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Sportsman/Olympic Aft End

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Sportsman/Olympic Aft End Empty Sportsman/Olympic Aft End

Post  dckrsn Tue May 04, 2021 8:58 pm

Are there any differences between the intake assemblies of
the Cox Sportsman and Olympic engines, other than the
anodizing? Asking for a friend(me).
Bob
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Post  Marleysky Tue May 04, 2021 9:14 pm

Other than the product part number and color of course , they look to be very interchangeable.
I wish i new how to blend two photos into one, but  here:  1100 series vs 1400 series

Sportsman/Olympic Aft End A4de8610
Sportsman/Olympic Aft End E8b33410
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Post  dckrsn Tue May 04, 2021 9:44 pm

Thank you-thank you. I'm about to embark on a resto on
an Olympic .15 for a friend, and It's going to be a runner.
Bearings on order.
Bob
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Post  James clive Wed May 05, 2021 4:14 am

Trial only
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Post  getback Wed May 05, 2021 7:08 am

I have both , But would have to take them apart ? If you want i will do it for you . Hey James clive !! Small Cox Logo
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Post  KariFS Wed May 05, 2021 8:14 am

Since the needle valves are the same on both, I would assume the needle valve body has the same internal geometry.

I have a loose Sportsman venturi/reed assy somewhere and I think one for an Olympic too, will check later today and compare to see if there is a difference in the intake diameter or shape. No need to risk your assembled engines’ finish Eric Wink

Bob, where did you get the bearings? Please post some pictures of the process Thumbs Up
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Post  dckrsn Wed May 05, 2021 12:14 pm

I accidentally posted the wrong part #
for the Olympic bearings. Sorry for any
grief caused. I actually ordered flanged
bearings, which I'm pretty sure is wrong.
Sorry,
Bob


Last edited by dckrsn on Sat May 15, 2021 4:43 pm; edited 1 time in total
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Post  KariFS Wed May 05, 2021 1:09 pm

Bob, Thanks for the bearing info Thumbs Up

I dug out the parts, here’s a pic:

Sportsman/Olympic Aft End Bcc41410

The intake port is considerably larger on the Olympic. A 3mm drill bit goes right through the red one, 3.2mm might go if persuaded a little. I didn’t Smile On the Sportsman part a 1.5mm bit goes right through, a 2.5mm does not. I seem to have lost my 2mm bit... Anyway, it is quite small compared to the one on the Olympic.

I’ll let you figure out the fractions of inch or drill bit #’s Very Happy
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Post  ffkiwi Thu May 06, 2021 1:45 am

Not only are the intake diameters different as shown above-but the reeds themselves are also different-the Olympic has a 'two tab' circular reed; the Sportsman has a cruciform style reed like the Classic Babe Bee 049....I could not say whether the separate .15 reed types are different thicknesses as well....

ChrisM
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PS I have found the Olympic disappointing in use-having poor suction (in a FF power duration model type use..)-I might at some stage try it with the Sportsman intake fitted in place of the Olympic one and see if the small venturi diameter improves the fuel draw....it ought to...
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Post  KariFS Thu May 06, 2021 4:27 am

Chris, do you have a picture of the reed you describe? On the parts lists Rene posted, both engines have the same part number 1108 for the reed valve. Maybe your version is some type of an aftermarket part or a later update?

A Sportsman backplate would be a good starting point for tuning an Olympic for ease of use and performance. Just drill the port gradually bigger. A 2.5mm to begin with maybe?

I am not sure what the Olympic was made for, it does say something about free flight on the package, and ball bearings indicate high rpm, maybe it was intended to have a pressure feed?

I have two Olympics, been toying with the idea of maybe converting one of them to diesel, for ”Weatherman” vintage speed class. Not going to happen any time soon, but I’ll keep the differences in port sizes in mind for that Smile
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Post  ffkiwi Thu May 06, 2021 4:53 am

@KariFS wrote:Chris, do you have a picture of the reed you describe? On the parts lists Rene posted, both engines have the same part number 1108 for the reed valve. Maybe your version is some type of an aftermarket part or a later update?

A Sportsman backplate would be a good starting point for tuning an Olympic for ease of use and performance. Just drill the port gradually bigger. A 2.5mm to begin with maybe?

I am not sure what the Olympic was made for, it does say something about free flight on the package, and ball bearings indicate high rpm, maybe it was intended to have a pressure feed?

I have two Olympics, been toying with the idea of maybe converting one of them to diesel, for ”Weatherman” vintage speed class. Not going to happen any time soon, but I’ll keep the differences in port sizes in mind for that Smile


I put mine in a Dixielander-for which it was an entirely appropriate choice-given the Dixielander came out in '58 and the Olympic in '59-it started, set and ran beautifully with the model held horizontally-and I'm talking 30% fuel here-so the sort of fuel it was designed for operation on-but when elevated to launch angle it would just sag and die-and this was nothing to do with needle setting.

As for the different reeds-I am 100% certain on this aspect....why? Well both my Olympics were bought second hand...and somewhat the worse for wear-cosmetically....you know that bloke?  Mr Pliers?....and his good mate, Mr Vice Grips?....well to cut a long story short-in 1993 I was on the NZ F1C team for the World Champs at Lost Hills...on the way we stopped at Tony and Addie Naccarrato's famous shop in Burbank [took us half a day to escape...it was paradise]..in between yakking, I casually asked Tony if he had any old Cox spares...'bound to-what are you after?' was the reply. "Any bits for an Olympic?" was my response. He had a rummage in the myriad of drawers-and pulled out several unmistakeable 'old style' Cox spares small paper envelopes-two of which contained the complete Olympic backplate and carb assemblies-absolutely mint.....these too had the 'tab' type reed fitted-so there's no doubt this is the way they came, ex factory.  The sportsman of course post dates the Olympic...and was around much longer than the Olympic-in production for 8 years rather than two. I would also be suspicious of the part number given-the Olympic was cat no 140, the Sportsman cat #110....so 1108 would be a Sportsman part-not an Olympic one-which would have a part number of 14xx....of course I bought the two carb units on the spot-plus a couple of starter springs-which most Olympic users discarded anyway-but I wanted a complete engine for the collection.

I'll try and post a photo at the weekend....
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Post  getback Thu May 06, 2021 7:17 am

I have the plain bearing in mine is this the earlier or the latter ? Cinco de Mayo
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Post  gkamysz Thu May 06, 2021 9:20 am

https://www.ebay.com/itm/274692360120 The reed looks like this.

I'm sure the Olympic was intended to be run at high RPM, going by the old reviews, propped for >15kRPM.
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Post  Scotland421 Thu May 06, 2021 10:20 am

If ye lug down the Olympic, ye wi have fuel draw problems. Let her wind up, use a competition grey 7X3.5 or 7X4.
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Post  ffkiwi Thu May 06, 2021 4:00 pm

@Scotland421 wrote:If ye lug down the Olympic, ye wi have fuel draw problems. Let her wind up, use a competition grey 7X3.5 or 7X4.

Well going by the published engine tests-that underprops it to a significant degree-there is absolutely no point in propping an engine to run faster than its BHP peak in the air-unless you want to wear it out faster....and the Olympic peaks in the range 16,500-17,000

Whilst on the subject of reeds-here's a link to the Sportsman type: https://www.ebay.com/itm/164845475576?hash=item26618e56f8:g:ctkAAOSwO7dfXobg quite different to the Olympic one

ChrisM
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Post  dckrsn Thu May 06, 2021 4:08 pm

Chris, Kari, Eric and Scotland421, thanks for
all your help. I Love This Forum!
Bob
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