piston kit advise

[17again]

sorry if this has been asked before. 

just looking to see if i need to fit the extra ring that comes with these piston kits? 

[oldelsieboy]

Mar 3, 2018 11:36:06 GMT 1 17again said:

sorry if this has been asked before. 

just looking to see if i need to fit the extra ring that comes with these piston kits? 

If it was not required, it would not be supplied.

OEB

[Deleted]

Stick the oil ring in. Like OEB says, it's supplied for a reason

[17again]

Does it go under the lower ring or top does anyone knOw?

[cb250g5]

I leave it out, having once stripped an engine to find one broken, and some of it missing entirely, didn't seem to cause any damage luckily.

I think it's only purpose is to stop a bit of piston slap when cold, so not a show-stopper either way.

Under lower ring I believe.

[steeley]

Hi , It goes under the lower ring and yes I have seen them broken up. I have left them out for many years with no problems.

[oldelsieboy]

I'm always a bit mystified when I read that people have found this ring broken with bits missing.
As it sits under the lower ring trapped between the piston & ring, how do the broken bits manage to escape.

OEB

[steeley]

Mar 3, 2018 14:29:38 GMT 1 oldelsieboy said:

I'm always a bit mystified when I read that people have found this ring broken with bits missing.
As it sits under the lower ring trapped between the piston & ring, how do the broken bits manage to escape.

OEB

Hi , as you know as the rings go past the ports / especially the exhaust they bulge into it . This is the main reason port edges need to be chamfered to give the rings an easy life. There was a post years ago on a forum where a chap suggested the expander ring out of the box didn't have enough kinks in it . As I said I leave them out these days.

[hudtm60]

Well....clearly you've seen this is a sensitive subject........so just to get your head spinning: Stan Stephens, an LC tuner of some repute, commented in an article on rebuilding and tuning an RD350LC (April '17 Classic Motorcycle Mechanics)

"Fit the rings on the pistons but leave out the thin expander rings. When the original genuine (Yamaha) rings were supplied, the bottom ring was made very weak and supple, it's strength and stiffness came from the wavy expander ring that went under the bottom ring, however the Mitaka pistons that we all use (they are actually better than the genuine: have you seen the price of the genuine ones) have a bottom ring the same strength as the top ring so the expanders are not needed, in addition the expanders tend to break up."

2 things:
1-I just bought Mitaka piston kit (Made in Japan) and there were no expander rings.
2-with yours not being Mitaka I wonder if the bottom ring IS 'weak & supple' like the gen Yam or is it as tough as the top one...

[Tobyjugs]

The last set of pistons i used were Prox and the bottom ring was thicker than the top ring. I thought this was odd as i work with pistons on a regular basis and this is the first time i have seen this.

[stusco]

Mar 3, 2018 20:01:31 GMT 1 Tobyjugs said:

The last set of pistons i used were Prox and the bottom ring was thicker than the top ring. I thought this was odd as i work with pistons on a regular basis and this is the first time i have seen this.

I think they always are so you can’t go wrong

[midlifecrisisrd]

I've always fitted them, especially with genuine pistons and rings.

Then 2 things happened

Firstly I discovered genuine banshee pistons and rings don't use them.

The bottom ring is thicker taking up the space.

Secondly I recently refreshed a ypvs engine and thought I'd change the rings.

Old set had no expander fitted

I fitted the new set with the expander as the rings came with them

Too tight in the bores so had to remove them

So some pistons can't take them

It's also funny when said that because folk found them broken so don't fit them

Did they know the make or quality?

We have all found broken rings. Does that mean we shouldn't fit them 😘

Steve

[Tobyjugs]

Mar 3, 2018 20:07:59 GMT 1 stusco said:

Mar 3, 2018 20:01:31 GMT 1 Tobyjugs said:

The last set of pistons i used were Prox and the bottom ring was thicker than the top ring. I thought this was odd as i work with pistons on a regular basis and this is the first time i have seen this.

I think they always are so you can’t go wrong

I have never noticed that the piston rings were wider on the bottom ring than on the top on a RD piston. Normally the top ring is bigger and stronger to withstand the rapid gas expansion.

[jessy03]

The new LC mitaka Pistons don’t come with expander ring, just the two rings however the ypvs ones I just bought have the expander ring included.

I’ve always fitted them never had an issue however on the last rebuild the expander rings had broken.

Jess

[abar121]

Mar 3, 2018 20:16:57 GMT 1 midlifecrisisrd said:

I've always fitted them, especially with genuine pistons and rings.

Then 2 things happened

Firstly I discovered genuine banshee pistons and rings don't use them.

The bottom ring is thicker taking up the space.

Secondly I recently refreshed a ypvs engine and thought I'd change the rings.

Old set had no expander fitted

I fitted the new set with the expander as the rings came with them

Too tight in the bores so had to remove them

So some pistons can't take them
....

I had exactly the same, so left them out. All good.

[JonW]

Ive been leaving them out for years as we had issues with them back in the day, really interesting to see the different views here. Wisecos are supplied sans rings, as I usually use those I was surprised to find a set in the TKRJs I just bought, so interested in the thoughts here.

[andy71330]

honed the barrels and fitted new rings last week complete with the expanding rings, the old ones where intact, hopefully have the engine running in two weeks, is this going to be an issue, cheers andy

[earthman]

Mar 3, 2018 18:07:44 GMT 1 hudtm60 said:

Well....clearly you've seen this is a sensitive subject........so just to get your head spinning: Stan Stephens, an LC tuner of some repute, commented in an article on rebuilding and tuning an RD350LC (April '17 Classic Motorcycle Mechanics)

"Fit the rings on the pistons but leave out the thin expander rings. When the original genuine (Yamaha) rings were supplied, the bottom ring was made very weak and supple, it's strength and stiffness came from the wavy expander ring that went under the bottom ring, however the Mitaka pistons that we all use (they are actually better than the genuine: have you seen the price of the genuine ones) have a bottom ring the same strength as the top ring so the expanders are not needed, in addition the expanders tend to break up."

2 things:
1-I just bought Mitaka piston kit (Made in Japan) and there were no expander rings.
2-with yours not being Mitaka I wonder if the bottom ring IS 'weak & supple' like the gen Yam or is it as tough as the top one...

Very interesting article that, thanks for posting.

[bare]

Mar 3, 2018 14:29:38 GMT 1 oldelsieboy said:

I'm always a bit mystified when I read that people have found this ring broken with bits missing.
As it sits under the lower ring trapped between the piston & ring, how do the broken bits manage to escape.
OEB

Agreed... Typically the Only reports of broken ones stem from some Crappy aftermarket piston set.
Usually (typically ?) supplied with Riken rings.
Genuine Yama spring rings Don't break up in use.
OEM Yama rings Outseal the aftermarket ones significantly.
Test this for yourself, I did.. it proved an eyeopener.

Caveat Emptor Kids. Your Engine.. your $$

[Mr Kipling]

Personally never had a problem with expander rings on any of my road or race engines.. having said that I only ever use quality piston kits..

[Deleted]

I've rebuilt a fair few engines over the years, and they've had some stick and done plenty of miles... always used the expanders and never seen a broken one. It's amazing what things have become a problem these days that never were.

[earthman]

I dunno what I'd do to be honest,....Stan is probably THE man when it comes to LC's, the amount of these engines that he's put together, how can you not take his advice??

[Deleted]

If it's a race engine leave them out. You can even leave the bottom ring off if you must, if you change the rings every other meeting this would be OK. That practice pre dates single ring piston kits. If it's a road engine and it comes as part of the piston kit then put them (all) in.

[17again]

thanks for the advise guys.

has any else use the same pistons with them in

are these TKRJ good pistons?