1976 Nitro Grass Drag Set Ups

[mrrupp1]

Looks like you were getting ready to break the other one also. One thing you want make sure when you replaced the drivers use at least a double wrapped roll pin. I think some guys use a grade 8 5/16 bolt. Roll pins have always worked for me. You may have to update the track and use 4 drivers. The liquid nitro's are really easy to put an updated track in. Clint

[midniterupper]

Thanks Clint, I did buy new spring/double roll type pins from Kevin and I'm glad we did. They are way heavier than a standard split pin and I think they are hardened also. The pins actually held up to the pressure and didn't bend at all. I believe we may have a 4 driver 121" x 15" Camoplast track up in the loft left over from our old Skidoo racing days. My wife raced a 2002 MXZ 700 in stock, I'll have to see if we can maybe slip that into it. Not sure if it will fit or not. Also have a nice 136" speed track left from then too if anyone could use it. More learning in store

[Ruppsforever]

Holy crap !! I never seen anything like that before with these style drive sprockets. I've used green sprockets before. I just looked and I have some used black ones. Not sure if there was an ungraded part with the different colors ?? Good question.

[mrmotors]

Question or perhaps a suggestion. Have any of you drag racers ever made those drivers from aluminum? With a CNC machine it wouldn't be a problem and I think it would a lot harder to try and rip the lugs off the track then break up drivers? I had thought about making drivers from aluminum for one of my 4 banded FA tracks, still might.

[midniterupper]

Sounds like it would work. A 4th axis would be helpful for indexing/alignments, pretty easy with today's software. I would have to study the geometry a little more, maybe do all the turning work first then set up on the Bridgeport with an rotary indexer for just the prototypes. You're always thinking!

[Ruppsforever]

Not related to what you are doing but yes we had aluminum drive sprockets and front idler wheels made for a 72 400 Nitro that we used to race. We got sick and tired of replacing the sprockets twice every winter. You won't ever have to worry about them breaking again !! I do think they will be heavier than plastic though.

[mrmotors]

Interesting, thanks for that Josh glad to know it's been done. I would add to that if one makes them from aluminum, get them finished up as you want and mounted to the shaft as they will be when ran, then, have the assy balanced. Have you had the balance checked on secondary sheaves and then also double check the balance of the primary clutch? They are turning 7500+ RPM and should be perfect as possible. I understand they are factory balanced, all I can say is having them checked wouldn't be the worst thing to be done.

[midniterupper]

Excellent advice! I want to rebuild the the P-85 completely, then when I finally get the correct arms in there along with finalizing the secondary with the correct spring and cam I plan on sending both to Cascade Balancing. They're spinning pretty high rpm's, would be nice to know everything is as smooth as possible. Don't want to violate natural frequencies!
Right now I'm waiting to order my new track drivers. I'll get a set of 4 and match them to my other Camoplast track. It's a 2.52 pitch, 121" length, .5" lug height, 4 driver, I think it should swap out okay. Right now it has 196 chisels in it so I gotta remedy that situation. Probably need to adjust the wheel centers for the rear axle set up (4 idler wheels) to accommodate the different track too. I need to adjust my tunnel protectors and re-rivet my aluminum battery box that I installed for my gages. Lots to do, Hopefully get everything back together in the next week or so.
Finally got some great weather here for sledding and testing!

[mutt]

I think rather than make aluminum drivers. Make a new hex shaft would only need to cut to length and round up the ends. Then can use all the latest drivers like Whal extroverts. Can make extra shafts shafts and sell them off easy

[midniterupper]

Hey, that's a great idea to remake the entire shaft out of hex stock. Could drill through to make it lighter. Would need a dividing head and a key slot cutter holder to machine in the spline, I'll have to see what I can come up with. Should be used ones available on line somewhere.
I was able to locate new steel coiled spring pins. Grainger has a great assortment of them, I ordered longer than the stock ones. I got 5/16" x 3" with 8700# shear strength, (Part # 41LW90) 5 for $6.00 plus shipping and tax. I went with longer because the standard length ones appeared to begin spinning or actually cutting through the hub on the new drivers. Original drivers had elongated holes in the hubs also. The new longer pins will definitely stick out from both side of the hubs, can trim them to a perfect fit.
Should be able to order the new drivers next week. Lots of work to do until then! I may have time to develop a prototype hex drive axle, keep you posted!

[nitrofa340]

Guys, there is no need to "make" a hex drive shaft. Keep in mind the entire drive system in that sled is Arctic Cat. A hex shaft from a '75 El Tigre will drop right in. The only fabrication required is a custom bushing on the pto end of the shaft if you want to retain the stock pto bearing & Rupp bearing cup.

[midniterupper]

Really? I had no idea another drive axle would fit in there, but it does make sense. It seems quite a few Cat parts are interchangeable with the Rupps. I don't know a good source for vintage cat parts, any suggestions?
So many options to consider, all great ideas! Can't wait to implement them into this sled. I know it's going to rock at the races! Thanks for all the support and helpful input, sure gives one lots to think about. My wife thought I needed a hearing aid but now she's catching on to the blank "Lost in Ruppland" look.....

[mutt]

You can get many vintage Cat parts right from Cat. Google up Alpha sports Center for whats available. Or lots of Cat drive stuff on E Bay. Thing is though most Tigers are 15 inch wide Nitros are wider depending on what the a measurement actually is, reguardless going to be short. The only chance is a 1986 El Tigre or Super Jag they ran a 16 inch track. Maybe fudge the chain gear on the spline and mount the bearing inboard? From how Cat does it. Your wider gears going to take up length also. Thought of it but without seeing actual length by putting hands on it, didnt want to shell out $ for someones E Bay estimate on length. $100 used close to $200 new NOS. On a side note a later model Cat chain case will swap in with chain adjuster and Wilwood juice brake, but takes a longer drive shaft even in the 15 inch wide track be aware of that

[Ruppsforever]

That was one thing that I never had done but always wanted to do. I never balanced and trued my driveshaft or sprockets. Also I never had my sheaves machined true. Never had any of my clutches balanced either. I always had these on my to do list but never did any of them. One thing that I did do though was always put the weights in the same spot and always put the clutches together exactly the same way every time after finding my fastest setup on the ice.

[midniterupper]

Great input from all, sure appreciate everyone's thoughts and ideas! The longer (3") track pins arrived, ordered 4 track drivers from Pipestone but they haven't arrived yet but there is plenty to do to keep me busy. The track I had in storage turned out to be a Camoplast Predator #9811R grass/ice track. I went to their website to verify the specs on it and it appears to be a good match so I'll try it. 4 drivers should help with the ratcheting problem, I'll true them up once in place on the drive shaft. Not quite sure of the spacing yet but shouldn't be too much of a puzzle. Need to ensure the correct spacing on the 4 wheel rear axle too. Still have to place the rear suspension inside the track to make sure the sliders align properly with the track windows. Not sure if the sliders will need to move in or out. Interesting note, my original Rupp rear idler wheels varied in the O.D. size by .125" which I thought was quite a bit so I'll replace those also.
Once I get the track on and the suspension back in place we can start testing again. I believe we have the jetting pretty close and the Primary clutching is very close now that we know it's engaging at 5700 and spinning at 8100 rpm. (Having an accurate tach sure helps!) Still want to play with springs and helixes on the secondary. Probably send off the clutches for balancing next month. Then of course once it's dry enough in spring, start testing the fuels to see any significant gains can be found there too.
Once the sled is pretty close to being race ready, I'll work on it's looks. Not the prettiest looking beast. I thought it was until I saw Bill Stull's creations! Well, we'll induce fear into the competition one way or the other I guess eh?
We may still have time this winter to get some Vintage races or Radar runs in yet
Thanks again for all the continued support! Keep you posted.....

[mrrupp1]

I have put several late model tracks under my Rupp liquids and the sliders line up fine, not sure on the Camoplast #9811R track that you have. But I'm sure you won't have a problem getting her in there. What gears are you going to use for the radar runs? The ones you use for drag racing or the 19-35 that they came stock with? The stock gears are a little to high for the mountains, unless your on the lakes and they work pretty good. I can't wait to see what this sled of yours can do. I think it's going to be an animal!!! Clint

[midniterupper]

Hi Clint, great to hear from you as always. The gearing that came with this sled is 19/39 which is what I have been using so far with our testing but I did find a 20 tooth top gear that may be interesting to play with, at least on the snow/ice tracks around here. Let me know what gearing you would recommend or try. I have heard that a 2:1 (2.00) ratio is ideal for drag racing but I like to think outside the box, especially if there may be a gain. Not quite sure what she'll end up doing but she feels pretty strong. The reason I say that is because when I had it out the last few times before the track drivers blew apart, it would pull hard out of the hole without ratcheting then around the 250' marker she would pull harder still and then the ratcheting would occur again unless I let up on the throttle!
I greatly appreciate your experience with installing other tracks on the chassis, it's something I haven't done other than on our skidoo's 20 years ago. I gotta drive my wife downstate tomorrow for her to help her mother for a week so I will have plenty of time to get this thing back together, can't wait! (Just don't tell her that!)
Keep you updated, getting exciting now!

[mrrupp1]

Hi Paul, I hope things are going well. I haven't done any real competitive drag racing so I'm the wrong person to give advice. I have done some radar runs and I'm oval racing now. Are oval tracks here are pretty short, the straights are only 350 feet. So we gear them around two to one (19/39 ) I have gone a tab bit lower. Now the radar runs we do 500FT and we do a 1000FT. For the 500FT track I do 19/39 or 20/39 and for the 1000FT I run the 19/35. That gearing works pretty good for the altitude we run at which is around 8000 to 10000 feet. Have a good one. Clint

[midniterupper]

Thanks Clint for your words of wisdom, Sure appreciate your help. Yesterday I stopped at the local sled salvage yard (Mickey's Sled Salvage in Mt. Pleasant Mi.) where I picked up some gears to play with. I've switched the drive chain from the 11 plate to the 13 plate chain and I got a 39 tooth bottom gear and also a 18, 19 and 20 tooth top gear to play with someday. I will stick with the 19/39 gearing that the sled came with and finish getting the sled together in regards to setting up the 4 driver front axle and track along with the 4 wheel rear axle that needs some tweaking.
Today I mounted longer tunnel protectors on the sled, hoping to eliminate some studs hitting inside the tunnel area. That took some time, removing the seat, fuel tank and radiator. I hope there is enough clearance for the studs going around the drive axle, wasn't sure if there is a trick to studding these sleds.
Regarding the 4 wheel set up for the rear axle, I had to order new outer wheels as the original Rupp wheels are different diameters, actually smaller by almost 1/8" so now they are new and all the same diameter. The aluminum spacers I made needed to be bored out by .010" for more clearance to allow the anti-seize to float around a little more. They also mushroomed on the end from sliding into the inside of axle slot on the rear suspension when I tightened the axle in position so I made room for stainless steel washers to distribute the pressure better.
I need to finish removing all the chisels from the Camoplast track I'll be using, then should be able to play with the spacing for the track drivers to get them in their correct position. Not sure if anyone may have those dimensions or not. I'll be sure to measure them and write them down if anyone needs them in the future.
Maybe tomorrow I'll have the track back in the sled and get some testing done over the weekend. The lake ice around here is not safe but there are some nice land tracks that shaped up nicely. Maybe I could sneak into the Soo after the I-500 tomorrow!
Thanks again for your help Clint! Until next time, -Paul

[mutt]

Theoretical speed full clutch shift, not and likely possible in most conditions

18/39 sloppy chain fit 73 mph
19/39 77 mph
20/39 81 mph
19/35 86 mph


If hasnt gone back in yet could you get a total length on your drive shaft