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Old 06-25-2013, 12:12 PM   #1
Lizrdbrth OP
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"Secondhand Rose", my flyweight CT90 project.

Not really a "project" yet. More of a pre-project fishing expedition.

Initially I plan to turn THIS:



Into something more like THIS, but with a skidplate, a real air cleaner, a front fender, capable of accepting a meaningful rack, kickstand that actually reaches the ground etc. Basically as light and bare bones as possible, enhancing the offroad ability yet retaining most of the utility of a stock CT:


(I forgot about the unwritten law which states that 99% of all motorsickle pics must be taken from the right side. Sure would like some better pics of this.)


The utility of THIS (Hugemoth. A very smart build when you pick it apart):



Successively incorporating elements of THESE (Salsa's bikes. I recently had the pleasure of discussing them with him but didn't have my manure assembled. Thanks, Don) I aleady have an RM fork:




THIS ( Scott Kirn's vintage trials bike):



Not so much like THIS. I'd like to at least carry a sammich or two. But a nice bit of engineering and The single front sowntube gave me an idea for a more weight-conscious skid.


Lizrdbrth screwed with this post 07-02-2013 at 12:40 AM
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Old 06-25-2013, 01:15 PM   #2
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Seems like you have a pretty good plan already outlined. What kind of thoughts/comments were you expecting from the peanut gallery?
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Old 06-25-2013, 02:04 PM   #3
Lizrdbrth OP
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Quote:
Originally Posted by Bronco638 View Post
Seems like you have a pretty good plan already outlined. What kind of thoughts/comments were you expecting from the peanut gallery?
While it's true that I have a "plan" it's only based on a few evening's worth of internet homework.

The Peanut Gallery in here knows the micro-displacement, motorcycle, pitbike and scooter world far better than I. I'm gunna live by my scales on this build cuz I'm kinda anal that way and will probably ask the collective if they're aware of something that is more or less "off the rack" in the scooter/moped/pitbike world which could be lightened and/or modified for the purpose, what breaks under severe use, what to throw away and what to keep, etc. I'm also betting there are more than a few in here who've put some thought into doing something similar and have a few ideas/pics to share before I get started.

So far I'm just a dude who wants a CT that I can toss over a barbed-wire fence or load down with a week's worth of gear for a total loaded weight equal to the unloaded weight of a stocker, if possible.

That, and this is the only location on the site which will even entertain the notion of building something like this.

I fear ridicule. I'm a fragile flower

Lizrdbrth screwed with this post 06-25-2013 at 03:06 PM
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Old 06-25-2013, 06:14 PM   #4
redprimo
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Might wasn't to take a look at http://motopeds.com for some ideas in a slightly different direction but similar in spirit.

You didn't mention your skills available for the build. Welding, machining, wrenching....

If it was me if consider something more like pit bike. Don't get me wrng I loveCT's, I own two of them, but they are what they are. You can add more power and you can make then lighter but they still are limited buy sub par suspension. Even if you swap front ends and lengthen the swing arm and add better shocks out would still be a compromise.

With a put bike platform to start you have the same motor options and a better rear suspension to start from.

Great build idea and I'll be watching this thread. I've been wanting to do Barstow to Vegas on one of my ct90.'s.
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Old 06-25-2013, 06:31 PM   #5
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The Motopeds are very impressive.

License plate is a must. Here in Cali road legality pretty much limits frame options.
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Old 06-25-2013, 07:16 PM   #6
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In California if it has pedals and 49cc or less it is a motorized bicycle and does not require a license plate. You can bore the stock cylinder out to 88cc and drop in a longer duration cam to get the z50 to perform like a stock ct90 and it will still look like a 50
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Old 06-25-2013, 08:32 PM   #7
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Quote:
Originally Posted by redprimo View Post
In California if it has pedals and 49cc or less it is a motorized bicycle and does not require a license plate. You can bore the stock cylinder out to 88cc and drop in a longer duration cam to get the z50 to perform like a stock ct90 and it will still look like a 50
And no longer be under 49cc..... thus needing a plate.....if you get caught

Isn't there a maximum speed of 30MPH too?
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Old 06-25-2013, 10:44 PM   #8
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Ok. A few parameters for Version 1:

1. Registered, plated, insured. I plan to ride it across the U.S. or any danged place I choose .
2. Minimum 17 inch wheels, front and rear. D.O.T. legal rubber.
3. At least twice the stock suspension travel, front and rear.
4. Clutched 4 spd., Hi-lo transmission.
5. Max. 52 inch-ish wheelbase, 4 inch-ish trail, or thereabouts.
6. 12v electrical upgrade, reasonably decent headlight.
7. Minimalist frame retaining sufficient structural integrity of existing rear monocoque to support suspension loads and a meaningful, removable rear rack of roughly stock dimensions but at 1/3 the weight.
8. Max fording depth intake and exhaust. Or at least no lower than stock.

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Old 06-26-2013, 06:46 AM   #9
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There are a bunch of guys currently running the TAT, from West to East, on CT90s. See the Ride Reports forum for the latest. They're all using new Lifan 125cc motors (I think). They stripped the CTs way down and used XL125 front forks. You might want to touch base with them when they get home and ask for an "after action report" to see what worked and what didn't.

#3 on your list might be an issue. Doubling the suspension travel, on the rear, may necessitate a longer/different swing arm. That might not be trivial.

I think this looks pretty much spot on:



The only thing I think I would do to that bike is to triangulate the down tube with another tube that runs from the headset to just under the seat. That one looks like it has a different swing arm, too. That and re-do the intake (to be higher).
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Old 06-26-2013, 09:24 AM   #10
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Quote:
Originally Posted by Bronco638 View Post

#3 on your list might be an issue. Doubling the suspension travel, on the rear, may necessitate a longer/different swing arm. That might not be trivial.
Fortunately doubling your travel isn't that dfficult when your old baseline was 3".

The rear is probably gunna require the most thought. If weight loss were not an issue I'd just lengthen an SL swingarm, throw some longer, heavier shocks on it and be done with it.

To do it well I'd probably have to roll my own. A lot of the aftermaket and O.E.M. stuff that could be modified to suit appears to be just as heavy, even in monoshock form. On a CT their monoshock platforms would add another 4" or so of rearward wheelbase length. Add to that another few inches of swingarm to accomodate the bigger wheels...

Oh, well. Not gunna obsess over it just yet. Over the weekend I hope to get out the scales and provide the collective with useless trivia in the form of component weights on the stocker and see whether my planned fork swap amounts to addition, or subtraction.

On big bikes the first 20 pounds are always fairly easy to shed. I didn't expect it to be as easy on these munchkins, but to their credit these things owe a lot of their longevity and durability to a bunch of overbuilt steel parts. The first twenty pounds could actually prove fairly easy.

Case in point: The stock front fender weighs 1 lb. 14.5 oz. and almost an even 2 pounds with bolts. A plastic YZ250 fender weighs 11.5 oz., with bolts. So there's a pound and a quarter in the first 5 minutes. Buddy seat: 5 lb. 7 oz. and so on. I'd bet even if you were a purist you could lighten one up considerably and still retain a mostly stock appearance if you were into it. Park the sweet original parts on the shelf so they won't get trashed.

I'll give a free Barry Manilow album to anyone who can guess how much the heat shields and screws on the stock muffler weigh. lol.

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Old 06-26-2013, 08:05 PM   #11
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The guys doing the TAT have had some successes and some failures. These little bikes are pretty heavy for their size with limited suspensions and power. They are, however, fun. I've got a '77 and a '78 that I don't have time for.
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Old 06-26-2013, 09:46 PM   #12
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I'm building a CT200 (old version of the CT90) with a Lifan 140. I bought both on ebay, as well as a lot of other pieces.

I didn't want a custom frame because of possible hassles getting it titled and registered. I can register the Honda frame with less problems.

(BTW, the CT200 is from 1964, so it doesn't need turn signals. That's a little weight reduction right there!)

The forks and tree are from an XL125, and I just scored a pair of 17" XR500 progressives for the rear on ebay for $40.

The wheels will be the stock 17" on the rear, and 19" on front, because they're common sizes and good for overall use.

I'm really not a fanatic about the weight, since no matter what, it will be lighter than my nearly 800lb full-dressed GL1000!
I just wanted something to hop on and have fun. The Goldwing is good for long highway trips, but it really is a lot of hassle to take on little trips around town. I also like to go out and explore the trails, and a little bike is easier to man-handle when the trail abruptly ends!

Good luck on your build!
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Old 06-26-2013, 10:21 PM   #13
Lizrdbrth OP
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I've also picked up a '64 C100. Not sure what I'm gunna do with it yet but I'm kind of curious if there were any noteworthy weight variations in the basic frames over the years.

I'm really not seeing much chance for that but it would be interesting to know.

Good luck with your project, as well.

I've noticed the TAT boys had some wheel failures and at least one bike's upper shock mounts sheered. I've seen a weld cracked where the main frame enters the monocoque and I've also seen one fractured swingarm on the 'net. Would be interested in hearing anyone's horror stories/solutions to known failure points under hard use.

I've got a harebrained idea for bolstering the strength of whatever's left of the rear section when I'm finished. It's possible that keeping the monocoque stuff could work out to be lighter than creating new supporting structures for the seat, rack, suspension attachment, etc.

Kinda looks as if some of the mods to the sheet metal on Mr. Kirn's trials bike may be intended to address some of these. I don't expect to bang on it like a trials bike but I'd like to have it last awhile.

I'm also kinda liking the idea of lowering the swingarm pivot, and also getting the brake rod up where it belongs. May swipe that.

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Old 06-27-2013, 02:05 AM   #14
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The little gordita scaled 195 lbs, even, with an empty tank tonight.

82.5 lbs., front. 112.5 rear.
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Old 06-29-2013, 07:19 PM   #15
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I do like the parameters of your project. If only Honda made a 200cc CT with a mono shovk rear suspension with 10" of travel.

Another option for a front end swap is a 75 or 76 cb200. It has a cable operated disc brake which let's you add adisc brake and still use the stock control levers with their associated switches I haven't done this swap but it is supposed to be pretty much a straight up bolt in with the triple of the cb fitting the head tube of the ct. the downside is that you don't get any gain on travel. What would be worth exploring is if you could fit the cb200 lowers on the xl100 fork tubes.
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