Is this piston right/wrong

[SP_BOTT]

Always a contentious question, I've always fitted the expander ring, as far as I can remember, but I've always tried to get genuine pistons too, Yam Kwak etc, and as said, supposed to add a little pressure to the bottom ring I believe.

[Luders]

I don't have any specific experience on this subject (using single ring race pistons) but, it must have been designed and there for a good reason surely?

I come from an engineering background and when components are designed, a lot of time, thought, testing and process is followed to ensure things serve a purpose and do not result in extensive warranty claims, costing the company financial penalties.

When people like myself think changing something is a good idea, it should always be in a measured, calculated and analytical approach.

That's my philosophy anyway and it serves me pretty well.

[DougB]

Interesting replies, thanks guys. I've always figured they're there for a reason as well, so fitted them. I just started to wonder if I was fitting them for the wrong reason! It Was mentioned by an aircooled RD friend that as far as he was aware the expander ring was provided in the kit as Riken always put them in, not knowing if the rings are going to be used with new pistons & bores or just for re-ringing old pistons in old barrels, as far as he knew the expander was only for use in old and used pistons/bores.

I'll be fitting them (they're going into old bores after all), but wouldn't it be great if the kit came with even a single instruction! I've been fitting Mitaka kits for years and never seen any info in the box. Might try and look up Riken and see if they have any info, the Mitaka UK site is just a catalogue really.

Top end going back together tomorrow, it'll be running by the weekend, soon find out how it sounds!

[Luders]

That's an interesting theory, let us know if you do find any information on it.

http://www.riken.co.jp/e/piston/b/b_1.html

[DougB]

Well the expander ring went in. Running and all sounds well at the moment, a few heat cycles and soon find out how it runs on the road. Need to get a few miles on it before Cadwell on August 2nd, I think I'll find out for definite if the engine's ok over the course of that weekend!

[philfingers]

that's me pissed! I got my pistons earlier in the year of PJ and got the old 'non' teflon ones!
How's it running now?
will be doing a bit more work to mine shortly

[DougB]

Got a definite answer on the expander rings (to fit, or not to fit.....) After taking the rings off all 4 of the new style Mitaka pistons I've bought, after each piston doing about 400 miles the expander rings on every piston were broken into either 2,3 or more pieces, literally one had shattered into bits. I spoke to Paul at PJME and he had a set with him that had done the same thing at a similar mileage to mine. He'd already spoken to Mitaka about it and had found out they know and have now advised to NOT PUT THE EXPANDER RING IN. That's the official line.

Hope it helps if anyone's rebuilding an engine with them. If you've already put an engine together with the expander behind the bottom ring I'd have it apart and get them back out (what's left of them).