Hi everyone, I finally started putting my top-end back together this afternoon. I ran into two more problems:

1) The (new) top ring on one of my pistons does not move smoothly in its gap, it gets caught and doesn't move all the way into the groove. Seems to be the piston - even the old rings don't fit back in!

2) The wristpins sent to me by Tyga are around 2 or 3 mm longer than the ones that were in there when I took the engine apart, meaning that I can't fit the pin between the two circlips. The new pins are 13111-KV3-7771.

The local wrecker, who seems to be a bit of a 2-stroke fan, told me the cylinder heads I have are from some in-between MC16-MC18 model, as they do not have a 'flat' at the top...I'm getting confused so any help would be great.
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'87 MC16

Oh and what does 'keystone' mean?
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'87 MC16

Try taking one of the old rings, fold it in half, and clean the piston ring grove with it.
Can't help ya with the other stuff, sorry

The keystone is the reason the top ring isn't "in properly", the top ring is not square profiled so only fits one way.
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Do a Forum search for Keystone.
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Andy.
NSR-WORLD.COM

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The rings have a tiny "N" stamped on them near the gap. This should always be facing UP. You may have it upside-down, which would make the keystone angle not lign up properly.

Recheck the wristpin thing. Install the first clip and be sure the pin sits ALL the way against it before you install the other clip.

I have no idea about the heads, but maybe if you post a pic, someone here can help.
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Paul Herr
'88 FZR4/GSXR/YZF Frankenbike
MY BIKE PICS

It is a top ring that your trying to put in the top groove is'nt it?the top and bottom rings are different shapes,the bottom ring wont fit in flush in the top groove.

Ok I will recheck the rings, it's possible I put two 'keystone' rings into one piston, meaning that both other rings don't fit in the top groove of the other piston. I tried for around an hour last night putting the wristpins in, I can put in the second circlip but it doesn't seat into its groove - the pin is just two long! Trust my luck to find out all of the minor changes Honda have made along the way It could be the pins are suited to pistons from a later model, so I might just have to order another set of pistons from Tyga
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'87 MC16

Ok the rings fit on ok now. Just my own ineptitude coming through (hey I'm just beginning...) But the wristpins still do not fit - I was hoping they would shrink overnight. Hopefully Tyga sent me the wrong ones, but no doubt it will be another week or two of pining for the powerband
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'87 MC16

There are two width's of piston. I had the same issue when I bought new ones after a seizure a couple of years back. Some are fully round, some have two flat sides on them.

The answer is to grind the pin until it fits. I had a competant bike shop do this as I didn't have the tools to ensure it was square. It's been fine for many thrashings and the odd race or two!
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I had considered this (grinding the pin) as the difference is minor on the face of things, but Paul from Tyga informed me that indeed there is a difference between the pins from the '16 and later models that they were not aware of. In the end, I have bought new pistons that will suit the new pins and rings I have, as well as the old MC16 barrels. Hopefully I can get more mileage out of the bike before the next rebuild this way, but as to if those ks are worth the extra $225...
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'87 MC16

ahug030 wrote:
I had considered this (grinding the pin) as the difference is minor on the face of things, but Paul from Tyga informed me that indeed there is a difference between the pins from the '16 and later models that they were not aware of. In the end, I have bought new pistons that will suit the new pins and rings I have, as well as the old MC16 barrels. Hopefully I can get more mileage out of the bike before the next rebuild this way, but as to if those ks are worth the extra $225...

Trying to get my head around this one... surely the better option would've been to get the other type of pins, or even have ends of the original ones ground down a few mm? Much less costlier!

You got to do the mileage now outta' principal!
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Andy.
NSR-WORLD.COM

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Well I was going to reuse the old pistons, but I was tossing up whether to get new pistons and do the job properly - the pin problem was obviously the tipping point.
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'87 MC16

Well good idea to do it properly! It's worth it in the end.
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Andy.
NSR-WORLD.COM

Please keep all responses to Forum posts on the Forum so that others may benefit.

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For all your info. The pin dimension of the NSRs are as follow:

MC16 - 15mm x 47mm

MC18~ - 15mm x 48.5mm

Honda obviously decided that more support was necessary.

There's different numbers for different models, but that's probably down to different manufacturers, or internal diameters or tapers or, or ,or.