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Post by stanlc7189 on Jul 20, 2017 12:44:02 GMT 1
Hi
I am in the process of replacing the piston rings on my 350LC due to excessive wear. The pistons are Mitaka (+ 0.75). I have obtained the corresponding rings, which consist of the two rings plus there is an additional 12-sided 'expander ring' , which I have been told should be fittrd underneath the bottom (thicker) ring.
I don't ever recall using one of these before. Can anyone confirm whether you have used these expander rings and are they necessary? Any advice greatly appreciated.
Cheers
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Post by headcoats on Jul 20, 2017 12:49:54 GMT 1
Don't think many folks use them as the expander ring can break up , well with aftermarket stuff
Is it Riken (??) brand rings they use with the Mitaka piston kits
Have the barrels been tuned as they can eat rings quicker |
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Post by oldelsieboy on Jul 20, 2017 13:04:29 GMT 1
Hi I am in the process of replacing the piston rings on my 350LC due to excessive wear. The pistons are Mitaka (+ 0.75). I have obtained the corresponding rings, which consist of the two rings plus there is an additional 12-sided 'expander ring' , which I have been told should be fittrd underneath the bottom (thicker) ring. I don't ever recall using one of these before. Can anyone confirm whether you have used these expander rings and are they necessary? Any advice greatly appreciated. Cheers They must be YPVS pistons as LC's do not have the expander ring. OEB |
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Post by stanlc7189 on Jul 20, 2017 15:42:26 GMT 1
Yes they are YPVS pistons. Don't like the idea of the expander rings. Can I leave them out or is it necessary to use them with YPVS pistons?
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Post by steeley on Jul 20, 2017 15:50:22 GMT 1
Hi ,myself I leave them out and had no problems. check the end gaps on the rings before boxing it all back together.
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Post by bare on Jul 20, 2017 17:47:16 GMT 1
Sigh.. FIT! the spring rings. Despite internet wisdom.
These are there to centralise the pistons in the bores.
To stop (or at least try damned hard to) Pistons from rattling in their holes.
Soo. Delete them then..if you don't mind your pistons sounding like rocks rattling about in an empty beer can.
OEM ones do not break, Rikens while not of the quality of Oems are at least Decent.
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Post by stanlc7189 on Jul 21, 2017 19:31:15 GMT 1
Thanks for your reply. My previous LC didn't have them fitted and didn't rattle but it didn't have YPVS pistons. Are the spring rings purely for YPVS pistons?
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Post by midlifecrisisrd on Jul 21, 2017 19:45:31 GMT 1
All ypvs pistons have them.
A lot of other bikes too
You will notice the lower piston groove is deeper than the ring which allows space for the expander
If you don't fit them the ring does not support the piston hence bare's comments on possible rattling
LC piston rings fill the ring slot so no need for one
Another useless fact is that banshee piston don't have an expander but have a deeper bottom ring
Steve
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Post by stanlc7189 on Jul 21, 2017 19:52:54 GMT 1
Ah, OK. That explains a lot. Looks like I need to fit them then.
Thanks for your advice
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antos
Drag-strip hero
Posts: 298 
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Post by antos on Jul 21, 2017 22:25:15 GMT 1
I fitted them in my f2 rebuild mate👍
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Post by steeley on Jul 22, 2017 5:21:52 GMT 1
As I said earlier I stopped fitting them on various engines and have had no problems . I have seen photos and read posts where folks have had them break up and the bits cause damage. And as for the piston sounding like a rock in a tin can, hmmmm no. no can't say I have ever had that sort of trouble .In fact the engines I have are pretty quiet ,or maybe I am deaf Lol.
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Post by bazzer5115 on Jul 23, 2017 8:15:15 GMT 1
I asked my engine tuner about fitting them after a fast road tune and rebore,and his advice was not to use them as they have been known to break up.
6,500 miles later all fine.
So in my other more recent engine rebuilds,they go straight in the bin.
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Post by markg64 on Jul 25, 2017 17:56:38 GMT 1
Hi I am in the process of replacing the piston rings on my 350LC due to excessive wear. The pistons are Mitaka (+ 0.75). I have obtained the corresponding rings, which consist of the two rings plus there is an additional 12-sided 'expander ring' , which I have been told should be fittrd underneath the bottom (thicker) ring. I don't ever recall using one of these before. Can anyone confirm whether you have used these expander rings and are they necessary? Any advice greatly appreciated. Cheers Hi just had my barrels rebored and tuned by Bob Farnham with mitaka pistons and he fitted the rings on for me and said not to use the expander rings as they can break and possibly cause damage inside your engine. Hope this helps Mark |
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Post by stanlc7189 on Jul 28, 2017 19:03:55 GMT 1
Thanks again for all your advice guys. Really appreciate your comments. I've chopped and changed my mind so many times based on these.
As i've already left them out, but not filled rad up or fitted carbs back, I think I'll get the engine running a few heat cycles followed by a break in run. If it rattles I'll consider stripping it down and fitting them.
Annoyingly, the whole point of fitting new rings was to restore compression. The 2-stroke racing specialists checked the bores and said they were fine but rings were worn. I had exactly 60 psi on both cylinders. Having fitted the new rings I checked the compression - guess what? The reading shows 60 psi on both cylinders again. Cylinder head gasket ok, no holes in cylinder head. WTF???
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Post by steeley on Jul 28, 2017 20:03:03 GMT 1
Hi ,were the bores and pistons measured up . Or was it just a compression test .
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Post by stanlc7189 on Jul 28, 2017 20:15:35 GMT 1
The tuners originally did the rebore and supplied pistons and rings 1600 miles ago. Went from +0.5 to +0.75. The pistons look fine with no blow by marks etc. I took the bores and rings down for them to check as I measured an excessive ring end gap but didn't have a bore gauge to measure bore wear properly. They checked the bores and said they were OK but confirmed rings were worn (after only 1600 miles) so got a new set for me, which are the ones in question. I did the compression test and have found the same readings before and after new rings with both cylinders showing 60 psi exactly, same as before
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Post by bare on Jul 28, 2017 20:15:38 GMT 1
IMO 60 psi would make for a seriously difficult to start engine 90 psi is in the iffy area.
Sure your Comp testing technique is OK? It's not as easy as it looks to be.
Different test operators often get varying results.
Sometimes..a simple ring replacement just doesn't work out.
Not even on my Lawnmower.. when I tried a ring replacement to revive an aged engine.
Good luck.
PS; Riken rings despite being widely sold are not of OEM quality. Not that one can get oems tho.
Rikens do seal and live a lot longer than 1600 miles.
Possibly 'something' was bungled
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Post by Tobyjugs on Jul 28, 2017 20:21:03 GMT 1
Did you try measuring the ring gap with the new piston ring placed in the barrel?
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Post by stanlc7189 on Jul 28, 2017 20:24:05 GMT 1
Engine started fine but struggled to get past 6000 rpm under load, misfiring at that point. I've stripped and ultrasonically cleaned the carbs, fitted new banshee coils from Norbo and checked timing etc. It was after that I bought a compression tester from Machine Mart and checked compression and found it was reading 60 psi on both cylinders, so focused on ring/bore wear. The gauge hose screws into the spark plug hole and I can't hear any hissing when kicking the engine over during the test.
I'm stumped to be honest.
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Post by stanlc7189 on Jul 28, 2017 20:27:18 GMT 1
Yes, tobyjugs. It seems ok at around 0.42 mm
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Post by stusco on Jul 28, 2017 20:27:20 GMT 1
Thanks again for all your advice guys. Really appreciate your comments. I've chopped and changed my mind so many times based on these. As i've already left them out, but not filled rad up or fitted carbs back, I think I'll get the engine running a few heat cycles followed by a break in run. If it rattles I'll consider stripping it down and fitting them. Annoyingly, the whole point of fitting new rings was to restore compression. The 2-stroke racing specialists checked the bores and said they were fine but rings were worn. I had exactly 60 psi on both cylinders. Having fitted the new rings I checked the compression - guess what? The reading shows 60 psi on both cylinders again. Cylinder head gasket ok, no holes in cylinder head. WTF??? I just did a compression test on mine 500 miles after a rebore I got 120 psi on both barrels |
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Post by stusco on Jul 28, 2017 20:34:49 GMT 1
Engine started fine but struggled to get past 6000 rpm under load, misfiring at that point. I've stripped and ultrasonically cleaned the carbs, fitted new banshee coils from Norbo and checked timing etc. It was after that I bought a compression tester from Machine Mart and checked compression and found it was reading 60 psi on both cylinders, so focused on ring/bore wear. The gauge hose screws into the spark plug hole and I can't hear any hissing when kicking the engine over during the test. I'm stumped to be honest. How are you doing your test? How many kicks ?throttle open ?or closed? |
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Post by stanlc7189 on Jul 28, 2017 20:38:59 GMT 1
First kick, 30 psi. Second kick 60 psi. Next 10-20 kicks no change 60 psi. Throttle open, although can't see what difference that would make because compression doesn't start until the piston crown has gone above the ports.
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Post by stusco on Jul 28, 2017 20:50:06 GMT 1
That's crap looks like you'll need to strip again
i was always told to do them with WOT
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Post by steeley on Jul 28, 2017 21:13:55 GMT 1
Hmmm, I know this is a dick dance but I would be taking the cylinders and pistons to some one else to have them measured up. 60psi after that amount of miles I don't think so mate. years ago I had an RD400 re bored at a shop I had used for years . the pistons I supplied were 350ypvs ones .when I rebuilt it I thought that went together easy. 2 weeks later when its rattling away I strip it back down and find out its been bored with too large a clearance . Any way my fault , in assuming the guy boring the cylinders knew the difference between air cooled and water cooled cylinders. Funny, no refund or sorry for dicking your cylinders bye eee . Any way hope you get sorted .
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Post by stusco on Jul 28, 2017 21:17:30 GMT 1
Hmmm, I know this is a dick dance but I would be taking the cylinders and pistons to some one else to have them measured up. 60psi after that amount of miles I don't think so mate. years ago I had an RD400 re bored at a shop I had used for years . the pistons I supplied were 350ypvs ones .when I rebuilt it I thought that went together easy. 2 weeks later when its rattling away I strip it back down and find out its been bored with too large a clearance . Any way my fault , in assuming the guy boring the cylinders knew the difference between air cooled and water cooled cylinders. Funny, no refund or sorry for dicking your cylinders bye eee . Any way hope you get sorted . I had the very same thing happen to me last summer although it was a ypvs engine |
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Post by Tobyjugs on Jul 28, 2017 21:20:06 GMT 1
Did the bike run perfectly after the tuner rebored the engine?
It seems odd that the piston rings have worn out after 1600 miles (piston rings are tough little buggers)
If it were me i would get two different people to measure the barrels, your tuner and another engineering shop that has calibrated measuring tools just incase of arguments
Why diid you want to check the compression?
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Post by reedpete on Jul 28, 2017 21:52:24 GMT 1
I asked my engine tuner about fitting them after a fast road tune and rebore,and his advice was not to use them as they have been known to break up. 6,500 miles later all fine. So in my other more recent engine rebuilds,they go straight in the bin. Maybe he means the whole lower ring 😁 |
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Post by stanlc7189 on Jul 28, 2017 22:13:49 GMT 1
Hi Tobyjugs
After the rebore, the bike ran fine. Then gradually I noticed it was struggling to make 9000 rpm. Then I noticed it was struggling to hit 6500 rpm under load so started to investigate. After all the previous stuff ( carbs, coils etc) I thought I'd check compression and discovered 60 psi, so immediately thought it was a bore or ring problem and took it apart. The 1600 miles was over a period of several years. The rebore was done in 2011. First sign of trouble was this year.
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Post by midlifecrisisrd on Jul 28, 2017 23:03:13 GMT 1
Have you checked the piston ring/groove clearance
If too tight they can bind
If your ring gap is in spec I can't see how the compression is so low unless the bores are oval
Steve
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