Scratch building a small Kaf from nothing...what would you do? WARNING: Long!!

Swagger

Putting boot to ass since 1967!
So a few days ago my buddy shows up at the shop on the goofiest bike. He's got this ratty old Honda C90....and by ratty I don't mean rattle-canned flat black and pasted with stickers. I mean it nasty. The upholstery on the seat is got, the lighting is all cobbled together from various bits including a rubber implement light for his headlight. The rims are rusty, the body work (what metal there is) and frame are rusty.....and it's a step thru. Ugh.

It didn't sound bad though when he pulled up, kinda had a nice note to the exhaust. Turns out the bike was his granddads and when the little motor puked it got parked behind a shed for years.....lots of them. Stan got it a few weeks back with the mind to restore it. Not worth it was his final judgment, however it's pretty solid so why not run it as is. A couple new tires, repacked bearings, knock the worst rust off and of course get the engine running. Well, the original lump was well and truly pooched so off the the interwebs looking for a suitable replacement.
He settled on a Chinese Lifan 128cc motor for it.
http://dratv.com/lifan120cc.html
He got two of them fresh and complete for $500(US) so one is waiting for another project.

Without going too much into the gritty details, I rode it. I wheelied the stinking thing....in the first two gears. No shit.
Now, it won't beat up on many other bikes on the road but I have to admit it was kinda fun and it got me thinking. We're all relatively familiar with small displacement race bike, so why not? The S90 chassis is...well.....marginal on a good day and a bit chubby for this application however......

Consider this: You can pick up a complete chassis kit based on Aermachi architecture:
http://www.aermacchi-racing.com/image/Framekits/Framekit_Drixton_B.jpg
This 'kit' weighs 26kilos......!!!!!....for those us us in the US that's a hair over 57 pounds. The motors weighs just under 50 pounds (21.4kilos) so thus far you're looking at roughly 107 pounds...say....49kilos. Add some allow rims on light hubs with modern discs...let's face it, nothing beats good light brakes, figure 30 pounds. Add say 20 pounds for misc. cables, minimal lighting, grips, bars etc. and suddenly you've got something pretty interesting. Let's be generous and say it's a total ready to ride weight of 160lbs or 73likos!
I've not seen dyno numbers for the bigger Lifan motors but it was a torquer and was relatively willing to wind up too.

Let's say it makes 15 ponys pushing 160 pounds down the road. That's pretty acceptable for in town or really tight canyon stuff and lets face it......that body/frame kit doesn't look too shabby.

Thoughts?
 
Re: Scratch building a small Kaf from nothing...what would you do? WARNING: Lon

Idea for the c90
posty bike for motorcross racing
 
I think its a great idea. I'd love to have fun throwing something like that around on a nice mountain road!

I just wonder if it would be worth the cash outlay.

How much is that frame kit?
 
Re: Scratch building a small Kaf from nothing...what would you do? WARNING: Lon

My Hodaka will give you an idea of the weight of a small bike with full size wheels as it weighs in at 171.5 lbs dry as is in this pic.
My goal is under 200lbs. fully wet and and ready to ride. I should be able to meet that goal or better it by a few pounds.

It's a very small two stroke 100cc bike with 18" alloy wheels,stock rear hub and CB350 front hub. With a aluminum/plastic tank,drilled hubs,no headlight,aluminum clip-ons it might be a little lighter but maybe not much. It may be possible to get a bike like what your wanting to build to weigh in at around 160lbs. or so dry.
Picture_0634.jpg
 
Re: Scratch building a small Kaf from nothing...what would you do? WARNING: Lon

Agreed on the cost, I was just using those beautiful chassis kits as an example.

I dunno why but lately I've really had wood for a laydown single like the old Aermachi's and the like. The center of gravity has got to be ridiculously low on something like that, notto mention the 'cool factor'.

I was the first to dis just about everything coming out of China, especially anything with an engine but I was pretty impressed with that Lifan motor for all of 128ccs.....pretty gutsy.
If I could find an S90 that would be fun to start with but I'll all but guarantee that frame would be at best made of spaghetti and the forks not much better. Perhaps I'll just grabo some CroMo or 531 and fire up the Miller...see what comes out.
 
I love the idea. Im a big fan a small displacement bikes; my belief has always been that speed is relative, and you can rail small bikes a low speeds and have a great time.

Why don't you look for aeromacchi basket cases. You can find them super cheap if you're patient. Then throw in the chinese motor and build a fun little round-town bike.
 
Re: Scratch building a small Kaf from nothing...what would you do? WARNING: Lon

Unfortunately, like the S90...the old Aermachi chassis isn't going to be anything to write home about. :'(

Chrisf, kinda what I was thinking myself....
 
Re: Scratch building a small Kaf from nothing...what would you do? WARNING: Lon

There is an excellent book on chassis design by Tony Foale. Just before I packed in the vintage racing, I had designed and was in the process of building a spondon/sealy style frame for a cb350 twin. Those frames have only 2 tubes that require mandrel bending. I made a frame jig out of an old lathe bed. I didn't weld at the time so my biggest challenge was getting a welder who was brave enough to tig it up for me :(. It was about 3/4 complete. I ended up giving all of the parts and jig to a buddy when I got out of the vintage stuff.
 
Re: Scratch building a small Kaf from nothing...what would you do? WARNING: Lon

I've been thinking about something like that myself, I run a small custom fab shop so materials and tooling isn't a problem.

I just got info from a guy that builds 220cc versions of that hodna/lifan motor. The lay down a respectable 28hp @9400rpm so that's even better than the 128 (I have no doubt) and he says his motors weigh a whopping 3 pounds more than the Honda 90 that it's based on. Modern technology.....whadaya know about that!?

So, a Seely Mk.III style frame, tig'd up in either 6061 or 7075 alloy, single sided Spondon style swing arm with mono-shock, USD forks from something appropriate.....Alloy hoops on modern dirtbike hubs (think light and discs).

What a riot that would be! Still not going to whup up on many people, but in the twisties, out to have fun or around town? Hell yeah!
 
Well I certainly would not build it in aluminum. As soon as you expose a weld arc to the 6061, the heat treatment goes out the door. I suppose you could build your jig to that it could stand re-heat treating it, but it would be tough. I wouldn't bother with the 7075. At those prices, you could just do it in Ti. Plus, I'd worry like crazy that the joint would work harden and crack; it's bound to happen.

Personally, I'd use 18, 20 and in some cases 22ga 4130. The only reason why I say 4130 is because it is easy to find with those wall thickness. I'd also look at T-45 coming out of Germany and France. It is very light and very strong. Best of all, it can be MIGed, which in specific instances will be a better process.

--Just my opinion, Chris
 
Re: Scratch building a small Kaf from nothing...what would you do? WARNING: Lon

Thanks for the input Chris. I deal with aluminum daily so I'm not too scared of it and having spent many hours on a Spondon alloy framed R1, I'm all for aluminum frames. Dunno where you're buying your materials from but my price is roughly 1/5th that of Ti. Ti would be cool just for the bragging rights but it's a bit brittle for my tastes though I've only messed with it a bit.I've got a good source for aircraft streamlined 4130...that's an interesting option as well. What I do have readily on hand is a shit load of Reynolds 531 in 18 and 20g.

I think I'll look into aluminum though. I have a heat treating furnace large enough to fit a bike frame and a sturdy jig so heat treating isn't a worry either. FYI: Heat treating furnaces are easy to make too so don't let that be an issue for you. Cinder blocks and a few layers of R22 and you're set. Besides, I can have an allow frame anodized for $45....it's good to be buddies with the guy that owns the ano shop!

Crap....I'm starting to spend a ton of energy on what was just mental gymnastics........looks like I can bring the entire thing in under 150 pounds. Argh! Now I'm starting to feel compelled........
 
tobiism said:
I think its a great idea. I'd love to have fun throwing something like that around on a nice mountain road!

I just wonder if it would be worth the cash outlay.

How much is that frame kit?

Her in the Uk fifty cc sports mopeds were very big until the laws changed and they were restricted to 30mph, Bu we still have a sort of madness called moped mayhem where adults who should know better race them on the track and on the dirt.
http://www.advan-yokohama.com/album/2007/other/Moped%20Mayhem/slides/hegarty%20lydden%202007(3).html that is link for 3 hour endurance race on mopeds. At sixteen you could ride a sports moped these were capable of fifty to sixty miles and hour an so lots of tuning goodies appeared and the bikes started to do up to 75mph. The bikes were things like Garelli, Yamaha fsie, suzuki ap50, kriedlers, Puch grandprix. Most youngsters started there lives on these and then decided if they liked cars or bikes at 17years old. The goverment then decided it was to dangerous for 16years and resrticted them to 30mph hence the end of them as all the old ones got thrashed into the ground leaving only resricted ones. Now if you can find a good one they are worth a lot of money in the uk. But lots of sites dedicated to theses small cc sports mopeds lots of tuning and info around, Might help with tuning. also look up moped mayhem in the uk if want a laugh. Here are some pics of the things people did to them.
 
Re: Scratch building a small Kaf from nothing...what would you do? WARNING: Lon

That blue Suzuki and the green Italian thing are cool, I don't care who you are. We need a class like that in the States for beginning riders (says the man with the six-month old daughter...).

;D
 
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