tortron Posted June 18, 2020 Author Share Posted June 18, 2020 On 16/06/2020 at 17:30, peteretep said: I have to say, I dont understand why you persevere with this bike. But good job for keeping at it On 16/06/2020 at 14:15, tortron said: Maybe I'm too retarded to work on anything Maybe you have a point 4 1 Quote Link to comment Share on other sites More sharing options...
tortron Posted June 18, 2020 Author Share Posted June 18, 2020 Continuing polishing turds Here is 40 years of performance excellence in the form of a gn125 combustion chamber this is with a 125 head gasket And this is with a 150head gasket And here is what I propose to improve it Quote Link to comment Share on other sites More sharing options...
tortron Posted June 18, 2020 Author Share Posted June 18, 2020 Maybe hard to see in the photos, but the edge of the chamber is very sharp. The surface in the chamber is pretty good as cast, I had 1 small bump next to the exh valve I would imagine smoothing these off is a good idea. Maybe help me run cheap fuel at least About 20 seconds with a die grinder with a sandpaper cone on it gets the edge rolled Repeat for both sides then 240, 400, 800, 1200, and a buffing wheel Nice and smooth transition now. I clean d up the sides of the bowl as much as I could be bothered and left the area in-between the valves slightly cleaner than as cast to promote turbulence (not at all because it's a tiny little area and also a GN) Next I'll remove the lettering from the valves and clean up the intake and exhaust. The intake as already about as good as it can get tbh, but I'll take the valve out and see what it looks like from that end. Then do some polishing work to the exhaust port - feel free to tell me how ive ruined the squish band or whatever below 5 2 Quote Link to comment Share on other sites More sharing options...
tortron Posted June 19, 2020 Author Share Posted June 19, 2020 Here are some pistons Totally flat gn125 piston on the left. Slightly domed big bore piston in the middle And domed gs150 piston on the right Gn125 head has those squish zones as shown above the GS looks like i has a more open chamber, and the dr200 looks to be entirely open it looks like the old dr125s at least are also more open than the gn125 (possibly the same as the old gn125s with the big knob piston) i assume pinging isnt an issue for the dr200 as long loaded WOT is not as common as on a gn125, and the gs looks to use the piston as a squish area. what i think has been causing the need for 98 is the slight dome shape on the big bore piston. I have a theory that the small flat area around the perimeter of it is not wide enough, so as the piston reached TDC rather than squish all the mix towards the combustion chamber, the raised dome is trapping some in the flat area of the piston as it comes close to the squish area edge. maybe that explains the damage to the intake skirt of the piston too? from pre ign. im hoping by breaking that edge a little it will improve the squish flow. i might also look for a flat top piston, but theres not many options with a 14mm pin diameter. long term a dr200 or lt230 head with a domed piston is probably the best for performace. sadly theres nothing long term about a GN 2 Quote Link to comment Share on other sites More sharing options...
tortron Posted June 19, 2020 Author Share Posted June 19, 2020 grubby exhaust port. They come ready to fit an EGR system for some markets. Little bit of cleaning up and smoothing out would help Quote Link to comment Share on other sites More sharing options...
tortron Posted June 19, 2020 Author Share Posted June 19, 2020 Intake is good, a very slight clean up of some casting marks and a little clean up of this machined transition Quote Link to comment Share on other sites More sharing options...
tortron Posted June 19, 2020 Author Share Posted June 19, 2020 Intake cleaned up with to 80 grit finish. I smoothe off the leading edge of the valve guide a little 4 Quote Link to comment Share on other sites More sharing options...
tortron Posted June 19, 2020 Author Share Posted June 19, 2020 And much the same in the exhaust port, but worked through all the grits Only tool I used was a power drill and a 6mm aluminium rod with a slot in the end to hold a bit of folded up sandpaper 8 1 Quote Link to comment Share on other sites More sharing options...
tortron Posted June 19, 2020 Author Share Posted June 19, 2020 oh yeah, i found a 160cc piston that might work. its flat top, so if it does then i needent have ruined the head by shaping it 1 Quote Link to comment Share on other sites More sharing options...
Mr Vapour Posted July 9, 2020 Share Posted July 9, 2020 Your an inspiration to all the gn owners on oldschool! Quote Link to comment Share on other sites More sharing options...
tortron Posted July 15, 2020 Author Share Posted July 15, 2020 Yeah It's got a big cam Numbers Above piston is slapping, I assumed this would be the case so I have one on the way. Might put 125 barrel back on and do some speed runs with new cam. Get quite a few views on the comparison vid One issue is that the hotcam does not have a rev counter gear on it. I suppose one could be cut off and attached. But I'm going to blank the head off and use an electronic one 5 Quote Link to comment Share on other sites More sharing options...
tortron Posted August 2, 2020 Author Share Posted August 2, 2020 AliExpress rev counter and gn125 mechanical rev counter both gutted Guts pulled apart, LEDs removed, wires extended Mounting holes drilled, existing hole embiggened for cables. Heat shield and case shield made from old welding helmet spatter shield. Double sided tape to help with vibrations. Needles cut and shut. Looks like there's a 3.6% difference between numbers when using a protractor on the two faces (reads high) I believe I can adjust that with the trim pot. Going to tune it live at 10000 rpm with an inductive counter and then seal the gauge up 7 Quote Link to comment Share on other sites More sharing options...
tortron Posted August 3, 2020 Author Share Posted August 3, 2020 Man some days I just CBF with this Gn125 piston - 57mm 150 kit 62mm Here's a 150 kit one and the CBF ones to show deck height with he small ends aligned Quote Link to comment Share on other sites More sharing options...
tortron Posted August 3, 2020 Author Share Posted August 3, 2020 This really opens up the world of Suzuki 125 tuning as people were trying to track down NLA wiseco big pistons for extra cc. Possibly I'm the first to figure this out thanks to the future of cheap Ali parts 8 Quote Link to comment Share on other sites More sharing options...
datlow Posted August 3, 2020 Share Posted August 3, 2020 rebox and profit?? Quote Link to comment Share on other sites More sharing options...
tortron Posted August 3, 2020 Author Share Posted August 3, 2020 Ehh dunno. Maybe. Not good pistons for a dr125 as they have an open combustion chamber and would want a domed piston. Might keep digging around and see what I come up with Quote Link to comment Share on other sites More sharing options...
tortron Posted October 28, 2020 Author Share Posted October 28, 2020 Did a speed run on current set up 125 cc polished chamber, exhaust port, intake at 120 grit lt230 hot cam stage 1 18" rear wheel 0-100kph in 24 seconds compare this to standard gn125 - 0-100 in 27 seconds 150 kit 0-100 in 23 seconds Not too shabby. Running rich in the midrange throttle/cruise. But WOT is the only place that matters for this. Is quicker than i thought, but havnt ridden it for a while so was surprised to see similar speed run as the 150 kit Now to pull it all apart again and install the 150 kit again 3 Quote Link to comment Share on other sites More sharing options...
tortron Posted October 29, 2020 Author Share Posted October 29, 2020 Lol I put the wrong friggan piston in But that confirms that a gs150 pistons dome is too high for the gn125 head. Even with a doubled up base gasket the piston hits the head, locking the engine up 1 1 Quote Link to comment Share on other sites More sharing options...
tortron Posted October 30, 2020 Author Share Posted October 30, 2020 Holy shit it goes hard for what it is now fudging the gear shifts on the same bit of road 0-100 in 20 seconds, A similar bit of flat road with better shifts - 0-100 in 17 seconds It now accelerates hard past 80kph and sits real happy at 100 (which was always my goal), even continuing to accelerate to 100 up hills rather than burbling along. Top speed is probably roughly the same as with just the 150 kit well chuffed with that expecially after the extended dicking around trying to get the parts. Am currently running 2 base gaskets and i will keep the fuel a little richer than i had it before so hopefully no pinging now either. Next/last on the list is the exhaust which is the last bit i can see to get decent gains out of, carb and ign could be changed to get the last little bit out but not high on list of things i want to spend money on. now to calibrate my tach and put a few hundred km on it to be sure its good comparison video to come soon 8 Quote Link to comment Share on other sites More sharing options...
tortron Posted October 30, 2020 Author Share Posted October 30, 2020 4 Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.