View Full Version : Mini-bike update

07-15-2006, 01:18 PM
Well i've had a heck of alot of fun working on my new mini-bike project. So far, I've got my centrifugal clutch setup made, my rear hub and brake drum and an adapter for the engine crankshaft. I also made a bearing for the input shaft. That was loads of fun - first time i'd ever done anything slightly complex on the lathe. I've got a little 1/8" groove cut inside the bearing to house a 5/8" rubber o-ring because the majority of the bearing (its about 1.5" long) is submersed in trans oil. Then i cut another groove to house the ball bearings. interestingly, i found that daisy's "quick silver" bb's make great ball bearings. They are nickle coated steel and hold up much better than the plain steel ones i had laying around. Anyway i loaded it with the bb's and popped in the inner race. It's kind of a funky design because i needed a lazy-susan type surface on one end but i got it all worked out. Today i'm starting on the innards of the transmission. I've got a design worked out that should work as a very primitive synchronizer and blocking ring setup. I'll have to see how that goes. When i get everything done i'll see about trying to post some pictures.

I have to thank everybody here, though, who helped me get started about a year ago. This project, by far, has been the most fun because its been done almost exclusively on the lathe and milling machine. Its helped me to get to know my lathe a little bit better and hopefully learn a bit too. Anyway thanks again for all the help and advice i've gotten!

07-15-2006, 01:50 PM
Can't wait to see how it turns out! Glad everything is going smoothly. Fred

07-15-2006, 06:57 PM

Oh and air gun bb's are not hard enough.

Alistair Hosie
07-15-2006, 07:07 PM
I was surpised at the bb's post too I would be suprised also if they would suffice Alistair

07-16-2006, 01:26 AM
Ture bb's are much softer than a quality ball bearing, but keep in mind three things. One, they are not the copper kind, they are steel (not that that always counts for much). Two, my goal with this mini-bike is to spend no money buying parts for it - it is made completely from metal and scrap parts i already had on hand ... the only other ball bearings i had on hand were used ones that came out of a HF super crappy bearing. Then three, the way my bearing is put together does not require any press fit components - rather its held together between the two "laxy-susan" type surfaces. Kinda hard to explain - i'll get pics as soon as i can. Anyway, the bb's will be easy to replace as they get sloppy and this only has to deal with a 5 hp engine and maybe 2000 rpm max. I had been planning on just using a bushing because that is what all the lawnmower type transmissions used but i opted for this instead - mostly for the fun of it! :) I'll let you know how long it takes for the bb's to wear out if i ever get it running decent :D

oh and the "input shaft" is actually driven by a belt so a little bit of run out won't destroy anything - just damage it ;)

07-16-2006, 07:28 AM
Heck, go out into the yard and get a bunch of same size pebbles it will do the same,ruin your bearing race.:D

There are no copper BB's, it is a coating.

07-16-2006, 10:07 AM
hmm pebbles - i like the way you think... :D

I had no idea that was just a coating; makes sense though. Solid coppper bb's would probably be expensive.

07-16-2006, 01:14 PM
The gold colored ones are solid gold though;),not good for bearings either.

07-16-2006, 02:30 PM
BB's!?! :eek:

I bet if you put a mic to a dozen of them you won't find two that agree. Nor will you find even one that's as close to a true sphere as the cheapest bearing you can find at Harbor Fright.

You might be able to score some relatively cheap balls at a hobby shop, they're used in R/C car differentials. 1/8" is pretty common, if you can adapt your design to them.

I've been accused of being a little cheap sometimes myself, so I understand where you're coming from. But bearings are a poor place to indulge your inner Scotsman!


07-16-2006, 04:42 PM
Actually i checked the ones i used with a caliper and they all agreed with each other...granted it was a caliper and not a mic, but even estimating into the 10,000ths place they were the same. Nevertheless, point well taken. In this application, i'm not too concerned about the quality of the bearing. The used ones from HF certainly wouldn't do, but new ones probably would have. I originally intended to use a bushing there, so the inner race is extra snug on the 5/8 shaft and there is really very little clearence between the two races. I saw the bb's there and thought, hmm, i'll give it a try. Even if the don't hold up past ten minutes, it'll start riding between the the two races (originally intended to be bushings anyway) with only a little more runout than what the original bushings had. Thanks for the input though, i'll be sure never to use them for anything important!

The hobby shop sounds like a good idea, i've got some bigger ball bearings that are from various 1" and bigger bearings but nothing that was really small enough for this 5/8" shaft. 1/8" balls would work pretty well though.

Actually that does lead to question i've been wondering lately - how do they make ball bearings or even bb's in large quantities while maintaining the accuracy needed of a bearing?

One more thing: started on the "synchronizers" (again same principle as a synchro but very primitvie) yesterday and produced some very beautiful scrap :D I need four holes drilled evenly about a 3/4" bore for some pins and, due to the size of shaft i was using for the hub, the biggest i could make them was 7/64", and even that was risky. Trying to drill three pieces that all match up perfectly when each is at least an inch deep with the 7/64 drill bit was more than i could do! I wanted to match drill them but i would need to drill through about 2.5" which wasnt going to happen with my 1.75 7/64" drill bit :) Today i'm making new hubs that are bigger in diameter so i can match drill 3/16" holes. (The stock i was using for hubs was either just over 1 and 1/16" or 1 and 13/16" - i was trying to save material and ended up wasting some...oh well. Today its the 1-3/16")

07-16-2006, 08:46 PM
another good place to find small ball bearings is bicycle shops, had a hard time finding small amounts in small sizes until someone told us about them


07-17-2006, 06:11 AM
Watch the "How its made"archives.