Messages

My '77 KTM GS125 (Sachs engine & hi-breather frame) has aluminium base plate, and '78 125 GS6 has fiberglass base

w/rgds:
Paavo Pernu
Technician,Age 39
KTM 125 GS  -77
KTM 125 GS6 -78

Edited by - paavojaelvis on 11/06/2002  3:07:09 PM

Crankcase volume is a compromise between proper primary compression ratio and (desired) max. fuel/air mixture volume, which could be sucked into the crankcase.
Bengt,  you are partially right, the _uneffective_ crankcase volume must be kept in a minimum. There are some areas in the crankcase, especially in older engines, that gas/air mixture gers "trapped" and will never reach the transfers when piston comes
down, like the very bottom of the case, space between main bearing and seal, etc. The volume of those areas has to be minimized. When you look at modern reed valve engines and the volume they  have behind the reeds in their crankcase, it's HUGE! And it's all located very close to transfer area. OK, primary compression ratio is lower than in the 70's, but with transfers having good flow characteristics and a pipe giving supercharging effect, there's no such need. Here's a link to a website, this guy has been tinkering with two stroke quads ans jet skis. http://www.macdizzy.com/2stroke.htm
Lots of theory, porting and crankcase stuff.  Have a look!

Paavo  

Sorry, I mistyped the address, it is: [email protected]

Paavo

Hi,
If you can't find any in the U.S., try Dr2Stroke in Switzerland. He has tons of NOS parts for KTM.  E-mail  [email protected]


w/rgds:
Paavo Pernu
Technician,Age 39
KTM 125 GS  -77
KTM 125 GS6 -78

Richard, I suppose, that it differs only in decals, as far as I know. Late 78 made KTM:s ("79 models")had a different frame, though.
Maybe somebody has more exact info with this issue...hey folks out there?

Paavo

Rick,
You must use auxiliary power source, eg. a battery or a charger, 12 V DC. Red one to positive, black one to negative. The pick up lead for the spark plug cable is connected normally. DO NOT connect coil lead (usually green) at all (you might ruin your Motoplat or CDI).  Tadaaa...it's flashing. =)

Paavo

Kära Bengt,
det syns, att vi måste tala (skriva) bara på engelska, jag är ganska tråkig med svenska, tyvärr. OK, if the shaft is in pristine condition, as you said, go ahead. But be careful with shimming to get the right amount of end play, as John highlighted above.

rgds
Paavo

Bengt,
the clutch basket may not be enough hard to cope with the stress from needle rollers, so at least you should use a bearing with an outer race. An INA HK type could be fine. For 16mm shaft there are three std sizes: HK1612, HK1616 and HK1622. The two last digits indicate width, all with 22mm o/d.
Make sure, that the shaft itself is not worn out and has no pitting. I would leave the con rod as it is, supposing you're not going to take out the very last HP:s from your engine...  

I hope this helps a bit.



w/rgds:
Paavo Pernu
Technician,Age 39
KTM 125 GS  -77
KTM 125 GS6 -78

16005 C3 bearing has slightly bigger radial play(in this size, the difference is only a few thousandths of a mm)to compensate heat expansion. So it gives a safety margin, when things get hot. I would use standard 16005 bearing in both applications, though.

w/rgds:
Paavo Pernu
Technician,Age 39
KTM 125 GS  -77
KTM 125 GS6 -78

Mike,
is the deck height measured from the edge of the piston crown to top of cyl. liner?  Ign. timing: 0.9-0.95 mm BTDC sounds odd, I thought it was around 2.5 mm (0.10")?  With combustion chamber volume I mean the chamber in cyl. head. Somebody has machined the sealing surface and I'd like to find out how much the chamber volume has decreased.

Thanks,

Paavo

Mick,
you're right, a -73 250 engine won't just "drop in".  Sorry, if I've confused you. My -78 125 has also a weird VIN: 855 10519, and the frame has been there since new.  The first number must identify the year, but the two following...? However, my -77 KTM GS (with Sachs engine), frame # 703 93849, makes sense. Did KTM change their frame numbering system many times during the 70's?  I know, 80's & 90's are a totally different story. About your frame, does it have a bolt-on tail piece above the rear fender? How about the rear brake pedal: cast alloy or stamped steel?

w/rgds:
Paavo Pernu
Technician,Age 39
KTM 125 GS  -77
KTM 125 GS6 -78

Hi, Mick!

Could it be a 80 cc KTM frame?
I have a feeling, that it might be...

w/rgds:
Paavo Pernu
Technician,Age 39
KTM 125 GS  -77
KTM 125 GS6 -78

Greetings from Finland!
I've been reading your posts quite a while and found this site as a huge Penton/KTM tech&tip databank, thanks to You, POGgers. What a magnificent job you've done!  I myself have been tinkering with my two 125 KTM:s to get them back into life again and this forum of yours has really helped me a lot. Unfortunately, I still have a couple of problems, and I hope you could give me a hand. It's about the -78 125 GS6: the deck height, combustion chamber volume and ignition timing in mm:s BTDC. Engine # is 8-5107922. No racing intentions, trails riding only.
I would really appreciate, if somebody of you could help me with this issue.

Keep up your good work, guys!


w/rgds:
Paavo Pernu
Technician,Age 39
KTM 125 GS  -77
KTM 125 GS6 -78