Hi GameWarden98,
Great build thread! I commend you for involving your son. I am also doing a Dune Cat build with my 6 & 7 year old girls. I posted a bunch of pictures on the main Muskin Dune Cat thread, on page 10. But I am gonna start a clean build thread.
I have 2 complete Dune Cats and one body. The first one I will have complete before Christmas (I hope) is an original orange/tangerine color. I did frame improvements, and the like for it. The next two I do will have new frames that I build from scratch with the improvements I am doing to this one. One of the three has been made from a uniquely different mold than the original Dune Cats. It is stretched about 10 longer than stock, has a 4inch raised seat pan, beefed up areas and other little differences. That is the one I will do for myself! I am currently planning on making a new mold for these bodies with the help of a local glass body maker here in Knoxville TN area. He has a number of bodies and has looked over the bodies I have and says it won't be problem to make them. I plan on selling the bodies bare with plans for the frame so dads like yourself can build new ones.
Just a couple of quick comments that can be helpful for you:
1. bolt stuck in crankshaft - use the easy-outs because they are designed to do that. Just don't strike them with a hammer because they are case hardened and might snap if you really hit them hard. You should drill a pilot hole in the broken bolt, then continue to go a larger size up until you can put the biggest size easy out and remove the bolt. Then chase the threads with a tap.
2. decals - Big Al on the other thread has taken the time to get the artwork put together. He sent me the PDF of this collection, and I will gladly send it to you. Send me a PM with your email addy. I am going to have some made locally at the print shop that does my decals, banners, signs, so if you want me to provide you some off my run that's no problem.
Of interesting note, the blue body I have has completely different decals than any other one I have seen. They are the real deal, and use the HPE Muskin Cat logo/head instead of "Miss Sandy Claws." I suspect this was done near the end of the run. I am going to have these scanned and made for the blue one.
3. engine - I like the B&S motors OK, but I am nearly 100% certain the factory engines were Tecumseh, which I like a lot better. Regardless, it is hard to justify putting any money into either of these heavy, old tech motors when you can buy a new Harbor Freight Predator 7HP for $119 all day long. And for another $109 you can buy a kit that adds electric starter, controls, charging stator, diode and wiring to make the motor more user friendly. Or you can look online and find new 9HP Robin Subaru engines with electric start for around $275-330. These are really high quality engines, made in USA in WI, and have an Overhead Cam design with less weight, fewer parts, quieter operation and designed for the D-I-Y mechanic to completely rebuild with basic tools. They even run forged crankshafts in a lot of the models. Just add a billet connecting rod for $85 and aluminum flywheel for $100, then remove the governor and you have a high revving machine. You can also find lots of used Briggs Animal engines which are a much better design than the old flat head B&S. Briggs discontinued the flat head in the late 90s for good reason.
4. Torque Converter - The Dune Cat, as a fellow owner mentioned above, runs a HoffCo symmetric unit with 7inch driven unit on the jackshaft which is located in the motor mounting frame. HoffCo became Comet, and if you want to run the original stuff just get a 20 series 7inch driven unit, and the correct length belt. I can help you with this if you need some support. I have the manuals and tables.
Comet Industries shutdown, then was bought by Certified Parts, along with Hoffco name products. So you can get any service part, plus brand new Torque Converter units, and the complete assembly called TAV2. The TAV2 is nice, but only available in the overdrive version which uses the 6inch driven unit. This will not give you as much torque multiplication as the 7inch unit, but will allow the kart to go faster on the top end with a 0.9 overdriven final ratio. You can see that I used the older TAV setup, modified with a 7inch driven unit. I did this because the 30 series (asymmetric v belt) stuff is more common, and I have a couple of these laying around from Carter Bros monster jeep projects I am doing. You can use the 20 series (symmetrical V belt) stuff just as well, according to the tech guru at Certified Parts. I used the TAV style unit because I wanted to make room for dual rear hydraulic discs for my kart.
Also, note that there are now chinese knock-offs of the Comet. They run about $169 where as the real deal made in USA Comet runs $199. Run the Comet stuff if you can because you have lots of tuning/adjustment parts available if you choose to use them.
5. Differential - I would ditch that solid axle/sprocket/centrifigal clutch. You lose the high quality engineering that HPE put into the more expensive differential. The diff allows you to turn on a dime, handle much better, whereas the solid axle will push you and not allow as tight a radius and it is harder to push the kart around as well. The Peerless 100 series diff that Northern Tool sells online for $119 is a direct replacement for the original. Peerless must have made the original, as they have been around for a while and they are USA.
If you return back to the diff, the brake must be mounted into a brake disc on the diff, or you can run the sprocket/brake combo like you are now. But don't put the brake disc on just one axle because the control will be lost. You will need to put one on each axle if you go that route. In my opinion, that is the best way to do it because you will stop the kart axles in the event of a diff failure. The diffs are very tough and good for about 16HP rated. I put about 240LB-FT of torque through these on the last Carter Bros Monster Jeep build using a 150cc GY6 engine. They hold up well as long as they are supported inboard by bearings, like the Dune Cat uses. If you only had bearings on the outer, you will fail the diff eventually by cracking the aluminum housing due to flexure.
Well, enough of this techno rambling for now. Enjoy your machine with your son!
PS - About the roll bar/cage, I like the front bumper idea. And I like the idea of a roll bar behind the seat that is higher than the driver's head in case of a rollover the bar will take the load. As for the rest of it, it is a huge detraction from the kart's beauty, yes. But safety is something we take a lot more seriously than back in the 60s-70s-80s when we grew up. I am going to do a single roll bar hoop tied back to the frame, and a bumper, and a RC wireless remote ignition kill system (runs $70; has 250 ft range). But very simple and along the theme of what was done in the 60s 70s Manx bodied dune buggies.
unk:
