Correct Sprocket Size

[Brian Smith]

Newbie looking for advice/ info on sprockets.  Have a '60 Dart Super K that I'm restoring back to dual West Bend 580's. Currently has a HUGE sprocket only slightly smaller than the rear tire that I assume was for the MC75 that was on it when I bought it. I want to go to the outboard sprockets and correct hubs for the live rear axle. Will any sprocket hub work?  Looking to make it very correct and original.  What diameter sprocket would it have come with originally?

[steve miller]

I think they have 6 inch rears ..?? need atleast 70-76 ..70 with duels 74 with one ..and 9 on top single twins should pull a 10 ..
lot depends on your weight where you run it bla bla bla ..
I only weight 135 ..I can run a 68 ..lol..

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if I had wild guess... id say its got either 78 or an 80 on it now ..

[doug tenney]

Brian, if you haven't already, check out Azusa Engineering's catalog.  They've been around since 1960 and are crucially important to this hobby.  Pretty much all kart shops are Azusa dealers.
There is one format of sprocket that everyone uses for vintage rear-engine karts: 4-9/16" hub, with 6 bolts on 5-1/4" bolt circle, with #35 chain.  Get aluminum split sprockets, so that you can change them if you whack one going off the edge of the track a bit, or want to change the ratio.
For your application, I'd start with roughly a 6.5:1 ratio.  So, if you have 10 teeth on your clutch sprocket, go with 65 or so teeth on your axle sprockets.  If you have a 9T clutch, 9 X 6.5 = 58T or 59T.
If the driver is over 180 lbs or so, and/or the track is tight, you could go to a 7.0:1 ratio.
Azusa's "Mark IV Vari-Hub" #1872 sprocket hub will work well and look at home on your kart.  I don't think it's the exact hub that was available in 1960 but only experts will be able to tell.  In fact, a lot of folks skip right over the Vari-Hub and go right to a machined sprocket hub.  Not vintage, they run more true and are easier to align with the clutch.  http://www.out2win.com/catalog/sprkthub.html.

[In general, be careful about how precise you adhere to being "period correct."  Karts matured a lot between 1960 and say, 1963... a lot of the very early stuff was prone to premature wear and outright breakage when driven hard.]

Along those lines, for chain, skip right to #35 "space chain," either EK or RLV brand.  Not period correct, but trust me, the chains from 1960 were constantly flying off, kinking up and stretching.  (Somewhere on Azusa's website there's a great write-up on the evolution of kart chain.)

Enjoy!

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You asked what it came with originally.  In those infancy years, a lot of karts didn't even have clutches.  So, direct-drive with 8:1 (9T/72T) seems to have been fairly common.  (In the absence of any clutch slippage, I suppose you needed a super low ratio to get moving.)

I never drove a kart with direct-drive, but I would guess that it's a hassle.

[ted johnson]

Most Super K pix I've seen have brake drum welded to the sprocket. If this is the case, you'll either have to switch to a different brake, or cut the drums off the sprockets and weld then to new steel sprockets. Photos of your current setup would help. TJ

[Brian Smith]

Thanks for the knowledgeable advice. I'm roughly 185, soon to be 180 if I stick to my New Years resolution... Just started stripping the kart down today and cutting all of the "extras" off that were welded on over the years. Looks like the brake drum hub is identical to the sprocket hub. Looking at pictures online, it would seem that the LH sprocket is sandwiched between the hub and drum. My Kart appears to have a wider rear axle than others I've seen, and is running 6 Inch tri star Azusa wheels in back. Will post pics later this week of the progress assuming I make some.

[steve miller]

yes sir pretty sure that's correct . I think all early bendix brakes use Azusa hub same as there sprocket hubs ..

been told  this is K series rupp ..??

ill sell it for 1100.00 ..has matched 580 five ports both have matched porting thin ring pistons full circle cranks go power intakes  tilly 314a gas carbs  rev grip clutches mega phone headers ..brand new tires  all bearings new axle control rods etc ...
   
   

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[Tom Smith]

   

[Randy Dacus]

Steve that's quite a deal, the only difference from my 61 Rupp Roadrunner is it came with Go Powers instead of steel wheels . Plus I think the early Darts came with the cast steering wheel not that nice Dart steering wheel that's on your Rupp .

[Brian Smith]

Steve- PM sent.

[steve miller]

..randy that steering wheel is the one that's smaller od. than a regular rupp steering wheel ...its only one i ever seen ..??.
kart came with it and kart also never had tabs on frame for tube tank that ran across rear ..and had rupp pedals ..not the cast aluminum ..??..