My Minor

[xboxrox]

I'm impressed, you guys know a lot about life, welding & metallurgy..! Even more about bikes..!

These factors will help you braze 'n solder better (think % of bond in the joint between the pieces 80%+ is great)
a) Low gas pressures -- keeps the heat from bouncing off the weldment -- oxy 6psi try 3 psi for fuel -- (can't remember BUT LOW pressure works) use a neutral flame
b) Joint fit-up -- keep tolerances close (.003" or less)
c) Clean base & filler metal (sanitary clean)
d) Best quality & proper Flux (clean & thinned with water if needed)
e) Proper torch manipulation (evenly heat the pieces) keep the torch moving

Aloha --
George (one new case Oahu today)

[tortron]

New project dog
Rescue, probably half English pointer. He's been plated and tagged apparently as he's got multiple vin numbers (micro chips lol) but is freshly regod
Pretty thin, but healthy. Not trained in any way but he's a sweetheart and learning the basics


Here he is helping me work under the exploder

[geezer101]

Nice tortron. And he's just doin' doggo stuff

[85Ram50]

Here is a picture of the oxy set up I have. Got the carrier with bottles at an estate sale and bought the hose and gauge kit at harbor freight. Normal sized fittings.The welder supply had to keep and test my bottles before they would sell me refills.

[geezer101]

That is a nice old school welding rig I get that gas suppliers have to make sure nobody does something sketchy with bottles and turn themselves into a crater but at least they don't hold you for ransom like they used to here.

[tortron]

got the GN back from suzuki
welded up with birdshit and fisheyes in the paint - so it matches the factory finish at least

bought a bunch of parts, but none of them ended up fitting (i got all the kick start components from a dr125, i had been told by someone that they had done a kickstart conversion to a gn, maybe an early gn, but this one doesnt have any of the castings inside the crankcase, got to use a dr bottom end to do it. Got a china performance cam, supposed to be a copy of the standard LT230 cam i believe, i ordered 3 of them since december last year, one finaly arrived, it was a standard cam at twice the price, so thats out, and 3rd i got a gs150 piston to see what i could do with it, would be good with a 200 or 230 head, but not for a gn125 head as shown below)

I said bugger it, and am getting a hotcams grind for the lt230, which should go well in this engine, but is expensive for a bike like this

so on to the work i can do


left to right. totally flat 125 piston, slightly domed big bore kit piston (which i have taken the sharp edges off the valve recesses and mirror polished), much more domed gs150 piston.

GN has squish areas like the head on the left. GS and i believe DR have a more open combustion chamber, and the DR200 and LT230 have a totally open combustion chamber and i beleve use a domed piston for the squish area. Early GNs have a piston with a big knuckle on top, so lets ignore those.

heres my head with a 125 head gasket (silver) and a 150 kit head gasket (black and 1/3rd the thickness)



heres a close up of the sharp edge of the squish area

and im talking cut yourself on it sharp.

Now, heres my piston thats in there now

Ive been getting blowby into the crankcase, and theres scuffing on the intake side only. I believe this has been caused by preignition.
I may have mentioned i have had to use premium 98 octane since i put the big bore kit in.

a short bit on squish areas
these act to prevent unwanted detonation by forcing the air fuel mix back towards the combustion chamber. You want a tight clearance to limit spots that can cause ignition, typically modern cars have a large squish area, and messing with them is generally discouraged

What i think is happening is that instead of the squish areas squishing the mix back towards the combustion chamber at TDC, that the clearance between the domed piston and the edge of that squish area is causing some of the mix to become trapped at the outer edge of the piston and causing preignition expecially when at high rpm or under load.
The flat edge on the piston is too narrow. Piston options are limited in this size with a 14mm pin size. Best performance option is to get a bigger head and a domed piston to match, next best is to get a flat top piston. next up is modify what i have and hope it works.
An extra base gasket is my back up plan.

I figured i could break that sharp edge to help the mix to flow past the dome edge better



i broke the edge, and cleaned everything up to 1500 grit and then a polishing mop. At a guess i took maybe 1mm from the sharp point and rounded it over. The consensus is that you want that edge sharp, maybe a quick sand so you dont cut yourself, but dont round it. Well most people arent having knocking issues and are using bigger domed pistons in a higher compression chamber designed for a flat top, so i think im good, but im yet to test it.

and then while the head was apart i cleaned it up. nothing major as its about as good as its going to get already. (better to get a larger head that already has bigger ports and valves)

Head is set up for EGR for some markets


little bit of a step on this machined section
casting is pretty good, just a little to clean up on the sides


80 grit finish on the intake

took a little off the leading edge of the valve guide



and similar with the exhaust, but i went through the grits and polished this



only tools used were an electric drill and a 6mm diameter aluminium rod with a slot in it to hold some sandpaper (and a polishing mop)


I have also polished the valve faces and backs (i left the back of the intake a bit rougher incase it helps the fuel tumble in) but mainly just to clean them up.

Sound about right Geezer?

[tortron]

oh i just found a piston that might suit for a 160cc. need to check out the height, but looks like it will work. its flat too

[geezer101]

Sounds spot on dude I haven't read up on your GN %100 - you derestricted the carb spacer and picked up a bigger main jet? I might round the back edge off the intake valve a little to improve fuel charge fill - and maybe index the spark plug so the open gap is facing into the roof of the combustion chamber just to be OCD.

[tortron]

Carb spacer seems fine from factory, (bike isn't restricted like some used to be) I ended up running the standard jetting, I tried bigger and smaller and all combinations of needle height with my wideband and standard was as good as it got (I think needle mods would improve it but I haven't been bothered to get into that drama too much yet)

You are probably correct on the intake valve, it was something I was thinking of today.
Same with the plug, I noticed it's facing away from the chamber when I took the head off, new one will be indexed