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Tortrons GN


tortron

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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

IMG_20200618_123757.thumb.jpg.d34d25b249b443dc34f72d97d71e821c.jpg

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Continuing polishing turds

Here is 40 years of performance excellence in the form of a gn125 combustion chamber

IMG_20200618_145059.thumb.jpg.8553b0bbf6c37061ea5c4d2e7b5b90d4.jpgthis is with a 125 head gasket

 

IMG_20200618_145116.thumb.jpg.e85a10bcaf844ea63a7feac06a05bff1.jpg

And this is with a 150head gasket

 

And here is what I propose to improve it

IMG_20200618_145138.thumb.jpg.3c48acb31e9a8f1da573a8166ac763f5.jpg

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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

IMG_20200618_145150.thumb.jpg.4a675086d01d5b0d6883536a1e47e0d3.jpg

I would imagine smoothing these off is a good idea. Maybe help me run cheap fuel at least

IMG_20200618_145202.thumb.jpg.4887dd09cf15bb6f4ec3a967bd5518d3.jpg

About 20 seconds with a die grinder with a sandpaper cone on it gets the edge rolled 

IMG_20200618_145215.thumb.jpg.14dc62be1dffcea088dd0b00fb0d9b9e.jpg

Repeat for both sides then 240, 400, 800, 1200, and a buffing wheel

IMG_20200618_145237.thumb.jpg.ba7c45fef474401256f9aaac8d9ce710.jpg

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 ;)

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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

 

 

 

IMG_20200619_105213.jpg

 

51101IO7utL._AC_.jpg

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

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  • 3 weeks later...

Yeah

It's got a big cam

IMG_20200715_130110.thumb.jpg.26da3a4f1b3c56014d6f312c304128ae.jpg

 

Numbers

IMG_20200715_130121.thumb.jpg.8f123bd72faee6b5657cdca97cba7bb1.jpg

 

 

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

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  • 3 weeks later...

AliExpress rev counter and gn125 mechanical rev counter both gutted

IMG_20200802_135341.thumb.jpg.aa399f35db540948a4b44b658084c6f8.jpg

Guts pulled apart, LEDs removed, wires extended

IMG_20200802_135420.thumb.jpg.55aeab4f5f64b2d2b9097971082c8e4a.jpg

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.

IMG_20200802_135447.thumb.jpg.52eb16bcbd4073b3250b702fa207c1da.jpg

IMG_20200802_135458.thumb.jpg.07b86e61ae9c36954dda9c91dc5c4070.jpg

 

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

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  • 2 months later...

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

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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

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