Question on Piston rings - Need some help! 1981 Honda C70 Rebuild

1981Honda

Member
I've got a 1981 Honda C70 Passport that I am rebuilding the top end on. I have been trying to use all OEM Honda Parts where possible so I can know I will have good reliability and longevity.

I bought a kit on eBay that includes a piston (which I will not use and is the wrong type) a new wrist pin, circlips, and a piston ring set. I bought this thinking that they were original Honda parts as the boxes say "Honda Genuine Parts" on them, and have little labels that say "Made in Japan" on them. Well after looking back at the ad and contacting the seller recently months after I bought them, the seller now says that they are "reproduction parts". So that listing was a bit misleading for me as I thought I was getting OEM Honda Parts.

I took the original piston rings and compared them to the replacement rings I have. The new oil ring is a different style from the old ring, with the older one is like a "mesh" style one and looks like it would work better. I'm not sure if I should use the new one. What do you guys think? Also, could I just reuse the original oil ring and just replace the 2 compression rings? The bike has 4,700 miles on it.

The new compression rings have a slight sort of groove cut around them too. The old rings do not appear to have that, or it is just worn off. Is that groove ok? Also, the 2 new rings look about the same, does it matter which one goes on the top or bottom? It seems hard to find original OEM or NOS Honda rings at a good price and ones that won't take a month to ship. Does it matter if I use OEM vs. Aftermarket reproduction parts? I'm really just concerned about getting longevity and reliability from the rings... and I know they are very, very critical for any engine to work well and last!!

Any input would be greatly appreciated!!! Thanks

Here are some pics of the rings, new and old, and the link to the listing on eBay that I bought the kit from.

 

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dirtbkr188

Active Member
As a general rule, you do NOT put aftermarket rings on an OEM piston, and vice versa, it never works.

Why is the piston from the kit the wrong one?
 

dirtbkr188

Active Member
Looking closer at the pic of your old piston, it is an aftermarket one, it has the corrugated ring with two thin rings on either side of it. Someone has been inside that engine before.
 

1981Honda

Member
Looking closer at the pic of your old piston, it is an aftermarket one, it has the corrugated ring with two thin rings on either side of it. Someone has been inside that engine before.
No one has been in that engine before. As far as I can tell nothing has been touched since it was made, gaskets look OEM, and the piston has markings on it that appear to be from Honda. As far as I know that oil ring is factory.
 

1981Honda

Member
As a general rule, you do NOT put aftermarket rings on an OEM piston, and vice versa, it never works.

Why is the piston from the kit the wrong one?

It is the wrong piston because I have the short rod style from 1981, and the piston is a little bit shorter than the aftermarket one. The aftermarket one also weighs 11 to 14 g more and I’m not comfortable using that because it’s gonna put more force on the connecting rod, especially when it’s running at many thousands of rpm’s.
 

1981Honda

Member
Looking closer at the pic of your old piston, it is an aftermarket one, it has the corrugated ring with two thin rings on either side of it. Someone has been inside that engine before.

According to my Clymer 50cc-110cc OHC Singles manual, this is what the OEM rings look like
 

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1981Honda

Member
Well, okay, suit yourself...
I guess It doesn’t help that you can’t be here while I disassemble the engine and see how “welded” all those old gaskets and seals have been on this engine, or see what the parts look like. The bike only has 4,700 miles so I really doubt anyone would have to do new rings in it in that span of time. I bought the bike with 2,173 miles on it to give some perspective.
 

OLD CT

Well-Known Member
One thing I know is the one piece oil control rings are not as good as the 3 piece. Anyone that has taken apart Early ct70's will find the one piece oil control ring is always cracked. So much for oem Honda rings! :LOL: Not their best idea. I wouldn't worry about using an aftermarket piston as long as it's correct. I would not use the one piece ''scraper'' oil ring setup. Too brittle!
 
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1981Honda

Member
One thing I know is the one piece oil control rings are not as good as the 3 piece. Anyone that has taken apart Early ct70's will find the one piece oil control ring is always cracked. So much for oem Honda rings! :LOL: Not their best idea. I wouldn't worry about using an aftermarket piston as long as it's correct. I would not use the one piece ''scraper'' oil ring setup. Too brittle!
Sounds good, that is what I was thinking with that one piece ring. Just seems like a bad design. Where can I find some OEM Honda piston rings for my bike? I may just reuse the original oil rings and replace the compression rings. Anyone have the Honda part #? I have the standard 47mm bore, not oversized.
 

1981Honda

Member
I just looked at that, the one problem with that one is it has the one piece oil scraper ring...

I'm trying to find a set with the 3 piece oil ring, If I do I'll post it here and let you guys look at it and see if it works. Went onto partzilla and just copying old part numbers and seeing If I can still get some
 

Robert thran

Well-Known Member
I’ve bought rings before that were not thick enough to fill the ring grooves,, I just assumed they were for late model motors? They were listed for Honda 70’s..? Beware….
 

1981Honda

Member
Man I'm having a TERRIBLE time trying to find the correct piston rings... figured it would be easy for a bike that has far surpassed 100 million plus produced.. Geez!

If I truly can't find the right rings, would these aftermarket ones be ok to use? They seem the closest to OEM as I can find, but they are kinda cheap, they have one chrome ring, and the correct oil ring, and match what the manual says the rings should be (one chrome, the 3 piece oil ring, and I hope the black one is tapered).

 
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1981Honda

Member
That piston is not the right style for my short rod bike. The wrist pin located in that piston is in a different spot than what is on my bike, so if I use that on my bike, it would result in low compression. Just bought this piston ring set on eBay. NOS parts from Indonesia. It will take 3 weeks to get here but I’m sick of scouring the internet for discontinued parts for my OEM piston. You would think it’d be easier for a bike that has surpassed 100 million produced. I think that ring set should work? Looks like it will to me, parts numbers match up.

 
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