hi chaps,

i need to replace one of the piston rings but i really dont want to fork out £35 for a set from motorworks (seems disgustingly over priced for a small metal ring). does anybody know of cheap alternatives? surely our friends in china sell some wonderful knock offs on ebay

thanks,
Mark

call me daft but would this work?...

http://www.ebay.co.uk/itm/LAMBRETTA-SX-200-PISTON-RING-66-8MM-/360715719415?pt=UK_Motorcycle_Parts&hash=item53fc5512f7

If it is the correct size and designed to be used with a nicasil bore it may be OK.

I have heard of trying to make savings, but never on a £35 piston ring when you consider what might happen if the cheaper one goes bang. You may save 315 in the short term but what could it cost you?

very true bikerboy, but bear in mind i am one piston in with 3 left to check. £35 can very easily turn into £140. add on top of that the various other parts i have to buy and my wallet is kicking me in the nads and running for the hills

Nice idea to try and save some money but I just think that if you need to do a rebuild of engine parts like that then it is better to bite the bullet and use bits that you know will work and last whatever the price.
I would change the lot rather than one anyway. What is wrong with the one that you believe needs changing? These engines go on for millions of miles without needing major engine work.

I must admit I thought a Lambretta was 2 stroke. I would not dream of using one.

K engines normally don't need anything more than routine servicing apart from making sure the timing chain and tensioner are good. If you are doing the work yourself maybe you are better of sourcing another engine. By the time you do all the rings, gasket sets and so on you could have a decent outlay.

Why replacing the piston ring anyway and why only one?

I can confirm that the Lambrettas used a cast iron cylinder that was not treated in any way whatsoever.  As a kid I can remember getting them rebored at the local machine shop.  

There is no way that I would put these rings to work in a K bike; that is not to say that it will not work, but you might wreck a motor in the course of saving a few shekels.

i only need one because i'm a ham fisted fool  snapped the damn thing in half by mistake. they were otherwise in pretty good order

maybe my annoyance at myself is getting the best of me and i should just bite the bullet and buy proper rings. still peeves me to pay that much for something that looks like it should come out of a kinder egg

We have all broken one at some point so you shouldn't beat yourself up over that, can happen anyone. At least it means its not an engine related problem. Going back to the Lambretta, as a two stroke and cast iron liner the characteristics are so far apart it would not be a wise move. Most brick engines never get rebuilt and you don't want to be stripping that one out again.

A bit of shopping around might find an alternative price, or someone here might have a set of rings lying around. But check on your bores, are they standard? As far as I know the very early pistons allowed the rings to rotate freely, they didn't have the little stop that's in all 2 strokes to stop the ring moving around on the piston and catching in the transfer ports. On the K this allowed oil to get past the rings when the bike was parked on the sidestand. I believe later ones do have this as a means of reducing the blue smokey start up. I am not recommending putting in a used set of rings but I would have more faith in that alternative than using the Lambretta option.

Ah, that explains the smokey starts... good to know.

To be honest i know very little about the compatibility of piston rings in relation to bores and i was kind of hoping for a cheap fix, but the more i read the more it seems obvious i'm going to end up buying the motorworks ones.

also, i swear to god BMW use bolts made out of playdough. i must have stripped or broke just about every single one by now (definitley using correct sockets). the only ones that fought back were the bolts connecting the pistons to the shaft... they snapped the flippin wrench in half haha

I imagine new headbolts too, at least I would irrespective of whether its recommended or not. Do you have a Clymer manual?

yeah i have the pdf version of the manual. and i think i'll be purchasing a great many bolts.

actually as i think on, what sealing product should i be using when putting the engine back together? do we have a favourite on here?

There is and I am not sure which. The guys in Australia are tops on a lot of these things. Three Bond appears regularly but I would be checking the Clymer at the very least. I think a lot of this is in earlier posts and a search [see top right on the menu across the top] of the forum might track it down.