DT125R FORUM

Hello guys, Daniel from Dan Racing here.

Due to the lack of tutorials in this forum I decided to make a little series of them to help some new tuners into the scene.
This specific tutorial on porting engine cases i'm using TDR125 cases(same as DT125RE/X) but theses things should apply to almost all of 2 stroke engine cases.

There are 3 main places to be carefull with, in all 3 of them, gasoline atomized into the air will flow through, being it's final destination, the cylinder.

1 & 2 - This is one of the most important areas, because it's the part that connects with the transfer ducts on the cylinder, this connection should flow as much as possible. In here you should place the cylinder on the cases and check for any kind of 'step' between the cylinder and this part of the cases. if there is a step it should be eliminated to avoid any major disrupt in the airflow to the cylinder.
If the cylinder is smaller than the cases, it's better to fill in the step in the cases with epoxy than cutting the cylinder, because the transfer ducts in the cylinder are made to mantain a straight area all the way to the actual port.

3 - TEXTURE - Texture in the cases should be like stock, altough after porting them it's very hard to get the stock texture again unless you use some kind of soft sand blasting. The texture should be rough, but not too rough. I like to use the dremel grinding stones to do stripes(all really close together like in the first picture) 90 degrees with the airflow(Airflow in black, blue are an example of the stripes, the stripes shouldnt be deep at all, just enough to create small disruptions in the airflow to keep fuel atomized, this should create very small horse power gains, but you actually should gain more fuel efficiency due to improved atomization so smaller jets needed to achive a good A/F Ratio.

I'd love you guys opinion, or just tell me what you guys to for yourselves in terms of porting, im currently working on a guide on how do port cylinders so stay tuned to the tutorials category.

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Well, finally got alot of progress done on the build for the last few days. little update:

Sold my old frame and swingarm, and with the money i bought another DT50X just without engine, already with engine mounts for DT125R engine and aprillia RS50 rims(going to sell them)!

Stripped the whole 'new' bike, welded the mounts a little better, sandblasted it(made my shop a total beach) and painted it matt black. I also closed up the bottom end. Everything that's a wear part in the engine has been replaced. Clutch setup is Stock DT125R plates(using the clutch damper) with Bandit 400 Clutch springs. I still gotta finish the cylinder booster ports on the Athena 170cc(Yes i made custom exhaust port with boosters) and yes YPVS will still work and got to fully machine the DT125YPVS head to my needs.
But i had to totally test fit the engine, looks great in there!!

Alot of progress is going to be made in the next few days so stay tuned!

Got around to building the front mounts, trying to get the motor lined up was the hardest.

I'm not a welder or anything close, so don't mind the bad weld looks, they seem strong, will try and reinforce them even more tomorrow.

The motor is finally sitting by itself, again everything is a mockup still, will build the engine when i get the frame done to avoid any metal shards

Heyo Guys!
Daniel from DAN RACING here

I bought this bike december 2017 like this, it almost didn't run and it was in pretty bad shape.

Up to now, I got it like this

It goes to 140km/h GPS speed power wheelies in 1st and second, clutch wheelies until 5th , nothing is left stock, everything is made to get everything out of the little 86cc.

But I wanted more, Something with more torque, with low end power and everything, I decided to do an engine swap.
I will be fully building a DT125R engine. Updates with more pictures coming soon :winking_face:

YOU CAN ALSO CHECK OUT THE BUILD IN MY YOUTUBE CHANNEL: https://www.youtube.com/c/DannyTVDANRACING

@NINJA I buy the cable with one end with a barrel(for the lever part of the cable) and the other one just a straight cable, then i just put one universal clutch 'cable harness' (i dont really know how to call them) in the engine side

@NINJA Sure hope it will, still have alot of money i need to spend on it tho :face_screaming_in_fear: :face_screaming_in_fear:

@NINJA said in DT50X Engine Swap & Build:

sure that you will get her looking real sweet and I agree with you about selling those RS wheels. Proper spoked wheels will make her look more of a Supermoto for-sure!

I have matt black rims with candy blue hubs anb chrome reinforced spokes coming

@NINJA Yeah it looks really good on here, with all the fairings and stuff looks really factory, I don't really like the looks of the mounts the previous owner made, maybe i got to make a skid plate or something to cover it up ehe

@pedrobatista10 said in Aprilia RS250 2001, should i go for this project? Need some advices:

@NINJA @Calum i think i will follow your advice's, because today i speak with a guy that work with importation of bikes/cars, and he told me that bikes before year 2001 its more difficult and expensive for make it legal, because need to make lots of tests and can take 1/2 months. and the frame i saw on germany is from 1996.

Don't buy it, trust me on this, i got a gut feeling your better off buyting a local

Ok boys I wasn't happy how the old engine mounts looked, so i went ahead and did stuff right
(Getting my driving license for cars also helped me move around and get more parts and stuff)

I ordered a machining shop to make me some bushings for the swingarm mount on the engine so it all lines up good without any play.


I cut off my previously made engine mounts, fabricated new ones and tached them in place. Tried to line up the engine the best i could on center with the frame.

Engine looks pretty lined up.

Going to check everything after dinner and finish the welds for the mounts

@Calum In here we make the DTR engine one of the best out there And i'll be running a 65mm bore with stroker crank by the way

@pedrobatista10 said in Aprilia RS125 2010 Spain's no.1:

And about the bike dying on 6k rpm, sound restricted for you?

I wouldn't port that cylinder unless it was for racing, because it's already a pretty balanced port map great for street.
Porting the cylinder is just going to make it less usable on the streets, your mechanics port job will probably just be widening the ports or just raising the exhaust a little bit as most mechanics don't really study or even care about the angles and then a cylinder just ends up loosing bottom end with some gains on top end but not worth the lost low end power for street.

@Glynn123 You said in my other post about me porting your cylinder, I advise you to send me the head aswell to get it machined to spec and derestrict it, as for rings, can't beat yamaha original ones for stock yamaha piston.

@Barrelman said in Oil from Crankcase breather and won't rev out:

Just imported 1989 dt125r. Now on the road but engine cuts out at about 8k revs. Checked YPVS valve which operated fine. Carb stripped and cleaned all good. However still won't rev out. Very occasionally it will rev almost to redline but mostly it cuts out (stutters). It's also kicking oil out of breather. Any suggestions

Bad crank seals most likely

Newer bikes come with more clutch plates and more clutch springs, which means the clutch springs dont need to be too strong in order to handle the torque. Older bikes run strong springs with fewer plates(For example the DTR engine im building im going for Bandit 400 springs to handle the torque because it doesn't have that many plates)

To be honest it may be top end, or even bottom end. because with a 'lock up' of the engine the engine gets ALOT of stress, just like a heat seazure. actually the same stress from heat seazures on the crank and bearings. and not @Calum , the clutch doesn't do sh*t under hard breaking or even heat seazure.
i've seen a dt125r seizing at about 140km/h, and even with grippy tyres(Pilot Street) the clutch didnt budge, he reacted quick and pulled in the clutch, saving him from eating asphalt, if you think correctly an emergency stop without clutch is a seizure the other way around. this can still break your piston, bearings, conrods etc.

@Bananper said in Coolant problem:

I have a weird problem on my dt. The coolant is going back to the expansion bottle and it gets filled up and leaks out, and when i open the radiator and rev the bike it spits out water. Ive tried two heads, and swapped headgaskets. Changed the bearing with the water pump. What could cause this?

Your cylinder gasket surface might not be good, or your nuts not torqued enough