Hello all,
I have a really nice, new to me 84 RZ350 yellow/black KR Edition with 7,000 miles on it.
I am going through it top to bottom right now, new seals, gaskets, etc....
I just had it bored 1st over and am using cast Pro-X pistons (personal preference).
I have been reading until my eyes are crossed regarding the expander ring that goes under the bottom ring on these Pro-X pistons.
I see some posts from way back saying there have been some broken off and destroying fresh top ends. Has quality improved since then, is this still an issue?
I know the stock Yamaha cast pistons I just removed had them in place, albeit one was sort of stuck and gummy but no damage, just worn bores on both sides.
I really need to decide which direction to go here. I spoke with Ed Toomey, he said run them, they're engineered for them so why not? But if they still potentially break and ruin top ends thats a no go from me?
What's the general consensus out there now days? I saw a reference "Chuck says toss them in the trash" but cant find that post...it must have been a long time ago, thus my question regarding are these still an issue, or has anything improved?
Thanks in advance
if you believe ron at fahron - which i do - bin them i asked him the same question years ago and that was his answer :cool:
cheers, gil
Chuck Q./ Supertune also says bin them. I've got about 1000 miles on my RZ rebuild/ Pro-X without the expander rings with NO issues.
Quote from: Evans Ward on March 07, 2025, 04:37:19 PMChuck Q./ Supertune also says bin them. I've got about 1000 miles on my RZ rebuild/ Pro-X without the expander rings with NO issues.
Have you noticed any additional piston rocking noise from them not being there?
no. and they don't control that, the skirt does. I haven't run expansion rings in 30+ years. bin em.
Quote from: m in sc on March 07, 2025, 08:15:35 PMno. and they don't control that, the skirt does. I haven't run expansion rings in 30+ years. bin em.
Fair enough, that's what I needed to hear. I wont use em if there's going to be no negative effects from their absence?
Any idea what the point of them is?
I know one of my pre-existing OEM pistons had the lower ring pretty well gooed up and stuck even with the expander in place behind it at 7,000 miles when I pulled it apart so if it's intent was to prevent sticking it didnt fix anything.