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Monty’s Big “O” Super Iso Pro chassis


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#1 dc-65x

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Posted 09 March 2019 - 05:26 PM

This is a Riggen ad from the January 1973 edition of Miniature Auto Racing Newspapermagazine:
 
Big O Iso Pro- (9).jpg
 
Here is the real deal:
 
new%20Big%20O%20Iso%20Pro%202.jpg
 
new%20Big%20O%20Iso%20Pro%203.jpg
 
I've had this chassis just sitting around for years:
 
new%20Big%20O%20Iso%20Pro%201.jpg
 
The late great Monty Ohren did a beautiful job on it...
 
new%20Big%20O%20Iso%20Pro%208.jpg
 
............especially considering he was making them quickly for Riggen:
 
new%20Big%20O%20Iso%20Pro%205.jpg
 
I love the ISO feature:
 
new%20Big%20O%20Iso%20Pro%206.jpg
 
My plan for this thread is to make my own version of this chassis, build it up into a complete car and eBay the original chassis. I'm much more of a builder than a collector so it's time to pass it on for someone to enjoy after I enjoy making my own.
 
It should be a fun project as Monty did all the hard work designing and building his originals. I'm just following along and doing my best to duplicate his design genius and workmanship.
 
Monty used Associated parts for his frames. I'll have to make do with Parma. The drop arm is almost identical but the pans shown won't do. I'll have to come up with something else:
 
Big%20O%20Iso%20Pro-%2019.jpg
 
Here are the front and rear axle tubes, plumber and Iso hinge tubes and a scratchbuilt motor bracket:
 
Big%20O%20Iso%20Pro-%2018.jpg
 
Time to start soldering...
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#2 Pablo

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Posted 09 March 2019 - 05:40 PM

Ultra cool. :heart:

- GL looks huge, is it the photo? I'm guessing .9" or more?
- Why doesn't it have a limiter for the Iso?
- How much Iso drop will you give your chassis?
 
Thanks, Capt. Rick. :D :popcorm1: :popcorm1:
Paul Wolcott

#3 Bill from NH

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Posted 09 March 2019 - 05:48 PM

Rick, nice project! There was one of these Big "O" Iso Pro chassis on eBay three or four months ago. I'm not sure whether it sold for between $80-$100 or if it was over $100.

You probably have some of the Associated slot car bodies to put on your chassis once it's completed. As I recall, there were at least four different ones.

I'll be keeping my eyes open on this build. :)
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#4 dc-65x

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Posted 09 March 2019 - 05:48 PM

Hi Pablo,
 
The guide lead "looks huge" because the wheelbase (WB) is only barely over 3-1/2" !  :shok: I will be lengthening the WB a bit to fit a special body I have for it. The rear axle to guide pivot length will be the same.
 
As far as a stop for the Iso, maybe it was a simplification for production??? The pans are not hinged either and I read that Monty's personal race chassis were hinged.
 
I might install a spring on the Iso like TonyP did on this one of his:
 
Tony P ISO chassis 42.JPG
 
Or I might just build it stock...
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#5 Pablo

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Posted 09 March 2019 - 06:30 PM

:victory: :sun_bespectacled:


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#6 Bill from NH

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Posted 09 March 2019 - 08:39 PM

Rick, it appears that Monty used all .063 for his main rails. We did that in the East with heavy glue, but I thought he might have used smaller sizes too in order to get more flex for spray glue conditions. The other Iso Pro chassis that was on eBay was still sealed in the box so its photos didn't show all the details, like yours does.Thanks! :)


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#7 Martin

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Posted 09 March 2019 - 09:11 PM

Good to see a pro build. :popcorm1:


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#8 dc-65x

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Posted 10 March 2019 - 11:01 AM

You probably have some of the Associated slot car bodies to put on your chassis once it's completed. As I recall, there were at least four different ones.

 
You're right Bill. I've got a complete Associated Porsche SS body kit to share but first here is the period MAR newsletter article that inspired my build. The main focus of the article is proper body mounting and air control techniques but a car with an Iso Pro chassis was built up for this article:
 
Click on the picture to enlarge
 
Big O Iso Pro- (6).jpg
 
Big O Iso Pro- (3).jpg
 
Big O Iso Pro- (2).jpg
 
Big O Iso Pro- (1).jpg
 
Big O Iso Pro-.jpg
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#9 Pablo

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Posted 10 March 2019 - 03:11 PM

Awesome, thanks for posting that :clapping: :good: :sun_bespectacled:


Paul Wolcott

#10 dc-65x

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Posted 11 March 2019 - 10:54 AM

You bet, Pablo. :victory:
 
I started the build with the drop arm instead of the rear end as I usually do with a "traditional" chassis.
 
Two 3/32" X 1/2" long hinge tubes and a .055" X 2 3/4" long piano wire "bumper" are lined up to be soldered in place. The bumper will be trimmed to length to match the width of the pans later:
 
Big%20O%20Iso%20Pro-%2021.jpg
 
Finishing the drop arm (that doesn't "drop" in this build :crazy: ) is a piece of 1/16" piano wire bent around it. The U-bent wire is 3 3/32" long:
 
Big%20O%20Iso%20Pro-%2027.jpg
 
The "heart" of this chassis buffed up a bit:
 
Big%20O%20Iso%20Pro-%2026.jpg
 
Big%20O%20Iso%20Pro-%2025.jpg
 
Attaching the rear axle tube with half rails is next...
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#11 Pablo

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Posted 11 March 2019 - 03:46 PM

Making a pro chassis, very cool.

Hitting a double bend in .063 wire just perfect, priceless personal satisfaction. :)
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#12 dc-65x

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Posted 12 March 2019 - 06:48 PM

Pablo, I thought I'd be using yards of piano wire to get that U-bend right. I lucked out and got it on the second try. :dance3:


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#13 SpeedyNH

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Posted 13 March 2019 - 05:36 PM

doesn't even look like you had to tweak it! nice job.

speedy


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#14 dc-65x

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Posted 13 March 2019 - 06:25 PM

Thanks Speedy

 

Time to connect the rear axle to the drop arm assembly.

The rear axle centerline (CL) to guide post CL is 4 5/8".

The right half rail is straight and positioned in front of the axle tube and the left rail is bent at about 9 degrees and is positioned behind:

 

Big%20O%20Iso%20Pro-%2034.jpg

 

The second set of half rails ready to go. This time the left hand rail is straight and the right hand has a little kink:

 

Big%20O%20Iso%20Pro-%2033.jpg

 

Here they are soldered into position:

 

Big%20O%20Iso%20Pro-%2032.jpg

 

It's starting to look like something :) :

 

Big%20O%20Iso%20Pro-%2030.jpg

 

Big%20O%20Iso%20Pro-%2028.jpg

 

The ISO front end is next...........


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#15 mike1972chev

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Posted 13 March 2019 - 07:12 PM

You do WAY pretty work. ;)


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#16 dc-65x

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Posted 15 March 2019 - 11:31 AM

Thanks Mike :)

 

Here the ISO hinge tubes are jigged up:

 

Big%20O%20Iso%20Pro-%2036.jpg

 

The tubes are set back about 1/16" from the edge of the half rails to allow for the bend in the ISO hinge:

 

Big%20O%20Iso%20Pro-%2037.jpg

 

Ready for the ISO front end:

 

Big%20O%20Iso%20Pro-%2035.jpg

 

 


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#17 Martin

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Posted 15 March 2019 - 02:40 PM

Great build Rick.

Could not help notice some of your steel rods have a nice radius on the end.  Do you have a reverse chamfer tool of some kind?. Nice detail.


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#18 dc-65x

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Posted 15 March 2019 - 02:51 PM

Thanks Martin. I use a file to chamfer the ends except on the pictured ISO rail. I used the Dremel cut off wheel to grind a full radius before I made the 90 degree bend.


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#19 Phil Hackett

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Posted 15 March 2019 - 03:22 PM

Rick, it appears that Monty used all .063 for his main rails. We did that in the East with heavy glue, but I thought he might have used smaller sizes too in order to get more flex for spray glue conditions. The other Iso Pro chassis that was on eBay was still sealed in the box so its photos didn't show all the details, like yours does.Thanks! :)

 

Spray glue didn't take hold in SoCal until the late 70s. When this chassis was built we were still throwing rooster tails of glue behind the cars. A double .063 chassis is appropriate for the time and place.

 

Personally, my chassis were .055 rails. I played with a .055 & .047 rail set up but it was too sensitive to glue and temperature.


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#20 Bill from NH

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Posted 15 March 2019 - 03:51 PM

Phil, thanks for the reply.


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#21 dc-65x

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Posted 15 March 2019 - 07:27 PM

The ISO rails are ready to go.........

 

Big%20O%20Iso%20Pro-%2041.jpg


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#22 dc-65x

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Posted 16 March 2019 - 04:45 PM

The ISO front end is installed:

 

Big%20O%20Iso%20Pro-%2040.jpg

 

Big%20O%20Iso%20Pro-%2038.jpg

 

I lengthened the wheelbase (WB) from just over 3 1/2" to 3 3/4" to fit the body I want to use. The rear axle to guide distance was left as is and that worked out to a 7/8" guide lead with the new WB:

 

Big%20O%20Iso%20Pro-%2039.jpg

 

Then I put the buff to the chassis and polished it out:

 

Big%20O%20Iso%20Pro-%2043.jpg

 

Big%20O%20Iso%20Pro-%2044.jpg

 

Big%20O%20Iso%20Pro-%2042.jpg

 

Just a few more details on the center section to go..........


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#23 SpeedyNH

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Posted 16 March 2019 - 05:20 PM

will you be doing any wire tying?


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#24 dc-65x

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Posted 16 March 2019 - 07:28 PM

Hi Steve,

 

My plan is to build it pretty much stock as shown in the MAR article I posted earlier. 


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#25 SpeedyNH

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Posted 16 March 2019 - 08:10 PM

ah I see


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