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Post by Bozzy on Jul 7, 2024 17:41:17 GMT 1
Hi just sorting top end and opened the box piston rings it has the two rings for pv pistons but also had a sort of thin metal bent to form circle no idea what this is assume packaging item
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Post by urbantangleweed on Jul 7, 2024 17:43:56 GMT 1
It's an expander ring, most people throw them in the bin rather than fit them.
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Post by Bozzy on Jul 7, 2024 19:26:08 GMT 1
Thanks see what they are now go onto bottom ring just checked my old pistons and they have them on the bottom rig looks pulled one out and is ok
These are mitaka pistons so wondered if rings etc designed for these to be fitted? What’s the general consensus?
Might speak to PJ’s tomorrow
Hoped to finish top end tonight looks like another hold off
Thanks
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Post by urbantangleweed on Jul 8, 2024 6:38:33 GMT 1
Correct, under the bottom ring. I've fitted them and I've not, never noticed any difference. It's your choice really but yes, they should be installed but as mentioned in my earlier post, most throw them in the bin.
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Post by Bozzy on Jul 8, 2024 11:36:31 GMT 1
Correct, under the bottom ring. I've fitted them and I've not, never noticed any difference. It's your choice really but yes, they should be installed but as mentioned in my earlier post, most throw them in the bin. Spoke to PJ’s and it appears they have loads calls on this and say best not to fit them. Looks like I will be taking them out
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Post by abar121 on Jul 8, 2024 14:32:34 GMT 1
I never fit them.
Make sure you gap the rings.
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Post by Bozzy on Jul 8, 2024 14:50:48 GMT 1
I never fit them. Make sure you gap the rings. I assumed as I had rebore new pistons etc that they would have been done. Checked the top ring of one piston and that was in spec.
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Post by abar121 on Jul 8, 2024 15:14:06 GMT 1
I never fit them. Make sure you gap the rings. I assumed as I had rebore new pistons etc that they would have been done. Checked the top ring of one piston and that was in spec. You should always check and gap the rings. I usually find one or two tight rings(!) on rebores from PJ, though not always.
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Post by Bozzy on Jul 8, 2024 22:02:30 GMT 1
Thanks will do as I need to remove expander rings anyway. Lucky I just put cylinders on with no base casket just to try so can remove rings and just check.
If needed is it a small diamond file to use or a normal fine file on
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Post by abar121 on Jul 9, 2024 9:01:47 GMT 1
I use a fine mini file, but either will do as long as you are careful and remove any burrs.
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Post by jon on Jul 9, 2024 19:03:31 GMT 1
I’ve taken engines apart before where the expander ring is broken up. However it was all there as I doubt the broken bits can get past the ring.
Banshees don’t have them, but their rings are wider.
I’m in two minds whether to use them or not. Without them the piston would potentially wear quicker?
Jon
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Post by Bozzy on Jul 10, 2024 10:01:44 GMT 1
Searching around and speaking to a few it appears they were originally more for the air cooled motors as a noise reduction method ... fitted the bottom ring is more solid and less side to side play in the ring.... I was surprised how much clearance in that bottom ring
However searching around etc I am more inclined to 100% take them out.. appears to be a few broken up report even though my original pistons had them and were ok risk appears to be broken bits overlapping and pushing out the ring.
I might regret it and end up sounding like a tractor! but advise to me has been more leave out than fit
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Post by midlifecrisisrd on Jul 10, 2024 10:32:05 GMT 1
If the piston can take them without being tight in the bore I've always fitted them
I have had pistons and ring kits that when you fit the expander it is too tight but this has usually been when fitting new rings in an unknown good used piston
I've only ever found them broken in abused engines
30k original unopened motors have always been fine and in one piece
To me they hold the piston central in the bore
This will be another what oil/ how to run in scenario with different opinions
Steve
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Post by Bozzy on Jul 10, 2024 15:42:03 GMT 1
Thanks Steve makes me question again. My old pistons with scores both sides still have them in place under the rings and it looks like pistons went through hell.
Only risk perhaps is the quality of the aftermarket material to OEM.
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Post by beardy on Jul 10, 2024 18:31:55 GMT 1
I sympathise with your dilemma. But I guess if the supplier that bored the barrels and supplied the pistons suggests not using them. I’d be swayed by them.
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Post by yamman1066 on Jul 10, 2024 19:24:28 GMT 1
i always fitted them if there with the pistons
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Post by Bozzy on Jul 10, 2024 22:58:51 GMT 1
just found this post 2019 rdlccrazy.proboards.com/thread/48246/expander-ring-good-fit?page=2Comment that makes you think is the one about the ring being designed to take the rear expander as I noticed a lot of side play in that ring... but overall opinion appears to be omit. What I might do is take one out one side and see impact on ring compressions and if any obvious difference in how far the ring compresses into the piston groove. have pistons fitted now so cant check in bore
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Post by Bozzy on Jul 12, 2024 9:54:36 GMT 1
Recently spoke to one of the old time two stroke tuners and he straightaway said dump them like the engine builder and quite a few on here. So if I do decide to keep them in thats going against some sound advice.. TBH its only the fact are the rings and grooves designed for the spacers........ worst thing new rebuild and motor sounds like a bag of nails.
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Post by urbantangleweed on Jul 12, 2024 12:07:18 GMT 1
Is this the room for the Hokey-Cokey?
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Post by Bozzy on Jul 12, 2024 23:33:24 GMT 1
Funny and so true 😀🤪 … stopping me building the thing up…Anyway a question that is easily answered piston ring gap hairs says 20mm from bottom err o thought it was 20mm from top?
Top ring is 0.3 nice fit so on spec bottom 0.35 is very snugg and 0.4 no chance spec says .35 to .5 thinking of just easing this off what’s thoughts?
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Post by JonW on Jul 13, 2024 1:59:17 GMT 1
My advice (and also feeling the same from others) is not to overthink this stuff to much. These bikes were built and ranted by us as dumb 18year olds who wouldnt have had acess to all this measuring, advice and specs.
ie. Is it within spec? If so it's good.
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Post by steeley on Jul 13, 2024 7:54:26 GMT 1
Hi , i have seen these end up in bits . I now just leave them in the box and chuck it in the bin .
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Post by Bozzy on Jul 13, 2024 17:57:26 GMT 1
Tbh that appears to be the general opinion
I was told today at yam dealership that originals don’t now come with that expander. Not sure if anyone has recently purchased a set to check this is true
Chaps saying this build last loads and races them and is main parts guy … interesting if it is correct… but did say he fitted them In many road bikes in past ….. nooooooo. But added go with tuners who say no and most engine builders
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Post by midlifecrisisrd on Jul 13, 2024 18:18:18 GMT 1
The only new (not NOS) ones now are the 2GU banshee ones, I have 2 sets of pistons/rings
They do not have the expander ring BUT the lower ring is deeper to take up the space
Steve
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Post by masonmart on Jul 13, 2024 21:29:07 GMT 1
My default position is 100% to put them in. The reason? Yamaha and the piston vendors know more than me about the subject, they are the experts and they recommend that they be fitted. Simples so why not just fit them?
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Post by reedpete on Jul 13, 2024 22:50:02 GMT 1
Some piston systems are designed to using them, others not… obviously you shouldn’t mix and match… and if the piston supplier went to all the trouble and cost to put them in the box then sounds like voodo hogwash to believe they should be left out.. However, If you prefer not to fit for whatever reason…then the lower ring will be doing next to nothing and you might as well take that out too. Will leave you will less friction , more power at high revs but higher top ring wear.
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Post by freddie19 on Jul 14, 2024 2:41:28 GMT 1
Guys I can't believe this conversation, Yamaha fitted them for a reason. Genuine Yamaha 31K ring sets always had them included.
I've owned my PowerValves for over 30 years and never had a problem with the OEM expander rings breaking, in fact I refitted the 15k mile originals to the Potenza pistons I used when I rebuilt my top end a few years ago as they still looked as new and better quality!👍
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Post by jon on Jul 14, 2024 9:41:43 GMT 1
As much as they can break up due to them being fragile, on the rare occasion I’ve found them broken all the parts are there so I don’t think they can go anywhere.
I’d worry there would be too much piston slap without them, and prematurely wear the piston and bore?
Jon
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Post by Bozzy on Jul 14, 2024 15:07:28 GMT 1
Right guys fitting them I keep thinking the same. Jon that’s my worry ok they not gen rings TP but that bottom ring is thinner and recessed back a lot further I noticed without
Perhaps I am doing wrong and going against other advice but they in the kit to fit and it’s designed for them if not I assume we would have the deeper banshee ring in the kit
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Post by abar121 on Jul 15, 2024 13:12:27 GMT 1
As above, you can only decide whether to fit them or not, if there is sufficient clearance for that piston / ring / bore combination.
That has not been the case for the last few RIK rings, Mitaka pistons and rebore (PJs) that I've had.
If it's too tight and you jam them in there, you'll be forking out again.
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