KR-1S.co.uk Forum

Just stripped the top end of my other engine for new rings and little ends, and noticed the left piston ring peg is very close to the piston surface (almost flat to it). I know KR pistons had trouble so how do you tell which piston is the modified type against the original?

isn't that a mitaka piston?

you can also check the piston if you look at the side there must be a hole in the side if so thats the older type piston with the ringpeg fault.

jarno wrote:isn't that a mitaka piston?

you can also check the piston if you look at the side there must be a hole in the side if so thats the older type piston with the ringpeg fault.

To be honest I couldn't tell you if it's Mitaka or not, I don't know how to tell. There's just a stamp inside on the skirt that looks like a mis-shaped letter a. Of the 2 pistons, this is the only peg that's close to the surface, the other 3 pegs are pressed in to various different depths. It's worried me, starting to think new pistons kits might be a better bet than new rings.

If you want a new set of pistons the tuning works are the best on price i have found he is selling the new type mitaka with the teflon coating on for £50 all in plus post

post a picture of the hole piston, taken from the side (looking at the piston pin).

JanBros wrote:post a picture of the hole piston, taken from the side (looking at the piston pin).

Yeah that's a mitaka. Doesn't look to have had a lot of use. I wouldn't trust that ring peg, it's going to come out is that. New piston time i'd say. Shame mitaka copied the earlier kr1 piston on this new batch

Dan

they didn't did they?

Yep

http://kr-1s.co.uk/forum/viewtopic.php? ... aka#p80601

I think i'd be willing to try them though.

Dan

I wonder why they did that.

Well I've ordered a pair from PJM so I'll be able to tell you for definite soon enough. I'm not surprised Mitaka used the old style ring peg pin though they've been making them in that style for RD's etc for years, not sure why it's been such a problem on the KR's. Maybe I should find out if they come with a good warranty

don't thinck the problem is related to the KR, simply to the original piston's, as those kind of ring-pegs are used in more piston's than the KR1S design.
But Kawasaki needed to do something so they took the S-design to show everyone they didn't need to fear anymore as it was now impossible for the peg to come out.

The new Mitaka pistons have turned up, very nice they look too. Great service from PJ motorcycles, ordered them Sunday and they turned up Tuesday morning!

Question to anyone who's done this. I've always fitted Mitaka pistons with the expander ring under the lower piston ring. Recently at and RD aircooled meeting one of the old Guru's said he leaves the expander out and just puts in the lower ring on its own to reduce friction and possible seizure. Now I'm planning on putting it all together, expander as well, but has anyone any thoughts?

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I think most people have left them out (not fitted) and havent had problems

bozbridge wrote:...Question to anyone who's done this. I've always fitted Mitaka pistons with the expander ring under the lower piston ring. Recently at and RD aircooled meeting one of the old Guru's said he leaves the expander out and just puts in the lower ring on its own to reduce friction and possible seizure. Now I'm planning on putting it all together, expander as well, but has anyone any thoughts?

On some pistons which are supplied with expanders, the bottom ring is narrower than the top ring to allow space for the expander - is yours like that? Doubtless omitting the expander would reduce friction, but it may also reduce the sealing capability of the bottom ring.

Is the expander provided to assist the bottom ring in sealing (because the bottom ring gets little assistance from the full pressure of combustion like the top ring, which helps in sealing the top ring)???

If one omits the expander, would it be akin to using a one-and-a-half ring piston???

Regards,
James