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| | Author | Message | | Allagro | This post is not being displayed . | AllagroDerestricted DangerJoined: 11 Apr 2013Karma :   |  Posted: 18:01 - 11 Apr 2013  Post subject: honda CB125T -T2 tuning |  | | hi there been trying for a few weeks to find information and people who have tuned these bikes whats available for these bikes in the tuning world? and what other parts from other engines could give me some help? im currently attempting to over bore the cylinders and use C70 pistons, has any one tried this idea before? any info would be greatly received thank nath | | | Back to top |   | You must be logged in to rate posts | |  | | Teflon-Mike | This post is not being displayed . | Teflon-Miketl;dr Joined: 01 Jun 2010Karma :   | Posted: 20:17 - 11 Apr 2013  Post subject: | | | T2 motor, as in the early twin-shock twin, is the most powerful production four-stroke 125 EVER... in good nick should chuck out about 16bhp, as much as the same era two-stroke twins, with more revs and more mid-range! First off make sure you have a genuine T2 motor, not a later, common as muck, 12bhp Super-Dream engine, or worse, even more common 360 crank CD Benley or CM Rebel engine, that makes about 11bhp on single carb. Good bits in your engine are the cam-shaft which was the wildest honda made, and about the best you cab fit a CB125 Twin; and the 26mm Carburettors. Make sure that you have them... again, 'Reduced effect' Super-Dream bits fit, to fix up a knacker. NOW, personally, I'd be inclined with a T2 to keep it stock. It is a classic and it does have that accolade of the most powerful production 125 four-stroke. And its a pretty nippy little bike, and I'm not too sure I would want to go much quicker than the genuine 18mph it offers with that cantankerouse cable operated front brake! (It was bad enough on a CB100N single I had the displeasure of, many many years ago, even for the time when a lot of new lightweights still came with drums!) Anyhow...16bhp... there aren't many Benley based motors that make much more power, and it is as much as the CB200 chucked out.... The CB Two-Fifty the bored and stroked 233cc 360 crank version of the Benley motor only knocked out 19bhp, while the most powerful variant was the CMX 250 Rebel, that was another 233cc 360 crank motor, but with twin CV carbs.... that made 21. So.... it's a bit mutable how far you may take one of these little babies.... If you have the 26mm carbs and the genuine T2 full-power cam, you are off to a good start, and we know that the head and valves are good enough to flow enough for 20ish bhp... so there is scope to find more by boring. Bug-bear though is that you cannot go over 142cc on the stock liners. You can get a kit to get this far from china for about £90, complete with pistons and rings... not really worth effing about with C70 slugs, when there's already CB125 pattern pistons that size. Reports, however suggest that the extra 17cc... about 15% make very little noticeable difference to peak power, though. But there just ins't enough metal in the sleeves in the barel to go much bigger... you could.... but you would be running on the finning ali. Bigger liners? Barels from one of the bigger bore motors? OK, well the biggest Benley based engines are 233cc and they get that from a 53x53 bore & stroke. The 200's are the same 53mm bore, but a slightly shorter stroke. 53mm bore on the 41mm CB125 crank-stroke gives 170cc... so you aren't going to get it all the way out to 200cc on stock 'big-bore-benley' barels. CB200.... conveniently had the same 41mm stroke as the 125... and to get 198cc, used 55.5mm bore. Bad news is that that is one over-bore BEYOND max over bore on a big-bore benley barel.... AND Big-Bore-Benley barels dont drop straight onto 125 crank cases.... the liners are too large for the cylinder apature. OK... machine the block to get bigger barels in..... over-bore a big-bore barel...... You now have to find suitable pistons.... you have gone beyond the bore size for any of the standard Benley engines; not that you would want to use any of the big-bore benley slugs anyway, as they are flat-top low compression jobs, and the gudgeon pin diameter is too big to fit the con-rod, but too small to be sleeved in the piston. So... boring out the 125 engine; First problem: is the liner size the cases will take. Second problem: how big you can bore 'big-bore-benley' liners Third Problem: finding suitable pistons to match con-rods AND liner bore Forth Problem: Making sure big pistons actually give you more power and dont rob it, having enough compression Its a big mine-field. I have trodden it very carefully, and my advice is that unless you are pretty nifty at getting stuff machined to suit, and really know what you are about... which if you're asking here you probably ent..... dont bother trying. 142cc big-bore kit is available off the shelf. Dont make much odds, but probably the best you can do reasonably cheaply and easily. Make sure it is a genuine T2 spec motor, and you do have the full power that spec offers. Maybe as 'improvements' consider upgrading to 12v electrics using later Benley or Superdream generator & Superdream CDi Ignition. Definitely consider what might be done to upgrade that cable disc brake. Otherwise.... just make the thing as tidy and well fettled as you can and enjoy it for what it is.... a classic tiddler. No matter how much you tune it, its never going to be very fast. Its a 125... But in that company its one that you ought not ride on L-Plates or A1 licence becouse its already more powerful than legal restrictions or anything you can buy new in the show-room today!____________________My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them! 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?' | | | Back to top |  | You must be logged in to rate posts | | | | Allagro | This post is not being displayed . | | AllagroDerestricted DangerJoined: 11 Apr 2013Karma : | | Posted: 21:06 - 11 Apr 2013 Post subject: | | wow i hadnt expected such info  as far as im aware its the original 1979 engine, it has 180 crank and two Kenlih (spelling) carbs, not sure on sizing but they have no butterflys just a slide. i totaly agree with keeping the bike origonal as much as possible and the cable oporated brake gets some getting used to ! the reason for the want of over bore is simply because the engine was burning oil on one side and rattling quite a lot. so its been in the garage for the last two years and now seeing droves of bikers on the road, i want it back! since stripping down the barrels and what not the one cylinder looked like its had a mouse with a small pickaxe at the bore and the piston was a little worn to say the least. the timing chain is like a wizards sleeve and the tensioner rubber split. so in short its knackerd. although the bottom end seems sound i have seen the "big bore" kit on ebay but the thing that holds me back is the " 142" stamped on the side. so hence boring out the 125 barrels. naughty i know. so my trawlings through the net have lead me to C70 pistons as they have the same gudgeon pin size, and most importantly the same compression height as the 44mm pistons, only the skirt length is different (bit longer) but i could get that machined down. simply because i cant find any over size pistons bigger the 1.5 im guessing thats where the chinese started with there kit. it does still have 6V electrics and points and condensers x2 however i was going to convert it to wasted spark and use a "pitbike" type CDI at the end of the day its a 125 and to expect massive improvements would be silly, but seeing these things shift on youtube as cafe racers spurs me on quite abit ive seen a few bikes with the motad 2-1 exhaust system do these give any advantages over two singles? great info btw. i wish id have came here a long while back | | | Back to top | | | You must be logged in to rate posts | | | | bladerunner | This post is not being displayed . | bladerunnerWorld Chat ChampionJoined: 09 Sep 2006Karma :  | | Posted: 22:42 - 11 Apr 2013 Post subject: | | As std they as said are pretty good for what they are...and already don't last as long as the lesser hp models. Bore and pistons can wear a lot quicker due to making better power at higher revs. You could look at refreshing the std motor first and upping the compression a little to give more mid range pull and acceleration but that's going to need access to a machine shop and some careful measuring...but should yield some good results....the 2 into 1 can help your top end hp as you have good cams as std and could gain a couple of mph and less weight than the twin system you have now. Last thing might be to look at the ignition system but that's a bit of work and not a great deal of gain.....lastly and just for a bit of fun......maybe a nitrous oxide setup if you can pick one up second hand......now that's worth a giggle and genuine extra burst of power for a small amount of time...but your limited to how far you can take it till the clutch can't cope! Deffo scare the 2 stroke lot for a few mins with that lot.  ____________________Current bikes...cbr929, KDX200's, Rd125lc mk2, RGV250's | | | Back to top | | | You must be logged in to rate posts | | | | Fizzer Thou | This post is not being displayed . | Fizzer ThouWorld Chat Champion Joined: 06 Aug 2011Karma :  | Posted: 22:47 - 11 Apr 2013  Post subject: | | | My little CB125T2 looked like this until recently https://i666.photobucket.com/albums/vv23/WiNot_Rhencullen/CB125T2/Picture381.jpg but now looks like this https://i666.photobucket.com/albums/vv23/WiNot_Rhencullen/CB125T2/2013-02-26201740_zpsaf1f862d.jpg due to this https://i666.photobucket.com/albums/vv23/WiNot_Rhencullen/CB125T2/2013-02-26201720_zps932913f1.jpg The piston skirts are quite badly scored,which has damaged the liners.So I bought the kit from fleabay https://i666.photobucket.com/albums/vv23/WiNot_Rhencullen/CB125T2/2013-03-19151408_zps9dda246d.jpg but the dowel holes need machining out so as to take the 'O' rings around the dowels.Still,rather this than new piston kits and the bore job which would cost more than the complete new kit.Just a shame that it is not as good as it seemed in the advert. But one thing that I have noticed is how restricted the exhaust port is.The bore of the exhaust is a lot bigger than the port itself,showing that the breathing is strangled by this.I may well open this up a touch with a dremel type tool and see how the flow rate increases.The valves had to come out anyway,so that I could replace the valve guide seals. Such a differance between the size of the 125 piston and a piston ring from the Yam R1 engine that I was working on recently https://i666.photobucket.com/albums/vv23/WiNot_Rhencullen/CB125T2/2013-03-19155752_zps8e748ad8.jpg This is from the Honda brochure of that time https://i666.photobucket.com/albums/vv23/WiNot_Rhencullen/Snaps/HondaLeaflets031.jpg https://i666.photobucket.com/albums/vv23/WiNot_Rhencullen/Snaps/HondaLeaflets030.jpg____________________Just talk bikes.What else is there? Always have a 'Plan B' | | | Back to top | | | You must be logged in to rate posts | | | | Allagro | This post is not being displayed . | | AllagroDerestricted DangerJoined: 11 Apr 2013Karma : | | Posted: 00:40 - 12 Apr 2013 Post subject: | | | thats exactly the bike i have. the silver beast lol i noticed the ports too, the exhaust valve seems quite small, but then again it is only 62 n a bit cc it doesnt need to be massive, referencing my mini tuning book some smaller valves flow more than a larger item,,maybe this is the case here? i have a spare barrel in decent condition if all goes pear shaped and i can always buy some standard pistons. when the bike was running it never wanted to pull high rpms. i put it down to 2 things witch were lean mixture cause the foam had gone from the filters and points bounce. i moved the needles up in the slides and that seemed to help but there was always that air of doubt about the breakers even though they were new. i think electronic ignition is a definite upgrade. but picking the right one is the trick part i feel. definately dont want anything like my NS125 it refuses to start the majority of the time, the "electric drill start" maybe the next way lol i was looking at modding a car ignition system as the principals are similar to a distributor | | | Back to top | | | You must be logged in to rate posts | | | | humanbeing | This post is not being displayed . | humanbeingNova SlayerJoined: 20 Mar 2011Karma :  | | Posted: 03:02 - 12 Apr 2013 Post subject: | | | Allagro wrote: | | im guessing thats where the chinese started with there kit... |
There was a 150 twin made by Qjiang (Keeway in export market). Those "kit"  is std parts for that engine. | | | Back to top | | | You must be logged in to rate posts | | | | bikenut | This post is not being displayed . | bikenutWorld Chat ChampionJoined: 21 Nov 2011Karma :  | | Posted: 10:30 - 12 Apr 2013 Post subject: | | | :D nice shop fizzer......... | | | Back to top |  | You must be logged in to rate posts | | | | Teflon-Mike | This post is not being displayed . | | Teflon-Miketl;drJoined: 01 Jun 2010Karma : | Posted: 16:18 - 12 Apr 2013  Post subject: | | Just Reading your post, Fizzer, this project on the move again, then? Was reading comment beneath the picture of the barrel kit.... | Snowie wrote: | | Who's Doing another Super-Dream?! |
Mild Panic in her voice - called accross the room as she walked in, and she spotted the shot of the barrel kit... all she could see on screen, and she identified the bike from it!  THAZ ma girl! True Nut & Crank biker in the making there, I reckon! | Allagro wrote: | | and the cable operated brake gets some getting used to ! |
My recollections of that bludy brake ..... I don't think its possible to get used to it.... and like a woman... when you thought you'd got used to it.... it would change the rules! The drums, on say an H100, which were consistently poor, tending to dire as they went out of adjustment; so while not wonderfully effective, they were at least consistently ineffective..... The Cable brake on the CB100 or CB125T, well, it COULD be very effective.... you just never knew when! | Allagro wrote: | | i have seen the "big bore" kit on ebay but the thing that holds me back is the " 142" stamped on the side. |
Tut, tut, tut.... so you want to cheat the excequer of the higher rate tax? Beat the system over what you might ride on L's or A1 (Which a CB125T is doing already by dint of its excessive powah! )..... Yeah, quite prominant on the barrel casting isn't it? Only I've fitted barrels and people have not even been able to work out which bit of the built up engine the barrel IS once its sandwhiched between the block and head, both being that much bigger! Meanwhile that marking is raised, but neneath the cam-chain tensioner adjuster and hidden between the carb float bowls... you have to be pretty clued up to even know where to look, and deturmined or lucky to find it...... while three strokes of a file will take it off before you paint the barrel! It's not a legal requirement to display the cylinder displacement But as said, 17cc, folk that have reported significant difference from them, have as likely been noting the as likely more significant difference of getting an engine possibly as low as 10bhp from worn bores, gummed rings, pitted valve seats, wide valve clerances and a stretched cam-chain retarded cam, back to 12 or 16bhp from reconditioning, as they are the tiny gain of maybe 1/2 a Hp from the extra 10% displacement! | Fizzer Thou wrote: | | But one thing that I have noticed is how restricted the exhaust port is |
Yeah... I have looked quizzed and pondered similar. But... hesitated over old sage advice of mentor, Pops; "Before asking why not, ask why so" Looking down them mouths, the valve is tiny, and the port tapers a heck of a lot from the valve mouth to the exhaust flange, and appeares to be masked hugely by the valve guide support boss. From the part number polling, seems that the bare head is common accross the Benley family; so we know that it has the flow capacity to handle discharge from a pot almost twice the size, with at least 25% more power, that suggests at least 25% more gas.... Sort of implies it cant be all THAT restrictive. On the big-bore-benleys, though they are making peak power a good 1000 rpm lower down the rev range, so aren't having to push it out as often... but then they also have mush softer cams with less duration or dwell, so they possibly still have to shift as much gas as quick... Leads me to ponder whether the shape of that port is about gas speed, rather than gas-flow rate, and the taper is tuned in anyway to get good scavenging at lower valve lifts.... In which case, if its already got the capacity to flow more than we need it to... opening it up might not help find any added oomph... but could hamper part throttle or lower rpm flow, where the larger port may not encourage the same gas speed for inertial scavenging... Though... by eye, it does look more like the port has simply been sculpted around the head architecture as much as anything else! That though is another consideration. Its a tiny engine, and while the valve guide boss looks to take up a heck of a lot of room in the port... there's actually not a heck of a lot of metal around it, and there is certainly not a lot of metal in the rocker tray.... I have to admit... I have been tempted to have a crack at a spare head with the rotary stones.... but always been a little dubiouse about it. | Allagro wrote: | | ive seen a few bikes with the motad 2-1 exhaust system do these give any advantages over two singles? |
Yes....but as Fizzer says, stock 'zorsts are not really that restrictive to begin with, so they are unlikely to be the weak-link in power production; and again, the pipe sizing is pretty much the same over the entire Benley family, the Big-Bore-Benleys, then suggesting that the pipes can flow more than enough gas for the power any of them have. Main gain, is likely to be weight. The stock twin-pipes are pretty hefty. On the Super-Dream's I have used OE Honda Twins; replacement pattern twins, then both Micron and Motad 2-1's. I have preference for the Motad's. They are lighter and to my eye more stylish than the Micron, they also have a slightly nicer 'note'. I suspect they are possibly the better flowing of the bunch as well; but only a suspicion based on trying to set up sick engines, where they have been more 'sensitive' to carb changes on the Motad. The Stock OE pipes are pretty good though, and I've had bikes that have still worn thier OE pipes after 30 years. Been rotten, and plated, but remained serviceable. Pattern twins don't seem anywhere near as durable, and watching how the brand new pattern pipes on snowie's bike have weathered in two and a half years, I doubt they will be about in a decade's time! The Microns, I have to say seem to last best; at least in the silencer. Every Micron I've had though has needed a pin-hole welding in the header.... Left hand, just at the acute bend, about 2 1/2 " from the port..... three have all gone at almost the exact same spot! The Motad's I've had to spot a couple of pin-holes in one or two down pipes... again in same spot.... the low-point at the bottom bend, and each has had a tel-tale skuff or dent where they have obviousely been 'Kerbed' bashed into a kerb-stone riding up onto a pavement!...... but all but one silencer has 'gone' in the same spot around the hanger bracket... though even that cant be considered TOO bad on a pipe a couple of decades old, and on the back of the silencer can be patched and not be obviouse. So I'd say that the 2-1's either Micron or Motad are probably 'better' than OE quality metal and finish, and a lot cheaper than OE Honda replacements if you can even get them! Patern twins are cheapest, but they are certainly not the same quality... but on an old bike like this? Good-Enough, for the most part. | Allagro wrote: | | i was going to convert it to wasted spark and use a "pitbike" type CDI |
I think it already is 'wasted spark', ignition; that simply means that it fires every revolution, once sparking in a pot of exhaust fumes before TDC, once on a pot of fresh charge before TDC on compression. 180 crank, though means you need two spark triggers 180 crank revs about, to get sparks at the right time on each pot. The motor uses two distinct ignition circuits, to provide sparks to each pot; so going CDi you would need two seperate circuits and two seperate CDi's. Pointless looking at pit-bikes for inspiration, though, when the later Super-Dream has as standard 12v CDi ignition, and its ignition components are the same on both the 12bhp 'Reduced effect' (Standard) model and the rare 'Full-Power' version some markets got. Using the Super-Dream rotor, generator cover and back-plate, would give you 12v charging, so you would need Super-Dream regulator and a 12v battery. Then you'd have to swap bulbs and horn to 12v items to stop them blowing on over-volts. Wiring and Switches though would be OK, and infact happier on 12v, as doubling the voltage for the same power halves the ampage. Double volts also means that contact corrosion is easier to over-come and the electrics ought to be more reliable accross the board. Its a good mod, and allows you to use more easily come by and often cheaper modern components or accessories; like upgrade to an H4 or even PIR headlamp...... Super-Dream genny, BTW is bludy powerful for a lightweight motor, and you can easily run a conventional car 55/50W 12v H$ halogen headlamp bulb off it! Super-Dream genny casing, is black and slightly different shape, so you may want to strip and paint to match the styling of the T2. But main thing is that of the Benley motors, only the Super-Dream case has the twin triggers for the ignition, you would need to make sparks for 180 motor. And keeping it stock Super-Dream with Super-Dream Regulator, CDi's & Coils..... its pretty much a plug & play conversion, the generator has the windings to power up the CDi's, then you have the triggers for them, and all should work as was intended. Well it has for me, using S-D genny to 12v a couple of 6v motor's now. | humanbeing wrote: | | There was a 150 twin made by Qjiang (Keeway in export market). Those "kit" is std parts for that engine |
Yup. The last incarnation of the CB125T was the TD-J. They made a host of revisions and standardised on the 'Reduced effect' engine's power of 12bhp, which when made in China and or fitted with the CM or Benley Single-Carb, fell to almost CG-Push-rod levels! It got a Hi-Vo toothed cam-chain running on gears rather than a duplex running on sprockets, so unfortunately the crank isn't directly interchangeable. It got small CV carburettors, and the cam-shaft was re-profiled to something even softer than the Reduced Effect engines, to suit the CV carbs and possibly the single carb 'ecconomy' variants. 142cc big-bore version, then was I think an attempt to claw back a bit of 'go' from it..... NOTE: The original T/T2 Cam is the HOTTEST profile available for the Benley 180 motors. The Super-Dream 'Reduced Effect' Cam has similar duration, but about 10% less lift and no more 'Dwell' Ie: the valves start opening at the same number of degrees before TDC or BDC and close as many Degrees after; and they aren't held fully open any longer. in the middle. So they have taken metal off the entire lobe, so the valve opens more slowly, rather than being opened as fast and held less open a tad longer. This means that even a worn but serviceable T/T2 cam, is likely to offer more oomph than even a good new Super-Dream Cam. If you have one.... LOOK AFTER IT! They are rare as hens teeth! Still listed in Honda Parts-Lists, they are unfortunately 'No-Longer-Available', and have a list price of about 300 Euro's or something daft! New-Old-Stock come up seldom... I have found ONE NOS Full-Power-Cam in three and a half years looking! You will find CB125T cams offered on E-Bay; they are usually the Chinese Jailing part, and as far as I can tell, the same profile as the 'soft' TD-J cam. They have the same valve lift as the Super-Dream cam... but they have less dwell, so the valve is not held fully open as long, while the duration, time between the valve starting to open and closing again, is also similarly shortened... its probably the 'softest' profile for the motor.____________________My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them! 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?' | | | Back to top | | | You must be logged in to rate posts | | | | Allagro | This post is not being displayed . | | AllagroDerestricted DangerJoined: 11 Apr 2013Karma : | | Posted: 07:44 - 13 Apr 2013 Post subject: | | | I see what you mean about the wasted spark. I was having a moment lol. What I ment was to use just one ignition trigger and a double ended coil and do it that way. At least I think it would work. What can I do about the tensioner? Are the singles similar? As there loads cheaper then the twin items. | | | Back to top | | | You must be logged in to rate posts | | | | bladerunner | This post is not being displayed . | | bladerunnerWorld Chat ChampionJoined: 09 Sep 2006Karma : | | Posted: 09:15 - 13 Apr 2013 Post subject: | | Peak torque at 10,500 rpm and peak hp at 11,500  all done with mineral oil and air cooled!!! Looking at the picks you seem to have a good workshop already......any thoughts on upping the compression ratio a little?____________________Current bikes...cbr929, KDX200's, Rd125lc mk2, RGV250's | | | Back to top | | | You must be logged in to rate posts | | | | Teflon-Mike | This post is not being displayed . | | Teflon-Miketl;drJoined: 01 Jun 2010Karma : | | Posted: 09:45 - 13 Apr 2013 Post subject: | | | Allagro wrote: | | I see what you mean about the wasted spark. I was having a moment lol. What I ment was to use just one ignition trigger and a double ended coil and do it that way. At least I think it would work. |
No. It wouldn't. It's the set up used on the 360 Crank Benley Engines, though, and they use one magneto winding, one trigger, one CDi and one coil with single Low-Tension winding, but siamesed twin HT windings, two HT leads to both plugs. Bothe pistons at TDC together.... Left Pot [Suck][Squash][Bang][Blow] Right pot [Bang][Blow][Suck][Squash] So when spark happens to set fire to the charge on the up-stroke on the left pot, spark on the Right pots plug is being 'wasted' in the exhaust gas of that' pots 'blow' stroke. When Right pot's on squalsh and gets spark to light the fire; left pots on its blow stroke, so that spark gets wasted. On your 180 Crank motor: One piston at Top Dead Centre other at Bottom Dead Centre. Left Pot [Suck][Squash][Bang][Blow] Right pot [Squash][Bang][Blow][Suck] If you had single trigger ignition timed for the left pot with siamesed coil, spark would happen just before TDC on the squash stroke for the left pot, but put a spark into the right pot just before bottom dead centre on the 'bang' stroke of the right. would set fire to something... but with bog all compression behind it, and only just before the exhaust valve opened! Then when next spark happened, the wasted spark on the left pot's exhaust stroke.... the siamese coil would put a spark into the right pot, that was almost finished sucking in a fresh charge, and about to compress it. So one cylinder might run... other one would be grossely mistimed! | Allagro wrote: | | What can I do about the tensioner? Are the singles similar? As there loads cheaper then the twin items. |
As far as I know the singles use a completely different tensioner arrangement. What is wrong with the one you have? Show us photo's. Its a bow-tensioner. https://images.cmsnl.com/img/partslists/honda-cb125t-england-cam-chain-tensioner_bigma000161e05_f5e8.gif There is an inert plastic guide blade on the 'tight side', the front of the engine, exhaust port side. If you look at the engine from the magneto side, the crank rotates anti-clockwise, so its pulling the cam-chain down at the front, so that side is tensioned by the crank. Tensioner sits on the back of the barrel, as that's the 'slack' side, the crank feeding chain round on the up run to the cam. https://i178.photobucket.com/albums/w269/teflons-torque/Little%20Dreams/LD07%20Eng%20Build/imag1856.jpg The tensioner blade is like an archery bow, and restrained at both ends. Bottom end is pegged in the crank-case. Top end... that's where the complicated bit is! But, ignore the rack & pinion adjuster.... you have a plate that the top of the blade is pegged to, and a spring that pulls that plate down towards the crank, and that plate is clamped to the barel on a bolt that lets it 'slide' up and down underneath. Make sense? Sprint tugs top of the tensioner blade and pulls it down, making it bow out, into the cam-chain, making the cam-chain go around it, taking up any slack. The Adjustor, is simply a pinion gear that engages in a rack on the sliding plate. The 'screw' thats on the end of sits in the block and it simply turns as the plate is pulled down.... but this means that you can 'lock' the tensioner by tightening up the lock-nut on that shaft, so that after the spring has taken up the slack on the can-chain, the adjuster cant move and put too much tension on it. NOW....... The tensioner mechanism is pretty robust. Its inert parts, that dont move very much, very often, and are incredibly unlikely to wear out. Its the tensioner blade that rubs against the chain that will wear. But normally not much. Its a roller chain, as soon as the plates of the chain have worn grooves into the plastic, then the rollers come to bear on it, and just roll up the blade, so they dont wear much more after, and can out live most of the rest of the engine. UNLESS damaged. Now; few common causes of damage, and the first, and most obviouse is a snapped cam-chain. When it breaks.... looks like this BTW https://i178.photobucket.com/albums/w269/teflons-torque/Little%20Dreams/LD07%20Eng%20Build/101_0192.jpg And its NASTY! Anyway, as the chain breaks down, it can start hacking into the tensioner blade, but when it breaks, then the end will 'wip' around and can start snagging on stuff, and the chain can ceg snagged on the tensioner mechanism and possibly bend it, but more likely, as the chain snaps, the crank will pull the chain off the cam, and then it will fall into the front of the cam chain tunnel, and get all tangled up, and the crank will come round and slam a piston into an open valve and stop, before much gets clogged up at the bottom, though may still jam down there, and some chain get fed up and chew the bottom of the tensioner blade. OK... you dont have a snapped cam-chain... but possible the engine has suffered a snapped cam-chain in the past..... More common, is that the cam-chain tensioner gets neglected, and never loosed off properly to let the spring take up tension. Now the chain running loose, it sounds clattery, and thats becouse its rattling side to side, NOT being pressed into tension by the tensioner blade. In this case, the chain can bounce around and the plates will 'nibble' the blade, and never get to bed in and make a groove for the rollers to run on. Most likely cause of a worn out tensioner blade. Next is over-tensioning, or under-tensioning. Under-Tensioning is basically as above, if tensioning not done during routine service. Read the book, it says to tension the chain while doing the tappets, and to make sure that the front is tight by winding the motor round anti-clockwise... If you go backwards, though you take slack off the tensioner side, andput tension on the tensioner side.... so if you then slacken the tensioner, let the spring take the blade up against the chain, and lock it off, soon as you turn the engine the right way, that tension is pulled round the front, and you have a chuink of slack on the back, not being taken up by the tensioner.... that's your under tension. Conversely, if you have rotated engine forwards, and got all the slack on the back, and then FORCE the blade into extra tension, turning the adjustor, which I think you can do if you dont hold the adjustor shaft still when you tighten the lock-nut.... then you can put strain on the tensioner blade, and that will tend to see it chew a bit, and wear more quickly. But how much damage can it do to the blade? And is it all that important? This is the question. However, as far as remidy goes; you ought need no more than a new tensioner blade. It's part 3 on that CMSL micro-fishe; Pt No: 14500464013. CMSL list it at 48Euro, which is a tad excessive; Dave Silvers Spares? £37.83 which will be genuine Honda Spares; Looking at e-bay, doesn't seem any UK stockists are offering them; couple from the US for about £20... but my first port of call would be to give Riders of Yeoville a call....01935 421681 or 01935 420508... they are one of the folk that bring the Jailing spares into the UK, and offer the barrel kits, and I've always found them pretty helpful; I cant see a tensioner blade listed on thier webby, but that doesn't mean that they don't have them or cant get them, and I would expect them to be about £15 for the Jailing part. IF you really need it... blade can look pretty bad, but not be unserviceable. What is more of a worry is whether the cam-chain is actually knackered! If so, then that's a £45 part, and you have to split the crank-cases to loop it over the crank... so full gasket kit and seals while you are in there... becouse its and endless chain; no split link or soft-link.____________________My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them! 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?' | | | Back to top | | | You must be logged in to rate posts | | | | humanbeing | This post is not being displayed . | | humanbeingNova SlayerJoined: 20 Mar 2011Karma : | | Posted: 14:51 - 13 Apr 2013 Post subject: | | | Plenty CB parts in Swatow, Guangdong, China. Buy via agent still save £££. https://item.taobao.com/item.htm?id=6195396251 Made by https://www.cojp.com.cn/ https://item.taobao.com/item.htm?id=20781736645 | | | Back to top | | | You must be logged in to rate posts | | | | Allagro | This post is not being displayed . | | AllagroDerestricted DangerJoined: 11 Apr 2013Karma : | | Posted: 19:59 - 13 Apr 2013 Post subject: | | | as requested some pictures | | | Back to top | | | You must be logged in to rate posts | | | | Allagro | This post is not being displayed . | | AllagroDerestricted DangerJoined: 11 Apr 2013Karma : | | Posted: 20:01 - 13 Apr 2013 Post subject: | | | hang on, trying to work this picture thing out [/img] | | | Back to top | | | You must be logged in to rate posts | | | | Teflon-Mike | This post is not being displayed . | | Teflon-Miketl;drJoined: 01 Jun 2010Karma : | | Posted: 20:18 - 14 Apr 2013 Post subject: | | | https://www.bikechatforums.com/download.php?id=88669 Upload.... use preview... right click, select 'Copy Image URL', past url into post dialogue box; then highlight it, and click the Img button at the top, or put {IMG} infront and {/IMG} at the end, except dont hold shift when you type the { so you get [ instead.... (cant use actual encoding tags in plain text or web-browser tries using them as commands! So, looks like Tensioner mechanism is OK and undamaged. Blade from bit we can see looks worn but serviceable, though you'd have to take it out & get better pic for us to tell; same with the guilde slipper from teh front.____________________My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them! 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?' | | | Back to top | | | You must be logged in to rate posts | |  | Old Thread Alert!There is a gap of 1 year, 364 days between these two posts... |  | | | marsheng | This post is not being displayed . | | marshengL Plate WarriorJoined: 14 Apr 2015Karma : | | Posted: 00:10 - 14 Apr 2015 Post subject: | | | I wanted to get in on this discussion. I have run my CB150 (Bored out CB125) for years on the track and it is very quick. Around 19.5 hp at the back wheel and 13K. Took many failures before I had it all worked out. I have a few CB125 twin motors which I reckon will be good for 22-23 hp as they should be able to run to +14k. I have made larger cylinder sleeves to take 48.5 mm pistons for other races and they have run quite well. This brings them up to 150 cc which is our race class size. I used XT75 pistons for the upgrade. They are hard to find!! Now it is time to make my own. What I would really like is a full race cam. Anyone have any idea where to get one ? Cheers Wallace New Zealand | | | Back to top | | | You must be logged in to rate posts | | | | marsheng | This post is not being displayed . | | marshengL Plate WarriorJoined: 14 Apr 2015Karma : | | Posted: 00:20 - 14 Apr 2015 Post subject: | | | A report on the first CB125-150 upgrade I did some years ago. It ran against the latest CBR150s. https://www.kiwibiker.co.nz/forums/showthread.php/111461-Greymouth-St-Races-k14-Bucket-Report?p=1129489810#post1129489810 My website. https://marshland.co.nz/CB150T.html Cheers | | | Back to top | | | You must be logged in to rate posts | | | | Vincent | This post is not being displayed because the poster is banned. Unhide this post / all posts. | VincentBanned Joined: 16 Oct 2006Karma :  | | Posted: 09:32 - 14 Apr 2015 Post subject: | | If you want more performance, sell it on and get a two stroke  I bought a CB125T for my son to take his test, 'soon sold it and bought a KH125 instead.____________________ Space Is Deep | | | Back to top | | | You must be logged in to rate posts | | | | marsheng | This post is not being displayed . | | marshengL Plate WarriorJoined: 14 Apr 2015Karma : | | Posted: 10:59 - 14 Apr 2015 Post subject: | | | Quote: | | I bought a CB125T for my son to take his test, 'soon sold it and bought a KH125 instead. |
I'm afraid to say unless the KH125 is highly modified, it has no chance. Here is some footage of my CB150. https://www.youtube.com/watch?v=lMsGv0ovG-c | | | Back to top | | | You must be logged in to rate posts | | | | Vincent | This post is not being displayed because the poster is banned. Unhide this post / all posts. | | VincentBannedJoined: 16 Oct 2006Karma : | | Posted: 11:56 - 14 Apr 2015 Post subject: | | | marsheng wrote: | | Quote: | | I bought a CB125T for my son to take his test, 'soon sold it and bought a KH125 instead. |
I'm afraid to say unless the KH125 is highly modified, it has no chance. Here is some footage of my CB150. https://www.youtube.com/watch?v=lMsGv0ovG-c |
Isn't the CB150 modified? Anyhow, we didn't swap because the KH was faster....which it was....we swapped it because it started up first time, everytime .....and it kept running. Oh, and didn't suffer badly from rust ____________________ Space Is Deep | | | Back to top | | | You must be logged in to rate posts | | | | hoolio | This post is not being displayed . | hoolioTwo Stroke SnifferJoined: 07 Dec 2014Karma :  | | Posted: 07:48 - 13 May 2015 Post subject: | | | Just wondering how you got on with the big bore set up and more so which 47mm pistons to use. | | | Back to top | | | You must be logged in to rate posts | | | | Iain. | This post is not being displayed . | Iain.Could Be A Chat Bot Joined: 04 Dec 2014Karma :  | | Posted: 08:33 - 13 May 2015 Post subject: | | | Teflon-Mike wrote: | | T2 motor, as in the early twin-shock twin, is the most powerful production four-stroke 125 EVER... |
Wrong. MRT125 runs 16.5bhp in standard trim once de-restricted. (Airbox restrictor & CDI wires need joining or clipping, cant remember which) MRT125 Pro black edition? +5bhp on top of that at the rear wheel. https://www.riejumoto.co.uk/documents/msds/MRT125%20SM%20Pro%20BLACK%20MCM022.pdf | | | Back to top | | | You must be logged in to rate posts | | | Old Thread Alert!There is a gap of 1 year, 264 days between these two posts... | | | | Bik3r1999 | This post is not being displayed . | Bik3r1999L Plate WarriorJoined: 31 Jan 2017Karma :  | | Posted: 16:52 - 31 Jan 2017 Post subject: Need help on my new engine in my CB125T | | | Okay.. So I have a Honda CB125TD-E 1988 bike. Everything on it works as normal. However, the engine seized and I took the bike off the road. I bought an engine that was listed as a Honda CB125TD-C 1989, thinking that it should work, maybe change a couple of parts and go from there. However, I have come across a problem. I have researched the engine number from my new (second hand, but new to me) engine, and it appears to be a Honda CM125C-C engine, not sure about the year. I was wondering if I could have some advice on how I could get this working. Firstly, the wiring on the left-hand side casing (alternator) was different, there were a wire that didn't connect up, and the colours were different too. I removed the casing (with alternator (pickup points)) from my old engine, and installed it to the new engine. The bike now turns over, but it won't start. I am assuming that this is due to the CM125C-C only having one Pickup Coil, and one CDI, however, my original engine had two. Both plugs spark, but it seems that they are not sparking at the right time, so I'm thinking that there is something different on the flywheel. I have researched and found a CM125 CDI for £40, but it looks identical. I've come to the conclusion that the single CDI for the CM125 tells both coils when to fire, however, using my original casing with the pickup points, it is not sparking at the right time. My original engine number begins with JC06E - 5016... However, my new engine number begins with JC05E - 5009... So that's as much information as I can provide, and my question is: Is there anything I can change/swap/modify to get this new engine, to run in my bike? Looking forward to seeing a reply | | | Back to top | | | You must be logged in to rate posts | | | | Kickstart | This post is not being displayed . | KickstartThe Oracle Joined: 04 Feb 2002Karma :  | | Posted: 20:06 - 31 Jan 2017 Post subject: | | | Hi Thought the cranks were different between the CB and the CM. 180 degree crank on the CB and 360 degree crank on the CM All the best Katy____________________Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing | | | Back to top | | | You must be logged in to rate posts | | | Old Thread Alert!The last post was made 8 years, 332 days ago. Instead of replying here, would creating a new thread be more useful? | | | | Display posts from previous: All Posts1 Day7 Days2 Weeks1 Month3 Months6 Months1 Year Oldest FirstNewest First | | This page may contain affiliate links, which means we may earn a small commission if a visitor clicks through and makes a purchase. By clicking on an affiliate link, you accept that third-party cookies will be set.   | Bike Chat Forums Index -> The Workshop | All times are GMTGoto page 1, 2 Next | | Page 1 of 2 | | You cannot post new topics in this forumYou cannot reply to topics in this forumYou cannot edit your posts in this forumYou cannot delete your posts in this forumYou cannot vote in polls in this forumYou cannot attach files in this forumYou cannot download files in this forum | Please explain your  rating | | I agree with this post This post is Underrated This post is Cool This post is Funny This post is Helpful This post is Interesting This post is Insightful This post is Informative | | Please be fair in your ratings! If yourrating is revoked you will lose karmaHave you read the ratings guide? | |
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