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Yo! Sorry if this is a subject that's been covered already. I'm new to the forum and couldn't seem to find anything. So! I bought a 1970 CL100 back in July from the second owner, who bought it back in 1973. He used it sparingly, but maintained it well until about five years ago,. It has sat since then. I stripped the bike to a motor and a frame, and all seems straight forward thus far except for the motor. Given the scooter-esque displacement, I'd like to add a little more get up and go, while simultaneously getting rid of any compression problems that may or may not be present. So, hey! Let's just bore it, right? BUT... I have no idea what the best compromise between sustained reliability and performance may be... I've heard of people boring the cylinder to fit a 750 sleeve and piston, and that it's extremely reliable, the only difference being that the 750 piston requires a 15mm wrist pin rather than the 14mm in the 100. That can be reamed, correct?

But is that even the best option? What would be the displacement, horsepower, and performance gains on this? Would anyone happen to have firsthand experience with doing such a modification on this bike? Any and all performance/reliability tips would also be greatly appreciated.
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hi, if you want to spent a few grand on the motor, it would do 90MPH. That's not going to happen.

If you think you can just fit a bigger piston and get big gains, easy, well you can't.

If you want to go faster, get a bigger bike.

Buy a manual, tune it and maintain it. Keep the motor stock. It will run like that until the end of time.

Danger, is my business."
 

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Standard CL100 bore is 52mm and CB750 bore is 61mm. That's a massive bore increase for such a small engine. Then you've got the wrong size gudgeon to deal with....

Have to agree with ol' witto - you need a bigger bike.
 

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Discussion Starter #5
I understand this is basically a scooter. I'm not trying to make it anything else. Buhhhhht If I'm going to take it all apart to hone it and replace the ring then I might as well add some displacement. I'm just asking for the best compromise, not a magical rocket from this baby sized vintage.
 

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I understand this is basically a scooter. I'm not trying to make it anything else. Buhhhhht If I'm going to take it all apart to hone it and replace the ring then I might as well add some displacement. I'm just asking for the best compromise, not a magical rocket from this baby sized vintage.
I doubt you will find rings or a stock +.25 piston. Don't strip it down before you have the right parts in you hand, or absolutely know that they are available. Plenty of pistons are available for the 125cc version of this motor, but not the 100cc version. CB/CL/SL/XL 100cc parts are a hassle.

A bigger piston on this bike will give you jack more horsepower. Forget buying some wonder piston kit off ebay from China to fit your bike: I'm 80% sure it will be crap quality.

The best compromise is to keep the bike 100% stock.

This " baby sized vintage " would haul a fat man from coast to coast and back.

Danger, is my business."
 

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Ding.........another bike gets its wings.

Powroll has kits for the 100 but you need some machining. You can use a 125 piston but I think the pins are slightly different.

I heard of folks doing the 750 piston work but what a machining and tuning nightmare. Stroking it out, compression issues.......just a lot of poop...for what.......18 hp.

But Wits correct.........you never get what you want out of this 100. Since your probably going to cut up the frame make a straight 125 by sourcing a motor or maybe a 175.

You have a good history being the 3rd owner of this classic honda..... but it would be a shame to cut it up to a cafe only to get a r top speed of 75mph....maybe.
 

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You can use a 125 piston but I think the pins are slightly different.
If only the 125cc piston wasn't the wrong size, the wrong piston crown shape, the wrong compression ratio, and wrong piston pin size.

Need I go on?

Yep:

There is no way in hell of reaming a CL100 rod to oversize, like zero, zippo or ziltch.

Danger, is my business."
 

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There is no way in hell of reaming a CL100 rod to oversize said:
Danger, is[/I] my business."
100 and 125 heads are the same size with the exception of bigger combustion area on the 125....interchangable. 125 piston will fit with 125 head..........no machining.......besides displacement. 125 rod, Powroll rod, or a Powroll stroker rod, etc. A 125 rod with a 750 piston will yield 150......I believe but not sure.

A lot of work for maybe 18 hp with exhaust
 

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… If I'm going to take it all apart to hone it and replace the ring then I might as well add some displacement...
Sorry CNorthness, but that makes no sense. It's like saying; if I'm going to service this ancient engine that no longer has access to OEM replacement parts, I might as well re-engineer it and replace everything with over-sized and mix-matched pieces while I'm in there.
 

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you're going to bore it to solve compression problems that you say may or may not exist? also when your first post stated that everything seemed straightforward except the engine??? nope... nope nope... don't put a wrench to that engine, you'll ruin it with that mindset.

put everything back together and learn to maintain the bike, or you'll be selling the whole garage full of boxes of bike in a few years.
 

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Ive been down the rabbit hole of making a Honda single faster.
On paper it can be done.
And if racing another stock bike it will be faster.

But other then that there is zero point.
 

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I get what you are all saying and agree with most of it. It will still be a small cc Honda and the OP doesn't know a lot, but that doesn't make it impossible. There are a ton of people messing with Honda single motors and chinese clones. Trouble is that few if any of them hang out here.

Start searching for Honda 100 pistons and pit bikes and TBoltUSA

Took me 2 seconds to find a stock type replacement piston CB100 | SL100 | CL100 | XL100 Piston Kit

There are forums full of guys playing with similar bikes if you do the research. Finding parts that will work in your motor is not as easy as for modern motors but the information and possibly parts are out there, but you will have to do the work to find it. Good luck - life is one long learning experience. Enjoy the journey.
 

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oldrice.com has some old articles about hopping these things up.

I agree that doing a big bore isn't the worst idea.
But the OP needs to understand what he is getting into, and be realistic about the outcome.
 

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Discussion Starter #20
Hmmm... Interesting. Thanks for the links and such.

But! It's decided. It's getting cafe'd! It's been a dream for far too long to keep stock. Hmmm... Interesting indeed. Sure, It's not a racer. But a cafe- commuter is appealing to me. Just for a first time full build, you know?

I understand that I'm inexperienced in this sort of work. But my main interest is learning. I've been in and out of cars my whole life, so I figured I'd try my hand at some motorcycle science. Thanks for those of you that understand that it can be done. That's my goal. I understand that it's hard, weird, and generally dumb work, but being that it CAN be done, I'm just looking for info. Thank you for the links and such. Any more support would be greatly appreciated.
 
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