+1.5 250 RZ pistons & rings?

[jools]

Makes you want to weep eh?
Meticulous resto and prep of my '83 250RZ, bored and new pistons +1mm OS, lovely, goes beaut', lend it to the lad, and what does he do? - he runs it out of 2 stroke oil. LH Piston and barrel perfect, RH piston and Barrel scuffed, -it's not deep 'pickup', but just enough to feel with your fingernail. I could probably hone it and put a set of rings in there, but I'd normally feel I should go oversize again, but can't find +1.5mm pistons. Dunno, any thoughts?
Going to cost a bomb. (Do you sometimes wonder WTF you bother?)
Anyone got any idea where to get +1.5mm pistons for an '83 RZ250 (yes, 250) ?

[hybrid]

Can you post a pic? Surely it doesn't need another bore job if it's that new.

[jools]

Well it's the damage from the seizure more than when it was rebored eh?
Pic doesn't help that much, you have to FEEL the things really eh?
I have a mate who's pretty wised up on 2-bangers, I'll show it to him, see if he reckons I could get away with a hone and one piston only. Otherwise it's trying to find 1.5mm OS pistons or re-sleeving and standard pistons.
(Either way not nice for the wallet).

[jools]

Here's a pic. Actually looks worse than it feels, but, not pretty eh?

[JonW]

Does the 250 share pistons with anything else I wonder? OEM dont go that big, so im guessing there must be something aftermarket out there...

[hybrid]

Well it's the damage from the seizure more than when it was rebored eh?
Pic doesn't help that much, you have to FEEL the things really eh?

I don't know if you were having a dig or not, so I'll just merrily assume you weren't and answer.
An old cylinder will already be worn, so may not be useful if it's honed.

A new bore is more likely to be able to be cleaned up.

And "FEEL" doesn't always tell the whole story. Sometimes you can just brush the cylinder with acid to remove the aluminium and clean up with emery etc.

[jools]

Mate, absolutely NOT having a dig. Your (all) input is greatly appreciated. My point was just to mention that it's had a 'fresh' rebore, and that it's the depth of the seizure damage that will determine whether a hone will be enough because it's on it's final bore, +1mm. So it looks like it would need a re-sleeve, which would cost a bomb.
When I got the bike it had issues with it's powervalves, they had got loose and fretted away at the housings in the barrels. So I got another set of barrels and reco'd them, which is the set I'm dealing with now. The original barrels do have at least one rebore left in them, so I'm thinking maybe to revert to those barrels, and possibly have oversize powervalve bushings made. I'm aware of the (Stan's?) acid technique, but it doesn't look like there's any aluminium in the bore scraping. Anyway I'll keep ya's informed.

[EPApolice]

Is the LC and the RZ piston the same? if so here you go and there are bigger sizes,
http://yambits.co.uk/rd250lc-piston-kit ... 38916.html

[jools]

That's a good question. And on the face of it they're not the same, although they may be interchangeable, see below:

Here's a pic of my pistons. Left: the original Yamaha +0.5mm, marked 29LOD (you can see why I changed it!)
Right: Mitaka +1mm (from Yambits) Which I had got and fitted a few years ago, Yambits Part no PTK057.
Note the big difference in port size/shapes (though the bike went fine with these smaller ported Mitakas).

(For Aussies there's an annoying thing with 250s, the UK didn't get them (or not many), so everything the poms supply is either for 350YPVS or pre-YPVS 250 LC (not powervalve).

The gudgeon to crown is same at 22mm, but the Mitaka has a longer skirt (why it's sitting higher in the pic). It's obviously for Pre YPVS motors, but does work in a 250YPVS.

Yambits have listed, +1.5 for "RD250LC '80-'86 (PNo PK058) But not +1mm, their listing for +1mm, PK057, is captioned For RD250LC '80-'82 Non YPVS only. (Surely they weren't selling non YPVS 250's in the UK in 1986?)

[JonW]

The uk never got the 250 ypvs AFAIK, and maybe there were some older LCs being sold from importer stock, but not many by 86. The law changed (cos of the 250LC) and there was basically no 250 market once that happened.

I think the pistons can be made to work in a ypvs, you just need to make the ports bigger I think. Same as you can use the ypvs pistons in an LC, you just remove the lower tabs (which the yambits pistons have btw, weird), which makes me interested in what you wrote is that the mitaka pistons are longer, as that seems counter to the advice (filing off the lower tang) to fit in the LC cases. hmm...

[jools]

Yep Jon, both of these pistons have run fine in my 250YPVS, the Mitaka with the longer skirt (by approx 5mm), smaller ports, (and also the port timing will be different too). Makes you wonder if the Mitaka LC porting would have any effect on the oiling on a powervalve, obviously it's going to be leaner, beacause it would pass less mixture, but I guess that would only be at full throttle where the extra port area of the Yammy piston would work. As you say... Hmmm !

[hybrid]

The LC piston also doesn't have the "tang" on the bottom of the skirt that rides on the bridge of the port. The one that us LC guys file off when using RZ pistons.

I don't know if this would cause any issues... I wouldn't think so though.
You could also make the LC windows bigger, but I doubt it would have all that much effect really.

[jools]

Has anyone run a larger than +0.1mm OS on the 250 YPVS?
I think that standard OS pistons stopped at +0.75, but I've run +0.1mm using pistons from the pre ypvs motor, and I've seen larger +1.5 OS pistons available. But, are we getting too thin on the liner to do that?

[hybrid]

Is there also PV clearance issues to be worried about?

[JonW]

should go up to 2.0mm i would think, like the 350, but ive not done it. FWIW the LC250 is 2.5 just like the 350 IIRC.