Wife Bike - CB100

Penetrating oil and then a propane torch and it should come off. That's what I always use on stubborn parts.
 
ffjmoore said:
Penetrating oil and then a propane torch and it should come off. That's what I always use on stubborn parts.

Going to try that this evening, just wanted to make sure that there wasn't some catch or pin or something that I need to remove. Sounds like its just stuck.
 
Well, thanks to a torch and a hammer I got the point advance off and then the head, cylinder, and piston. I wish now I would never have taken it apart.

WP_000531.jpg


WP_000529.jpg


WP_000525.jpg


Need to see if I can find an engine shop to find prices on getting it bored out, or I'll have to get a new cylinder. One on ebay in good shape for about $50. Getting it bored should be alot less than that I would think. Its also easier to find OS pistons that stock size ones im finding.
 
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=130581583123

or even take it out to 134cc with a cb550 piston.
There is the meat to do this on a 125 barrel but dunno if it's the same for the 100.
 
When I did my 125 I went .50 over. The boring cost $50. I wouldn't go to big on a 100 because its a waste. You could always find a 125 motor or the crank and to end. There are 125 cylinder and piston kits on Ebay for $70. But if you just want a low budget build I would great a .25-.50 over bore piston depending on how bad the cylinder is and then slap it back together. Might want to do a new cam chain while your in there as .well.
 
The 550 piston is .5mm lower then the 125 piston so you end up with lower compression. So I have read. I have both pistons side by side and it is hard to tell .5mm but looking closely its there. I haven't done the math on how much it would lower compression.
 
good luck with the build, looks like its coming along nicely.
shame to find the piston in such a bad state but better to find out now than when you kick it over for
the first time.
least you know it will be done right!
more pics please!
 
ffjmoore said:
The 550 piston is .5mm lower then the 125 piston so you end up with lower compression. So I have read. I have both pistons side by side and it is hard to tell .5mm but looking closely its there. I haven't done the math on how much it would lower compression.

Can't you just deck the head .5mm?
 
I picked up a new cylinder that looks really good on ebay for $45 shipped (mine cant be reused) the machine shop I called charges $50 so it was easier to get get that one.
I'll just get it check the diameter and then get a piston to match, it looks like it was re-done recently so im not sure it it over OS or not.

I had thought about going with a 125 cylinder and piston but I didn't know if it would just match up or if I was going to need to change anything out.

Can I just slap this bitch on there? http://www.ebay.com/itm/Honda-Cylinder-Bore-56-5mm-CB125-CL-XL-SL125-124CM3-New-/180714824640?pt=Motorcycles_Parts_Accessories&vxp=mtr&hash=item2a137163c0

I'll have to re-jet anyways so better to do it now I suppose.
 
JSJamboree said:
I picked up a new cylinder that looks really good on ebay for $45 shipped (mine cant be reused) the machine shop I called charges $50 so it was easier to get get that one.

Same as ........ mine is going to need a rebore at some time, it's done about 30k and gets a little smokey. It's cheaper to get a new piston and barrel that have a rebore, which seems a bit wasteful, and for my engine (the pushrod one) I can get a 150cc piston, rings, small end, gaskets, barrel and complete large valve head for $150. Crazy.
 
The 125 has a different crank, longer stroke I believe. So you would also need that. The 100 has smaller valves.
 
ffjmoore said:
The 125 has a different crank, longer stroke I believe. So you would also need that. The 100 has smaller valves.

After some additional research, the 100 and the 125 have the same stroke at 49.9mm and both run 9.5:1 compression. On the same note, the valves are interchangeable on them as well, so it seems that truely the only difference is the cylinder bore /displacement.

So, a new piston is going to be $40, or for $65 I can move it up to a 125 and get an additional .5 hp
 
Where did you find your info? A guy I know bought a bike that was rebuilt using both 100 & 125 and it has low compression. We were thinking it was because the crank was different but if they are the same I wonder what it could be.
 
Ok, found out what the difference is on the lower end. The 100 has a 14mm wrist pin and the 125 has a 15mm pin. Info its from powroll website.
 
ffjmoore said:
Ok, found out what the difference is on the lower end. The 100 has a 14mm wrist pin and the 125 has a 15mm pin. Info its from powroll website.

The information I was pulling was from the shop manual and the parts guide. It however, mentions nothing about the wrist pin size. Guess as long as the crank looks good then i'll be staying with the 100cc piston.

The 125 "kit" comes with a 15mm pin, i'll measure what mine is but im guessing your correct and it'll be 14mm
 
The 100 has a 1mm smaller wrist pin
the valves do not swap from all years models and such. not all 125s are the same and the 100s are smaller.
If looking for a hot set up the XR200 head is the way to go. or at least a latter 125 2 piece head as they flow better
 
Back
Top Bottom