

 

Wheel insert bored out to fit a 2-56 screw for the Cox "acorn nut" and micro bead blasted: 

 

 

Front wheel OD on the left is 31/32". Rear wheel OD on the right is 1 1/16":

 

 

 

 

[olescratch]

  I like getting new ideas from people on this site.  How were you able to turn the wheels down to make inserts?

[Pablo]

Wheels don't get any sexier than that     

[dc-65x]

Thanks Pablo, I like them too.
 
Hi John. Here's the process I used on a previous build. It is virtually the same as what I did on the Cheetah's American Mags.
 

Those oxidized Cox Ferrari wheels are going to become some nifty wheel inserts for my Russkit setscrew wheels. Maybe in the day I could have scrounged up some plastic Ferrari wheel inserts from a Strombecker kit or whatever. Today, I found the Cox Extra Narrow front wheels on eBay for $5.99.
 
My Cyclone Bench Top micro bead blaster started the process:
 

 
This handy little blaster is only 18" wide and costs a bit over $160. I run it off a small pancake air compressor I got on sale at Sears. The glass bead dust all over the place is the result of the gloves finally rotting out. I didn't notice the holes until I was done.........too late! New gloves are on the way for $9.40.
 
Micro bead blasting makes quick work of the old Cox wheels:
 

 
Here's a before and after "the blast". Notice all the casting "flash" on the middle wheel. It is quickly trimmed off with an Exacto knife as shown on the right:
 

 
The next step in the wheel insert process is to turn the diameter of the wheels to .500": Depending on the wheel, it can be held in the lathe with the chuck or a collet:
 

 
The inserts were the right diameter but too thick. A blank "pot chuck" is bored to .500" to hold the insert:
 

 
Now the insert can be narrowed up:
 

 
Here's the finished product. The rear inserts (on the right) were left a bit thicker than the front:
 

 
The finished inserts weigh almost nothing:
 

 
A little blue paint on the inserts and black on the insides of the rims. A final touch was to remove the blue paint from the lug nuts and their done:
 

 

[dc-65x]

Chassis time. I'm building, for lack of a better description, a pre-jail door chassis from 1965 or so. I'm using Buzco front and rear motor brackets:

 

 

Also using Garvic "duffys" (bearing retainers):

 

 

50+ years of oxidation was quickly removed with a Tarn X soaked Scotch-Brite pad.

Both brackets were slotted to allow the motor to be removed from the chassis:

 

 

In order for the motor to be lifted up out of the chassis it must be slid forward to free the endbell bearing from the bracket. I shortened the endbell bearing to minimize this movement to 1/16". The front half of the bearing is oversized and I suppose it was intended as an "oil reservoir": 

 

 

A 1/16" spacer is shown by the arrow to space the front bracket forward. The 4 main pin tube rails are soldered in place:

 

 

[dc-65x]

To connect the front axle I bent the lower rails inward as was shown in the Russkit Scratch Builder Kit instructions:

 

 

I could have left the motor level as some did but I went the "low CG" route as Jim Russell did in this 1964 article:

 

 

Angling the front of the motor down as far as possible was also a modification done to kit cars back in the day:

 

 

Here's what it looks like on the jig:

 

 

 

The basic "center section" trimmed and cleaned up:

 

 

[Larry Horner]

Rick, I've noticed over the years that you tend to use a lot of brass tubing as opposed to rod. Just curious but is there a particular reason or is this just a personal preference? I can see that weight might be one reason but this is already a pretty minimal chassis. Looking good so far!

[dc-65x]

Hi Larry,

 

The Russkit Scratch Builders Kit instruction sheet actually recommends using brass tube for the top rails and brass rod for the bottom. I can only speak to what we were doing in my area of Southern California in the early 60's. Motors weren't very powerful and traction was limited so light weight was king.