BEng

I can see the argument from both side, I also love the good old petrol engine, but i think it only because i was brought up with it. Like Cynic the petrol engine is so inefficient, and the electric motor is defiantly the way forward. In my opinion I think what they should do is say to F1 or Moto GP teams for example, any electricity you can generate whilst driving or riding around the track in a race is free to use. So by doing this power generation would improve i.e. KERS, battery technology would increase, electric motor would be lighter, smaller more powerful. The amount of money these teams throw at technology upgrades is silly, but eventually it all works its way down to our cars and bike. Anyway in 20 years when all motorsport is using electric and not petrol the racing will still be just as good, and we will just be to say to our kids "I remember when we they used to use petrol and it was really noisy and smelly... but it was great"

I wasn’t sure whether to add this post here in the “Project” section but I thought I would add it here as all of the information is about tuning a DT125R and not really about build my DT125R. Anyway I have copied the following few paragraphs from the new members section, so sorry if you have seen some of this before. But there is some new stuff, and I will be updating the forum as I find out more info. So the work I have done on my DT is as follows. I have from the bottom up, replaced the main bearings and all the seals. I have matched the transfer ports in the crank cases to match the gasket and barrel, smoothed out some of the rough edge and matched ports to flow with the barrel. Polished the crank cases around the crank shaft area, I know this doesn’t do much but I like smooth surfaces and it didn’t cost me anything but my own time. The reed cage already had some sort of after market fiberglass reed. I don’t know of the make, but there was nothing wrong with them, so I used them. These reeds were a lot longer than they needed to be so I moved the reeds back to the mounting face and re drilled the 3 mounting screws, this I believe will do three things. a) Make the end of the reeds move to just 1mm passed the end of the open hole, where I wanted it. It now means I can open the hole out closer to the mounting face which will increase the intact area. c) The reed stops are now be mounted in the new position which means two things i) with out bending the stops which I believe you should never do, it will increase the amount the reeds open relative to the reed block, which will increase flow thorough the reed block, it will move the reed stop out of the way on the rear transfer port which it covers quite a lot. On the rest of the reed cage I smoothed out the opening and opened up the holes so there was open only 1mm contact around the hole for the reed petals. I had to have the barrel rebored because it was damaged, so it is now 57.5mm. I brought a good quality piston, but still had to clean up the inside of the new piston the remove all the sharp edges. I added a nice 2mm chamfer to the bottom edge of the piston to help stop the oil from being removed whilst the piston is on the downward stroke. To finish off the piston I polished the top. On the barrel front, I matched the transfer ports to the newly modified crank cases and gaskets (I know I said gaskets, I will come to that in a bit). I flowed the bottom edges of the transfer ports, and smoothed the whole area. I widened and slightly raised the exhaust port. This made the shape a lot better, from a square to an oval, this will help increase ring life. I then matched the power valve to the new port shape and smoothed the rest of the port, and finally polished the port. Next I measured the height I would need to arise the barrel by to match the piston at bottom dead centre to the bottom of the transfer ports. This worked out to be 1.7mm with one gasket. As a gasket was .5mm I then made a new gasket out of metal, which was 1.2mm in thickness. So now as a base gasket I have a metal plate of 1.2mm sandwiched between two normal base gasket. After I had done this I then measure the squish band clearance. To get down to the 0.9mm I wanted, I had to machine 2.1mm from the top of the barrel. The cylinder head I’m using is the 3MB type, apart from polishing the squish area, I didn’t need to do anything else with it. I have installed a Pipercross air filter, because the bike had no air filter at all. It already had a Dep front and rear box. I have also fitted the power valve control motor. Although the bike is the 90MY the wiring loom is from a later bike, not sure of the year, as I brought the loom off EBay. When I have the bike "run-in", I will let you all know how it is going. So far I have done 250 miles and all is going very well. The bike is pulling very strong in all gears and will pull 10.5k rpm with out any problem, even in top. I have not let it go anymore myself, but I’m sure it would if I let it. Now I’m not sure about what the gearing is supposed to be on the DT so any feedback would be nice J. I have been looking through my Haynes manual and on the net/forums and it seem to be that 88-90 should be 17/55 and 91 onwards used 16/57. At the moment I have the 16/57 combination, but I have ordered a 17 and 55 sprocket. I know it needs gearing up, but I don’t know how much, I have a feeling it will need more but until I try the 17/55 combination I won’t know. Another question I have is, what speed should I see, for what revs. I’m running standard size wheels and tyres, front 2.75-21 and 4.10-18. At 10k rpm in top gear my speedometer is showing 80mph, which works out to be 8mph/1k rpm, does this sound right? O and something else, in previous posts there is lots of question about the reed switch in the speedometer, and what to do about the wiring. I have a set of old DT125R clocks which don’t have the reed switch so the wires which would go to the reed switch are connected to nothing. And my bike revs to the red line without any problem and goes faster than 65mph which lots of people say seems to be a problem. So I would conclude from this that the just need to be open circuit and not shorted to earth as some people have suggested. Vince

I had my rebore done SEP in Kegworth http://www.sep-kegworth.co.uk/. They also supplied me with the quality Mitaka piston, and cheaper than PJME.

Welcome Erik

Sorry showing my age now, didn't think of using something as new as a "mountain bike thumb front derailleur changer"

lol, typo, that should have said "maybe"

About 20 years ago, when I had my first dt125, the last model before the dt125r, C Reg I believe. I was thinking of trying to do something similar to what Cynic suggested, but never got around to it. I just opened the power valve full and left it like that. If you used your old oil pump cable, it would not work quite right. As you only want the power valve to open when the revs are more then 7k. If it was connected to your throttle and at low revs say 4k you give it full throttle the power valve would open fully and the engine would bog down a bit and not accelerate as hard as it should because it would have to much exhaust valve timing. Then when it got to 7k it would start going like an idiot. I was thinking of using a throttle cable and lever from an old lawn mower, and mounting it on the left hand side handlebar. Then connecting the cable to the pulley on the power valve, then on the other side of the pulley connecting a spring which is man enough to pulley the back closed, but not to strong that it would pull the lever closed. The pulley would need to have some stops on it so it could only move from closed to fully open and no more. So it wouldn't be a 2 minute job. So what you would have is an extra lever on the left handlebar which you operate with your left thumb. When the lever is shut the power valve is closed and when you push the lever open the power valve would be fully open. The way I would envisage it working would be when you were riding around town or didn't need the extra power you would close the lever and this would give you loads of bottom end and a nice and easy bike to ride at slow to medium speed. Then when you want the power you open the throttle full, the engine would rev up (in gear I'm talking now, not in neutral), then at say 7k you would push open the power valve level. This would open the power valve and release the extra power. When you get to 10k and change to the next gear, although the revs drop you are still over 7k so you can leave the power valve lever where it is, and just keep going through the rest of the gears at full speed and on full power. Then when you slow down you can close it again and start all over again. Now this wouldn't be the best or easiest thing to use but it would give you full power when needed or a nice easy bike to ride around town. Now as I said earlier, I never got around to this because when I was younger I couldn't be bothered and I loved the power band I got from having the power valve full open. But anyway, I thought I would share my thoughts. Vince PS I have done 170 miles on my DT125R now, and I'm starting to open it up, and yes it does fly. I'll keep you posted how it goes when I let it have full throttle. PPS sorry for the long reply, when i get started I just cant stop .. lol

A great link. If I had the money and could find one I would love a NR 750. Oval piston....., could you imagine taking that to your local machine shop and saying can you rebore this 0.5mm oversize lol.

Welcome

welcome

The frame looks great. I wish I had completely stripped my bike, whilst I was rebuilding it. I might use it for now and in the winter strip it all and power coat the frame, it makes so much difference to the look of the finished bike.

My first bike was when I was 16 and it was FS1E – DX 49cc, (the DX had a disc brake, as if it needed it lol). The pic is not the actual bike, just for demo. It was an R reg (the first time around) and it also had pedals, which meant if you wanted you could pedal it, but it also meant it was unrestricted, so not the normal 3 bhp but a whopping 4.5 bhp. Which meant it would fly, well in moped terms anyway, on a good day it would do 45 on the flat.

Happy Birthday

Welcome to YOC

Yea sorry for the long intro, it started as a quick post to say hello, and I just got carried away. May I will start a new post.