possible solution for 78mm pistons...

[tahoespringskier]

Hi all -

First things first. I've been lurking on the forum for a couple months researching the GS, then bought one for $400 and started working on it. I wouldn't have done it without all your helpful posts, ideas and enthusiasm, so THANKS.   

Second: I've got a beater 89,  first bike, having a blast, and have put 4k on it this month. Installed progessive springs but still need to change fork seals, converted petcock to non-vacuum/no-reserve, tossed CA emissions nonsense to simplify fuel delivery, and added a windscreen (kind of a pain w/ the clipons). I'm making weekend trips to Tahoe from the Bay, and the ol' girl feels a little down on power at 5k ft. above sea level. SOOO...I've started reading up on the big bore stuff.

Third: I'm a tinkerer, and my favorite mod is one that costs little and relies on ingenuity and thinking around corners. In that spirit, I've looked around a little for bigger pistons, and plan to do overbore/re-jet/lunchbox/etc. all at the same time.

But I'm not paying 6 bills for pistons, dammit. I saw this recently, and thought it might be made to work. They've got 17mm wrist pins, and the boss MIGHT survive a 1mm overbore to accept the 18mm pin the GS uses. The Wiseco guy said they "don't recommend" modifying pistons as it might weaken them. Which makes perfect sense. But if there's enough meat there, it could just work. Anybody care to discuss/flame/defame/help/etc.?

http://cgi.ebay.com/ebaymotors/KAWASAKI-KLX300-WISECO-PISTON-STD-BORE-KLX-300-97-07_W0QQitemZ300124914581QQcmdZViewItem

[Oklahoma_Mike]

that will be a lot of work for a end result of a gernade motor.
You will have to figure your Comp ratio with that setup as well. It would suck to do all the work to make it work and then end up with a 9-1 ratio.

If you are looking for a little more zing above the standard mods try working the head port/polish and such.

[sledge]

4 issues jumping out at me...

1, The distance from the piston crown to the center line of the wrist-pin, any greater than stock and you will bang into the valves on TDC but it might be possible to loose a bit of metal from the top to compensate. Any less and you start to loose compression.
3, Distance below the wrist pin bore center line to bottom of skirt, any larger than stock may foul the crank.
2, Reaming out the wrist-pin bore by 1mm might be possible assuming enough metal is present in the area but you will also have to machine 2 new and deeper grooves for the pin retaining circlips.....tricky, unless you are or know a good machinist.
4, New pistons with original rods and crank will have to be balanced as an assembly.

[cosmiccharlie]

Check this thread out!

http://gstwins.com/gsboard/index.php?topic=14401.0

[Chuck]

If your main problem is power delivery at high altitude, a jetting change would get you there quicker.

[dgyver]

Check this thread out!

http://gstwins.com/gsboard/index.php?topic=14401.0

Just buy the ones that are known to work. They are in one of my motors now.