View Full Version : '98 RS50/TZR125R hybrid

11-17-2015, 04:28 AM
Hi everyone, I thought it was about time I joined up and showed you a project that's slowly been developed over the last couple of years. It started with a very worn out RS50 that had a 70cc cylinder fitted, but retained the stock head, so unsurprisingly it had a seized holed piston. Almost everything else on the bike was tired and abused.


We sold the old engine, along with the exhaust etc to fund buying a TZR125 engine. Like Matt's CR project (which I used as inspiration) I had to cut out the middle of the swingarm to fit the engine, then use some spacers to fit the engine (different sized swingarm spindle between the models)and get the chain alignment correct. I also added some extra support on the swingarm cross brace to keep it stiff.

New front mounts were also welded in to match the new engine, and that was the easy bit done.. This was with a pipe I had made for a different bike, tied on to check the fitting;


Because it was going to be for my partner Alison, she dictated how she wanted it to look, which meant no fairing, classic round headlight and a bit less racey than standard. We both preferred the look and feel of the bike without the extra tank cover on, it felt smaller and she liked that. This gave us lots of problems though! neither paint or body filler would stick very well to the plastic fuel tank, bubbling up. She came up with the idea of covering it with comic book cut outs which did the trick, even though she'd prefer it to be purple, this was a fun way to solve the issue.


Everything else was re-painted, cleaned, bearings replaced, the loom was the RS one, modded for the different engine. The stock RS rad seems to be coping ok so far which is good..

So, the motor was in but it didn't run too good. The head gasket kept blowing, so I machined the head to use an O ring instead, which meant the chamber needed machining to get the squish and volume correct again. The carburation needed a lot of work to dial in without the airbox... standard it ran a 210 main jet, and at the moment it's gone to over 500 and still possibly a touch too lean. The pipe is quite low revving, in order to make the bike nice and easy to ride for Alison, peaking at about 9500. Here it was dynoed at about 27.5hp, which would be about 30 on a dynojet dyno.. but it feels really nice to ride, along the tight lanes where we live..


11-17-2015, 04:42 AM
Because the clocks had to be mounted to the yok they needed to be split into the parts and reassembled without the tacho (which wouldn't work with the TZR engine), I also added a cheap little ignition switch.. it all sits together quite well.



The shock is a Fastace one, 1200lb spring which is a bit firm, but not far off. Weight is 105kg without fuel. This is me riding it at a trackday last summer;


And a bit of onboard footage from the local roads.. http://www.youtube.com/watch?v=8UqgCZFXerg

(http://www.youtube.com/watch?v=8UqgCZFXerg)Now Alison has since passed her test and wants a bigger bike, I'm embarking on improving the bike a bit, so I'm in the middle of lightening it with a new subframe and Honda RS seat unit, smaller headlight and clocks, mounted from the frame to improve the steering.. plus I have a larger carb to go on and plan to tune the cylinder a bit more, and make a revvier pipe.


Anyway... there was many more little things that I haven't mentioned but I don't want to bore you all!

11-17-2015, 07:34 AM
Awesome! I am putting a dt125 motor in my rs right now also! You have any pictures of the power valve setup?

11-17-2015, 07:44 AM

11-17-2015, 09:08 AM
The powervalve set up is quite complicated! Originally it had the 3 wire servo that came with the engine (with integral control module), but the timing was out for my pipe losing top end power. So I got an RD350 YPVS (or they were called RZ's in the US) servo and seperate controlling box, which I modded to give me the facility to control the rpm points.


servo is mounted off the top of the engine cradle frame, with cables made from scratch. Note also rad cap located inside the frame rail for neatness..

11-17-2015, 11:22 AM
Nicely done--any photos of the bike with the Comic tank on it?

11-17-2015, 12:27 PM
Awesome thanks for the pictures! Wouldnt it have been easier to use a Tzr125 pipe? And what gearing did you go with?

11-17-2015, 01:42 PM
Picture of it 'finished' last year;


I make lots of pipes for other two strokes, so it was easier and cheaper to make one from scratch! gearing is 38t rear, 15t front I think, good for about 90mph. Not having a fairing cuts top speed a bit though.

Alison has just passed her test though, now she wants a bigger bike I can set the little RS up to be a bit sportier, so this winter it's being lightened and tweaked, larger carburettor, a revvier pipe and perhaps some cylinder tuning to get it up to 30+hp with luck. Also less weight with a Honda seat, and mounting all the clocks/lights off the frame at the front. should get it down to about 98kg without fuel.. Here it is at the moment;


11-17-2015, 02:33 PM
Oh my that is totally wild! The purple grape color looks good enough to eat. :lol:

Twenty Seven HP wasn't enough for Alison? Damn!

11-17-2015, 03:10 PM
hehe... I wouldn't have done it all purple myself, but she's a girl, so she's allowed :D

I don't think she really got on too well with the little two stroke, a bigger bike is often easier to ride. So now she is getting a bigger bike it means I can make the RS a little more to my own liking. I like little two strokes.

Oh, here's a bit of onboard footage https://www.youtube.com/watch?v=8UqgCZFXerg

11-17-2015, 08:46 PM
That's weird--your second post wasn't showing up previously. Lots of fun photos.


11-18-2015, 03:38 AM
Ah yeah, I think it's because it was my first reply post so had to have a moderator allow it.. sorry for the repeats!

11-18-2015, 03:44 AM
That's the great thing about Devon. Endless back roads that are pretty much deserted (Except for the tractors). Great fun.

11-18-2015, 04:49 AM
can you tell me a little bit more about how you made that pipe? the header and first taper looks absolutely gorgeous, was it hydro formed?

I recently bought a slip roll, brake, shear, and belt sander setup so I am not far away from beginning my own pipes also.. any tips would be appreciated.

11-18-2015, 07:01 AM
Yeah, all my pipes I hydroform the whole thing because I'm not so good at welding... also I find it quicker to do a whole chamber like this. The downside is it can be less accurate following the design dimensions, the pipe doesn't always come out fully round.

The whole pipe is done in one go, then sliced into sections and rotated to fit the bike. In the last pic (bike with twin headlights on), you can see a collection of pipe sections on the floor, waiting to be welded up. Those are for a Yamaha 250...but I used the same design on the RS because I knew it would give the type I wanted. It's much more of an old school paper and pencil way to do it, cone pipes can be worked on cad and then the sections printed onto paper ready to use. So I'm not sure what advice I can give really Matt..apart form make the pipes in card first to check the fit, and tack everything before fully welding. The rest, well... you'll work it out I'm sure :)

11-18-2015, 08:42 AM
That is some beautiful countryside to enjoy on a small two-stroke motorcycle. Neat bike.

11-18-2015, 11:36 AM

i'm attempting to do it exactly the way you described. we will see how they turn out. I have thought about trying to duplicate the RSA pipe

11-18-2015, 11:53 AM
Looks like you got the hang of it already! I would suggest the RSA pipe could be too short and high revving for your engine though? would be interesting to try it for sure, and with the ignition mapped to suit it could go ok. Be prepared to fiddle about with the length a bit afterwards to fine tune the rpm.

And thanks Freedomgli.. it is indeed a nice place to ride :)

11-18-2015, 01:24 PM
Looks like a little slice of Heaven. :D

11-18-2015, 03:05 PM
Looks like you got the hang of it already! I would suggest the RSA pipe could be too short and high revving for your engine though? would be interesting to try it for sure, and with the ignition mapped to suit it could go ok. Be prepared to fiddle about with the length a bit afterwards to fine tune the rpm.

And thanks Freedomgli.. it is indeed a nice place to ride :)

I was thinking about adding 15-25mm of length to the header to bring it down maybe 800-1000rpm, but we will see. I have to go home first and set everything up. When I install my genuine RS125 cylinder I would like to get 40 to the rear wheel. I would like peak power at 12-12.5k; It might take a longer rod to get everything right and keep the skirt wear to a minimum, but we will see. I really like your bike. great job.

12-13-2015, 05:49 PM
This needs updates

12-15-2015, 05:23 AM
OK, so been busy inbetween other jobs with the lightening of the bike. The new Honda RS seat needed a new subframe, so I made one using an old steel tube from an old garden chair (don't tell the old folks), with a little minimoto fuel cell for the 2t oil tank, held on by arms cut from a strimmer handle.

My brother can get powder coating done where he works, so that's now a nice shade of black;


The oil tank has the RS level sensor installed using the top of a pop bottle being glued on as the mounting. For topping up I put in a neat hinged flap;

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There was no space for the battery under the seat, so I made a new mounting box and put it under the tank. IT's an electric start TZR, so it does need one, and not having an airbox meant the space was there. The only downside is it looks a bit messy;


So I made some carbon covers for each side. Not the best of quality, but they do the job of tidying it up.


I chopped the lower engine cradle tubes out, which lost another 0.7kg... and have a Michelin Sporty to put on the front (I never liked the Conti that was on it). I just have a bit of wiring to sort out and it's nearly there...

12-16-2015, 04:04 AM
Back end is pretty much done now, apart from painting the seat....I don't think everyone's going to like what we have planned for it!


12-16-2015, 03:16 PM
Loving it! Why did you end up keeping the oil tank?

12-17-2015, 04:20 AM
Just because it's so much easier to live with on a day to day basis, no measuring out the oil, or only filling up a certain amount at the fuel pump.. I have Yamaha 250 here that is premix and it's a pain in the ass.... (especially the rate it drinks the stuff!)

02-22-2016, 03:59 AM
Bit of an update.. got around to painting the new seat unit over the weekend, the little TZ-RS logo was done by hand (old school..paint and brushes!) and the flowers were cut from fabric which we're going to cover the tank in and glued on prior to lacquering. Paint doesn't stick to the fuel tank plastic (we run without the outer cover on as it makes the bike feel smaller, and loses weight, which is always good), hence trying fabric to cover it.. Shame it's still so wet and muddy here though :(


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02-22-2016, 04:50 AM
Totally awesome!

02-28-2016, 04:12 AM
What a brilliant bike, I love to see perfectly built precision builds but I think your on to something really good here!! The thing looks totally real world useable and is so interesting, congratulations on doing a grand job and something different!!

02-28-2016, 06:21 AM
Thanks! yeah, it can take a while to fine tune a bike to work nicely, just getting the engine in is only the start of it all! it's been 2 years or so of constant adjustments, but it's getting there.. Just re-covered the tank, so test fitted it to see how it looks. Not very masculine, but we like it


02-28-2016, 06:51 PM
Mrs. Xero loves the daisy theme !!!
If this is truly for your Feminine Significant Other, then top props !!!
Way outside the norm, but completely unique and in my opinion worth the effort to satisfy the Mrs. ...

On the other side of that coin, if this is for you then ...

02-28-2016, 09:36 PM
He could be a child of the 60's, and Prince would most certainly approve. Even though he'd have to wear 9" heels to straddle the seat. :lol:


02-29-2016, 03:53 AM
Hahaha It is kind of a joint project with Alison, she's a girl so she's allowed purple. I kind of don't mind the daisies, it's a bit of fun and I don't mind riding bikes that are a bit out of the ordinary. At least it makes people smile :o

and it could've been pink with Hello Kitty and unicorns on it. I had to draw the line somewhere..

04-21-2016, 02:48 PM
So I made a new pipe with the aim of a bit more top end rpm and longer overrev. As this is a bit of a test pipe I made form scraps of steel I have, hence the extra seams at the rear...



And I managed to get it on the dyno today;


The lower peaking curve is the old pipe. So a bit less at the bottom, but smoother power with less sharp drop off after peak. It feels nice to ride, better when riding hard..

04-21-2016, 03:08 PM
Wow! That's a lot for a "fifty" lolz ;)

Are you hydroforming the pipes?

Very nice work. :)

04-21-2016, 03:32 PM
Keep up the good work! That pipe is mega cool.

04-21-2016, 04:22 PM
Yup, pipes pumped up with water! I still want to try for 30hp, but the local dyno's been sold so it makes development a bit harder. Goes well as it is though, if my camera works I might try another video sometime.

04-26-2016, 05:43 PM
Post up that crazy fork part

04-27-2016, 04:09 AM
OK...I was going to make sure it actually worked before posting it, but here's my attempt at making an emulator valve for the fork (which have been available from Race Tech for years, but I fancied having a go myself)


For those that haven't seen them before, they sit on top of the damper rod, held on by the main fork spring (ideally the spring would need to be shortened a touch to compensate for this extra spacer, but I was running a little extra perload anyway, so it's not such a big change). The idea is the small hole in the middle 'cap' controls damping under lower forces, so handling and when you hit the brakes, with the smaller than stock hole giving firmer damping and a more stable feel to the front end. When a bump is encountered, the small hole would give a really hard hit, so the whole 'cap' lifts off against the little valve spring on top, giving more area for the damping oil to pass through, and thus softer damping. It's a way of getting progressive damping like more modern forks.


The cap fits and rises inside the main fork spring, so that limits the size I could use (because the stock springs taper to a smaller diameter at the ends), but I managed to get 6x3mm holes in there, about 70% more area than the stock compression area (extra holes are drilling in the damper rod to allow it to flow the extra amount, and let the valve control the damping). The small bleed hole in the cap is 3mm, and about 30% less than the stock holes. So you can see the potential for the change in damping. Firmer handling, but softer over bumps.

For me, the main goal was to soften the ride over bumps, around here there can be some pretty harsh beaten up old lanes, and the bike skips across them giving a harsh ride. I am running 15wt fork oil with just the one fork giving the damping like stock, and that gave good handling. Here's the 6 holes from underneath;


The point at which the cap starts to relieve pressure is controlled by the strength of the valve spring, and the amount of preload. My first setting gave a bit too firm a ride, for sure it was working though, hitting the brake and it dived a lot slower than before, and the front felt like it was being held up by the damping in corners more. Perhaps a bit too much... normally if you set the forks like that they'd be waaay too hard over bumps, but these weren't..so the valve is kinda doing it's job.

I wound the valve preload off a bit, and had another ride, a bit softer on the handling, and felt a bit more comfortable...better..but still a bit harsh over bigger bumps which was the main aim. So, still some work to do dialling them in. Perhaps they need even more area with the valve open, or a softer valve spring..we shall see...

04-27-2016, 12:51 PM
So I added some extra holes to the damper rod, opened up the ports in my valve, cut 20mm off the end of the fork spring that was a smaller diameter (allowing oil to flow more openly from the side of the 'cap' when it lifts) and made a spacer to compensate for that length. Along with less preload on the valve spring, the aim was to try and see if that would give me the softer damping needed over bumps.

And it does... albeit at the expense of low speed damping, so hopefully with some adjustment of the valve spring I can increase the low speed damping, and retain that softer feel over bumps. Here's the modded valve with larger ports;


05-28-2016, 04:48 AM
So, I've also had a go at stripping the Fastace shock to soften the comp damping, removing some of the shims (I did research it a bit beforehand) and trying to retain the nice feel of firm damping, but without the jarring over bumps. Really it needs filling with nitrogen, but I used air for the time being. Seems to have helped a bit... It's fun doing things like that for the first time, and being able to feel the difference it makes.

And I've made a new, new pipe, the previous pipe was half of a pair for a 250, so that's had it's other pair made and gone to a racer for testing, which meant the RS needed a pipe of it's own.


And I've got a new Sava to go on the back too..

05-28-2016, 09:15 AM
I love this bike so much

05-28-2016, 12:37 PM
It is gorgeous. The attention to detail--even the back of the plate has Zebra stripes!

05-28-2016, 06:35 PM
btw if you think you get those emulators working well enough to sell, i'll buy a set for both of my bikes

05-29-2016, 02:24 PM
Cheers guys.. your bikes are so sweet it's a bit of an inspiration to be honest!

hah...yeah, the zebra print number plate was Alison's idea to cover it up (it was pretty messy).

I'm still not totally convinced on the home made emulator yet... I was actually going to get some Race Tech Chinese knock offs from XSMike's (which should fit in the RS forks with a bit of work and some adadpters) and use my own spring on it, so if you wanted to try them Matt, that's what I'd do.

05-29-2016, 10:21 PM
You know Martin the thing I'm really liking about this foro right now is how we are all helping each other and getting better at our craft. It was really awesome having Matt out here for a couple of days. Friday we wrenched, went to the D-Store and watched FP2, Matt got some cool bits, then we wrenched some more. Saturday was Derbi de Mayo--it was a really great time. :)

05-29-2016, 10:29 PM
I even crashed one of rob's pristine bikes and I didn't even get yelled at! although I did get to take a nice souvenir of a sprained ankle home with me!

Martin I'll buy you the xs emulators if you can make them work

05-30-2016, 09:03 AM
hmm... Well I still have the Aprilia set up of damping in one fork only, so not sure how my settings would convert to your twin damping... it would just be a matter of fine tuning the emulator spring weight and preload. And making some spacers... but yeah I'm for having a go. Reckon you could ship them (or even just one) over to me cheaper than the $55 for shipping XSMike wants.. (that's the main reason I didn't get them) I'm happy to make the spacers needed for you to try them though.

05-30-2016, 09:30 PM
ok. PM me your address and I'll see what I can do.

08-03-2016, 11:47 AM
Couple of updates for the little bike... It's now got a Lithium battery saving 1.25kg in weight, they are amazing things, it's just like an empty plastic box but seems to work really well. Looking for other things to lose some more weight I've started making an alloy front engine stay and bottom frame cross member.


Not looking amazing, but they are bolted ready in their jigs for a friend to weld them up for me. Eagle eyed viewers will spot the jig for the engine stay is in fact made from old RS50 rear subframe tubing! For the bottom cross member I plan to hack off the sidestand mount and sandwich it between my new tube and the frame, so the sidestand is still there. It's all a lot of work for probably only 1.5kg of weight loss, but doing things like this is fun and great for figuring out what's possible for later projects.

And... I adapted my zeeltronic box to work with this engine (it also fits a couple of 250's I also have), which shows good promise, just needs a bit more dialling in. Damn shame the local dyno was sold recently though...

08-03-2016, 02:53 PM
you have rs250's also?

08-03-2016, 03:47 PM
I have a much modified Yamaha TDR250;


and a friend's TZR250 3MA trackbike;


08-03-2016, 03:49 PM
freaking awesome!!! I love that frame on the tzr

08-04-2016, 03:48 AM
Yeah, you can see why a few people have put 500cc engines in that frame, it's big and strong! shame the motor is under peforming at the moment, but I blame that on my mate over-porting it..

08-17-2016, 03:39 PM
hi martin great build love the look and the vids looks fun
i was hoping you maybe able to help
ive got my sons old rx50 1998 i plan to do a swap
for a little fun
ive come across and seen a few tzr engines and now ive seen your build
i am more thinking it would be a fun bike once done
few things i wondered will i need a tzr cdi full wiring loom and power valve servo
i have read a lot of good builds but none with how they do the wiring
that not being one of my strong point
was hoping you may be able to point me in the right direction
thanks si

08-18-2016, 04:00 AM
hmm... mine is a hybrid really, mostly Aprilia loom on the bike, and little bits from the TZR. Certainly you'll need the TZR cdi, reg/rec unit (if you need a battery for leccy start) and powervalve servo. For an off road styled bike, I'd look for a DT125R engine as they are kick start (well, as another option of the list of engines at least).

The wires out of the engine can be linked direct to the cdi (bypassing the RS loom), the TZR reg rec can have the output 12v tapped into the RS loom at any point, the pv servo needs 12v, earth and the rpm feed form the cdi (well, depends on the model), errm... so basically you don't need the TZR loom, but it can be a bit of a head scratch as to wiring in the Yamaha parts in the neatest way.

Plus of course the (Yamaha) exhaust would need new mounts, the TZR carb plus cables. And chances are you'll have to run a foam pod filter so expect a bit of work with re-jetting.

08-19-2016, 07:02 AM
thanks for the reply martin
well on thoughts i decided to go with a yz engine
so im thinking wont be over difficult on wiring
but i was thinking of a project similar to yours
but maybe wait until i get a rs frame
thanks for the information really helps if i plan another project

08-19-2016, 02:59 PM
Yup, YZ's would be a very small loom and much more self contained, without the need for the battery and road legal stuff. Depends if it's going to be a road bike, and what the budget is, YZ engines seem to go for a lot of money..

08-19-2016, 04:23 PM
well my son had me put the malossi kit on another bike
id be looking at a bit of money just to replace that
and well on all the other stuff he had broke in the past year
i thought get an old yz 80 engine as its allready reg as an 80
so shouldnt be too bad to get it legal for daytime use
just a project for fun really
and to be fair i think work out a lot cheaper than re kitting it etc
and maybe wait until he finished with the bike he uses now and look into a project like yours for the future
i do like it

10-04-2016, 12:27 PM
A bit of an update on the little Purple peril... the alloy front engine frame and lower frame cross member arrived back welded up and after a bit of paint, they went in no problem. I was I admit slightly disappointed after all the work to only have lost 1kg from the weight, but hey, it's better than nothing and adds a bit of extra kudos to the thing.

Then I swapped over to a new MC18 Sava Rear tyre (now actually called 'Mitas' instead of Sava by the way) and lost the tube that was in there before (I think the last owner couldn't get the bead to seal so used a tube instead), which lost another kg. All good, and it rolls into corners smoother, but wow... there's no grip in the wet though! Maybe it was partly the poor tarmac around here, but some places it can light up the rear in 3rd and get the back end fishtailling... kinda fun, but not exactly confidence inspiring!

I tried a later model RS50 radial master cylinder to try and improve the power/feel of the front brake, and yeah, it helped quite a bit. The only problem is it would hit my dash, so that was no go. As a bit of an experiment I altered the position of the little 'button' that presses on the piston mounted on the lever. Moving it 3mm closer to the pivot point should increase leverage in return for a bit more lever movement. I just slotted the holes and packed the space with a piece of aluminum.. works pretty well to be honest, quite a bit sharper feel and more power.

Today I put in one of the cheap MikesXS valve emulators in the fork (the one side with the damping already), though I did shorten Matt's adapter so I didn't have to shorten the spring. Still not had a chance to test ride it, but at the moment it feels lighter damped than my own valve. Will need to see...

I had got hold of a GPR125/Derbi SC1 swingarm fairly cheap to see if it would go in the RS frame. I figured being alloy it would be a neat swap and lose a bit of weight. Issues initially are the spindles are 16mm and it's 40mm longer. I knew I'd have to weld on a lug for the rear brake hanger, and a new shock mount, but before I started work I thought I'd strip out the RS swingarm just to see how much lighter the alloy arm would be. (afterall, if it only saves a few grams it wouldn't be worth the effort)


Oh. ahh.... so the nice alloy swingarm actually weighs just under 2kg MORE than the steel one! (RS arm 3.6kg, GPR 5.5kg) oh well.. suppose I better list it on ebay again and sell it on.

Since the original build the bike has lost about 14kg! I weighed it at 101kg with a full tank of fuel.

10-04-2016, 02:18 PM
Sounds similar to issues I'm having with my 'hybrid' bike, fitting the GPR / RS4 swingarm to the stock RS50 frame.

10-04-2016, 02:50 PM
The RS4 arm is a much easier start point, but dare I say pretty heavy..

10-04-2016, 05:09 PM
so the nice alloy swingarm actually weighs just under 2kg MORE than the steel one!

That's a bitch !!!
Go figure ...
I have been eye-balling the Swingarm and other steel chunks on my RS as well for potential weight saving areas.
Figured I would end up fabricating a custom aluminum Swingarm to gain any real reduction, this pretty much locks in that feeling.

I have been buying piles of titanium for trick one-offs and even more purchasing of titanium fasteners.
That stuff adds up quick $$$$$$$$$$$$$$

Would like to see some pictures of your Engine Cradle and Cross Member ...

The Front Brake on these RS's seem to be hit or miss, meaning my OEM set-up is ultra touchy and real quick.
Others have reported vague feedback and lack of stopping power.
I'm your typical A-hole when it comes to brakes (front) and use them hard, but this RS really keeps me on my toes when running deep.
Others have swapped over to a Brembo Master and say it's much better, that's up next for my RS.

Keep the mods coming ...

10-05-2016, 06:37 AM
The front cradle is just a direct copy of the old one (which had the lower parts removed already, which lost 0.7kg), so not much to see now it's painted black. The bottom cross tube sandwiches the sidestand bracket against the frame with an extra mount, I'll take a pic later, but seems to be working ok so far. I wanted to retain the thick steel stand mount...not sure I'd trust an alloy one!

I'd love a Brembo master cylinder, but that's quite an investment for me, so I always look for a budget alternative..or even better free! Sometimes making or modifying a part is more fun and rewarding than buying something.

10-06-2016, 09:15 AM
Picture of the lower cross tube. You can see the stand plate has been cut off the old one, and sandwiched against the frame. Because the chain runs pretty close to one of the mounting bolts, I drilled and cut a thread in a new mounting point, with the new bolt going from the inside out. I know it looks a bit crude, but so far so good and it feels pretty solid.

You can also see the added bracing to the swingarm, and our old vintage Homelite saw...


10-07-2016, 06:05 PM
Martin, I really love what you're doing here !
it seems really muddy there, you might need some knobbies !!! :D
Oh and the TDR !!! I'm so jealous !

10-12-2016, 03:29 AM
The TDR is probably the bike I'd keep if I only had to have one...

Anyway, I've been real slack in updating about testing with a fork valve from Matt in the RS. Because I'm still running the stock springs (albeit shortened very slightly) I shortened one of his adaptors so I didn't have to cut any more off the springs. The shorter the spring the greater the spring rate, which is actually a very neat way of firming up the forks, and seeing as the standard RS springs are long enough that's what I would do if I wanted a firmer rate. But I find the stock springs pretty good for my skinny ass...

Still on single damped forks so I just put the valve in that side. I'd already drilled the lower damper holes in the rod. I used a valve spring of around 20lb/in, with 7 turns preload. 15wt fork oil to the standard height.

It feels good certainly softer than my own home made valve, more progressive over harsh hits. Wether it needs a bit more low speed damping I haven't decided yet, but so far so good.

Of course if you're running much stiffer springs you'll need different settings, so I'm not sure if my results would be any help, but yeah.. it feels nice! Cheers Matt!

10-12-2016, 06:49 PM
Thank you for the update Martin!

02-17-2017, 05:03 PM
Winter in the UK means it's pretty wet and muddy where we are.. I went for one ride out to help out at a local vintage fairground museum 3 miles away and came back with the bike covered in crud.. not nice! Anyway, first update for this thread was fitting this shortened RS125 Arrow can;


... and that's about it. However, I've just got hold of a lightly used Athena 170cc top end for the engine... I know they get mixed reviews (same kit as the Derbi 125) but that's mostly due to the fact it uses the same basic casting as the Athena 125cc cylinder, so the 170cc doesn't get the benefit from 170cc sized ports. Still... the extra bottom end and midrange will still be nice, and anyway, I love a bit of porting work, so there must be a way to get a bit more from it..

Because I design pipes for bikes I have a cutting edge engine simulator. Put in the details and it punts out a predicted power curve.. (that's a massive over-simplification!.. it's very very complicated) And with a fairly close correlation with the original TZR engine and the dyno runs I've done, I know I can kinda trust the predictions is makes. I put in the 170cc details and worked out a good porting spec to aim for. With fairly modest changes and a larger stinger tube, here's what the simulator predicted;


You have to remove about 15% to get rear wheel hp, so the 125 spec gave 26hp (green-matches what the dyno showed), the stock 170cc top end predicted 31.5hp (black), and with extra porting 35hp (red)... I also have a 32mm carb to try which might yield another 1-2hp...

So it may be looking at an extra 8-9hp with added boost everywhere... pretty cool I reckon! I have also looked into fitting a YZ125 top end from the late 80's, but they are pretty hard to find in good condition especially with powervalves included. But anyway, that would only really benefit at the top end, whereas the 170 kit will really improve it everywhere, perfect for road riding. Porting will be done next week I expect...

03-10-2017, 05:27 AM
Nothing to report here, because the shop took over 3 weeks to send me some replacement Wossner piston clips, and then they weren't legit Wossner clips! useless bastards, so now I'm waiting for another shop to send me some..

Porting went ok, added 5mm to the total exhaust width, and lifted the transfers just over 1mm. I didn't want to lift the whole cylinder because the exhaust timing was good as it was.



I'm thinking it may need the higher flow fuel tap. I have a blaster tap already, but the problem is the base of the tank has bowed where over time the original tap has deformed the plastic. I tried the Blaster tap and there's no way it'll seal... so, I need to try and flatten the surface somehow and get it to work...

Elsewhere I've just finished making a pipe for a 100cc yamaha, with a 175cc top end fitted... boy, that thing has some torque now! if the RS improves by a similar amount, then it's going to be awesome!


03-10-2017, 07:22 AM
i love this bike!!!

03-10-2017, 08:26 AM
Elsewhere I've just finished making a pipe for a 100cc yamaha, with a 175cc top end fitted... boy, that thing has some torque now! if the RS improves by a similar amount, then it's going to be awesome!


Ha ha cool I've ridden one of those with a serious setup, scary ride would pull wheelies in first 4 gears! :D

Had a YY Pang pipe and was bored and stroked to 190cc I believe! Is that a DT175 top end or similar are you running the stock 50mm stroke or the 54mm one off the 135cc model?

03-10-2017, 08:36 AM
Thats sweet bike!! :D

03-10-2017, 03:03 PM
The little Yam just has a (standard) DT175 top end and a 26mm carb on the original 50mm stroke bottom end. It's a roadbike so the guy isn't after the ultimate performance, just a nice use-able fun ride. I can't imagine what they are like to ride with enough power to wheelie in 4th!!

03-15-2017, 03:07 PM
Well, I finally got to try the 170 when some legit circlips arrived.. First impression were a bit poor I have to say, good bottom end power for sure, but the more it revved out the more disappointing it was. Maybe the carburation needed more changes.. I wasn't sure.. Anyway, I checked the powervalve alignment this morning, and yep, everything looked fine from the outside, but looking up the exhaust port showed it was way off, about 3mm closed in the open position. A quick fiddle to line it up properly.. and another quick spin around the local lanes.

Bingo! Now it was working right.. the exhaust has the sharp bark to it, and it kicks on to the redline nicely. Much much better! I'm really happy with it after the first run, very strong everywhere, and really useable, smooth power and it'll just elevate the front wheel in 2nd now, or lift it into a proper power wheelie with a dab of the clutch. Might have to gear it up a bit.. and I still have to fine tune the carburation and ignition timing.. but it's awesome!

03-16-2017, 04:22 PM
Here it is hanging out in the hallway of the house.. about the only spare space at the moment!


06-17-2017, 09:43 AM
The little 170 continues happily, still running well. it's hilarious in the wet though, the MC18 rear tyre is just awful, it'll spin up easily in 3rd! not exactly confidence inspiring..

The front brake has always been ok, it had enough power but just lacked that bit of bite I like from a front brake. So, as I had some spare Ducati calipers left over from a friend's project I thought I'd have a go at mounting one up on the RS. Usual job of cardboard cut out template to work out the shape, then a real plate in 8mm aluminium. The caliper just rubbed the wheel spokes, so I spaced the disc out with a washer behind each mounting bolt. Then a couple of spacers for the new caliper, bleed it up..


The plate has threaded holes and the original mounts now have the bolt head on the inside. Hope that kinda makes sense? Seems rigid enough anyway..the lower bolt goes all the way through as a mounting point for the speedo pick up on the outer side.


Feels pretty nice initially with the stock 13mm master cylinder, good feel and more power, just need to bed the pads in more and hopefully it'll get even better!

06-17-2017, 12:04 PM
Looking good Martin!

06-17-2017, 09:31 PM
Nice !!

06-18-2017, 03:28 AM
Thanks guys.. first proper test ride with it yesterday.. Wow! brake feels at least twice as powerful now, it's going to take some getting used to. I think I might play about with the lever ratio to lose a bit of bite in exchange for a slightly harder lever feel.

06-18-2017, 09:20 AM
what master cylinder are you using?

want to make another bracket? :)

06-19-2017, 01:21 AM
Such an inspiration this bike !
if it wasn't for Martin, I would've never done the rear shock.
Lovin' the front brake upgrade.
Keep up the great work !

06-19-2017, 03:19 AM
Little bikes get overlooked here, I mean, apart from the fact nobody has a clue what on earth it is, which is understandable, they don't appreciate the thought and care that goes into it, just because it's a small bike. If it was an R1 or something they might be more impressed. Anyway.. glad you all do!

With the standard caliper I found improvement by adjusting the standard 13mm master cylinder pivot. I moved the hole closer to the piston by 1.5mm, and then moved the little button on the lever towards the pivot by 3mm, so it effectively increased the lever ratio and gave the brake more power and better feel. Kinda like an adjustable lever ratio radial set up, but on the cheap!

For the Brembo caliper I've gone back to a fully standard mastercylinder, otherwise the lever had too much travel. So 13mm in other words.

The pads have a too large swept area so they overhang the outer edge of the disc, but I can't see that being a problem, what do you think?

Yeah I could probably make another mounting plate and spacers Matt. It's all done by hacksaw and files by hand, so don't expect CNC machined engineering perfection! You may have to find some suitable washers for the disc spacing (1.5-2mm) and make sure you get a 40mm mount caliper.

07-01-2017, 11:14 AM
A couple of friends came over and I let them have a go on the RS..;





They both loved it!

08-04-2017, 08:14 AM
yeah people dont think these motor swaps will be nearly as good as they end up, but after building two of them, i'm convinced its the way to go

08-04-2017, 12:36 PM
There's a foro over here where they just don't get little bikes. Bunch of fucking compensators. lolz It's actually really sad, but marketing has shaped the mind set, and it's really difficult to overcome.

09-17-2017, 06:17 AM
Little piece on it in a UK magazine!


I actually hate the term Yamarilia, or Apriliaha etc... but anyway.. maybe that's why Alison called it Pipsqueek instead.

09-19-2017, 01:41 AM
That's really cool!

01-20-2018, 07:12 AM
So, it's winter here, which means rain, mud, wet leaves, mud, rain and then some hail and rain. But, I have been working on two main ideas for the RS.. Firstly I got a Mikuni TMX35 carb for it, which needed a different manifold and a bit of work to fit. Once the weather dries up I'll fit it properly and start work on dialling it in. Although the reed block is too small for the carb, it should still help top end power. If I can't get it to run cleanly low down and be easy to use then I won't use it though, as it has to be simple for when Alison rides it.

Next was an idea to fit a cartridge in one of the forks. I've done this to other bikes, using R6 cartridges, which worked really well. The real challenge is fitting it inside the smaller RS fork. Because the stock springs suit me well, I figured I'd just need the one side damping. After about three days of head scratching, machining and bouncing it up and down, I think I've got it good enough for initial testing.


It's from a ZX6/9 (not sure which), which Alison found in a skip (dumpster I think in the US), and I got hold of a cheap used RS fork to modify, so I can go back to the current set up if it's no good (and I haven't spent a lot of money). The compression isn't adjustable, but has a little side bleed to control low speed comp damping, which may need to be opened up if it's too harsh. The rebound adjuster still works at the top, and preload of course (though because the fork top is just pushed in, you have to hold it with a screwdriver at the side to wind in the preload) I will need to experiment with oil grade and level, plus fork springs etc.. then hope the action is smooth enough to take advantage of the sophisticated damping. At the moment it handles great, until you hit a bump when it feels harsh and tankslaps. I'm hoping for the firmness to keep it handling good, but get some softness over bumps. The Race tech emulator doesn't seem to help with the bumps much.. Anyway, I'll only experiment with this once I have time and it's dry for easy testing..

01-20-2018, 09:05 AM
Wow, great project and nice work!

Sent from my ONEPLUS A5010 using Tapatalk

01-20-2018, 01:17 PM
Very nice Martin! Looking forward to hearing about how it goes.

03-17-2018, 04:54 AM
So, had some time in the workshop and put the adjustable fork in. The rebound damping has a wide range and works real well, full in it's like treacle instead of fork oil, and then full out the forks bounce back like a pogo... so hopefully somewhere in between will work. Like the Goldilocks of damping..

The compression I can only wait and try once I get to ride it on the roads, that will have to be tuned with either different oil or redrilling the bleed hole I put in (instead of having an adjuster).

The only issue really is this fork has a lot of stiction, it was like that before I modded it, I'm just hoping a bit of use will bed it in a little. Just a shame we're back to temperatures outside not much above freezing at the moment :(


03-29-2018, 03:51 PM
Despite almost endless rain, I've manged a few rides now with this fork conversion. I really like it! The aim was to gain plushness, without making it too soft. It rides bumps very sweetly now, but never feels bouncy because I can dial in the adjustable rebound. Feels nicer on the brakes too, bit more dive, but that gives the feeling the tyre is being pinned to the road.

Ok, so not a mod for everyone... but I'm happy!

Next addition... can you spot it?


ok, kinda hard to miss it... Got it fitted this morning, and then it started raining again. Damn it!

04-28-2018, 03:04 PM
Yeah, all my pipes I hydroform the whole thing because I'm not so good at welding... also I find it quicker to do a whole chamber like this. The downside is it can be less accurate following the design dimensions, the pipe doesn't always come out fully round.

The whole pipe is done in one go, then sliced into sections and rotated to fit the bike. In the last pic (bike with twin headlights on), you can see a collection of pipe sections on the floor, waiting to be welded up. Those are for a Yamaha 250...but I used the same design on the RS because I knew it would give the type I wanted. It's much more of an old school paper and pencil way to do it, cone pipes can be worked on cad and then the sections printed onto paper ready to use. So I'm not sure what advice I can give really Matt..apart form make the pipes in card first to check the fit, and tack everything before fully welding. The rest, well... you'll work it out I'm sure :)
Hi Martin, what do you use to hydroform?

04-29-2018, 03:39 AM

That and a plumbers test pump, you need about 700psi to get a useable end shape, and even then plenty of hammering to help it form.

04-29-2018, 06:20 AM
I’ve seen pressure washers used on YouTube but none of them comes out as net as yours. Nice work mate.

04-29-2018, 07:44 AM
Hand pumps give you much more control, and also it's 100% quieter! it can take 30-40 minutes of tapping with a hammer while under pressure, so to have a pressure washer blaring away would be just too unpleasant. Also, if you spring a leak it makes a hell of a mess, whereas with the hand pump it just sprays a bit and loses pressure. Mine aren't as neat as some I've seen, but they do the job.

04-29-2018, 10:32 AM
hey martin let’s see the hand pump you’re using!

04-29-2018, 01:58 PM
I'd like to try a steam boiler test pump as they can go over 1000psi, but you have to be aware that the steel stretches and goes fatter than the original dimensions. Even with 700 psi I allow for a 5% increase in belly diameter.

A hydraulic fitment connects the pump to the chamber, and cheap brass garden pump the other end for bleeding the air out.

This is the one I use, they're pretty common..there must be equivalents in the US? https://www.ebay.co.uk/itm/ROTHENBERGER-RP-50-60-WATER-PRESSURE-TEST-PUMP-50BAR-725PSI/292516249706?hash=item441b53c06a:g:RD8AAOSwklBau~q O

(https://www.ebay.co.uk/itm/ROTHENBERGER-RP-50-60-WATER-PRESSURE-TEST-PUMP-50BAR-725PSI/292516249706?hash=item441b53c06a:g:RD8AAOSwklBau~q O)