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CB125T cams and tuning

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ajb235
Two Stroke Sniffer



Joined: 25 Jul 2018
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PostPosted: 22:16 - 25 Jul 2018    Post subject: CB125T cams and tuning Reply with quote

I'm about to purchase a CB125T' and have spent some time on BCF reading posts from Teflon Mike, 5 years ago on this subject. Good to see that Teflon Mike is still around,and I would ask him
a) are there any identifying marks or numbers on the cam which would identify it as the performance cam
b) was a batch of these cams ever made?

The bike in question is a W reg 1981 machine, com star wheels, cable operated front disc and revcounter reading up to 13000 rpm.

Will this have the desired cam fitted?
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Teflon-Mike
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PostPosted: 23:19 - 25 Jul 2018    Post subject: Reply with quote

The full-power cam is Honda part number suffix 309, OTMH.

No, there's no identifying marks on a 309, or other cam AFAIK.

Yes, a W-Reg twin-shock CB125T 'should' have the full-power motor, with ISTR points rather than CDI ignition, larger 26mm PD carbs, and the 309 profile cam.

There's not a lot of other differences between T & TD- the motors, other than TD's normally painted black, whilst the 360 timed 'soft' motors used in the CM & CD retained the grey finish and looked almost identical to the early 125-Ts pretty much throughout!

Whether such an old bike still HAS the 309 cam, or even 180 timed CB engine, and even if it does, whether its in serviceable condition, are very big consequential questions!

These little motors tend to be reasonably well lubricated, but running them low on oil, or running them out of oil, which isn't too uncommon, tends to result in the cam-shaft being the first thing to get staved of lube, and in dire case wreck cam then head.

There weren't an awfully large number of them sold in the UK to start with; in 250 Learner days, they weren't particularly cheap compared to other, usually two-stroke offerings, and they weren't enormously cheaper to tax or insure; and IF those were significant purchase considerations, buyers probably looked more closely at MZ250's or GP100's or myriad 'cheaper' bikes that were usually as fast or faster.

Survival rate, is then rather low, and I have spotted a number of earlier T-Shocks that actually have later 'Reduced effect' Super-Dream engines, or CM/CD motors in them, and opened up at least one T motor to find no cam at all! whether robbed for a TD-x or just the killer component, I will never know!

Did I ever get involved in having a batch of 309 profile cams reproduce? No. And AFAIK no-one else did either, small demand just didn't warrant it.

CB125T cams and tuning..... begs query what your interest and intent here is.

If you want to do a conscientious restoration of a twin-shock 'T' then that 309 profile cam would be something you probably want or want to keep.... but a brochure condition T-Shocl, is probably not a hugely valuable bike, and as an unseen component not going to win any added brownie points in concourse.

If you want as much power as you can get on L-Plates?

Well, CB125T twin-shock, technically would require restriction to make it A1 licence / Learner-Legal.. as brochure it's about 2bhp over max power limit, and I think a few kilo's over max permitted power-to weight ratio... if any-one was to ask such impertinent questions of such and 'old' four-stroke 125....

If you really want a hot-snot A1/Learner-Legal, its probably NOT the ideal starting place, and you could get as much, much more easily with an over the counter Learner bike of more modern times, and if prepared to risk life and licence for even more, then plenty of alternative Learner-Illegals that would offer so much more so much easily, to consider; mostly two-stroke!

As the starting place for trying to max out possible power of a 125 twin engine, for academic interest, that cam has to be the place to start; at 17bhp it made the little twin make almost as much power as any of the Benley engine's up to and including the the CD200's, that only made 15bhp.

Later '233's didn't make a lot more; around 20bhp, but the crank-cases were machined for the bigger barrels, and they used the 360 timed crank and ignition, trying to better that, from some Honda-Parts bin mix and match is no easy feat.

Cheaper and easier and more reliable to just chuck a big-bore benley engine into a 125 frame 'as is'.....

Given the rather horrible cable operated disc on the T-Shock T... and rather less than inspiring T-Shock back end.. I'm NOT so sure that I would pick one as a base for a hot-rod up street-bike TBH.... but still.

Upgrading one with disc-brake and better suspension, would rather ruin what genuine classic interest and value the thing does have, and it still wouldn't likely be particularly more inspiring for it.

Doing something devious with the much more common and less 'classic' Super-Dream with its better mono-shock back suspension, and hydraulic disc brakes as standard, would offer many more potential candidates as donor... most of them probably in my back-garden! And less work to make it into an un-pre-supposing streamer, retaining pretty much all of its 'boring' looks, and not having anything to scream 'modified' on show.

But your bike, your call...
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ajb235
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PostPosted: 09:46 - 26 Jul 2018    Post subject: Reply with quote

Many thanks for your informed and useful reply.
Perhaps I should clarify my reasons for taking the 125 twin route.
BCF have christened me as a learner rider, and rather than mislead anyone, I am not 17 , more like 70! I have had many bikes, but now ride in a group of similar age profile riders, and we came to a decision to leave the powerful, heavy stuff that we have aspired to, and tackle the quiet country roads of Northern England on lightweight bikes of no more than 125cc. If there's a bit of a classic , rather than Chinese, go for it, so the CB125T appeals. I've always been interested in tuning, starting with my 4hp Bantam in 1964. Recently I ve had the Yamaha FZR 250, and screamed around at 19000 rpm, with no tuning to do, but it was a little tiring, not much below 12000.
I recently owned a CD200 Benly, lovely machine cdi, electric start etc, but outside the 125 limit!
I saw a little video on YouTube of a guy with a CB 125 T on the dyno, pulling 14000 rpm. With a weight of only 78 kg, this would be fun on the road.
So that's where I'm heading, lose any excess weight, cafe racer look, maybe CBR250RR carbs and a decent front disc brake.
I would keep all the bits I cut off/take off, in the interest of rebuilding as a future classic perhaps when I'm 80, but there's a lot of fun to be had in the meantime.
cheers for now

ajb235
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stevo as b4
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PostPosted: 19:11 - 26 Jul 2018    Post subject: Reply with quote

There's nowt wrong in your case or my case for 125cc tuning or engine conversions etc, as we are out of the (spotty 17yr old wanting to beat/cheat the law on our flappy cable tied on L-plates) category. Laughing

I don't know much about small Honda twins, but if your looking for the rare performance cam and you have the specs, like lobe centre angles, Base circle diameter and lift etc, then you could always approach a firm like Cat cams who would make you a one off cam for a price.

I don't know if these little Honda's used CV carbs, but if so a small pair of flat slides could help maybe, as could a tuned length 2-1 exhaust, if you could calculate the primary pipe lengths, diameter, and collector angles for pushing peak scavenging efficiency up closer to the 12000rpm range maybe?

No idea on if any big bore kits or if CB 175/185 pistons would fit, and how much you could increase compression and how you'd go about it. You might be able to get the cam sprocket slotted for vernier adjustment to dial in your cam for the best top end power?

Lastly if it's a CDI ignition (it wants to be at 14000rpm) then assuming you want to go silly with your wallet, you might be able to get an Ignitec or similar CDI that you could programme to give a more suitable advance curve for high octane fuel and a performance cam etc?

My bike isn't a CB125T but I'm expecting worthwhile gains from from a better exhaust system and a programmable ignition too.

Last bit of sperg from me, is I recommend you trying to get hold of a spare engine as tuning things can provide you with plenty of scrap metal or melted scrap metal, along the way until it's perfected or you find out the limitations and predictable service life of all the metal spinning bits.

I've got 3 engines now and a few spare bits here and there, as I don't want to have to shelve a project due to running out of unobtainable bits after a failed experiment or when you push something that bit too far before knowing where to draw the line with vaguely reliable. Laughing
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Teflon-Mike
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PostPosted: 19:47 - 26 Jul 2018    Post subject: Reply with quote

ajb235 wrote:
I am not 17 , more like 70!
No-fool-Like-an-Old-Fool....
Riding since I was 7, about 40 years now, my Mum & Dad, were still asking me, until I was 30, when I was going to grow-out of these motorbikes.... I got an earache reprieve for a decade.... NOW it's "Dont you think you are too old to still be pigging about with bikes!"
Hey! They have lifted the age limit for "Over 40's Trials" to 50! I'm still TOO young, to 'start'!!!!
Actually little ambition, having started in "School-Boy", progressed to "Adult", competed in "Classic" it's still a goal to aspire to! ALL on the same bike I've had since I was 15! But Still.
ajb235 wrote:
now ride in a group of similar age profile riders, and we came to a decision to leave the powerful, heavy stuff that we have aspired to, and tackle the quiet country roads of Northern England on lightweight bikes of no more than 125cc.

Any acquantance of "tony1951"? He's up your way, similar age and messin'bout with a Honda CG; maybe drop him a PM.
ajb235 wrote:
If there's a bit of a classic , rather than Chinese, go for it, so the CB125T appeals. I've always been interested in tuning, starting with my 4hp Bantam in 1964. Recently I ve had the Yamaha FZR 250, and screamed around at 19000 rpm, with no tuning to do, but it was a little tiring, not much below 12000.
I recently owned a CD200 Benly, lovely machine cdi, electric start etc, but outside the 125 limit!


Hmmmm... well, tuning the CB125Twin 'for-speed' is a route to madness... ask my psyciatrist and bank manager!

As stock, the full-power T-Shock, is about the most powerful, seriel production four-stroke 125 ever made. It's quite a hairy device.... mostly because of that russian roulette front brake!Lol But still.

There is some contension over the matter; there was a Peugot scooter, that used a centrifugal super-charger (Belt driven Turbo, for uninitiated), that could' make more power, about 20bhp, BUT, as sold, it was A1 14.5bhp complient, in full-power form it was never 'standard', it was a dealer or DIY mod to "De-Restrict".

The 125T and T2, then do have some genuine classic cudos in standard form, and reletively so rare, I'd be rather sanguine about hacking one about with ideas of Cafe-Racer-ing, TBH.... though, even at my tender years, a lot of that would be contemplating an aching back, I still suffer even without ace-bars! But see opening comment... lol.

As far as muggering with the motor?

That 309 cam is the key component to finding the power pottential of the twin; but valve timing does mean it will only work on 180 timed 125's.

The heads are actually rather good; they use the same head and valves on all the sloper Benly derivates, up to the most powerful, CMX250, that had the 53x53 bore stroke, on 360 crank, with twin CV's and managed about 21bhp.

There is little to no gain to be found there 'porting' the head, it already has more than enough flow capacity for a lot more gas than 125 motor will suck, and the port walls are rather thin in places, especially around the valve guide boss where it is most tempting to start shaving metal.

Valves are diddy, but reasonable for the motor/head, and in Hemi combustion chamber, rather close. Trying to make space for bigger valves, would beg filling the combustion chamber, and valve guide drillings with ali-weld, and starting from scratch re-cutting. A lot of work for small gain.

Carbs? PD26's are reather crude slide affairs, they aren't the most sophisticated, but they are big enough and they work... and conveniently match up to the manifilds pretty well. That manifoold is rather awkward and you would again have to make from scratch to fit much else, and given that CBR250.... well, how cheap and easy will you find bits for such a rare, non UK market device? But if you could, they are a parallel banked 'set' of carbs, with common butterfly rail and choke interconnect; not as easy as just lopping two off the end of the bank for a twin, and if you did, you would have to split them to mount 'splayed' on the 125 twin, and make a LOT of problems, probably not to find any benefits.

If you really want CV's, then off the shelf, you can buy the ones used on the CMX250, for reletive pennies from e-bay; and the manifolds and stubs to suit; they were used on the CMX250 and chinky derivatives, especially the big bore box cars, sorry quads sold on US market. But would beg loosing the OE airbox.

Exhaust? Like carbs and head, much the same and certainly the same header diameter used on the 10bhp 125's, through the 13 &17bhp 125's up through the 19-21bhp 'two-fifties'; no likely gains to be found there, either lopping off silencers or looking for anything more 'free-flow'.

Short of boring the bugga out, there's not a huge scope of likely targets to make anything much if any better.

Remember, out the crate, this engine, at forty years old!!! With air-cooling, two valves per cylinder, and simple slide carbs, makes MORE power than contemprary hot snot four-stroke 125's, that with water-cooling, 4valve heads and fuel injection cant do any better! And especially in the case of the YZF-R125 are a little on the fragile side before any-one tries adding lumpy cam or mapping the EFI!

And the old T-Shock, is a sack of spuds or two lighter than any of these things before you try lopping anything off it!

Of ALL the things you could do to a T/T2?

Well, OE 'Have a Drama on a Yokahama" rubber is top target. Decent modern rubber is GOOD. I think that they have been discontinued now, but we run Mitchelin M45's on the Pup, in T/T2 narrower sizes. Soft-ish compound, they grip! And I deck the pegs on the Super-Dream on them with abandon; in fact I did it by accident first time out to scrub them in for our Snowie!

Next up the old punger T-Shock suspension is a bit bouncy. T/T2 use narrrower forks than the TD's, and not a lot that can be done with them, but decent fork oil and a few 2p's preloading the springs can stiffen them up a lot. Haynes ISTR suggests using water thin ATF fluid in them, any wt fork oil, 5 or 10 will make them significantly more useful.

Back end plungers had effall damping from, the off, and sealed units, other than winding up the pre-load not a lot to be done with them, but plenty of better after market items available; check the pit-bike emporiums.

Top target for upgrade though has to be that suicide front disc. My main experience with one was on a CB100N, and it was effin-orrible! I am reliably assured that decent pads... if you can track them down, and IF you pay assidiouse attension to setting up the brake and cable very carefully, can make it almost 'good'..... but I still have flash backs to the CB100N.. I am not convinced!

A hydraulic caliper from something like a 125 super-dream would give better availability of better more modern pads, and full hydraulic actualtion. Provided the caliper and master cylinder were properly fettled and overhauled first.

Not sure about the fork hanger arrangement on the T/T2, I would expect to have to fabricate an adapter to take a hydro caliper; but posibly not as stand out obviouse as a TD front end or anything, It would probably be where I looked for significant improvement.

Otherwise I would tend to try and leave the thing as standard as possible.......

On the 12.5bhp 'reduced effect' Pup, even carrying excess weight, baited by a couple of local lads on more powerful and full faired YZF-R125, deturmined to show me what a 'real' sports bike can do, when they spotted the L-Plate.... They haven't been in my rear-view more than a couple of corners! And had a good dice with a chap on an Fazer 600 on the twisties coming back from a show!

Rather more grin inducing, to my mind to do it on something that looks like hum-drum low cost commuter, than something that looks modified....

A-N-D on a twisty road? If a heavier, 'Restricted' 125 Super-Dream wont discrace itself, even against 80horse big-bikes, no reason a lighter, full power T/T2 should....

Meanwhile; long considered opinion for a hot benley motor, was to use the 125's 44mm stroke 180 crank, topped with over bored CB'Two-Fifty' 53mm barels, over bored to 55,5mm to give samebore and stroke as the older CB200; 309 Cam, PD26's and Super-Dream CDi ignition... that's about the ultimate spec of Benley motor, and aught be 'good' for something in the mid 20's bhp wise; as much as any managed with the 53/53 big bore motors, plus a bit. BUT, hinges on having that cam; begs the crank cases machining to take the bigger barels; begs some pretty considered parts hunting amd machine mods to make them all fit... A-N-D you have about as much oomph as an out the box unrestricted NS125..... big work for small gains.... and is it really worth it, when you can still dust most 4T stuff that can wear an L-Plate on the 'reduced effect' motor..

With the full-power twin-shock? I would be inclined to restore to brochure and keep it classic; the most powerful 'production' four-stroke 125, it will always be that, even sat still.

I'd save doing the dispicable to the common as muck Super-Dream, that has more scope to capitolise on it, as well as more you can do, and isn't such a 'classic', and is still a pretty potent sports 4T125....

Remember the CX500 Turdo?

I have always had a hankering to build a silver 125 Super-Dream with a square headlamp Power-Bronze full fairing; Decalled up in factory style dayglo orange stickers declaring "Turbo" on the side; and one, maybe two of these Chinky pit bike blowers.... Would work pretty well, and probably better on a soft cam CM/CD engine; but hey, who cares.. it got a TURBO!

Given how many times I have been accosted and accused of riding a 250, and had folk a good half decade or more older than me, wax lyrical about when THEY had one 'back in the day' obliviouse of the very obviouse 125 decals on the side-panels, and abscent T-Shocks... I have always wondered how many would, at meets, start telling me they remember reading about the 125Turbo in the magazines, and how it was made in itally, and such a pitty the 125 L-Plate laws and power limit, put the kybosh on it, and start asking me how hard parts were to get for it LoL!! Another project, for another life-time perhaps!

ANYWAY... your bike your call. Bottom line is that the 125 twin doesn NOT lend itself to much more tuning than the factory gave it, but a lot of scope for part-bin pondering that in the cold metal makes as many problems as likely solved.

Have fun!
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Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'
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stevo as b4
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PostPosted: 13:42 - 27 Jul 2018    Post subject: Reply with quote

The thing is though while I'm OT is the Yamaha YZF125R engine developed with Minarelli is that they were never looking to design the ultimate 125 four stroke sports bike engine. Far from it, they wanted a cheap to produce lump that only had to nail the 14.6bhp upper limit and pass emissions regs then and now.

Banging on about how Yamaha couldn't find the 2.5bhp extra the 40yr old Honda twin had isnt very relevant or realistic. Could Honda make the CB125T pass euro 4? Wink

Yamaha did alot of things IMO in their engine design that were not in the interests of going after maximum bhp. The long stroke and low revving peak are just easy examples. I think they went long stroke as they wanted to make more torque lower down and have a more learner friendly easy to ride motor. That was after they knew they'd hit the easy target of 14.6bhp, and their 4valve head would easily flow all the air they needed. That's my take on it anyway.

Yamaha could have topped the 20bhp FI Peugeot as a walk in the park if they'd have adopted FZR or R6 architecture and de-tuned it a bit. The 125 law had them round the throat, and to a lesser extent so did emissions, but also longevity. Could you trust the masses of learner riders to look after a 20bhp+ 125 that revved to 14-15k and service the thing like a track day ridden R6?

Four stroke development has come on massively in the last couple of decades, and unlike 2T's there's plenty of scope to work on further developments and improvements them.
The current 250MX bikes make say 42-43bhp (claimed) and they leave even KTM's latest (legendary SX125) engine way behind on track. With the 2strokes allowed 150cc they in expert hands can match them just, but novice riders still get lapped by the 250's.
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Fizzer Thou
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PostPosted: 13:56 - 27 Jul 2018    Post subject: Reply with quote

I own a CB125-T2 that I have been doing up as a project for quite a few years now Thumbs Up

https://i666.photobucket.com/albums/vv23/WiNot_Rhencullen/CB125T2/Picture387.jpg~original

Unfortunately the pistons and valve guides are so worn that I ended up buying a pattern set of barrel and pistons,with the intention of finishing off the project.But that was before I became a grandad and much of my spare time is helping my daughter do up her house

https://i666.photobucket.com/albums/vv23/WiNot_Rhencullen/CB125T2/2013-03-19151443_zps3389c7cf.jpg~original

The camshaft,followers and bearings are all good so if you need any dimensions while the engine is in bits,then just ask Thumbs Up Wink
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Teflon-Mike
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PostPosted: 22:32 - 28 Jul 2018    Post subject: Reply with quote

stevo as b4 wrote:
Banging on about how Yamaha couldn't find the 2.5bhp extra the 40yr old Honda twin had isnt very relevant or realistic.


It is relevent. At 40 years old, the CB125Twin, is now in a world of 'Classics' or 'Antiques' depending on your point of view.

As such, it's the main 'feature' of the thing which marks it out from the crowd, as something 'special', as it did when new.

Comparison to the contemprary CBR or YZF-R125, is valid, demonstrating just how audaciouse a feat that was, not merely in it's own era, but to the modern age.

stevo as b4 wrote:
Could Honda make the CB125T pass euro 4? Wink


Hmmm... probably... Interesting that the motor lasted as long as it did in seriel production, before being migrated to China, for some more, where it was evolved even further, noteably by Regal-AJS with water-cooling and EFi... meeting emmissions standard up to Euro-3, and possibly 4, in the latest incarnations.... much de-tuned, though.

In 1977 when they launched the CB125Twin, the market was very much more performance orientated, and after three decades of essentially re-hashed 1930's technology, craved the high-tech of multi-cylinder engines, overhead cams, and reletively big power.

In 2017? The market is some-what more immure to 'technology', the major marketing demands are styling, not performance, whilst the main imperative on the manufactuer, is to meet regulatory, significantly emmissions, constraints.

What remains in both cases though, is that, throughout, the manufacturers over-riding imperative has been to make a profit... and to do that, deliver the market a product that meets or exceeds expectations, at a cost it will pay.

Launch model CB125Twin, claimed 17bhp, or 136bhp-per-liter. That was pretty audaciouse, for a production engine... Remember, it was the same year they launched the CBX-1000 'Six', which with 24 valves!, only claimed 103bhp for its full liter displacement.... Not much, over-the counter, could break the 100bhp/liter mark. The probably faster Suzuki GS1000 of the same year, with 4-cylinders only achieved around 85bhp, the Kawasaki Z1000 about the same... and with that displacement, they didn't have to work so hard to give them 'bottom', and with that much excess, they could stand a much fatter price tag in the show-room!

Intreguing, now, is that 'almost' 200bhp per liter is available off the shelf, in something like the BMW-R1-Replica; This would sort of suggest that scaled down, using contemprary technology and techniques, they aught to be able to achieve around 25bhp from a 'production' 125... but.. given how the power of modern liter-bikes has noteably been achieved by more conventional tuning, pushing peak power further and further up the rev-range, and leaving the shear-displacement to retain an adequete 'bottom', likely that to make a 1/8 liter four-stroke 'rideable' it would probably have to be de-tuned, and significantly, to around the CB125Twin's 17bhp level....

Could it meet emmissions? Possibly... but at what cost?

Interesting example here would not be the YZF-R125, but the first-generation, 'Sega-Super-Hang-On' CBR125....

A look at that bike, as a whole, and it is quite obviousely and significantly built down to a price, with sophisticated multi-link mono-shock arrangement utilised on the 125 Super-Dream, superceded by a reletively crude, direct acting single shock-absorber; its sports-bike aping 'beam' frame, made not of extruded aluminium, but pressed steel, etc etc etc.

As sold, that only managed a "Reduced Effect" 125-Twin matching 13bhp. An HRC "race-kit" was available for it, though, and in some markets was importer-fitted to 'homologate' the model for production racing; but even with that Factory-Endorsed 'tuning' it still only managed about the same 17bhp of the 125Twin, and I very much doubt met EPA regs!

But brings me back to the CB125-Twin, and what makes it a 'Classic' something of enduring excellence that stands out amongst its peers of it's own era.

Personally, I find 'more' in the MK2 mono-shock TD-C to aplaud as classic virtue; it inherited that high-revving two-stroke power rivaling four-stroke engine, and in the 'other-markets' full power variants, still achieved 17bhp, with the merits of better CDi ignition; and de-rigeur for the era mono-schock suspension, and those second generation Com-star wheels; a proper hydraulic disc brake, and no kick-starter.

Probably more than the original T-Shock T/T2, it deserves 'classic' recognition, as a product of its era.. a-n-d if nothing else, how the omnipotent 'Onda can get so much so right.. and yet still get it sooooo wrong!

The little Super-Dream tried to be all things to all men, with the power and performance of the two-strokes, the technical features of the big-bikes, and yet still be every-day all round civilised, which made it rather 'boring' compared to more raucus, and oft cheaper offerings, thanks to rising Yen, like the Yamaha RD125LC.

Most remarkeable, about the 125 Super-Dream, now, is how much of what it offered back in 1982 is NOT remarkeable, but standard fare on a contemprary light-weight; like the electric start and hydraulic disk front brake.

Older, Twin-Shock, CB125Twin, though, remains something that is a genuine classic, a product of its era, and that high reving two-cylinder motor, mostly what it was all about; packing race-track tech into a road-going proddy bike, screaming away to then unheard of RPM's, matching the speed of the two-smokes, and doing it without the smog-screen... well... as long as the piston rings lasted!Lol!
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Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'
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stevo as b4
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PostPosted: 21:32 - 30 Jul 2018    Post subject: Reply with quote

Still don't get you and don't think your getting it either TM.

1, CB125T can't be compared that well to your YZF125R's etc. The former did have a strong jewel like engine that was relatively reliable for its performance if the oil was changed enough. Negligence could fuck one up when an RD 125LC is only on its second or third piston though.

The CB was built to be a mini superdream and have some sporting spirit of the larger twins etc. It engine wise was not really designed down to a price like the modern Yamaha was. Also they had to throw alot at it to get that 17.5bhp, and the cost of making it a twin wasn't a huge consideration.

The Yamaha was designed to restricted legislation where the Honda was not. Emissions regs play a big role too. Its hard these days to make power and be clean and have good mpg too. The Honda didn't have the hardest corner of that triangle to balance.

The 15bhp is a limit that was and is easy for a modern engine of that size to meet. As I said all that undersquare bore/stroke stuff was done for a reason because they didn't need all the chips stacked in their favour, and were looking at the torque/ learner friendly use, and probably mpg optimisation too.

I don't doubt a de-tuned Chinese later incarnation of the same 40year old Honda engine with EFI, catalysts and soft cam profiles could just scrape a Euro 4 pass. It'd be a pretty shit engine once all done though.

20bhp+ from an R6 derived design 125 single would be easy and reliable today, if not really that useable or forgiving to ride for a beginner or ex car driver newbie etc. But it's not a huge technical engineering challenge either.

Oh and your bit about the 80's CB125T matching the speed of the 80's two strokes. Let's say your comparing 81 Honda's to 1982> smokers, well yeah I do agree with you then, if you left the 12bhp restrictions fitted that is.

Don't know if you've got official speed test data for the Superdream, but let's say it did a genuine true 80mph all screamed out to 12k in top. That's 2mph faster than your AR 125 did at Mira, or matches the RG gamma exactly.

Trouble was people didn't leave AR's and RG's in as supplied 12bhp trim for longer than the first service at best, so in reality how many CB125's actually sat neck and neck on the highway for miles on end with these bikes is probably negligible.

The same sort of owners that looked after their superdreams to the book and didn't wreak cams or end up with them leaving their own blue trail, would also have been the same owners that wernt changing pistons on their RD125LC's every fortnight too.
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Teflon-Mike
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PostPosted: 00:17 - 31 Jul 2018    Post subject: Reply with quote

Curiously, I actually did leave my AR's motor bog-stock, for the almost two and a half years I owned it, before the Ins-Co did..... I had FAR too much experience of RD125's shot-gun spannies and molten Mahl pistons, and 'mates' expecting a miricle with a two-pence piece and a chewing gum wrapper Laughing Oh, and GP100's and Honda H100's etc etc etc!!!

Definitely a skew argument though; but my point is that the 135bhp per liter of the 1977 125 Twin, was remarkable, and audacious, and the bikes most notable claim to fame in its own time; and so audacious it still stands favorable comparison to contemporary 125's 40 years on.

Yes; they probably could make a 17-20bhp 4T 125, if they really wanted to; point is that they don't.

Whether that's because of the A1 power limits; whether that's because of emissions, or whether its simply because modern market would rather have pointy plastic and pretty paint for their money, matters little; no contemporary 4T 125 boasts 135bhp per liter! CB125 Twin, 40 years ago, did.
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stevo as b4
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PostPosted: 20:02 - 31 Jul 2018    Post subject: Reply with quote

A legend in its own 1977 lunch time then? Ok I'll give it it's moment. Maybe Sochiro's best 125cc road legal moment?

But Mr Yamaha and Suzuki etc always had technology of their own to make a pinnacle 125 of the time, and I bet they considered an RD125LC that was un-restricted but left standard and looked after against the book to be almost an equal in reliability as well as on a higher performance tier.

Honda were good at 4stroke twins sure thing, but did they ever get as much as 36bhp from 305cc?
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ajb235
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PostPosted: 23:07 - 04 Sep 2018    Post subject: CB125T tuning Reply with quote

Finally purchased a CB 125 T today. I am checking out the carbs to see if they are the 26mm size that I wanted, indicating a "full power" bike.
The carbs have the letters PD cast into the body, and a number starting 26A stamped just below the PD cast letters.
I haven't had the carbs off yet, but I have pulled the slides out and these are 20mm diameter, which I assume is the choke or Venturi size in the carb.
Are these 26mm carbs?
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Teflon-Mike
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PostPosted: 05:24 - 05 Sep 2018    Post subject: Reply with quote

If they are marked PD26, yes they should be.
IF fiddling be effin careful of the rubber inlet manifolds they bolt to; they are unobtanium, and prone to cvrack/split, especially if carbs messed with clumsily, more so if any-one tries to pull them off without first removing air-box.air-box trumpets.
Pleeez DONT cafe it... restore it!
There's enough crate-chop-cafe-scramblers out there built out of good resto-fodder, and remember the 125T was not common, and a standard, and working one even less so!
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jjdugen
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PostPosted: 08:20 - 05 Sep 2018    Post subject: Reply with quote

I go back to the 60's, not the anemic offerings of the late 70's / 80's.
These were actually built to be able to race.... in the TT et. al. That is where your time and effort should be directed.
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ajb235
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PostPosted: 09:01 - 05 Sep 2018    Post subject: CB125T Reply with quote

Teflon-Mike wrote:
If they are marked PD26, yes they should be.
IF fiddling be effin careful of the rubber inlet manifolds they bolt to; they are unobtanium, and prone to cvrack/split, especially if carbs messed with clumsily, more so if any-one tries to pull them off without first removing air-box.air-box trumpets.
Pleeez DONT cafe it... restore it!
There's enough crate-chop-cafe-scramblers out there built out of good resto-fodder, and remember the 125T was not common, and a standard, and working one even less so!


Thanks for reassurance on carb sizes. I''m trying to establish the date of manufacturers/ uk first registration. 1981?? I will have to apply a V5C and a new reg. no. from DVLA. I will probably need to get a letter of validation from an owners club or similar. Who could do this?
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ajb235
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PostPosted: 10:56 - 20 Sep 2018    Post subject: Camshaft woes! Reply with quote

Got the top end stripped, first thing I noticed was the slack timing chain
Then further in , the camshaft bearing on one side
Is oval looks like 100 thou wear. So I got my new
Chinese replacements today £10.50 on EBay
And I’m hoping they will solve the problem. Nice fit on the cam, I will trial assemble the head and see if I can get the correct chain tension
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tittymcarsefa...
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PostPosted: 16:00 - 30 Sep 2018    Post subject: Reply with quote

If you are looking for power there are many oem options for increasing bore sizes and bigger valves and stuff but tbh it is far less work to drop a 250 in from a rebel, cb two fifty, or a cd250u, or the chinese 250 quad bike engines.not quite the same engine layout 180 vs 360 timing but far easier to get power up.

You could even sacrifice stealth and go 300cc watercooled using the smc quad bike engines

All these 40 year old bikes are in the historic class now so will no donly be getting more and more popular (free tax + mot exempt).


Last edited by tittymcarseface on 14:18 - 01 Oct 2018; edited 1 time in total
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Teflon-Mike
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PostPosted: 17:21 - 30 Sep 2018    Post subject: Reply with quote

The CB125T2 sold in the UK up until 1982, the CB125TD-C 'mono-shock' coming into the show-room some months ahead of either the UK 125 Learner-Laws of the last of the T2's being sold.

It's most likely then, that even a 1981 registration would me manufactured in late 1980, and everything else older than that.

I believe Honda UK have records of all official UK imports and sales by the frame number, and you can request a 'search' and dating letter from them, though like most clubs they do charge. If non UK bike, and many have come into the country from Ireland and Itally in recent decades, 'search' would chuck up the original market destination as well as exact model spec from frame number.

REGISTRATION:- the very first thing I would do is do a frame number search with Honda UK; see what we got. Next up I would try and see if its on the DVLA data-base; unless its come in from abraud and never been registered, its likely it is, and or was....

Risk here, and a big one, is that the bike was declared 'scrap' on the V5 at some point in bikes former life; either by owner, which is not so likley, but if confiscated by plod or council if dumped or uised by scroats on waste-land, would have been subject to an official disposal notice, and DVLA informed of such same as if 'catted' by insurance co.

IF the original frame number was reghistered... you could get the original number-plate and a new V5 for it... BUT, if it's been 'scrapped'... then it beggs both a 'super MOT' via Vosa as well as Vosa ident check to ensure it IS the bike being declared for registration; this is not a cheap process, and if it was neded, to mt mind it would deem the bike a parts donor not a viable resto-base.

If never registered in the UK, eg imported from italy or ireland or switzerland or similar; THEN, self registration is possible, BUT you need a dating letter, proof of auntenticity from recognised authority, like original importers or noted owners club. BUT, p[rocedure is that the bike has to be road-worthy before registration, so you have to restore the damn thing, get it MOT'd, then possibly submit for VOSA inspection, have it insured all on the frame number (good game getting insurance without a reg-no BTW!) THEN you can submit the p[aper-work to DVLA to try get a V5, before getting a reg-plate made, and using on the road....

IE; you have to spend all the money, and do all the work, BEFORE you hit the possible pit-fall of being told "S9orry, we scrapped that bike twenty years ago, it cant be returned to the road! and you are left with a wonderfully painted and expensive lawn ornament.

I actually cut the frame of an early wire-wheel 'T' model in half to get the engine out of it, because it had a destruction notice against the frame number / reg, and just not worth even trying to get round to get to road.

Proceed with caution, and do the paper-work before the paint-work; make sure you have all you will need, or plan to get the thing registered BEFORE you start spending time or money on the metal-work, or it could all be an even bigger waste than most old 'ondaz!
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redeem ouzzer
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PostPosted: 00:15 - 01 Oct 2018    Post subject: Reply with quote

stevo as b4 wrote:
A legend in its own 1977 lunch time then? Ok I'll give it it's moment. Maybe Sochiro's best 125cc road legal moment?

But Mr Yamaha and Suzuki etc always had technology of their own to make a pinnacle 125 of the time, and I bet they considered an RD125LC that was un-restricted but left standard and looked after against the book to be almost an equal in reliability as well as on a higher performance tier.

Honda were good at 4stroke twins sure thing, but did they ever get as much as 36bhp from 305cc?


Nail
On
Head

A properly jetted LC (or most other 125 2t’s of that era) will last a long time as well as being easier and cheaper to rebuild than a CB125T. I could probably rebuild an LC quicker than the time it takes to fuck around doing the valve clearances on the CB. The only advantage I can see of the pooper dream 125 is fuel economy, but it’s hardly going to be C90 levels of frugal when it revs to 12k (and will probably spend most of its time between a 8k and the rev limiter because it has sod all bottom end).

TLDR - if you tune a 125 4t that can mix it with a 2t it’s going to have similar (or worse) engine life, require more servicing and still have a less entertaining power delivery.
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temeluchus
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PostPosted: 03:18 - 01 Oct 2018    Post subject: Re: CB125T tuning Reply with quote

ajb235 wrote:

Are these 26mm carbs?


For some reason I think the PD series measures the bore of the hole in the flange end rather than the actual choke size.

It's the size its supposed to be at 20 odd mm at the choke (slide).
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ajb235
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Joined: 25 Jul 2018
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PostPosted: 16:55 - 17 Apr 2019    Post subject: CB125T up and running Reply with quote

Finally got my CB125T on the road today.
I had the cam reprofiled to what I thought were the "desirable" hot cam timings, and it wants to rev but no more than about 10k. I have open carbs, I couldn't find any inlet connection hoses or air filters.
So to compensate I am thinking I should increase the main jet size. The other factor is the 142 cc conversion. The exhaust have been cut open and the inner down pipe removed.
From various websites I have found that the standard main jet size is 88. I would go up to 100 with my mods.
Has anyone tried this, or have any recommendations?
I think I'm going to be busy trying to sort the front brake too....
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Fizzer Thou
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PostPosted: 20:12 - 18 Apr 2019    Post subject: Reply with quote

That mechanical front brake is over complicated and it took me a while to make it work correctly.If I could find an easy way to bolt on a hydraulic caliper I would,especially as I have a spare twin piston caliper in my box of spares.

But it was the unobtanium gasket for the front brake that was easy to sort.I found that a cereal packet seemed to be the correct thickness,so I cut one out with a scalpel

https://oi666.photobucket.com/albums/vv23/WiNot_Rhencullen/CB125T2/PIC_0001-1.jpg~original

These pages are from the Honda catalogue of that time...

https://oi666.photobucket.com/albums/vv23/WiNot_Rhencullen/Snaps/HondaLeaflets031.jpg~original
https://oi666.photobucket.com/albums/vv23/WiNot_Rhencullen/Snaps/HondaLeaflets030.jpg~original
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ajb235
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PostPosted: 20:39 - 18 Apr 2019    Post subject: CB125T front brake Reply with quote

I've checked it all out, it's clean and well lubricated, the cable is free, and it's set up correctly. The only thing that isn't right is the pivot arm that holds the caliper. It's on a hinge pin that allows the caliper to float on the disc. Either the pin or the hole in the casting is worn. I don't think that this affects the braking(or does it?) but the calipers rattles against the disc while riding over uneven surfaces.
So I'm looking for a suitable hydraulic system that stops, and looks as near standard as possible. The difficult part will be making a bracket to mount the caliper on the forks.
Or I would swap out the front end if I could retain the Comstar whee.
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ajb235
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PostPosted: 20:44 - 18 Apr 2019    Post subject: CB125T front brake Reply with quote

I've checked it all out, it's clean and well lubricated, the cable is free, and it's set up correctly. The only thing that isn't right is the pivot arm that holds the caliper. It's on a hinge pin that allows the caliper to float on the disc. Either the pin or the hole in the casting is worn. I don't think that this affects the braking(or does it?) but the calipers rattles against the disc while riding over uneven surfaces.
So I'm looking for a suitable hydraulic system that stops, and looks as near standard as possible. The difficult part will be making a bracket to mount the caliper on the forks.
Or I would swap out the front end if I could retain the Comstar whee.
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stevo as b4
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PostPosted: 20:32 - 02 May 2019    Post subject: Reply with quote

Just read the specs again on that cool looking for its time CB125T. Ultimately it's a case of four stroke lack of torque again though and at an excess of rpm for its level of power.

Less than 8in/ft at nearly 11k, when a 12bhp AR125 has 8.4in/ft at 7000, and a KMX125 having 13ib/ft at 9000rpm.

I know which bikes I'd want to be riding and which would be the easiest for a learner to use too!
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