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I like to bore my cylinder(it has rust so I need to anyway)and want to go a bit bigger w/o any mods..just a big bore piston.I once bought a big bore piston for my SL125 back a long time ago from Powroll, it was 135cc and made a difference in climbing hills,etc.
Do any of you members know which pistons will fit from another make/model bike? or do I have to buy a special 'CB125S big bore kit'? ;My bike is a 1981' CB125S.
edit:I changed the title now because I came to realize that a bigger sleeve isn't just a bore out and 'drop in' project.The crankcase opening/spigot is 70mm on these 2nd generation(Honda code '383') CB125S models which gives me room there and there is room inside the aluminum cylinder 'outer' to go bigger.
Re: What oem piston will be a good 'drop-in' overbore for my 81' CB125S ?
I was looking at a used XL185 cylinder/piston on ebay & thought that'd be good if i could get the lower cyl. skirt to fit down inside my 81' CB125S cases.. but maybe the stroke/cyl. height difference w/ the XL185 motor would mess me up.The XL185 has a flat top piston and the STD. 81' CB125S piston(13101-437-003) plus the oversizes from Honda have the nice rounded piston crown 'Hemi' style which I think will give me better power than the flat-top style piston. Have any of you Caf'e CB125S dudes experimented w/ different pistons in your bikes? Let me know or PM me because I've got to find a solution to this soon so I can get it back on the road right away.I NEED to take a long ride and get away from here.A long camping trip on my bike is what i'm looking to do !
Re: What oem piston will be a good 'drop-in' overbore for my 81' CB125S ?
I read about the 750 piston swap back when I was sorting my 125S motor. My understanding is that if you do that route you need to use the 750 piston liner also, because the stock liner gets pretty thin once you're at that much bore. I ended up finding a NOS big bore kit, put mine out to 135cc. Sadly, I haven't ridden it yet so no comment on performance.
Re: What oem piston will be a good 'drop-in' overbore for my 81' CB125S ?
Hey Cal ,thanks for getting back to me;that's what I was thinking about the liner.. Can you tell me if you had to bore out the cylinder(aluminum 'outer') before you installed the CB750 liner? also did you have to modify the length of the CB750 liner in any way ? and was boring out the lower crankcase opening required for the 81' CB125S ?
Re: What oem piston will be a good 'drop-in' overbore for my 81' CB125S ?
I did a little reading after posting here, seems you may also have to turn down the piston itself a little. May be a little more involved than my first impression.
Re: What oem piston will be a good 'drop-in' overbore for my 81' CB125S ?
coyote13 said:
I did a little reading after posting here, seems you may also have to turn down the piston itself a little. May be a little more involved than my first impression.
gotcha coyote..
How about Do you know anywhere I can find an NOS set of 1mm 4th over Honda oem rings pt.# 13051-440-003 ?? ???
I only found one set of them in Singapore.. which will be almost a month and want to find them soon because I've got the stock NOS 1mm over Honda piston & all the places that say: "we can get it" online are coming up short for me so far.. The search is on and hoping to find/confirm a set of'em soon. Help ! :'(
Re: What oem piston will be a good 'drop-in' overbore for my 81' CB125S ?
I didn't actually do the 750 liner and piston, just did some reading about it. My understanding was that you would have to machine the aluminum jug, and probably have to open up the case a little bit to accept it. Same would be true with a 175/185/200 cylinder.
I was lucky and found a NOS kit specifically for the 125s, so when I sent in my cylinder to get cleaned up I had them bore it out for me.
Re: What oem piston will be a good 'drop-in' overbore for my 81' CB125S ?
Check the stock sleeve diameter and if it's 68mm then I don't see why it wouldn't drop in.
That would actually be cheaper than the route I went, too. I picked up my piston & ring set for $60, then had to pay for the overbore.
Re: What oem piston will be a good 'drop-in' overbore for my 81' CB125S ?
CALfeRacer said:
I didn't actually do the 750 liner and piston, just did some reading about it. My understanding was that you would have to machine the aluminum jug, and probably have to open up the case a little bit to accept it. Same would be true with a 175/185/200 cylinder.
I was lucky and found a NOS kit specifically for the 125s, so when I sent in my cylinder to get cleaned up I had them bore it out for me.
CAL,
When you say "NOS kit", what size bore we talking about? and does it have the same style piston crown as your orig. piston ? I'm looking on ebay and seeing different options avail... the cheapest and 'easiest' would be a 145cc Chinese aluminum cylinder,flat top piston,rings,gaskets kit w/ no steel liner.. all aluminum w/ a cheap Nikasil coating Free shipping all for a measly $50-60 : I wonder how many miles I could roll on that bike at 55-60mph all day long(which is the way I would be driving it on a few journeys)until that coating would start to flake off and leave me stranded somewhere...
The 'scooter craze' killed the CB125's and I refuse to get a plastic scooter.
Re: What oem piston will be a good 'drop-in' overbore for my 81' CB125S ?
I can't remember the exact size off the top of my head, but I did the math and it comes out to 134-135cc. The NOS is "new old stock" so basically a part from the late 70's/sometime in the 80's that was never opened or used. I can't remember the brand either, but it was not Honda. It's not completely flat, but not domed like the stock piston.
Re: What oem piston will be a good 'drop-in' overbore for my 81' CB125S ?
Have you considered the Lifan option? Can squeeze a 200cc motor in your frame with a silly amount of ease, while maintaining a good level of reliability and longevity.
And I believe you'd pick up a 6 speed going that route as well.
Re: What oem piston will be a good 'drop-in' overbore for my 81' CB125S ?
coyote13 said:
Have you considered the Lifan option? Can squeeze a 200cc motor in your frame with a silly amount of ease, while maintaining a good level of reliability and longevity.
And I believe you'd pick up a 6 speed going that route as well.
Re: What oem piston will be a good 'drop-in' overbore for my 81' CB125S ?
The XR200 engine is a longer stroke(57.8mm) engine for more midrange,etc. and I'll be finishing that project engine at a later time.
I still like the CB125S engine w/ it's 49.5mm stroke and want to ask if anyone on here has done the CB750 cylinder liner install w/ CB750 61mm piston? I'm going to do this project once I learn a bit more. I like the shape of the ports in this 81' CB125S better than when I did my old SL125 w/ Powroll(135cc piston and 10cc more stroker crank for a total of 145cc)a number of years ago when Powroll was still going strong;the ports are bigger than the old style one-piece head. The 145cc big bore for this little motor w/ the older CB750 parts is my present 'Plan' when I get some more tech. expertise info. to begin and complete the job ! ;D 8)
Re: What oem piston will be a good 'drop-in' overbore for my 81' CB125S ?
CALfeRacer said:
I can't remember the exact size off the top of my head, but I did the math and it comes out to 134-135cc. The NOS is "new old stock" so basically a part from the late 70's/sometime in the 80's that was never opened or used. I can't remember the brand either, but it was not Honda. It's not completely flat, but not domed like the stock piston.
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