TOPIC:

A coarse hone eh? To do that I'd just have to remove the cylinder part of the engine & take it to... who does that kind of work?

Also would lapping the valves help?

Being a rare bike, I'd take the top end off and decide then.
Steve

G'day, I'm working towards my coarse hone. I lapped my valves today then went to clean off the carbon from my pistons. It turns out I'm running 1 stock piston and 1 non-stock piston.

Stock piston on the far side.
This is the non-stocker

ART 116 apparently. Now, I've seen these ART pistons mentioned before but I can't find any sort of catalog or any other info. Does anyone know anything about these?
There is actually a NOS KZ305 piston for sale on Fleabay for a very reasonable price. Would it be wise just grab it and put it in? It was always that right side that was the smokeyest.
Here's another photo of that piston with a few marks on it...

Seeking advice and recommendations...
Thanks
Hama

No eBay APP ID and/or Cert ID defined in Kunena configurationWhat makes that difficult is the 13mm pin size. Gpz 550 pistons are 58mm with 13mm pins. I did consider a gpz630 using oversive kz305 pistons, just finding four NOS and rings might be difficult..

The kz 400 , 500 and 550 fours plus gpz305 all use this 13mm pin.

Another alternative is to buy some cheapo pit bike pistons,, these also use this odd 13mm pin size. The Chinese GY6 motor is seen on many different models irrespective of what the brand is.

:.

If you are boring it out bigger, don't go silly on it as once the liners get too thin it can cause unreliability. See the 1170 /1260 boring out thread here recently .

Can't really tell but the oil ring looks stuck down to me on the ART piston.

No eBay APP ID and/or Cert ID defined in Kunena configuration

Tyrell Corp wrote: What makes that difficult is the 13mm pin size. Gpz 550 pistons are 58mm with 13mm pins. I did consider a gpz630 using oversive kz305 pistons, just finding four NOS and rings might be difficult..

The kz 400 , 500 and 550 fours plus gpz305 all use this 13mm pin.

Another alternative is to buy some cheapo pit bike pistons,, these also use this odd 13mm pin size. The Chinese GY6 motor is seen on many different models irrespective of what the brand is.

:.

If you are boring it out bigger, don't go silly on it as once the liners get too thin it can cause unreliability. See the 1170 /1260 boring out thread here recently .

Thanks for the info, that is gold and really helps my thinking on this. So with some new clarity I went out to the garage this morning and placed my ruler over the cylinder bores expecting 55mm. What I got (not entirely accurate I know) was 61mm!!! That's already a 6mm overbore and it might bring the GPZ550 big bore kit into play as they are 61mm. The other reason the 550 pistons should work is the stroke is the same as the 305 at 52.4mm.

Pic of your measurements?
Steve

Ooops, my mistake. I was looking at the specs in the front of factory service manual - which is of course for a KZ250. In the supplement further back the specs for the KZ305 show a 61mm bore. Mystery solved!

So, I've purchased a std NOS kz305 piston off e-bay. That should come through in a few weeks. Now I'm quite keen to order a couple of those Wiseco K615 pistons & rings etc get it all nice & new in there...

No eBay APP ID and/or Cert ID defined in Kunena configurationAnd here they are on fleabay, pretty good price too. $330NZD including shipping

Tyrell Corp, if you were considering o/s KZ305 pistons for you GPz then you must have been sure that they would be compatible. So I'll take that as an endorsement that these will work. It looks like I'll get a compression increase from 9.5 to 10.25:1 is there any thing else I should look out for? Ooooh I'm quiet excited by this.

Thanks for sticking with me on this fellas I'm sure I must be as annoying as hell with my pesky little 305!
What can I say - I dabbled in a 750 for a while, it didn't end well!

As I understand it, the GPz305 motor is like half a 550 motor, but 61mm bore instead of 58. You need to check the piston deck height installed.

(Don't quote me on that as I've never owned a 305, just some research I did many moons ago about going the other way to GPz630).

Buying a pair of Wiseco 61mm 2402 could work, try to find the later XA type with the slipper piston and skinny rings, the earlier XC design rings are unobtainable now.

Bear in mind the 61mm bore doesn't give you any more meat to take away from the bores if it is tight, likewise if the bores are worn then the new piston could be too loose in there. The only way to know is get a machinist to measure the bores and pistons...even new pistons are slightly different sizes.

Going form 9.5 to 10.25 CR alone without other tuning won't really make much of a difference in performance.

61 2402 XA is what I've just purchased so hopefully they will do the job. Thanks.