Topic: cb125 with 185cc engine. how does this work?

[73hutch]

i came across this listing last night. i wrote the seller to ask how he did it and he told me a shop did it for him. does anyone know how this is possible and what the engine might have come from? also does anyone know if cb100 and cb125 engines are interchangeable?

here's the ebay link and photos
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=250868698673&ssPageName=ADME:X:RTQ:MOTORS:1123#v4-39

[Coyote13]

The 100 and 125 should be interchangeable.  Not sure exactly how to get to 185, but I'm pretty certain it involves the sleeve and piston from a cb750, a stroked crank and a shortened rod.  Don't quote me on all that, but it seems I've read that somewhere or another.  Not a ton of info out there for these little guys, but you can find it if your google-fu is strong.

[kirkn]

That's the engine right out of an XL185S of the late 70s (with some sweet black-out and polishing treatments).  I wouldn't have guessed it to be quite a bolt-in, but in looks nice.

The main differences are in the taller cylinder/head of the 185.  I'm sure that one has a custom head stay (or deleted) and some custom intake plumbing.  Looks sweet.

As far as interchangeability 100 to 125 - yep, they're fully interchangeable.  However, not among all years - that is, there were a couple significant upgrades along the way, and early models don't 'drop-in' swap for late models.  But early-to-early and late-to-late are completely interchangeable.

And, you're wrong about not much info out there on the 100s/125s - they're hot hot HOT in AHRMA racing, and there's a ton of info out there.  2 or 3 dedicated forums that I can think of right off hand...   

Kirk

[Coyote13]

Well Kirk, do us all a favor and let us in!  I've got a 100 sitting in the back yard at the moment that needs some attention, and I'd love any info that's out there!

Thanks man

[kirkn]

http://autos.groups.yahoo.com/group/CB125/

http://www.thumpertalk.com/forum/     (go to the Vintage sub-forum)

http://forum1.aimoo.com/XLBoard

[faux fiddy]

The 100 and 125 should be interchangeable.  Not sure exactly how to get to 185, but I'm pretty certain it involves the sleeve and piston from a cb750, a stroked crank and a shortened rod.  Don't quote me on all that, but it seems I've read that somewhere or another.  Not a ton of info out there for these little guys, but you can find it if your google-fu is strong.

Not sure, but I think the wrist pins on the 100 are same as the 80,  125 is larger.

As far as bolting in the whole motor, things might match up okay.

[grcamna2]

I thought I'd revive this thread because I want to put an 83' XL200R motor into a CB125S,anymore idea's on it from you members? any of you done this ? The OP never did finish this thread...     

I like how his exhaust came out,it looks like he used an OEM type muffler and heat shield from another model;it looks like he could have used the stock carb. on it...

[grcamna2]

I'm curious how he attatched his footpegs to the bottom of the engine ?

[grcamna2]

I wonder how vibration is on it ? it must be a torque monster on that light machine 

[grcamna2]

I'll be doing this motor swap myself,changing out my CB125 stock engine for an 83' XL200R.I'll have to work out something w/ the rear sprocket because the XL takes 520 drive chain.I'll be needing to find an exhaust solution for it also because the stock XL exhaust is huge 

[grcamna2]

bump

[grcamna2]

bump

[RAFster122s]

The stock exhaust clearly can't be used.
The S90s have the ability to go to 105cc with a big bore kit but you are having to change the carb as well as the exhaust. The carb is the easy part. Fashioning a custom exhaust is about the only way to do it as nothing close to stock fitment from other bike is easy... So, making the exhaust a two piece affair and doing a little porting work is needed to take advantage of the longer duration camshaft that is available for that motor. Some guys just skip that route and bolt up a good 140cc horizontal motor, that's a Taiwanese motor usually for better life and some of the aftermarket motors are quickly junk while others are reliable and well made and give good life.
The 100cc can easily drop into a C70 Passport and guys have squeezed a 120cc but clearances are really tight and you won't be using a legshield with that mod.
The Sym Symba is a nice little bike of 88cc capacity that is a modern Honda Cub...Sym built Honda parts for them for a couple decades so, when their relationship with Honda ended (I think it ended) they started building bikes for themselves.  They make a high quality small motorcycle (tiddler, as termed by many small bike owners...)
The Symba is quite peppy and can easily and quickly do 50-55mph. It is a fun bike and it handles very nicely. I test road one after they came out...but, their 2500-2800 price is a little high, but getting 75-100 miles a gallon is very tempting if you live in a big city. The CB550 or a CB350/360 make for nicer city bikes, the CX500 makes an excellent commuter bike but it is rather boring, very good low end acceleration, just horrible brakes stock, But that is easily improved with a twin pot Honda caliper and a set of stainless braided brake hoses and appropriate sized MC or even the stock one gives good brake feel with the larger caliper piston area.

Dropping a 185 in a CB125 I would want to get rid of that mechanical front disk brake that is so problematic and either put a different set of forks or convert it to disk with hydraulic brakes...
Stopping is important and anytime you do that kind of hp mod, stopping gets to be more important.

If you do the upgrade, please create a thread on it...

The CA95 154cc motor's cylinders and reworking the stock head for the CA72/CB72 125cc bike to give it a boost, it was a Honda supported upgrade. The CA72 had twin carbs as the CA95 had a single powerjet carb on some models.
I forget the model now, but the first small bike motor that Honda developed that had 20 bhp was sometimes fit to the CB72 or even a CA95...they had a vertical/upright motor and one model that had the forward slant... The later was used in the upgrade...but then you faced the other upgrades. Was it the CB175? Been too long and it is too early/late to remember that right now.  Migraine headache doesn't help...

I forget the member ID here who did several CB125 rebuilds...
He built some nice ones... should be in the Other bikes or Project Bikes area...but it is more than a year old.

David

[grcamna2]

The stock exhaust clearly can't be used.
The S90s have the ability to go to 105cc with a big bore kit but you are having to change the carb as well as the exhaust. The carb is the easy part. Fashioning a custom exhaust is about the only way to do it as nothing close to stock fitment from other bike is easy... So, making the exhaust a two piece affair and doing a little porting work is needed to take advantage of the longer duration camshaft that is available for that motor. Some guys just skip that route and bolt up a good 140cc horizontal motor, that's a Taiwanese motor usually for better life and some of the aftermarket motors are quickly junk while others are reliable and well made and give good life.
The 100cc can easily drop into a C70 Passport and guys have squeezed a 120cc but clearances are really tight and you won't be using a legshield with that mod.
The Sym Symba is a nice little bike of 88cc capacity that is a modern Honda Cub...Sym built Honda parts for them for a couple decades so, when their relationship with Honda ended (I think it ended) they started building bikes for themselves.  They make a high quality small motorcycle (tiddler, as termed by many small bike owners...)
The Symba is quite peppy and can easily and quickly do 50-55mph. It is a fun bike and it handles very nicely. I test road one after they came out...but, their 2500-2800 price is a little high, but getting 75-100 miles a gallon is very tempting if you live in a big city. The CB550 or a CB350/360 make for nicer city bikes, the CX500 makes an excellent commuter bike but it is rather boring, very good low end acceleration, just horrible brakes stock, But that is easily improved with a twin pot Honda caliper and a set of stainless braided brake hoses and appropriate sized MC or even the stock one gives good brake feel with the larger caliper piston area.

Dropping a 185 in a CB125 I would want to get rid of that mechanical front disk brake that is so problematic and either put a different set of forks or convert it to disk with hydraulic brakes...
Stopping is important and anytime you do that kind of hp mod, stopping gets to be more important.

If you do the upgrade, please create a thread on it...

The CA95 154cc motor's cylinders and reworking the stock head for the CA72/CB72 125cc bike to give it a boost, it was a Honda supported upgrade. The CA72 had twin carbs as the CA95 had a single powerjet carb on some models.
I forget the model now, but the first small bike motor that Honda developed that had 20 bhp was sometimes fit to the CB72 or even a CA95...they had a vertical/upright motor and one model that had the forward slant... The later was used in the upgrade...but then you faced the other upgrades. Was it the CB175? Been too long and it is too early/late to remember that right now.  Migraine headache doesn't help...

I forget the member ID here who did several CB125 rebuilds...
He built some nice ones... should be in the Other bikes or Project Bikes area...but it is more than a year old.

David

Thanks for the info David,I'm still collecting parts for the thing and already have a pr. of CB400F front forks w/ light springs and a CB175 front drum,when i start putting it together I'll start a thread.I think the bike that 'FlyingJ' was building is called 'Big Blue' from about a yr. ago.The main thing I'll be doing to mine is a custom 1.5" headpipe to a larger muffler.The 'challenge' is finding a shop to do the custom bend headpipe;ask an 'auto muffler shop' to bend a 'motorcycle pipe' and they turn away..

[Don R]

 I read the 200XL swap can be done. that has a 6 speed too right?  I've just converted my 72 cl100 to 12 volts with a 360 stator and oregon rec/reg. so far, so good.

[Don R]

  There's a 125 chinese cylinder on ebay for $55 or so with a piston, rings etc. Google powroll for the big bore and stroker info. The 185 or 200 swap would be awesome. I'd do one if I found the engine reasonable.

[grcamna2]

I read the 200XL swap can be done. that has a 6 speed too right?  I've just converted my 72 cl100 to 12 volts with a 360 stator and oregon rec/reg. so far, so good.

Don,
This stuff i'll be saying here applies to the later 2-piece cylinder head models;the XL200R 2-valve engine is a direct bolt-in except for the top engine mount which needs to be fabbed up from the old CB125S mount because the cyl. head mounts farther back on the rear of the cylinder head and the cylinder is 8.2mm taller which will certainly fit in your frame and you'll also need to make a custom headpipe w/ more flow.The 1981' and newer CB125S models already have the frame ready to fit where the rear bolts line up to fit the different crankcase shape of the XL185 & XL/XR200 engines.The older model CB100 and 125's just need a bit of trimming w/ a small grinder to the frame between the 2 rearmost engine mount bolts on the right side.The 83-84' XL200R 2-valve engine has the 12 volt system and can be used on any XL/XR185/200 engine.A 1980-83' XR200R engine already has a 6 spd. trans. stock and the bottom footpeg mounts cast into the crankcases which is a good swap;the XL200R & XL185S both have the same bore and stroke and the same 5 speed and will not accept a 6 spd. XR200R trans.(wider gearsets) but will accept a 1979'- & up XL125S  6 speed trans because it's narrow enough to fit where the XL185/200 5 speeds fit & therefore a direct swap.The thing to remember is the CB100/125's have 4.055 primary gearing and all the XL & XR's have 3.333 which is taller gearing but these engines are real easy to switch primary gearing:just swap the clutch and crank gear sets ! I just bought a bottom end from an 82' XL125S and the crankcase spigot(1979 and up) will accept the XL185/200 cylinder(or the china 61mm 145 kit but that has too much compression and the piston needs to be 'flat topped' otherwise you'll cook the engine)and the XL185/200 longer stroke crankshaft and I have an XL185 crank that i'll be installing into that and building a high torque engine w/ a JMR ported head 
I think the best engine you can find for your swap is the 1979' XR185 or 1980-83' XR200,these early models still have the lower footpeg bosses cast into the cases but w/ an older dirtbike engine you'll need to rebuild it first & if you can find a complete left side stator w/ rotor and sidecover(plus wiring harness..)from the 83-84 XL200R you'll have 196wts. to power your lights.I bought a whole 83' XL200R cheap for parts and I've been selling off the stuff on it I don't need.

I did run into a snag installing the footpegs from my 81' CB125S on the custom XR185(same thing for all the early XL185 and XR200's)engine.They mount-up to the bolt holes exactly the same but the right side clutch cover(I found that some of the early pre-86' XR200R clutch covers do come cast w/ the special cut-out for the right footpeg bar mount underneath but not the later ones like I had.. a 1991' XR200R) w/ the decompressor never had a special cut-out cast into it for the right footpeg of the 125S so it hits the right engine case.I did grind-down the upper curve of the footpeg(so i wouldn't ever have a problem w/ Any clutch cover/footpeg clearance issue again) bar and give it enough clearance to fit;I then braced the lower curve(where the exh. pipe passes through) w/ a piece of angle iron specially fit to give it plenty of strength while allowing the custom pipe to easily clear the lower part.I want this little bike to be my small bullet-proof street bike for local rides to the store,etc. and making sure I have all the details done correctly before I fire it up and begin the Break-in process either today or tomorrow.

[grcamna2]

  There's a 125 chinese cylinder on ebay for $55 or so with a piston, rings etc. Google powroll for the big bore and stroker info. The 185 or 200 swap would be awesome. I'd do one if I found the engine reasonable.

I have a spare 61mm 145cc china cylinder/piston kit w/ 0 miles if you want but you need a larger crankcase spigot(at least 68mm wide) on your CB100 engine to make it fit..,it'll work on a 1981'-82' CB125S,I have one on my 81'.

[grcamna2]

Don,
I'm also looking for a good 80-83' XR200 engine,if you happen to run into two and you know where I can buy one for a good deal please PM me.The toughest thing is finding one w/ a good left side crankcase 

[grcamna2]

Don,
I'm also looking for a good 80-83' XR200 engine,if you happen to run into two and you know where I can buy one for a good deal please PM me.The toughest thing is finding one w/ a good left side crankcase 

Found the XR200 engine for a good deal on CL;the original owner blew-up the top end and he correctly stored the bottom-end in NM. for 20yrs.I found it and he shipped it.The engine has very low hrs. and all the inside parts are excellent;it's all cleaned-up and ready to be assembled.I couldn't pass it up for $75.This will be my spare as I'm also building the custom XR185 engine using an 82' XL125S bottom-end w/ 6 speed trans and compatible crankcase spigot for the bigger bore top-end plus XR185 crank fits right in.I look forward to having a fun little 'speedster' 

[cbinvb]

I have a spare 61mm 145cc china cylinder/piston kit w/ 0 miles if you want but you need a larger crankcase spigot(at least 68mm wide) on your CB100 engine to make it fit..,it'll work on a 1981'-82' CB125S,I have one on my 81'.

I am building up an 82 CB125s motor.  You still have these parts?

[grcamna2]

I have a spare 61mm 145cc china cylinder/piston kit w/ 0 miles if you want but you need a larger crankcase spigot(at least 68mm wide) on your CB100 engine to make it fit..,it'll work on a 1981'-82' CB125S,I have one on my 81'.

I am building up an 82 CB125s motor.  You still have these parts?

Yes,I do have this Big-bore cylinder and piston all fresh parts and never installed including gaskets,PM me if interested.

[grcamna2]

I read the 200XL swap can be done. that has a 6 speed too right?  I've just converted my 72 cl100 to 12 volts with a 360 stator and oregon rec/reg. so far, so good.

Don,I'm also converting the XL185S stator/charging system from 6vts. over to 12vts. by just switching over to a different R/R;I'll have to change all my lights,horn,flasher also but not my CDi because it's direct from the stator w/ it's own special power coil and therefore doesn't need changed to 12vts.

[RAFster122s]

GRCAMNA2,

How do you find a XR200 motor like that?

I'm amazed how some people find great deals like these.

David

Don,
I'm also looking for a good 80-83' XR200 engine,if you happen to run into two and you know where I can buy one for a good deal please PM me.The toughest thing is finding one w/ a good left side crankcase 

Found the XR200 engine for a good deal on CL;the original owner blew-up the top end and he correctly stored the bottom-end in NM. for 20yrs.I found it and he shipped it.The engine has very low hrs. and all the inside parts are excellent;it's all cleaned-up and ready to be assembled.I couldn't pass it up for $75.This will be my spare as I'm also building the custom XR185 engine using an 82' XL125S bottom-end w/ 6 speed trans and compatible crankcase spigot for the bigger bore top-end plus XR185 crank fits right in.I look forward to having a fun little 'speedster' 

[grcamna2]

GRCAMNA2,

How do you find a XR200 motor like that?

I'm amazed how some people find great deals like these.

David

Don,
I'm also looking for a good 80-83' XR200 engine,if you happen to run into two and you know where I can buy one for a good deal please PM me.The toughest thing is finding one w/ a good left side crankcase 

Found the XR200 engine for a good deal on CL;the original owner blew-up the top end and he correctly stored the bottom-end in NM. for 20yrs.I found it and he shipped it.The engine has very low hrs. and all the inside parts are excellent;it's all cleaned-up and ready to be assembled.I couldn't pass it up for $75.This will be my spare as I'm also building the custom XR185 engine using an 82' XL125S bottom-end w/ 6 speed trans and compatible crankcase spigot for the bigger bore top-end plus XR185 crank fits right in.I look forward to having a fun little 'speedster' 

David,
I kept looking on CL w/ searchtempest.com for over a yr. until I found it in NM. The owner had it for like 20 yrs. and tried to sell it numerous times. I guess folks out West there just want a larger engine for desert racing,etc.
I got blessed is what it was.