100 replies to this topic

[dc-65x]

Rodney and I are conducting a challenge of sorts. We want to see how fast we can get the old Pittman 703 through 706 series motors to go. The rules are simple, no neo magnets, no rewound or non-Pittman armatures.

We’re just doing this for fun of course. Both of us have had REALLY bad luck getting these things to perform so we’re pulling out all the stops in this challenge.

But first I need a body to build the car around. I looked through what I had and found a Lancer Cooper Olds... what’s that? I Googled Cooper Olds and...



HOLY SMOKES! Look at them pipes!!!! What is this thing? Whatever it was I had to build it. Here are some more picture of it:





... and a later "pipe-less" version:



Turns out this is the old Penske Zerex Special that Bruce McLaren extensively modified:



Here's what his website had to say about the car:

This was Bruce's first race car for the American series. The chassis was rebuilt in the UK and was based on rebuilding from just behind the front suspension to just ahead of the rear suspension with a new McLaren-designed tube frame that was welded in. This chassis was far stiffer that the willowy Zerex original and it had the sophistication of having the water and oil flowing through the chassis tubes. There was no time to fabricate the new exhaust system and the car was flown to Mosport with eight stub exhausts poking up through the tail. First time out it won at Mosport that year and at Brands hatch at the end of August 1963.

The car had three names, one "The Jolly Green Giant" (because due to a lack of time to finish the car, a handyman's store was visited and a can of garden gate green was obtained), the second name was the "Zerex Special" (re-framed and re-engineered, which the car was more commonly known as) and for various reasons Bruce decreed that the car should be known as the "Cooper Oldsmobile". Officially the car was a Cooper Oldsmobile when Bruce won with it at Mosport in June, 1964. The car won another race in the Guards Trophy at Brands Hatch at the end of August that year

"The Jolly Green Giant", eh? I guess that explains these pictures of scale models finished in green:



I rather favor the darker version:



Anywho, time to build a "race motor" from one of these old turds :



Which one shall it be... or will it be a little bit of both?

[JohnnySlotcar]

706 fer sure! Re-gear it so it winds out real fast.

John

[MG Brown]

Is there a Porsche-Cooper body available in 1/24? It might be more suitable for your project....

[Hworth08]

The race cars are faster now, safer, and better engineered. But the cars haven't improved near as much as the TRAILERS!!

The 706, such a well-built motor for it's time!

[dc-65x]

Hey John,

A 706 will be "part" of the build for sure .

I'll let some other "Bloger" go with the Porsche-Cooper. The Cooper Olds has me hooked with "them pipes".

[Hworth08]

Don't those motor mount the same way? Two holes in the bottom and the one long screw in the front??

[don.siegel]

Yep, or usually just the two screws on a bottom plate... the long screw was sometimes used in the Kemtron type chassis.

A 706 is already going to be kind of a tight fit in the Cooper Olds, but would be well nigh impossible in the "Pooper"! That's a great car, though, and would love to see a model of it, but it was tiny! A friend sent me two books on sports car racing in the Pacific Northwest, where Pete Lovely drove the Pooper, and it was quite a car - very effective too!

Rick, what are you going to be able to do without rewinding or changing the magnet? Braverman had an article or two on these types of motors (probably the 705), but it was his usual: add ball bearings and drill some lightening holes! I picked up an old one with ball bearings installed at the time, and it's got a little more kick than usual, don't know if the builder did anything else to it; it doesn't look rewound. Remember that these need a long run-in, too: at least a good hour, more like two to get the brushes really seated.

I'll be looking forward to this one!

Don

[dc-65x]

Hey Don H, the motors are meant to be mounted with 2 screws on the bottom…….or top depending on your point of view . That’s too easy so, “We don’t need no stinking screws” .

Don S, the Cooper Olds body is a tight squeeze around the mighty Pittman but it fits. That’s why I choose a body first. But now to the motor.

I looked into the latest, greatest of the 700 series first…the 706. What caught my eye were the pole pieces. They are massive and fit tightly around the armature for a tight and precise air gap:



That might make them a real torque monster. But the last time I ran one it was a real dog. It was new out of the package and not broken in so maybe it would have perked up with some running. The earlier 703-4-5 motors use Pittman’s time honored pole pieces of a heavy sheet metal stamped to form a looser and less controlled air gap. Maybe less torque and more RPM than a 706?

One thing for sure, those big thick pole pieces on the 706 make that motor HEAVY at a full 3 ounces (85 grams):



The 705 weighs in a 2.55 ounces (72 grams):



The magnets seemed the same between the 704-5 and the 706. Both had about the same gauss reading after 40+ years:



A big difference is in the armature windings. Both arms appear the same down to the comm timing except for the color of the windings. The 704-5 wire is brown and I get an OHM reading of about 2.3. The 706 windings are red and the OHM reading is 1.3. So the 706 should be a hotter (faster) arm.

Another difference is the 704-5’s are held together by crimping the pole pieces to the brass end plates. Any alignment was probably done in a jig at the factory when they crimped the motor together during assembly. The 706 on the other hand is made up of precision pieces that self align and it’s held together with machine screws.

So, what to do…..

705: Lighter, potentially higher revving air gap, slower armature but it really looks COOL!

706: Heavier, tight and precise air gap and alignment potential, hotter armature but it’s UGLY!

The motor I chose was…………………BOTH!

I’m building the cool looking, light weight, hopefully high revving 705 motor with a hot 706 armature. Here’s the old stock toad in all its glory before the build started:





Time to start hacking it up!

[don.siegel]

Sounds pretty wishy-washy to me Rick - want to get the best of both worlds, eh? Not very Kosher is all I can say!

More seriously, should be an interesting experiment. Like I said above, these motors really do need a very long run-in time - I remember first putting them on the track and going "Is that all there is, my friends? Keep right on dancing..." No, what I said was unprintable, but after quite a bit of track time, they become ... decent! The Ram XL-500 may be the fastest of these, since it has a 3-pole arm and much heavier windings - but again, pretty heavy (I'll weigh one to find out) and the magnet is limited. It was close to an average 36D, or the K&B Hellcat...

Don

[Prof. Fate]

Hi

Don't forget the copies Strombecker did!

Anyway, as a side story, the Cooper's motor was originally the same 2.7 climax as the Indy Cooper. The motor was acquired from that car and used by Penske and finally blew up in '64 at Continental Divide in Colorado. Philippe decades later found the motor and had Quinn Epperly rebuild it so that it could go back to its original home. You can see it in the other thread P did about his trip to england.

From the era of the 704/6, I have a survivor in a Maserati 300s and several others. Periodically, WE have a simple race for the cars at one of the local tracks. These motors usually only do about 18 to 20K. Back in '63, a lot of clubs used these motors for home tracks with short straights. The big commercial tracks didn't work.

Ecurie Martini/Alan Schwartz also on this board also has several survivors in 1/24 with these motors.

Fate

[don.siegel]

For what it's worth, one of most enjoyable races we held was a "Pittman Challenge", after I found a lot of old DC706 motors and matching Rannalli chassis. I put together 5 different cars with period vac-form bodies, and everybody got to run a qualifying time and then we had a final. They were all well matched and very enjoyable to drive on the American Black. You just have to get used to the idea that you're going to "drive" them, and not "punch" them between the corners... Not to mention that with all that weight in the back they really like to hang out their tails on the turns!

When the guys in NorCal were organizing some vintage races, I seem to remember that the DC65 was the hottest Pittman motor to have on a Blue King type track - clearly faster than these or the other types. On a short track, they don't seem to be much of an advantage, and the brakes aren't as good. (again, this is all anecdotal evidence, without a lot of development work).

Don

[boxerdog]

I know out of the several I built, the Ram "clone" of the 705 was faster than the rest, and the 196-style motors also performed well. Pittman did make a few lots of "6-volt" 705s for Norcal tracks in the 60's that were fast, too. I think Rick has a good plan, although maybe machining the 706 pole pieces might be an option.

[Larry LS]

Get a Pittman DC-70 6 volt arm for your 706 or whatever. They can be a big booster for the car.
I rewound 3 of mine to what I called a 4 volt version for a 52 hour enduro we had near here in Lompoc. CA..

I had three of them that could be swapped in and out in less than a minute. We could then
change motors, tires and check the brush wear every couple of hours by removing just two screws.
I still have one of those motors left that still runs fine with the original brushes still in it.

The mags can be re-zapped easy with my old Simco zapper. Which I still have
This was all done back in Dec.1965. We ran 16,759 laps in 52 hours.
We finished 2nd by 189 laps to a similar setup team but they ran DC65 motors that had been rewound also,
they were a bit faster per lap being lighter over all.

A long tiring race but fun overall. There were four team members for each team that ran and there were 6 teams.
I had three high school teenagers that ran with me. One of us ran an hour, one marshalled an hour and one took care
of the car and one slept for an hour in my VW van.

[dc-65x]

Thanks for everyone’s comments and memories, fun stuff!

I looked into the DC70-6V armature but the new ones I have all have shafts that are too short. I thought about Ram and Strombecker armatures too but they are out for this project as this is a Pittman only challenge.

So, here’s the rusty old dog all torn down to its pieces-parts:



Next I decided to “add lightness” to the motor….didn’t Colin Chapman say that? Anywho, I drilled 7/32” holes through both pole pieces. This also eliminated the tapped motor mounting holes (there’s no going back now!). I micro-bead blasted them to get rid of every trace of rust:



They looked pretty nice but not being able to leave well enough alone…..I polished the pee out of them:



Add more lightness, I need to drill more holes…….

[dc-65x]

More holes.........must drill more holes.....



More lightness added:



Now to replace that heavy brass spur gear....

[TSR]

Rick,
When you are finished, I will show you a picture of what is left of the real car, as its sits in a field in South America...

[n.elmholt]

Rick,
When you are finished, I will show you a picture of what is left of the real car, as its sits in a field in South America...

Please don't - there are enough depressed people around

[dc-65x]

I'm sure it won't be good. That's a shame.

[Hworth08]

Rumor is that Philippe is about to the car and thinks it can be completely restored for under three grand.

Or maybe that's what the wheels would cost! I can't remember my self-made rumor.

[Prof. Fate]

Hi

Remember, P, I was hunting for the car 20 odd years ago when you were hunting for the Cooper/indy! Sad, sitting in a field hosting mice and weeds.

Do you have the photos now?

Fate

[TSR]

The remains of the car are in Venezuela and very unlikely to be saved by anyone... at any price.
If Roger Penske or the McLaren people could have got to it, trust me they would have, even if the cost would have been over a million bucks for a few rusted tubes.
In fact, some of the tubing discarded by Bruce McLaren when he rebuilt and widened the car in 1964 did survive, but that does not make a car...
There are three different body configurations, all three were made as clear-plastic vacuum formed bodies in the 1/24 scale, in 1962 through 1964.

[mdiv]

Rick,

Where's the body?

Mikey

[dc-65x]

Here it is Mikey. Look how wacky the wheel wells were cut out at the factory. There is a good 1/8" difference side to side:



I'll use my Rick's Jig to get things squared up:



I also epoxied and balanced the 706 armature (705 in the background):



I checked the shaft straightness in my lathe and it was excellent. When I put the arm into the Team Pittman balancer 2 poles swung down so fast I couldn't believe it. It took 3 deep holes drilled into each pole to get it balanced.

Drilling holes.........need to drill more holes......where's that spur gear .

[mdiv]

Cool beans, Rick, what manufacturer for that body? It looks a lil crooked

--Mikey

[dc-65x]

Mikey,

I think, but can't prove, it's a Lancer body. They listed a Cooper Olds in their body list.

It's crooked because the wheel wells were cut out incorrectly by the factory. Fortunately, using my Rick's jig, I could re-cut them for the larger scale tires I'm using and get the body to sit Korrectly  .

I want to replace the heavy brass 48P spur gear with a lightweight Weldun aluminum 64P gear. I also want to change to a lower numerical ratio for more top speed. But where do you start with a fixed rear axle setup like the Pittman has ?

I used the internet and Googled gear formula and got the scoop. You can easily determine the center to center distance of a pinion and spur gear. The stock Pittman gears are a 9T and a 31T. You add the number of teeth on the pinion and spur together (9+31=40) Then you divide that by the gears pitch, which is 48, times two (48 X 2 = 96). So the magic center distance is 40 / 96 = .417".

Applying the magic formula with 64P Weldun gears I came up with a 13T pinion and a 41T spur for a center to center distance of .422". That seemed close enough to try and sure enough they mesh just fine in the Pittman setup. The ratio changed from the stock 3.44 : 1 to a taller 3.15 : 1 for, hopefully, more top speed.

But first I had to drill more holes! Add lightness!



Hey Duffy lookie! I remembered how to drill an 8-hole bolt circle without a rotary fixture using the good old 45-45-90 (Isosceles Right Triangle). With that done I'm sure I've lightened the gear by at least a billionth of a gram .

Here are all the parts modified along with full ball bearings and new brushes and springs.



Compared with the stock rusty motor parts:



Time to align, clamp and solder this motor together .