DT125R FORUM

been a while, ive just recently started doing some work on the bike again, took a long break over the winter, you lose the will to work on the bike when its negative degrees in the garage.

Ive been getting some stuff going this past week, I was able to go over to my neighbours company/workshop where he had a lathe i was able to use. So I threw together an adapter that is slipfitted over the cylinder skirt, which then centers up in a simple 3-jaw chuck lathe, I did this cause I didn't have access to a four jaw, but that's ofcourse the preferred method to go. I then skimmed and bored the barrel, still have lots to go cause I think a piston had exploded in that barrel before so there's a lot of material missing over the exhaust port.

https://i.imgur.com/LhPCUF0.mp4

https://i.imgur.com/usIIdnO.mp4
Some vids I took at the lathe.

I also just last night finished up making a port map for my 3mb barrel, I later printed it, cut everything out and used it as a porting guide

As you can see I added some 8mm auxiliary exhaust ports.

I then just started porting, the only tools I had to use was a normal dremel with a flexshaft and some carbide and diamond burs aswell.

Ofcourse its not even close to a perfect port job, but it being my first time without and real porting tools I'm really happy with the result, its not finished yet, the ports need to be cleaned up, barrel needs a rebore which ill do in the lathe this week and the exhaust port needs to be polished cause it got some dings from the dremel. I went conservative with this first iteration, they open at 188 degrees, my main port opens at 200 degrees. Its just a test and if they need to be higher ill raise them a tiny bit.
I then also need to attack the power valve to get passages for the gases to flow through that aswell.

Some other stuff I've been working on is an airboot for my 32mm carb so I can use the stock airbox, the opening for the carb is 55mm compared to the roughly 38mm stock carb and boot. No matter how much heat or force used it didn't fit.

My tacho fixture on the case had also been stripped so took an hour to mock a new model up in solidworks so I could 3dprint

I was also able to pick some wr426f forks up for free, however the shape they're in isn't the best, the aluminium has corroded and pitted all over the fork tubes, its nothing deep tho so its only visual, so whenever I get a front axle for it and get the bearing cup made I'm chucking them on aswell

Its been a while, i just felt like popping in here again and updating everyone, if anyones even interested in my original project anymore, but yeah my cylinder boost porting is still at a standstill. Started school again and dont have the proper stuff to get everything done with that currently but im still planning on doing it so dont worry, with dyno numbers.

However ive been doing some other things in the garage, when one projects gets put to the side u need to come up with something else to do, so im currently in the middle of building my own homemade intertia dyno.

Might not look like much, the base of it is an old electrical engine i picked up for free from an electrical engine workshop mechanic place, the rotor might be a little small and light, but it should do fine with 1st gear pulls and seeing as i dont think anything over 30hp will get dynoed on it everything should be fine. Will it give exact numbers? Probably not, more like ballpark numbers, u cant really expect to get numbers youd get on a namebrand dyno from this thing.
But it will work as a great tuning help, actually being able to visulize if that change you made actually had a positive or negative impact on your engine in the format of an easy to read graph instead of 0-60mph timed runs.

Coupled together with this i managed to pick up the discontinoued ArDyno arduino pcb shield that Alex from the twostroke stuffing channel on youtube once made. (great guy and great channel that i recommend every bike interested person in this forum to check out)

Im using a crankshaft positioning sensor to monitor the rpms of the rotor

I also while scrolling aliexpress came across some vforce 3 reed valves for around 10 pounds for the honda cr125, so i picked one up since ive heard that the cr125 reeds fit the Dtr engine block.



Looked and felt good for being a replica from aliexpress

I had to do some slight surgery to the inlet manifold since these reeds dont use the same style of stuffer that the dtr reeds do

Also hade to take the dremel to the vforce reeds, the actual reed part fit into the engine no problem but the bolt holes didnt line up, so i had to basically open them up so i could fit bolts through everything.
But its all working good and i dont think its pulling any air through my dremel modifications, can i tell a big difference in how the bike handles? Not really but that might also be because i dont ride it too much, would i be disappointed if i paid the 120 pounds for a real pair? Yes, but since these were a fraction of that im happy with it

Im planning on designing everything i need in cad and getting it 3d printed so this wont be as much of a hodge podge as it is currently.

Last little project ive been working on is putting together another expansion chamber but for my scooter instead, its my daily commuter since i dont have my license to ride the dtr yet, its coming together quite good, its all gonna be painted black before im done so dont worry about the rust

Sorry for such a long post that maybe shouldnt be on this forum tbh, hope someone takes the time to read it and finds it interesting, god i wish i could write this much at school

@declan @Calum @SpookDog

This is my first attempt at uploading pictures so i hope it goes well

https://imgur.com/a/kU2p88h

I couldnt find how you get the pictures onto the thread but heres a link to imgur where theyre uploaded in the right order, first picture is the software i used to design it and all the dimensions i used, there might be something wrong in there and if it is pleaes tell me.

I cut all the plat cones out with an angle grinder and went around the edges with a flap disk to smooth all the jagged edges down, a hand held sheet metal cutter could also probably work fine, i found it a little tough to get through the 0.9mm thick mild steel with it though, and it also leaves a curled up edge were you make the cut, it could just be hit with a rubber mallet and it would be fixed but the grinder went faster

The welds are by no mean even close to perfect, but after you grind it all down it looks okay

@spookdog

Yeah, ur probably correct, this basket is fine but its the one in my bike currently that is worse, and since this basket was broken anyway i wanted to have a look

Also, it would work to rivet it back together, however, for someone to do that at home might be difficult, youd need a hydraulic press and probably a lathe to machine the rivets since theyre conical on one side

I would just think its easier to get the holes threaded to m6 and use some bolts and alot of loctite, atleast for people without a developed workshop at home, i got no experience with loctite however so idk if theres stuff strong enough to hold the bolts in place

Posting this from my phone so no clue if the pictures are going up like theyre supposed to

Small update, ive not really been in the garage since fall break ended but this is what ive done this weekend

I was curious if you could change the bushings in the clutch basket, since my engine is clanking alot and making wierd sounds and i somewhat remember the clutcj basket being somwhat loose when i put it in, so since i have another dtr basket laying in my garage, a broken one, i decided to see if it can be opened up and i was thinking if i could maybe cad up some bushings for the clutch in the bike.

This is what it looked like, and it can infact be redone if u have a sloppy basket and these bushings get worn out, the only thing is i think you would have to thread those three holes where there had previously been pins holding it all together.

I also decided to cad up an attachment to my dremel that i can use to port my barrel, since all 90 degree grinders are so expensive and ive seen other peopel doing similar things i decided to mock it up in cad.
this is what i came up with, still a rough idea tho

Might not look like anything, but it will be powered by a rubberband or something along those lines, i got this idea from two stroke stuffing on youtube on his video on a homemade 90 degree grinder https://www.youtube.com/watch?v=W6V5Piz_Uz8
Im scavenging parts from a 90 degree attachment i bought off of ebay that fits onto the dremel but it was too big to fit inside the bore

@SpookDog
Not really, if u look at production dynos its often just one roller, with the bike tied down and with the stop at the front it doesnt move, however ive been thinking and my conclusion is that it probably still wont work, seeing as the roller needs to be heavier, or larger diameter

This because the engine doesnt have the same resistance on the rollers as when its on ground, this causes the engine on the bike to rev to like 13k and the roller speeda up way too fast for accurate measurements i would think, havent tested that far yet however cause i had other stuff coming up

Hi again everyone, a little update on my dyno project i have going on, im thinking of maybe creating a another thread in the Off Topic section of more in depth instructions and how i did everything if there is demand for it, otherwise everything like anything in the world now adays can be found on youtube

Yesterday i got to building the front wheel "holder" where u slot the front wheel into so the whole bike doesnt move forward, used as many screws as possible and it seems relitivly bomb proof, the last thing i would want is to build a bike launcher that would shoot my bike off into my workshop and for all the gasoline to pour out, ignite, and then the whole garage would be ash, so keeping the bike steady and sturdy intop of both the dyno and my wooden pallets is priority number one

Oh yeah im also building everything ontop of wooden pallets, my first instinct was to weld a frame up from some square metal but i quickly realized that the price would skyrocket that way and me only being 17 with a very limited budget had to grab what i already had available to me, and it was these four wooden pallets, so far they work great and are really sturdy, im thinking of adding some wheels so i could eventually push the whole thing around in my garage. The pallets also keep everything really accesible and its really easy to spot if something goes loose, also alot of ratchet strap points.

Today i got most of everything buttoned together, and it was my first time actually getting the bike up on everything.

I screwed the front wheel holder in place after taking some rough measuremtns of where it shiuld be to keep the rear wheel right over the rotor.

Just came back in from my first testrun, im as happy as ever and honestly really proud that nothing broke or flew of in the garage, it did however open my eyes to some stuff i need to make it functional.
Dynoing it on knobbies wont happen, the tiny test run i did everything shook like an earthquake, also realized the importance of an exhaust fan because the whole room was filled with smoke only from the tiny video ill link below, also thinking about adding some actual hooks into the pallets for even better ratchet points because i honestly cant be too safe with this.

Dont mind the mess

I dont know if u can post a video on here but here is the link to the first ever test run https://imgur.com/JT99Urx

Bike isnt running perfect and it isnt really a big pull, its more just to make it a proof of concept even for myself, no computer or software plugged in either at the moment so didnt get any graphs or info yet, but its coming

Now my dilemma is if i should try to do a burn out to get a diy flat dyno ready tire, buy some street tires for the rims and wheels i have currently or wait and buy some supermoto wheels when i find a good pair that fits my budget, its my dream to have a pair of supermotos on there, but its just expensive, especially with shipping from uk to sweden. But if u have a pair or know anyone thats selling or parting out their bike with sumos on it im interested for the right price

sorry for yet another long post

https://www.rzrd500.com/phpBB3/viewtopic.php?t=16273

Just found this program, seems like a fresh well made excel sheet that contains everything you need in one program, and its free to use for anyone, maybe someone in the forum will find it useful

@SpookDog

All in all i spent around 2 months making it, though i had school during the day and some days i didnt feel like going out in the garage, but maybe around 20-30 hours for me, might take longer for someone that has no idea what they are doing and someone really skilled with a welder might do it in under 20, but its not a short project and u gotta have loads of patience but when u see the end result and ride the bike and feel the increased power every second of it was worth it in my opinion, it was also honestly a really fun project, a fun thing to try over the summer break or while stuck in lockdown

@declan

Im starting my computer as im writing this to upload the pictures if i manage to do it

In all honesty it was pretty easy, and it doesnt demand thaaat much skill, or it does if u want an absolutely flawless pipe but for one that looks pretty good and makes difference minimal skill is required, the most importsnt skill to have for making ur own pipe is patience and even more patience, spending loads of time trying to get good cone shapes that fit with the next cones etc, or laying down good welds that penetrate but doesnt make a mess on the inside etc, it takes a long time but it isnt as challengine as people make it out to be, and i say this with never have touched a welder or done any kind of fabrications before, just a dream and goal in mind and lots of patience gets u there

This is a little thread about how i made my own expansion chamber at 16 years old, it was the first time i ever touched some sort of welding device and i had to make do with a mig welder for this exhaust, it worked great and was easy to learn, tho tig wouldve been the best option its expensive and i dont have one available to me.
But all in all, this project costed me 10 pounds, and that was how much i paid for my 1m^2 piece of sheet metal. Im not counting costs of the welder or weld gas etc, or all the other tools i used like a slip roller etc, i am lucky enough to have a great neighbour with a big workshop that let me use his equipment.

I used 0,9mm thick metal, for me it was perfect, thick enough to get okay welds on without blowing through and thin enough to not have a nightmare trying to bend it into the cones, in all honesty the slip roller is useless when it comes to making cones, id recommend that u do it on a round spikey object instead like an anvil but it also works great if u just clamped a piece of tubing in a vice and pounded the flat sheet metal with a rubber mallet around the pipe.

Since its my first ever pipe i didnt know what to plug into the software that spits out all the dimensions so i made it at 30hp at 10500 revs, also went in the middle when deciding a power band, i dont want it to be only between 10000-10500 but i also wanna be able to feel when u hit the powerband so i went roughly 50% in the middle in the software

I know the underslung design has many people torn, i think it looks pretty cool, unique and aggresive, but honestly for me it came down to the fact that an underslung is so much easier to make rather than a standard one, it saved me loads of time since im doing piecuts cause i didnt know the angles before hand, piecuts isnt optimal but i dont think it has a noticeable impact anyway, but yeah, for my first pipe underslung was the best option, and now when im finished im absolutely in love with the look if im gonna be honest

All i really mean to say with this thread is that nothing is impossible, if u have the tools laying around, maybe u have a dad with a welder or good friend with one etc, its not that hard to be honest give it a try, even if you dont know how a welder works beforehand just like me, its a great project to learn loads about the 2 stroke engine but also about metal fabrication

I will edit this with picture as soon as i wake up tomorrow since im not on my computer at the moment, sadly i didnt even take that many pictures tbh

@ninja lovely mate, thanks a ton!

@Calum
Thanks for putting it that way, makes it easier to understand, so i was wrong to say it increases top end, the correct way to put it would be that it favours top end? Since it lets you get there faster?

Also yeah, its what im scared of, the guy in the dyno video i sent, had around 6hp at 5k and 29hp at 10k, the bike wouldnt be fun to ride and you wouldnt be able to use all that power if ur not like on a track or something, however he had the powervalve pinned open, ill try and get it so that the boost ports are completely closed of and then they slowly begin to open with the exhaust port as the rpms climb

@Calum you sure it doesnt break 20hp? People say they get 20+ with a dep and the derestricted head, no clue how factual that is tho since none of them have dyno papers, also might just be that you have a really torquey bike instead as high torque doesnt translate into high hp from what ive been taught

It depends what you think is too hard to get, i just bought all the tools to boost port a 3mb barrel and work on the transfers, a lad i came in contact with dyno tested his boost ported setup and reached 29hp, he didnt touch the transfers either. You get that done and you also go over the head to check that its all okay, mine had 1,1mm squishgap which is too much, get a bigger carb, software says 34mm is optimal to reach 30hp however its an old software so you cant rely on that fully. Get a good pipe made, either make one urself or get one by the portuegese dude on ebay, probably missed alot of stuff like the zeeltronic and maybe running an inner rotor ignition for top end power

Nothing is impossible, u just have to put alot of work and effort in for the desired result, and if you dont have all the knowledge thats something u have to learn aswell, however i worded myself wrong in my original comment, u wont get 30hp by just doing work to the barrel, you will need supporting mods aswell, but its very possible, think about the karting and GP guys that get 50hp out of theyre 125's(with a rebuild after every race however)

@GeirA
Idk why sweden has done it they way they have but basically postnord, which takes care of the packages as soon as they enter sweden, take 70kr just to handle the package, and then they also take 10% of what the package was worth and add it onto the 70kr, so even the smallest things end up expensive, except if u order from wish, since wish takes care of the fees but shipping from wish is always around 70kr anyway, so there is no real good way of buyinf chinese things into sweden anymore

@declan
Yeah its a cool concept but i dont really see why u would do that, looks weird on the bike aswell to just have a big black box next to the cylinder